carlege

awesome

Oddjob

What about the width - were they narrower than stock?

944meister

Yes they are slightly narrower than stock, but its shouldn't be anything to worry about since the pistons/con rods are theoretically inline with the bearings. I have access to some very precise measuring tools and i will compare them to the glyco's before they get installed

Oddjob

My concern with that is:

Stress is force / area. If they are narrower, the area carrying the load is proportionally reduced, so the stress is increased by that same percentage. If the bearing material is 10% stronger, and the area is 15% less, then you have a weaker solution.

944meister

I understand that, however these bearings are used on cars that produce far more power than an S2.

944meister

update: the clevite CB-1628H bearings are .002" thinner than the std. glyco bearings and the locating notch is wider as well. it could be ground down to fit in the locating groove, but i did not bother since there was more oil clearance than i would have wanted, i ended up replacing with a set of std. glyco's.

john gill

Hello there

Curious as to how you measured the clearances , I take it that you didnt machine the notch and fit them to the crank ?
I would have 2 thou in a performance engine would be ok ?

Thanks

JET951

I do not know if any one has thought of this but the connecting rod bearings like the crankshaft main bearings are never ever designed to make contact with their corresponding metal counterpart , meaning if there is even a fraction of a second contact between the metal surfaces then the slipper bearing in question is now badly damaged ( flatspotted / hammered/ galled ) what ever way you want to put it its damaged and Will Fail very shortly .

But how I hear you ask ?
Answer = lack of oil film strength & or oil pressure at that bearing/s and OR the conrod bolts have stretched ( mechanical overrev / downshift over rev )

Meaning if its the first & most common cause then the first line of defence is oil pressure between the bearing shell & the crank journal , the second line of defence is oil film strength , combined you will have reliability
Note } the above relies in that the said bearings are in excellent condition before being flogged at the track & not already damaged

Now to background info }

A) 944 / 951 / 944S2 / 968 do have a small flaw in their road going crankshaft design , and that tiny flaw shows up at high core temp ( read very high oil temp) and at high RPM , no 2 conrod bearing will starve of oil pressure compared to no's 1 , 3 , 4 ,
The 928 series has the same tiny flaw and its no 2 & 6 conrod bearings ( same journal on crank)
The same period 911 air-cooled engines are similar , they will starve 2 & 5 conrod bearings if insufficient oil pressure is NOT supplied & how do we induce this insufficient oil starvation condition in these last century Porsche engines ?

Answer = Easy , run too low oil viscosity , add high oil temp & Max revs at a track or even road = BOOM

The Flaw is that all the above are road engines and like all road engines they have radially feed oil pressure into the crank to feed the conrod bearings , this means the oil at high engine RPM has to fight against centrifical forces , where as AXIALLY feed oil pressure into the crank ( like the Porsche 917 engine ) sometimes known as nose fed and later Porsche dedicated RACE engines do not have radially feed oil feed , thats just for road cars that pretend to be race engines

How do we get around it ?
Answer = easy just increase oil viscosity up to where the owners manual says so ( for road conditions)
For track , you must increase oil viscosity further & add extra oil film strength , hence why oil companies make racing oils , which by the way are all higher in ZDDP which gives higher oil film strength

B) We have been competing 951's ( 944 turbo's) in either 2.5L single cam engines or 3.0L twin cam ( custom of our design)turbo engines( 440+HP) for years on the race track with NO crank ( connecting rod failures at all ).
With two Drivers Championships and two Motorkahana Championships in the bag along with countless lap records & a heap of customer 944 & 944S2 & 951's with class winning & Championship results with no crank/ connecting failures at all

The reason & answer/ Clue is simple ( its in the owners manual that came with the car )
Oil Viscosity & in turn oil film strength , in other words in the owners manual( oil vis page) it states( for road use of say a 944/ 944S / 944S2 / 951 / 968/ 928, from minus ten deg cel to Unlimited high ambient temps use a 20w-50 engine oil ( shaded look at me section )
This is a last century oil viscosity for a last century engine design , nothing wrong with that at all , its just a fact .

Now the basics }

What is engine oil film strength ?

