951 rebuild
02-08-2002, 04:19 PM
#16
Race Director
From reading Huntley's statement, does he mean to say that they drilled a hole 90-degrees away from the existing one in the rod-journal? So as to place the hole at the outermost part of the journal? Then when it spins at high-RPM, centrifugal force would tend to force the oil outwards, through that hole and to the bearing?
That certainly sounds like it would work well, I think I'll have to get mine drilled like that.
That certainly sounds like it would work well, I think I'll have to get mine drilled like that.
02-08-2002, 06:24 PM
#17
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I don't understand that HR is talking about.
1. There is no such thing as "centrifugal force". There is a centrifugal affect caused by centripetal force.
2. Why would it matter where the hole was? I don't get it.
...Tabor... who has had some physics classes, but plans to take more.
1. There is no such thing as "centrifugal force". There is a centrifugal affect caused by centripetal force.
2. Why would it matter where the hole was? I don't get it.
...Tabor... who has had some physics classes, but plans to take more.
02-09-2002, 09:39 PM
#18
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Hi Ski,
Mike at LR here, how is the project going? I heard from Dave that you were having to delay the teardown, work sucks doesn't it. When you get the pistons out, you might consider having the sides coated too. Keep us informed as to your progress and don't fall off into the deep blue sea.
Mike
Mike at LR here, how is the project going? I heard from Dave that you were having to delay the teardown, work sucks doesn't it. When you get the pistons out, you might consider having the sides coated too. Keep us informed as to your progress and don't fall off into the deep blue sea.
Mike
02-09-2002, 10:03 PM
#19
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Yeah,,,work sucks,,I have to go to Brazil with no time on the beaches,,well the thread above shows what parts I have ordered being shipped direct to the mechanic,,we hope to start April 8th and be done by Friday since we are changing to all your NEW parts and not having to rebuild..
I figured I would do a couple of oil changes through mileage then come see you two in OK City and get some dyno time, write up and pics. Maybe we'll get creative on the MAF..HA!
Bret
I figured I would do a couple of oil changes through mileage then come see you two in OK City and get some dyno time, write up and pics. Maybe we'll get creative on the MAF..HA!
Bret
02-10-2002, 01:51 AM
#20
Race Car
Danno,"Then when it spins at high-RPM, centrifugal force would tend to force the oil outwards, through that hole and to the bearing?"
Sounds great, and makes sense, but I'm not convinced.
Bearings lacking lube, would show wear at a higher rate than the others.
I've torn down running engines and see no more wear than, #'s 1, 3 &4..?
A bearing at "half life" would have clearance, eceeding specs and therefore providing a "path of least resistance" for the oil to escape between the crank and the rod bearing, causing problems in other journals farther from the oil pump.
Big American V-8's have two rods per crank journal to supply with oil. And the 454's long stroke hampers high RPM operation.
I find much more creedance in the theory of cavitation....!
My $.02
Sounds great, and makes sense, but I'm not convinced.
Bearings lacking lube, would show wear at a higher rate than the others.
I've torn down running engines and see no more wear than, #'s 1, 3 &4..?
A bearing at "half life" would have clearance, eceeding specs and therefore providing a "path of least resistance" for the oil to escape between the crank and the rod bearing, causing problems in other journals farther from the oil pump.
Big American V-8's have two rods per crank journal to supply with oil. And the 454's long stroke hampers high RPM operation.
I find much more creedance in the theory of cavitation....!
My $.02
02-10-2002, 05:43 AM
#21
Race Director
What I want to know, is why the #2 has way more wear than the others? It's dramatic! I guess we'd have to put tranducers into each of the rod-journals and do real-time data-logging at various RPMs to really find out what the story is with the #2 rod-bearing problem.
Also Huntley's claim of no failures within a couple thousand miles don't really predict much. I'm sure my #2 bearing that was toasted at 195k-miles looked fine a few thousand miles after it left the factory.
