2/6 Rod bearing fix?
02-28-2014, 09:32 PM
#31
Former Vendor
Virtually every V8 rod on the planet has an offset. That offset varies, from one engine to another, by the amount that the heads are staggered from side to side and how wide the crank journals are.
This was a huge problem with 928 stroker engines, for years. The Chevy rod, that the early stroker engine builders used, had/has the wrong offset for the 928 engine. The side thrust forces placed on the pistons and cylinder walls is crazy, when using the Chevy rod....because the offset problem moves the pin end of the rod away from the center of the piston pin. The side loading ruined the bores, very quickly, unless the rods were very, very stiff.
Look at any 928 connecting rod and the offset is instantly visible....like Tuomo says, they cut 2mm off of one side of the 944 rod to make it fit into a 928 engine. The bearing is centered on the 944, so by definition, the bearing is no longer centered, in the 928 application.
This was a huge problem with 928 stroker engines, for years. The Chevy rod, that the early stroker engine builders used, had/has the wrong offset for the 928 engine. The side thrust forces placed on the pistons and cylinder walls is crazy, when using the Chevy rod....because the offset problem moves the pin end of the rod away from the center of the piston pin. The side loading ruined the bores, very quickly, unless the rods were very, very stiff.
Look at any 928 connecting rod and the offset is instantly visible....like Tuomo says, they cut 2mm off of one side of the 944 rod to make it fit into a 928 engine. The bearing is centered on the 944, so by definition, the bearing is no longer centered, in the 928 application.
02-28-2014, 11:01 PM
#32
Agree with you on the early strokers, no question about that one, I am going by memory here so I will just tentatively say this, I think the rod at the big end is almost 27 mm wide, the cheek side of the rod has the extra material around 2 mm. That leaves around 24 mm for the bearing length plus some material in the rod so that the rod bearing is slightly recessed when it rubs against the other rod. The bank offset I believe is 50 mm? So if that recess on the rod to rod side is 1 mm it would seem that the rod is perfectly centred under the piston. There is a few ifs in there but I can't confirm this until an engine of mine is mocked up to check its deck height etc.
Virtually every V8 rod on the planet has an offset. That offset varies, from one engine to another, by the amount that the heads are staggered from side to side and how wide the crank journals are.
This was a huge problem with 928 stroker engines, for years. The Chevy rod, that the early stroker engine builders used, had/has the wrong offset for the 928 engine. The side thrust forces placed on the pistons and cylinder walls is crazy, when using the Chevy rod....because the offset problem moves the pin end of the rod away from the center of the piston pin. The side loading ruined the bores, very quickly, unless the rods were very, very stiff.
Look at any 928 connecting rod and the offset is instantly visible....like Tuomo says, they cut 2mm off of one side of the 944 rod to make it fit into a 928 engine. The bearing is centered on the 944, so by definition, the bearing is no longer centered, in the 928 application.
This was a huge problem with 928 stroker engines, for years. The Chevy rod, that the early stroker engine builders used, had/has the wrong offset for the 928 engine. The side thrust forces placed on the pistons and cylinder walls is crazy, when using the Chevy rod....because the offset problem moves the pin end of the rod away from the center of the piston pin. The side loading ruined the bores, very quickly, unless the rods were very, very stiff.
Look at any 928 connecting rod and the offset is instantly visible....like Tuomo says, they cut 2mm off of one side of the 944 rod to make it fit into a 928 engine. The bearing is centered on the 944, so by definition, the bearing is no longer centered, in the 928 application.
03-01-2014, 01:08 AM
#33
Race Director
this is a very simple answer......what race 928's live and which ones don't....another factor is the pace that the race 928 is driven.....sure a novice on street tires learning in a DE will live for a while on the insanely crappy S4 system....
However a real race 928 on slicks with a proper driver......that won't live long....literally minutes is the truth...
There are two things I have learned racing 928's for 5 years.... One is Doc knows what he is talking about.....he has forgotten more about 928's than I ever hope I can learn....this is why I call on him as often as I can...