Answer = The ability of the engine oil to keep metal parts away from each other , like cam lobes from scratching into the hydraulic lifter faces or alloy pistons not galling against the alloy cylinders or the ability to just give that last fraction of a second defence( last line of defence) against lowish oil pressure in no 2 con rod journal / bearing at high RPM with very high oil temps

Hence the reason( in regards to proper racing of last century engines ) of monograde racing oils like Brad Penn SAE 50 wt racing oil for long distance events or the extreme Brad Penn SAE 70 wt oil for drag car engines ( no 5w-40 or 15w-50 ) engine oils here because they( engines) just fall to bits because of lack of oil film strength

How do you increase engine oil film strength on this planet in this universe ?
Answer = two things combined }
1) increase oil viscosity from say 5w-40 to say 20w50 ( instant increase in oil film strength)
2) increase the levels ( up to a point ) of ZDDP anti wear film
combine the both = maximum oil film strength , remove one = lower oil film strength , very basic stuff

Now what we do with our own 951 & customers 951's / 944S2's etc }

For the track , first prepare the car with the following }

A) Sump off and new big end ( con rod bearings ) standard Glyco bearings
If its a turbo with more HP then aftermarket rods & standard Glyco bearings

B) Head off and new valve guides ( twin cam 944S , 944S2 , 968 must have new chain between cams & slipper guides) , providing the chain sprockets are not worn

C) Later type oil thermostat

D) Much larger oil cooler ( optional for NA ) Not an option for Turbo , and when I mean larger I mean three times the size

E) we do not run dry sump or acusump at all , even with the use of slick racing tyres on the track

F) standard oil baffle in sump & standard sump , we do NOT modify the crank or oil pick up one bit

G) custom crankcase ventilation system , so we control the crankcase venting on the track ( important)

H) This is the clincher , higher racing oil viscosity ( as opposed to the road 20w-50 oil vis) , meaning we run 25w-60 Valvoline racing , Minimum viscosity , meaning this is the absolute "minimum" viscosity the 951 should ever hit the track with

I) Sump off after every season ( simple to do) and recheck the condition of the conrod ( bigend) bearing shells ( no 2 particularly) and then depending on boost you can increase the checking intervals to say every 18 months

Note } 25 year old "standard" conrods are generally OK for just road use , these days to get a 944S2 , 968 , 951 ready for the track and if the funds are OK , we will install a new set ( 4 ) of good quality aftermarket conrods while the sump & head is off , this completely gets rid of metal fatigue worries at the track & guarantees perfect roundness of the conrod & conrod bearing for the crank journal


This is not rocket science its just a basic understanding of a basic 4 cylinder well designed engine that does not take this century car engine oils ( read low viscosity / low ZDDP/ low oil film strength) well at all & neither should it because it was designed deep into last century when the use of oils like a 20w-50 as an engine oil was the complete norm

Regards
Bruce Buchanan
Buchanan Automotive 40+ years working on Porsche cars

Duke

That is a very good post Bruce/Sean. What type of G's does the cars you mention pull on your tracks? Steadily ~1.2?

For an all out race car that can pull over 1.4 G spinning above 7000 rpm a dry sump is probably the only solution along with the good suggestions above.
A club sport type of car might survive if checking/replacing the bearings yearly but that is probably too much work for the average owner.

944meister

i used a pair of micrometers to compare the thickness of the new clevites to the new glycos, i could still use the height gage at work (accurate to .0001") to check them before i return the clevites. i did not grind the notch down, so i just replaced with a set of glycos, plus the locating notch would slightly offset the clevite bearing (very minimal). i got some amsoil 20w-50 im putting in the car when i get it all back together. the amsoil is better and a little more expesnive than the mobil1 15w-50 ive been using, but it has a 15,000mi service life, so in the long run it is cheaper since i would be changing the oil less. ill probably change it after 10,000mi the first time around, or send in a sample to get tested. thanks for the great info jet951, its good to get info from someone in a very hot climate, i feel more comfortable with my bearing decision now.

john gill

I wish to state straight up that I have no experience with the 4 cylinder porsche engine , but am now convinced that you cannot compete in any race with a wet sump engine in the v8 variant . This is the way to show up the inherant flaw in the design of this engine , in that it fills the heads with oil , uncovering the oil pump suction pipe and severly aerating the oil .
Unlike the above post , the 1/5 bearing get the first gulp of air destroying the oil film , have a look at the oil circuit in the cradle you will see , why if you aply simple fluid dynamics .
how do I know I have replaced the bearing 3 times in the last 2 years .
I complete in the local Porsche club events , last year placed 3rd in class . SO am not hanging around twiddling my thumbs.
My engine has installled the 944 oil limit valves in the heads and has an I and J scraper system ( although I now believe that this convoluted scraper helped prevent the returning to the sump and greatly contributed to the problem) . ANd I run 60 weight racing oil (AMsoil) .
I know when the bearings are worn with gathering data , the pressure starts to fall off at idle, deteriated for me too fast last time so the crank will need a grind .
SOft bearings (glyco) dont stand up to much stress, otherwise why would people develop stronger and better units , the glyco coating is so soft you can scratch it off with your fingers .
Hence my interest in the bearings .