Also Huntley's claim of no failures within a couple thousand miles don't really predict much. I'm sure my #2 bearing that was toasted at 195k-miles looked fine a few thousand miles after it left the factory.
02-11-2002, 11:46 PM
#22
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We have been doing these cranks since 1999 and to date have done 40+ units, again no failures ever. We have the distinct advantage of seeing lots and lots of 944 cars and running them hard on our dyno and on track for many years. This is not just a theory but a proven fact with lots of 'real' world time.
02-12-2002, 01:24 AM
#23
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Huntley Racing,
I don't doubt that you have a lot of expierience. But your centrifugal force proposition leaves me uneasy.
The oil travels through the center of the crank, right? If so, wouldn't centrifugal as you call it (centripetal as I call it) force have just as much affect in all directions? If the oil "hole" is not in the center, I see what you car saying, but if it is in the center, I don't understand.
I don't doubt that you have a lot of expierience. But your centrifugal force proposition leaves me uneasy.
The oil travels through the center of the crank, right? If so, wouldn't centrifugal as you call it (centripetal as I call it) force have just as much affect in all directions? If the oil "hole" is not in the center, I see what you car saying, but if it is in the center, I don't understand.
02-12-2002, 02:48 AM
#24
Race Director
We might be talking about two different things here. The oil passage is centralized inside the crank. But because oil-pressure is exerted evenly in all direction, the passageway can even be offset to one side if you want. Or it can be square in cross-section, whatever.
However, the oil exit hole's location on the rod-journal is what Huntley is talking about.
The problem is that oil exit hole on the rod-journal is not on the very outside. It's on the side of the rod-journal and lies 90-degrees to the direction oil would natrually flow due to centripedal force (inside -> outside).
I don't have a fluid-FEA package to model this, but imagine an infinitely small particle of oil. And it's at the very outside of the inner bore of the rod-journal. Centripedal force would be greatest at this point for any given RPM because that particle would travel the largest diameter through each rotation. In order for this oil drop to get out the rod-journal hole, it has to travel towards the center of the crank, against the centripedal force. The force driving this oil particle inwards? Oil pressure!
If we take the sums of all the particles of oil inside the rod-journal, ALL of those beyond the oil-hole when the crank spins has to use oil-pressure to fight centripedal force. So 1/2 of all the oil inside the rod-journal has to fight centripedal force to get out of the journal hole.
At low RPMs, centripedal force is low, thus oil-pressure has no problems pushing the oil back towards the crank and out the hole. But at high-RPMs, centripedal force can be such that oil beyond the hole is trapped inside the journal.
Here's a perfect example. Take a bucket of water and fill it up halfway with water. Then drill a hole halfway up the side of the bucket. Then swing the bucket sideways, up and down, all around. If you swing it fast enough, no water falls out right?
Now drill another hole on the BOTTOM of the bucket. Swing it around in a circle again. Centripedal force will push out the water even faster! The location of the hole is crucial.
That's the modification that Huntley is talking about. Drill another hole, but not cross-drilling a hole on the opposite side of the journal. That would just be replicating the same problem times 2. No, drill it 90-degrees away from the existing hole on the outermost edge of the rod-journal when it swings around. Another way to look at it, is to drill a hole such that it swings the largest diameter possible when the crank turns.
This still doesn't explain why the #2 rod-bearing/journal is the most vulnerable in stock trim though...
However, the oil exit hole's location on the rod-journal is what Huntley is talking about.
The problem is that oil exit hole on the rod-journal is not on the very outside. It's on the side of the rod-journal and lies 90-degrees to the direction oil would natrually flow due to centripedal force (inside -> outside).
I don't have a fluid-FEA package to model this, but imagine an infinitely small particle of oil. And it's at the very outside of the inner bore of the rod-journal. Centripedal force would be greatest at this point for any given RPM because that particle would travel the largest diameter through each rotation. In order for this oil drop to get out the rod-journal hole, it has to travel towards the center of the crank, against the centripedal force. The force driving this oil particle inwards? Oil pressure!