The other is this....the OB pan, with 3/8th spacer + quality race oil WORKS.....adding a good cooler and accusump is a great idea.... I am not an engineer, I am merely a person who wants a race 928 to live as long as possible on track....and honestly I have the record for most hours on track....176 on my old lemons racer (granted not on slicks..but a $300 used engine with 117k to start)...& over 25 on my current racer (purely on slicks, with different drivers)....so I am confident to say I speak from experience....
The internet creates interesting debates from so called experts.....people who talk a great game from internet research only counts for so much..... I care about one thing...real world results....not whatever some internet guru tells me ....
However a real race 928 on slicks with a proper driver......that won't live long....literally minutes is the truth...
There are two things I have learned racing 928's for 5 years.... One is Doc knows what he is talking about.....he has forgotten more about 928's than I ever hope I can learn....this is why I call on him as often as I can...
The other is this....the OB pan, with 3/8th spacer + quality race oil WORKS.....adding a good cooler and accusump is a great idea.... I am not an engineer, I am merely a person who wants a race 928 to live as long as possible on track....and honestly I have the record for most hours on track....176 on my old lemons racer (granted not on slicks..but a $300 used engine with 117k to start)...& over 25 on my current racer (purely on slicks, with different drivers)....so I am confident to say I speak from experience....
The internet creates interesting debates from so called experts.....people who talk a great game from internet research only counts for so much..... I care about one thing...real world results....not whatever some internet guru tells me ....
03-01-2014, 05:52 AM
#34
Rennlist Member
Join Date: Feb 2011
Location: Mostly in my workshop located in Sweden.
Posts: 2,235
Received 467 Likes
on
250 Posts
THE SOFT GLYCO ROD BEARING SAGA.
First Glyco is the manufacturer of both 928 OEM and aftermarket rod bearings. The only difference is the tolerances they are made with, which has been thoroughly explained in this forum by Mr. Brown.
The soft Glyco rod bearings not only causes problems in the 928 engine but in other engines as well. The first time I was faced with a problem of extensive rod bearing failures was in the early 70´s when I for several customers started to modify the new generation of BMW flat twin motorcycles engines for higher power output. Increasing the 750cc engine to 1000cc, doubling the power, increasing the red line to 9000 rpm, we started to see repeating rod bearing failure.
I did everything to overcome the problem, increased oil pressure, porting of the oil channels in the block, different crankshaft oil drilling but nothing helped.
It was not until I tried other rod bearings we saw a solution to the problem. Found an automotive rod bearing made Clevite that could be modified to fit. Note this is not a H-bearing (high performance) but a standard type of bearing. I use it even today with great success.
At an early stage of failing the top layer of the BMW OEM/Glyco bearing looked like it began to flow in the opposite direction of rotation. The size of the BMW motorcycle rod bearing (48mm) is not much smaller than for the 928 (52mm).
Åke
First Glyco is the manufacturer of both 928 OEM and aftermarket rod bearings. The only difference is the tolerances they are made with, which has been thoroughly explained in this forum by Mr. Brown.
The soft Glyco rod bearings not only causes problems in the 928 engine but in other engines as well. The first time I was faced with a problem of extensive rod bearing failures was in the early 70´s when I for several customers started to modify the new generation of BMW flat twin motorcycles engines for higher power output. Increasing the 750cc engine to 1000cc, doubling the power, increasing the red line to 9000 rpm, we started to see repeating rod bearing failure.
I did everything to overcome the problem, increased oil pressure, porting of the oil channels in the block, different crankshaft oil drilling but nothing helped.
It was not until I tried other rod bearings we saw a solution to the problem. Found an automotive rod bearing made Clevite that could be modified to fit. Note this is not a H-bearing (high performance) but a standard type of bearing. I use it even today with great success.
At an early stage of failing the top layer of the BMW OEM/Glyco bearing looked like it began to flow in the opposite direction of rotation. The size of the BMW motorcycle rod bearing (48mm) is not much smaller than for the 928 (52mm).