JET951

Hi John , I know what you are getting at and I agree to some extent( in principle) , however the experience we have had with the twin cam 4 cylinder 944 Porsche engines ( 944S2 , 944S2 custom low comp turbo engines , 968 engines) which in effect are basically 1/2 a 928 engine ( in principle ) is that we do not have any issue with too much oil in the the head ( Now ) , or put it another way we have no issue with oil return back to the sump ( qualified) , however we did see the reason why people thought there is an issue in that area ( more info see below )

But & its a Hugh but , we "did" have Hugh problems with way too hot engine oil with only three laps in , we even had a customer with a modified 944S2 ( normally aspirated ) that when driven ( read thrashed) at the track his engine was showing 140 deg cel oil temp in just 4 laps of Eastern Creek raceway( all these cars have VDO oil temp gauges) , the same engine today with its 3 times larger oil cooler( than standard) is 115 deg cel , and correspondingly the same racing oil viscosity is showing .8 + bar higher at idle( & higher at all other revs) after a track session , just because of oil temp

Why is that important ?
Answer = the engine oil at the 130 deg + cel and above mark just drops the oil viscosity to such an extent you "will Loose oil pressure " , if you control the oil temp you will keep control of oil pressure .
Remember on this planet the hotter the engine oil the lower the oil pressure , as you stated its simple fluid dynamics .
So I recommend a large stand alone oil cooler ( not the one Porsche fitted 1990 - 1995 928 series ) way too small for the track

Now the next thing we had big issues with was crankcase ventilation , by trial & error we have found the sweet spot ( for want of a better expression) of the use of a in-house designed crankcase ventilation system that before( meaning standard) was interfering with the oil return ( back to the sump) of the oil that was already in the head + other issues related to excessive vent pressures .

By the way the standard crankcase ventilation design on a 928S4 is "only just good enough for road conditions) , we work on a lot of 928 series cars as you know & I can not remember a better candidate for a hugely improved crankcase ventilation system than a quadcam 5.0L or 5.4L Porsche V8 or for that matter the entire 928 series , after all they were designed for emissions and road going conditions only and in that context they are "Just adequate to cope ", however on the track pulling revs the crankcase ventilation system is completely inadequate and has to be modified to cope .
If you still have the standard system , then you will have trouble & this will interfere to a degree with oil return due to the pressurisation of the areas that should not be pressurised ( read crankcase) .

The next thing you must do is get rid of the scraper( who's idea was that ? ) , it just slows the oil back to the sump.

The next thing is , I know you dont want to hear this but here it is , the conrod bearings ( bigends) are never ever ever ever ever allowed to touch / contact / hit / the corresponding journal at all , yes I mean never ever , it wouldn't matter if they were made kryptonite ( superman stuff) , they will instantaneously be damaged ( meaning flat spotted / galled etc)because the forces are so Hugh , so preversly the so called soft Glyco bearings are very kind to the crank journals

Lastly do not machine the crank( you mentioned this) and then return to the track , it just doesn't work , we will never ever machine a Porsche crank ( never ever ) be it 928 , 944 , 911 etc etc etc , there are technical reasons I will not go into here because it will fill thirty pages and I do not have the time ( unless you pay me ) , if you need a crank buy a 2nd hand one ( they are plentiful for the time being ) and back to standard size .

I can go on but ran out of time

BB

Eric_Oz_S2

Bruce,

Good post. PS - the LSD I got from you is still going strong!

I think I know what you are getting at with the cc ventilation. I seam to get a bit of leakage of oil from the cam cover no matter what I try. On the road you don't normally get any problems, but on the track I get oil weaping out from the gasket area. I think some is also blown out through the rms. So what is the answer to this problem? Do you modify the AOS and install a separate catch can. (I suspect I need to replace the AOS o rings as well - on the list of things to do.

My car is supercharged now so the crankcase vent pipe is connected just before the supercharger.

M758

So is there anything you can share that might apply to a 944 motor?

dgt

JET951, Could you shed more light on the crank case ventilation modifications you've implemented for a 944/951? Thx, Doug