If we take the sums of all the particles of oil inside the rod-journal, ALL of those beyond the oil-hole when the crank spins has to use oil-pressure to fight centripedal force. So 1/2 of all the oil inside the rod-journal has to fight centripedal force to get out of the journal hole.
At low RPMs, centripedal force is low, thus oil-pressure has no problems pushing the oil back towards the crank and out the hole. But at high-RPMs, centripedal force can be such that oil beyond the hole is trapped inside the journal.
Here's a perfect example. Take a bucket of water and fill it up halfway with water. Then drill a hole halfway up the side of the bucket. Then swing the bucket sideways, up and down, all around. If you swing it fast enough, no water falls out right?
Now drill another hole on the BOTTOM of the bucket. Swing it around in a circle again. Centripedal force will push out the water even faster! The location of the hole is crucial.
That's the modification that Huntley is talking about. Drill another hole, but not cross-drilling a hole on the opposite side of the journal. That would just be replicating the same problem times 2. No, drill it 90-degrees away from the existing hole on the outermost edge of the rod-journal when it swings around. Another way to look at it, is to drill a hole such that it swings the largest diameter possible when the crank turns.
This still doesn't explain why the #2 rod-bearing/journal is the most vulnerable in stock trim though...
02-12-2002, 04:32 AM
#26
Race Car
Still not buying it,
The exact reasons, stated are the reasons, the force will cause the oil to be exhausted fom the port.
The rod journal is offset from the crank centerline, and it is this reason that such a force will allow oil to escape without problems.
There is no cuplike void in the crank rod journal to cause a "reserve", and extra oil weighting.
While I'm not disagreeing with claims made, i simply beleive the factory design to be sufficient.
Remember, at high revs, there should be 50 psi or so, behind this "affected" oil.
IMO, engine braking, is the probable the cause of these failures, since stress on the rod bearings, due to the resistance to stretch and compression loading is more present during this condition, and experienced more on the racetrack....
I'd be interested to hear of ANY #2 rod bearing failures on cars equiped with automatic trannys.
The exact reasons, stated are the reasons, the force will cause the oil to be exhausted fom the port.
The rod journal is offset from the crank centerline, and it is this reason that such a force will allow oil to escape without problems.
There is no cuplike void in the crank rod journal to cause a "reserve", and extra oil weighting.
While I'm not disagreeing with claims made, i simply beleive the factory design to be sufficient.
Remember, at high revs, there should be 50 psi or so, behind this "affected" oil.
IMO, engine braking, is the probable the cause of these failures, since stress on the rod bearings, due to the resistance to stretch and compression loading is more present during this condition, and experienced more on the racetrack....
I'd be interested to hear of ANY #2 rod bearing failures on cars equiped with automatic trannys.
02-12-2002, 06:30 AM
#27
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Here's some info I found on the net from Devek. In case some here don't know, the 928 also suffers from catastrophic rod bearing failure. On the 928 it is the 2/6 rode bearings...
Our testing has shown that the 2/6 rod bearing failure is caused by TWO
issues, and the main reason for the failure is not the one most commonly
thought.
We have spent years understanding the issue, 3 engine builds testing
"theory" and teardowns and lots of engineering and here is the summary. How
good is the summary, well, they are good enough for Porsche AG to purchase
our solution for their racing 928 customers!
First, the 2/6 oiling path is the least contributing factor to the failure!
This is the common misconception.
The main factor is simply oil starvation, and the 2/6 rod bearing feed off
the crank is the first to get the gulp of oil/air.
Where does the air come from, well if you are cornering at 1g, the the oil
in the pan is at a 45 degree angle, and depending on oil level, will uncover
the pickup....hence the air!
The secondary factor is from off angle oiling of the 2/6 journal off the
crank. This is a minor issue and if oil pressure is sufficient, it is a non
issue at any rpm.