Åke
03-01-2014, 07:43 AM
#35
Drifting
Interestingly we have never had any issue with the standard Glyco rod or main crank bearings for that matter for the last few decades , we have made numerous track orientated Porsche engines , be it 944 951 ( lots ) 944S2 , 968 & 928 ( 4.7L & 5.0L )
The defining factors ( that we have found)for the life of the conrod bearings ( just simple track experience over decades) with either our own Porsche's or customer Porsche's }
A) very High Oil film Strength engine oil ( and I mean high oil film strength )
B) not allow the engine oil to get more than 10 degrees cel higher than the coolant temp ( if possible), oil coolers etc + good crankcase vebtilation
C) do not allow the engine oil to foam , so no oils that are low on viscosity & no oils that are high in detergents , like street " emmission " oils or worse diesel oils etc , meaning for track work we use way above 25w-60 racing oil viscosity
D ) The conrods , we only use new high quality conrods for club track work , be it Carrillo , Wossner , Arrow etc etc , these conrods are replaced depending on the number of track hours & horse power developed , so in other words these conrods are not left there forever , but the standard crank is never changed & its not modified in any way
As an experiment we even put Sean's ( JET 951 ) road car onto the track with his modified 3.0L 16V 951 Turbo with the standard wet sump and standard 951 oil baffle ( so no dry sump ) and on E85 with 1,3+ bar boost and the fantastic Vitesse stage 5 , she pumps out a reliable 615 HP to see how reliable she is with that much power and standard crank & standard rod bearings , no issues at all , all we get is Sean catching up to & passing GT3's , and this poor old 1986 951 road car , with full sound insulation , full steel body panels , A/C , six speaker sound system , read heavy for weekend track car , and whats even more terrifing ( for the standard crank & rod bearings ) is Sean's 3.0L 16V Porsche does this on racing slicks , so the issues with oil in the sump should be a disaster , but its not .
And in the last few years , Sean ( JET 951 ) has won the PCNSW open class two years running ( open class is GT3's , Gt2's & unlimited HP Porsche's )
And he has won the outright PCNSW Motorkhana championship ( USA Autocross ) for the last 4 years on this engine ( wet sump & standard road going Glyco bearings ), this is to make the point that this engine ( and other customer engines) are competeing at the pointy end of the club track Supersprints & Motorkhana events
Why ?
Answer = the reasons above
PS = in case you are wondering , how do you increase oil film strength in an engine oil on this planet ?
Answer =
A ) increase oil viscosity
B ) increase the amount of AW ZDDP package ( up to a point ) in the oil
Its been interesting watching people wreck cranks / rods over the last ten years + in all sorts of last century Porsche's , be it 944/968/951 , 928 ( all ) etc, at track events & even on the road when pushed hard , the common denominator has been an engine oil with too lower viscosity for the RPM & core temp , meaning oil temp etc & I just keep on warning people about it
Plus in regards to this is the amount of Porsche's (944 & 928 all versions) we have done the basic "first track event preparation work " before a customer has taken his / her Porsche to the track for the first time & luckily for them & us , the 20-25 + year old sump gasket is leaking way too much , so among other initial preparations we have removed the sump & ( if a 928 ) we remove conrod journals 2 & 6 & a 944 journal no 2 & we are struck at the number of these bearings & just these are worn & the strong correlation with these worn conrod bearings in these road cars ( not track )and the use of low viscosity so called synthetic engine oils like 5w-40 etc ( for street use ) has been amazing , but if these same last century Porsche's had been on a good oil film strength oil ( like a 15w-50 or 20w-50 ) the conrod bearings ( all were like new ) on these 25 year old last century Porsche's
So the ones we picked up in preparation with worn conrod bearings would not have survived at the track for long , but the ones with no wear can be left as is and just new conrod nuts & sump gasket
If you are interested in how well a 1986 951 ( modified 30.L 16V E85 ) road car goes on the track ( with a wet sump ), just click on Sean's "YouTube " link below , best way to identify his 951 with the in car camera is the number 89 on the windscreen
The defining factors ( that we have found)for the life of the conrod bearings ( just simple track experience over decades) with either our own Porsche's or customer Porsche's }
A) very High Oil film Strength engine oil ( and I mean high oil film strength )
B) not allow the engine oil to get more than 10 degrees cel higher than the coolant temp ( if possible), oil coolers etc + good crankcase vebtilation
C) do not allow the engine oil to foam , so no oils that are low on viscosity & no oils that are high in detergents , like street " emmission " oils or worse diesel oils etc , meaning for track work we use way above 25w-60 racing oil viscosity
D ) The conrods , we only use new high quality conrods for club track work , be it Carrillo , Wossner , Arrow etc etc , these conrods are replaced depending on the number of track hours & horse power developed , so in other words these conrods are not left there forever , but the standard crank is never changed & its not modified in any way
As an experiment we even put Sean's ( JET 951 ) road car onto the track with his modified 3.0L 16V 951 Turbo with the standard wet sump and standard 951 oil baffle ( so no dry sump ) and on E85 with 1,3+ bar boost and the fantastic Vitesse stage 5 , she pumps out a reliable 615 HP to see how reliable she is with that much power and standard crank & standard rod bearings , no issues at all , all we get is Sean catching up to & passing GT3's , and this poor old 1986 951 road car , with full sound insulation , full steel body panels , A/C , six speaker sound system , read heavy for weekend track car , and whats even more terrifing ( for the standard crank & rod bearings ) is Sean's 3.0L 16V Porsche does this on racing slicks , so the issues with oil in the sump should be a disaster , but its not .
And in the last few years , Sean ( JET 951 ) has won the PCNSW open class two years running ( open class is GT3's , Gt2's & unlimited HP Porsche's )
And he has won the outright PCNSW Motorkhana championship ( USA Autocross ) for the last 4 years on this engine ( wet sump & standard road going Glyco bearings ), this is to make the point that this engine ( and other customer engines) are competeing at the pointy end of the club track Supersprints & Motorkhana events
Why ?
Answer = the reasons above
PS = in case you are wondering , how do you increase oil film strength in an engine oil on this planet ?
Answer =
A ) increase oil viscosity
B ) increase the amount of AW ZDDP package ( up to a point ) in the oil
Its been interesting watching people wreck cranks / rods over the last ten years + in all sorts of last century Porsche's , be it 944/968/951 , 928 ( all ) etc, at track events & even on the road when pushed hard , the common denominator has been an engine oil with too lower viscosity for the RPM & core temp , meaning oil temp etc & I just keep on warning people about it
Plus in regards to this is the amount of Porsche's (944 & 928 all versions) we have done the basic "first track event preparation work " before a customer has taken his / her Porsche to the track for the first time & luckily for them & us , the 20-25 + year old sump gasket is leaking way too much , so among other initial preparations we have removed the sump & ( if a 928 ) we remove conrod journals 2 & 6 & a 944 journal no 2 & we are struck at the number of these bearings & just these are worn & the strong correlation with these worn conrod bearings in these road cars ( not track )and the use of low viscosity so called synthetic engine oils like 5w-40 etc ( for street use ) has been amazing , but if these same last century Porsche's had been on a good oil film strength oil ( like a 15w-50 or 20w-50 ) the conrod bearings ( all were like new ) on these 25 year old last century Porsche's
So the ones we picked up in preparation with worn conrod bearings would not have survived at the track for long , but the ones with no wear can be left as is and just new conrod nuts & sump gasket
If you are interested in how well a 1986 951 ( modified 30.L 16V E85 ) road car goes on the track ( with a wet sump ), just click on Sean's "YouTube " link below , best way to identify his 951 with the in car camera is the number 89 on the windscreen
03-01-2014, 08:26 AM
#36
Nordschleife Master
Virtually every V8 rod on the planet has an offset. That offset varies, from one engine to another, by the amount that the heads are staggered from side to side and how wide the crank journals are.