The oil starvation, or lack of oil in the pan is caused by the fact that oil
is pumped into/upto the head in large quantities by high rpm and the head
acts as a oil "pan" of its own. The crank also spins up a batch of oil and
keeps it in suspension, especially at high rpm. This oil cloud circles the
crank and is the reason most race engine have "scrapers" in the case. Up to
two quarts of oil can be circling the crank at high rpm! In some cases it
can be more as the S4 is known to "pump" oil up the oil filler tower and
keep it there!
When there is not enough oil in the pan (caused by the high rpm pumping of
oil to other areas, like the head, etc.), then under cornering at 1 g, the
oil pickup is uncovered!
So, the worst thing you can do to your engine is this...a 6500 rpm corner
entry, a 1 or more g corner force while maintaining 6000+rpm...you are sure
to pick up some air...and do it enough times, the bearing will fail.
It will happen more frequently and sooner on a S4 then on an early engine
with the same cornering capability due to the fact that there are less
places for the oil to stay in the head and the paths in the head are
smaller. So more oil stays in the pan.
The solution as originally develop by DEVEK is as follows...use our Accusump
systems! The DEVEK Accusump systems have two levels, street and race and
each one offers a different level of protection, but only for so long.
Approximately 10 - 17 seconds depending on oil type, temp, etc. These are
the systems that are purchased and recommended by the factory.
An addition item is to decrease the amount of oil available to the head by
increasing the spring pressure or my favorite, decreasing the feed orifice.
The other method, again as developed by DEVEK (by the late Bob DEVore) and
currently used by other racers, is a simple dry sump system that uses the
original oil pump to feed the engine from a remote tank, rather than the oil
pan and a scavenger pump to fill the tank...
And of course, you can just dry sump the system externally and depend on no
stock oils systems.
On OUR Scat stroker cranks, we simply pick up oil off the number three main
bearing to make is a straight shot to feed the 2/6 rod bearings...so as some
one correctly pointed out, it is routed like a chevy. This is unlike our
drilled cranks, which have a modified oil pathway.
I hope this clears up most of the misconceptions about a weakness of our
engines and clarifies why some folks believe that the engine will last
longer if the rev's are lower.....less oil pumped out of the pan.
Oh, by the way, can it happen to a non racer? YUP, if your oil level is
low, and you are running at 6000+ rpm for a hundred miles of so...it can
happen. And this has happened.
More information is available in our catalog or give me a call or email....
Warmest Regards,
Marc
--
Marc M. Thomas
DEVEK
The White Car
450hp/470tq on the ground
210 mph 'on the street
THE fastest 928 on the planet.
Our testing has shown that the 2/6 rod bearing failure is caused by TWO
issues, and the main reason for the failure is not the one most commonly
thought.
We have spent years understanding the issue, 3 engine builds testing
"theory" and teardowns and lots of engineering and here is the summary. How
good is the summary, well, they are good enough for Porsche AG to purchase
our solution for their racing 928 customers!
First, the 2/6 oiling path is the least contributing factor to the failure!
This is the common misconception.
The main factor is simply oil starvation, and the 2/6 rod bearing feed off
the crank is the first to get the gulp of oil/air.
Where does the air come from, well if you are cornering at 1g, the the oil
in the pan is at a 45 degree angle, and depending on oil level, will uncover
the pickup....hence the air!
The secondary factor is from off angle oiling of the 2/6 journal off the
crank. This is a minor issue and if oil pressure is sufficient, it is a non
issue at any rpm.
The oil starvation, or lack of oil in the pan is caused by the fact that oil
is pumped into/upto the head in large quantities by high rpm and the head
acts as a oil "pan" of its own. The crank also spins up a batch of oil and
keeps it in suspension, especially at high rpm. This oil cloud circles the
crank and is the reason most race engine have "scrapers" in the case. Up to
two quarts of oil can be circling the crank at high rpm! In some cases it
can be more as the S4 is known to "pump" oil up the oil filler tower and
keep it there!