This was a huge problem with 928 stroker engines, for years. The Chevy rod, that the early stroker engine builders used, had/has the wrong offset for the 928 engine. The side thrust forces placed on the pistons and cylinder walls is crazy, when using the Chevy rod....because the offset problem moves the pin end of the rod away from the center of the piston pin. The side loading ruined the bores, very quickly, unless the rods were very, very stiff.
Look at any 928 connecting rod and the offset is instantly visible....like Tuomo says, they cut 2mm off of one side of the 944 rod to make it fit into a 928 engine. The bearing is centered on the 944, so by definition, the bearing is no longer centered, in the 928 application.
This was a huge problem with 928 stroker engines, for years. The Chevy rod, that the early stroker engine builders used, had/has the wrong offset for the 928 engine. The side thrust forces placed on the pistons and cylinder walls is crazy, when using the Chevy rod....because the offset problem moves the pin end of the rod away from the center of the piston pin. The side loading ruined the bores, very quickly, unless the rods were very, very stiff.
Look at any 928 connecting rod and the offset is instantly visible....like Tuomo says, they cut 2mm off of one side of the 944 rod to make it fit into a 928 engine. The bearing is centered on the 944, so by definition, the bearing is no longer centered, in the 928 application.
03-01-2014, 08:59 AM
#37
Rennlist Member
Join Date: Feb 2011
Location: Mostly in my workshop located in Sweden.
Posts: 2,235
Received 467 Likes
on
250 Posts
The 928 stock rod is not symmetric. Regardless, there is no side loadin or side bending moment issue. Why? Because the rod beam is centered relative to the piston and the bearing is centered relative to the rod beam, thus the piston, beam, and rod are in perfect alignment. This all that matters. Whether something is shaved off from the cheek of the rod or not is irrelevant for the force vectors as long as those three things are aligned. The rod cheeks are not even stressed, they simply locate the rod relative to the bore in crankshaft guided rod engines.
Åke
03-01-2014, 10:11 AM
#38
Nordschleife Master
I love a good oiling thread. Since I've blown up a few engines in a variety of ways, including 2/6 seizing, I always pay attention.
I'm surprised at Jet951's analysis. Most people think it's about oil starvation and not oil quality. Perhaps better oil prevents wear during starvation. In that case it may be track use patterns determined by driver habits and track layout.
Then again, I'm not surprised at Iceman617's proposition. He should be clear that his car is an automatic and doesn't run high RPMs. And "high" means near or past 6500. Also, I believe the car sees short, "technical" courses that are easier on foaming.
Personally, I'm running an Ishihara-Johnson windage kit for oil control So far, so good. Lots of screen and baffles to keep windage down plus covers and trap doors to keep oil in the sump. Super cool and complicated. My home track is 3.1 miles with a full 1 mile front straight so very hard on foaming and oil rolling out of the front sump.
The 928 has a poor and even fragile oiling system. With the shallow front sump and closeness of the pan to the crank there are windage problems. The crank drilling isn't good for high RPMs and the channels in the lower girdle route foamy oil to the 2/6 journal. The bearing materials are suspect as well. This leads to failures.
Addressing oiling failures can be done in a wide variety of ways. Engine use is critical in evaluating these solutions. We should always include that when discussing "the solution" to a multi-dimensional problem. People need to context to determine if a solution will actually address their needs.
I'm surprised at Jet951's analysis. Most people think it's about oil starvation and not oil quality. Perhaps better oil prevents wear during starvation. In that case it may be track use patterns determined by driver habits and track layout.
Then again, I'm not surprised at Iceman617's proposition. He should be clear that his car is an automatic and doesn't run high RPMs. And "high" means near or past 6500. Also, I believe the car sees short, "technical" courses that are easier on foaming.
Personally, I'm running an Ishihara-Johnson windage kit for oil control So far, so good. Lots of screen and baffles to keep windage down plus covers and trap doors to keep oil in the sump. Super cool and complicated. My home track is 3.1 miles with a full 1 mile front straight so very hard on foaming and oil rolling out of the front sump.
The 928 has a poor and even fragile oiling system. With the shallow front sump and closeness of the pan to the crank there are windage problems. The crank drilling isn't good for high RPMs and the channels in the lower girdle route foamy oil to the 2/6 journal. The bearing materials are suspect as well. This leads to failures.
Addressing oiling failures can be done in a wide variety of ways. Engine use is critical in evaluating these solutions. We should always include that when discussing "the solution" to a multi-dimensional problem. People need to context to determine if a solution will actually address their needs.
03-01-2014, 11:47 AM
#39
Remember that with e85 on jet's car there will be 0 to nill detonation.
03-01-2014, 05:54 PM
#40
Former Vendor
The 928 stock rod is not symmetric. Regardless, there is no side loadin or side bending moment issue. Why? Because the rod beam is centered relative to the piston and the bearing is centered relative to the rod beam, thus the piston, beam, and rod are in perfect alignment. This all that matters. Whether something is shaved off from the cheek of the rod or not is irrelevant for the force vectors as long as those three things are aligned. The rod cheeks are not even stressed, they simply locate the rod relative to the bore in crankshaft guided rod engines.
What possibly could change with both varying explosions and rpms?
Once you've taken a few thousand engines apart, what "should" be happening and "what really" happens significantly diverges. Theory is great...reality is much better.
Wrist pins batter the **** out of the circlips.....meaning the wrist pins are acting like small hammers on those circlips. How does this happen if everything is perfectly in alignment?
Keep in mind that the rods are moving on the crankshaft from side to side as the crankshaft is moving back and forth on it's thrust bearing....and that rod, with the bearing not centered in the middle of the rod, is rocking towards the unsupported section.....stopped only by the thrust surface on the side of the rod.
My point, in this thread, is pretty simple. If you narrow that bearing down, that rocking "moment" can only get worse.
Let's just keep this really simple:
Logically, is there any way a "narrower" rod bearing would make the rocking of the rod on the journal any better?
03-01-2014, 09:22 PM
#41
Race Director
Glen
while we ran the "same" oiling system, we have had drastically different results....my current car is a 5 speed....and the fastest race 928 based off power-weight....there isn't another race 928 around that can match my lap times period..... Yes I shift at 6000rpm....no point going higher....
As for technical tracks....Thunderhill is a documented 928-944 killer with T2 for about 7 seconds at 1.5G+ (peaks of 1.9).....I haven't driven anywhere else in casper
As I said before...I believe in results...not old failures from years and years ago.... Sure an engine you blew up 10 years ago is data, but not nearly as important as current data....& I drive my car all season long....every year....
Like Doc Brown says....what runs and what doesn't???
while we ran the "same" oiling system, we have had drastically different results....my current car is a 5 speed....and the fastest race 928 based off power-weight....there isn't another race 928 around that can match my lap times period..... Yes I shift at 6000rpm....no point going higher....
As for technical tracks....Thunderhill is a documented 928-944 killer with T2 for about 7 seconds at 1.5G+ (peaks of 1.9).....I haven't driven anywhere else in casper
As I said before...I believe in results...not old failures from years and years ago.... Sure an engine you blew up 10 years ago is data, but not nearly as important as current data....& I drive my car all season long....every year....
Like Doc Brown says....what runs and what doesn't???
I love a good oiling thread. Since I've blown up a few engines in a variety of ways, including 2/6 seizing, I always pay attention.
I'm surprised at Jet951's analysis. Most people think it's about oil starvation and not oil quality. Perhaps better oil prevents wear during starvation. In that case it may be track use patterns determined by driver habits and track layout.
Then again, I'm not surprised at Iceman617's proposition. He should be clear that his car is an automatic and doesn't run high RPMs. And "high" means near or past 6500. Also, I believe the car sees short, "technical" courses that are easier on foaming.