When there is not enough oil in the pan (caused by the high rpm pumping of
oil to other areas, like the head, etc.), then under cornering at 1 g, the
oil pickup is uncovered!
So, the worst thing you can do to your engine is this...a 6500 rpm corner
entry, a 1 or more g corner force while maintaining 6000+rpm...you are sure
to pick up some air...and do it enough times, the bearing will fail.
It will happen more frequently and sooner on a S4 then on an early engine
with the same cornering capability due to the fact that there are less
places for the oil to stay in the head and the paths in the head are
smaller. So more oil stays in the pan.
The solution as originally develop by DEVEK is as follows...use our Accusump
systems! The DEVEK Accusump systems have two levels, street and race and
each one offers a different level of protection, but only for so long.
Approximately 10 - 17 seconds depending on oil type, temp, etc. These are
the systems that are purchased and recommended by the factory.
An addition item is to decrease the amount of oil available to the head by
increasing the spring pressure or my favorite, decreasing the feed orifice.
The other method, again as developed by DEVEK (by the late Bob DEVore) and
currently used by other racers, is a simple dry sump system that uses the
original oil pump to feed the engine from a remote tank, rather than the oil
pan and a scavenger pump to fill the tank...
And of course, you can just dry sump the system externally and depend on no
stock oils systems.
On OUR Scat stroker cranks, we simply pick up oil off the number three main
bearing to make is a straight shot to feed the 2/6 rod bearings...so as some
one correctly pointed out, it is routed like a chevy. This is unlike our
drilled cranks, which have a modified oil pathway.
I hope this clears up most of the misconceptions about a weakness of our
engines and clarifies why some folks believe that the engine will last
longer if the rev's are lower.....less oil pumped out of the pan.
Oh, by the way, can it happen to a non racer? YUP, if your oil level is
low, and you are running at 6000+ rpm for a hundred miles of so...it can
happen. And this has happened.
More information is available in our catalog or give me a call or email....
Warmest Regards,
Marc
--
Marc M. Thomas
DEVEK
The White Car
450hp/470tq on the ground
210 mph 'on the street
THE fastest 928 on the planet.
02-12-2002, 06:36 AM
#28
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Another post I found from Devek...
There appears to be some confusion on how the cranks fail, why they fail and the fixes.
DEVEK researched these issues which resulted in a factory visit to review the data. The factory then recommended the purchase of our accusump kits for their racing customers. In some cases, they purchased the kits for the customers. So far, no customer who has installed a DEVEK racing kit has lost an engine. One German racer is still racing on the same engine as he did last year, rather than pay for the usual 3 rebuilds per season!
The accusump should not be plumbed into the oil cooler lines as there are times when the cooler is not fully open due to temp conditions.
In under 6500/7000 rpm constant running or high rpm cornering, the failure is due to oil starvation.
It takes over 7000+ rpm to have a differential gap in the bearing that can support a altered flow amount necessary to service the 2/6 bearing. Oil pressure operates on bearing clearance. In order for it to flow in one direction rather than in another, then one bearing gap must be larger than others
The fixes are simple............use an accusump, a scraper plate in the case or GTS baffle in the pan,and/or keep the revs low to prevent oil starvation. If the engine is out, it will not hurt to have the redrilling performed on the crank as well as using the above items.
And if you want to run 7000+ rpms, redrill the crank and revise the bearings, plus all the above.
And if you got the bucks, use a dry sump and make some more power.
Marc
DEVEK
There appears to be some confusion on how the cranks fail, why they fail and the fixes.
DEVEK researched these issues which resulted in a factory visit to review the data. The factory then recommended the purchase of our accusump kits for their racing customers. In some cases, they purchased the kits for the customers. So far, no customer who has installed a DEVEK racing kit has lost an engine. One German racer is still racing on the same engine as he did last year, rather than pay for the usual 3 rebuilds per season!