Personally, I'm running an Ishihara-Johnson windage kit for oil control So far, so good. Lots of screen and baffles to keep windage down plus covers and trap doors to keep oil in the sump. Super cool and complicated. My home track is 3.1 miles with a full 1 mile front straight so very hard on foaming and oil rolling out of the front sump.
The 928 has a poor and even fragile oiling system. With the shallow front sump and closeness of the pan to the crank there are windage problems. The crank drilling isn't good for high RPMs and the channels in the lower girdle route foamy oil to the 2/6 journal. The bearing materials are suspect as well. This leads to failures.
Addressing oiling failures can be done in a wide variety of ways. Engine use is critical in evaluating these solutions. We should always include that when discussing "the solution" to a multi-dimensional problem. People need to context to determine if a solution will actually address their needs.
I'm surprised at Jet951's analysis. Most people think it's about oil starvation and not oil quality. Perhaps better oil prevents wear during starvation. In that case it may be track use patterns determined by driver habits and track layout.
Then again, I'm not surprised at Iceman617's proposition. He should be clear that his car is an automatic and doesn't run high RPMs. And "high" means near or past 6500. Also, I believe the car sees short, "technical" courses that are easier on foaming.
Personally, I'm running an Ishihara-Johnson windage kit for oil control So far, so good. Lots of screen and baffles to keep windage down plus covers and trap doors to keep oil in the sump. Super cool and complicated. My home track is 3.1 miles with a full 1 mile front straight so very hard on foaming and oil rolling out of the front sump.
The 928 has a poor and even fragile oiling system. With the shallow front sump and closeness of the pan to the crank there are windage problems. The crank drilling isn't good for high RPMs and the channels in the lower girdle route foamy oil to the 2/6 journal. The bearing materials are suspect as well. This leads to failures.
Addressing oiling failures can be done in a wide variety of ways. Engine use is critical in evaluating these solutions. We should always include that when discussing "the solution" to a multi-dimensional problem. People need to context to determine if a solution will actually address their needs.
03-02-2014, 11:30 AM
#42
Nordschleife Master
Lower shift points save these engines. I wonder what shift point results in no bearing problems at all.
And don't even try to understand why?
Blowing up engines is an expensive business. This is a complex problem and others deserve more.
03-02-2014, 05:25 PM
#43
Race Director
Glen
I apologize for my post, it was overly harsh and critical.....
I agree that much more research-data is needed to determine exactly why some 928's with identical setups live a long time on track and others die quickly...
I think it is related to a few well known issues
1: oil starvation
2: soft rod bearings, especially if glyco not original bearings
3: excessive oil flow to the heads (mostly 32V)
4: excessive crankcase pressures
Here is what I have done to reduce oil related issues in my 928's
1: OB pan with 3/8th spacer...this is better than nothing, but an accusump is a good idea too
2: rod bearings are bad.....only way to fix it is to change the crank-rods to take a better bearing
3: I think the 16V 928 engines flow less oil to the heads.....
4: Crankcase pressures cause oil to get injected into the intake in stock setups.....this can lead to detonation and effects #2 dramatically....my answer is to disconnect all routes for oil into the intake. I vent the top oil filler to a simple separator to atmosphere....fine for a race car...not for a street car.... Since casper has an OB pan, but not 3/8th spacer (yet) I fill the oil to 1/3-1/2 on the dipstick....if I fill it to the full mark it spits excessively and makes a mess....vs just a tiny bit damp if the levels are lower.....
The other "magic" is my shift point of 6000rpm.....given caspers power curves I could gain a little performance by shifting at 6200 or so.....but I just don't want to do it unless I know exactly how the engine was built.....I know the engine was rebuilt in 1992 for $10k and it makes great power....I just don't want to push it too far....
bottom line is we all need to work together and share data to determine a logical repeatable course to keep our engines alive under race conditions!!!!
I apologize for my post, it was overly harsh and critical.....
I agree that much more research-data is needed to determine exactly why some 928's with identical setups live a long time on track and others die quickly...
I think it is related to a few well known issues
1: oil starvation
2: soft rod bearings, especially if glyco not original bearings
3: excessive oil flow to the heads (mostly 32V)
4: excessive crankcase pressures
Here is what I have done to reduce oil related issues in my 928's
1: OB pan with 3/8th spacer...this is better than nothing, but an accusump is a good idea too
2: rod bearings are bad.....only way to fix it is to change the crank-rods to take a better bearing
3: I think the 16V 928 engines flow less oil to the heads.....
4: Crankcase pressures cause oil to get injected into the intake in stock setups.....this can lead to detonation and effects #2 dramatically....my answer is to disconnect all routes for oil into the intake. I vent the top oil filler to a simple separator to atmosphere....fine for a race car...not for a street car.... Since casper has an OB pan, but not 3/8th spacer (yet) I fill the oil to 1/3-1/2 on the dipstick....if I fill it to the full mark it spits excessively and makes a mess....vs just a tiny bit damp if the levels are lower.....
The other "magic" is my shift point of 6000rpm.....given caspers power curves I could gain a little performance by shifting at 6200 or so.....but I just don't want to do it unless I know exactly how the engine was built.....I know the engine was rebuilt in 1992 for $10k and it makes great power....I just don't want to push it too far....
bottom line is we all need to work together and share data to determine a logical repeatable course to keep our engines alive under race conditions!!!!
03-02-2014, 08:13 PM
#45
Drifting
What about dynamic loading on the crank at high rpms? This could be a factor in what Greg is describing. I have always heard and read all cranks bend or flex under load. Long crank, alloy cradle..
The big 928 motor would seem to be a low rpm motor design and if used differently, bad things may happen.
I don't think the max rpm on the tach means do it all day.
I wish people with track experience and good experiences with certain racing oils would include the brand oil they are using.
The big 928 motor would seem to be a low rpm motor design and if used differently, bad things may happen.
I don't think the max rpm on the tach means do it all day.
I wish people with track experience and good experiences with certain racing oils would include the brand oil they are using.
I agree that everything is in alignment...in the stock 928 scenario....but this is not true with the Chevy offset rod in the 928 engine. And in the stock 928 application, this is only true when everything is sitting still and there are no forces.
What possibly could change with both varying explosions and rpms?
Once you've taken a few thousand engines apart, what "should" be happening and "what really" happens significantly diverges. Theory is great...reality is much better.
Wrist pins batter the **** out of the circlips.....meaning the wrist pins are acting like small hammers on those circlips. How does this happen if everything is perfectly in alignment?
Keep in mind that the rods are moving on the crankshaft from side to side as the crankshaft is moving back and forth on it's thrust bearing....and that rod, with the bearing not centered in the middle of the rod, is rocking towards the unsupported section.....stopped only by the thrust surface on the side of the rod.
My point, in this thread, is pretty simple. If you narrow that bearing down, that rocking "moment" can only get worse.
Let's just keep this really simple:
Logically, is there any way a "narrower" rod bearing would make the rocking of the rod on the journal any better?
What possibly could change with both varying explosions and rpms?
Once you've taken a few thousand engines apart, what "should" be happening and "what really" happens significantly diverges. Theory is great...reality is much better.
Wrist pins batter the **** out of the circlips.....meaning the wrist pins are acting like small hammers on those circlips. How does this happen if everything is perfectly in alignment?
Keep in mind that the rods are moving on the crankshaft from side to side as the crankshaft is moving back and forth on it's thrust bearing....and that rod, with the bearing not centered in the middle of the rod, is rocking towards the unsupported section.....stopped only by the thrust surface on the side of the rod.
My point, in this thread, is pretty simple. If you narrow that bearing down, that rocking "moment" can only get worse.
Let's just keep this really simple:
Logically, is there any way a "narrower" rod bearing would make the rocking of the rod on the journal any better?
Last edited by The Fixer; 03-02-2014 at 10:04 PM. Reason: clarity