The accusump should not be plumbed into the oil cooler lines as there are times when the cooler is not fully open due to temp conditions.
In under 6500/7000 rpm constant running or high rpm cornering, the failure is due to oil starvation.
It takes over 7000+ rpm to have a differential gap in the bearing that can support a altered flow amount necessary to service the 2/6 bearing. Oil pressure operates on bearing clearance. In order for it to flow in one direction rather than in another, then one bearing gap must be larger than others
The fixes are simple............use an accusump, a scraper plate in the case or GTS baffle in the pan,and/or keep the revs low to prevent oil starvation. If the engine is out, it will not hurt to have the redrilling performed on the crank as well as using the above items.
And if you want to run 7000+ rpms, redrill the crank and revise the bearings, plus all the above.
And if you got the bucks, use a dry sump and make some more power.
Marc
DEVEK
02-12-2002, 06:42 AM
#29
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My guess is that the 944 failures are similar to the 928 failures. What I get from reading the Devek information is:
1. Don't exceed 6000 rpm in corners(unfortunatly most of the aftermarket chips raise revlimiter to 7000 rpm - why? it just hurts the engine).
I don't understand the reason for the increased revs because max power is usually at 5800 rpm on the 8-valve cars and the power peaks are near optimal on the 3-4 and 4-5 shift if you use 6000 rpm as a shifting point (with good chips - see Farzaan's dyno results at <a href="http://www.novustelecom.net/~fkassam/dyno/dyno.html)." target="_blank">http://www.novustelecom.net/~fkassam/dyno/dyno.html).</a>
2. Install a pan baffle if you don't have one.
3. If you want high rpm go for accusump and redrilling of the crank.
As some of you know I blew the #2 on my street car a while ago (87 944S with Koni yellows, stiff suspension, and 17"). It happened at about 7000 rpm around a corner in 3rd gear. With the information above its seems that it was inevitable (high rpm, 16 valve head, high cornering force).
1. Don't exceed 6000 rpm in corners(unfortunatly most of the aftermarket chips raise revlimiter to 7000 rpm - why? it just hurts the engine).
I don't understand the reason for the increased revs because max power is usually at 5800 rpm on the 8-valve cars and the power peaks are near optimal on the 3-4 and 4-5 shift if you use 6000 rpm as a shifting point (with good chips - see Farzaan's dyno results at <a href="http://www.novustelecom.net/~fkassam/dyno/dyno.html)." target="_blank">http://www.novustelecom.net/~fkassam/dyno/dyno.html).</a>
2. Install a pan baffle if you don't have one.
3. If you want high rpm go for accusump and redrilling of the crank.
As some of you know I blew the #2 on my street car a while ago (87 944S with Koni yellows, stiff suspension, and 17"). It happened at about 7000 rpm around a corner in 3rd gear. With the information above its seems that it was inevitable (high rpm, 16 valve head, high cornering force).
02-12-2002, 01:06 PM
#30
Done With Sidepatch
Rennlist Member
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The crank also spins up a batch of oil and
keeps it in suspension, especially at high rpm. This oil cloud circles the
crank and is the reason most race engine have "scrapers" in the case. Up to
two quarts of oil can be circling the crank at high rpm!
Would "knife edging" a crankshaft help prevent this...Coupled with the fact a knife edged crank is light, less rotating mass, and would allow the engine to rev quicker...or did I miss the boat on this...
I'm toying with the knife edge idea myself <img src="confused.gif" border="0">
keeps it in suspension, especially at high rpm. This oil cloud circles the
crank and is the reason most race engine have "scrapers" in the case. Up to
two quarts of oil can be circling the crank at high rpm!
Would "knife edging" a crankshaft help prevent this...Coupled with the fact a knife edged crank is light, less rotating mass, and would allow the engine to rev quicker...or did I miss the boat on this...
I'm toying with the knife edge idea myself <img src="confused.gif" border="0">