refresh951

As I have researched high power builds on this forum I have been astonished at the number of these builds that saw their demise due to the #2 rod bearing failure. Whether it be at the track or the street, the #2 rod bearing failure is an issue that MUST be solved. Every couple weeks or so a motor goes down. Who really can blame those who have made the move to an LS motor when a VERY expensive motor can grenade seemingly at any time! A dry sump is a sure way to fix it if installed properly but not really practical for the average modder. I think Sid's stroker build may improve things because the rod bearings are smaller and you can use a much better, modern bearing but only time will tell. I would like to generate a best practices list in an attempt to avoid the issue. I know this is been covered before in many threads but thought it would be good to get a fairly exhaustive list in one place. What would your advice be to someone trying to minimize the risk of this failure?

Preliminary List Subject to Change

Usage List:

1) Use higher viscosity oil, 20w-50 Street, 25w-60 track
2) Avoid running over stock redline (6500 rpm)
3) Regularly change the oil and filter (every 2000-3000 miles)
4) Avoid oil overfill (top line) and oil under-fill (bottom line)
5)

Rebuild List:

1) Careful inspection of the oil pickup tube for cracking.
2) Cross drill the crank (especially #2 and #3) and properly chamfer the oil holes.
3) Check crank for straightness with a 0.001" max runout (see here)
4)
5)

refresh951

The top of the list for me would be to not run over the stock redline without a dry sump. I see a clear pattern that if you run over the stock redline, the risk of this failure goes up considerably. I personally am going to run my build at a lower max redline of 6400 rpm until I have a complete understanding of this failure.

Van

At all costs, reduce the potential for foaming oil. Foam is not a good lubricant.

I'd have to guess that common causes of "foaming" are:
-Over-fill the oil - the crankshaft will hit it and whip it up
-Cracked oil pickup tube - pump will suck up air
-Low oil - exposed pickup sucks up air

Then, of course, the #2 bearing is at the end of an "oil supply chain" - so it will always get the least pressure and lowest flow.

1987Porsche944WithRealLongName

Some guy from the 928 boards showed up a while back saying a big issue was between the metallurgy of the crank and bearings. You can't just change the bearing material without giving the crank attention though and he was pushing for some custom made crankshaft that was really expensive.

He was also selling it himself so there's no real proof of anything.

Paulyy

Maybe it could be the choice of oil also? I know patrick is over 7k rpm as a track car but not sure on his bearing status (stock bottom end)

Dave (CEP) says 7000 would be fine but i guess if you sit at 7k for long periods of time it'll damage?

rlm328

Cross drill the crank, open up the oil channels.

A lot of these problems were solved with the 2.7 / 3 liter blocks. And probably be your starting point for a re-build.

refresh951

I was amazed at the max crank runout allowed by the manual:

Typical Crank Runout: 0.04-0.06 mm (0.0016"-0.0024")
Max Crank Runout: 0.08 mm max (0.0031")

0.003" does seem high especially considering main bearing oil clearance is spec'd at 0.0007"-0.0038" for new bearings.

Here is some input on crank prep by Michael Mount to be considered:

"Here's some more input, some repetitive...

My 'race prep' for the 944 cranks includes checking for straight (.001 runout max.), cross-drilling #2 and #3, properly chamfering the holes, balancing and polishing. Then it gets measured so the oil clearance (critical!) can be set. The rod big ends are also checked for round, the ID sized for the oil clearance (varies with application), and each rod checked for length and twist. After corrections the rods are weighed and balanced.

The above processes are critical to maximize rod bearing life. Keep in mind the rod bearing is a street design that is being asked to survive a severe performance application. Ignoring proper preparation is an expensive mistake.

Here's a mod that's worked out great for the next step: Cut the rod journals to Chevrolet size (2") and use NASCAR type performance rod bearings. These bearings are designed (dimensions and construction) for racing and are light years ahead of the Glyco street bearing. A custom rod is required.

Of course dry sump eliminates the oil supply problems and even adds power due to windage and crankcase vacuum control. It's the best solution (along with the prep above), but also has to be done properly.

Hope this helps,
MM"

333pg333

I did run my stock motor up to 7000rpm but I had big oil cooler, very custom wet sump, ran a proper 25w/60 race oil with plenty of ZDDP...and didn't run it like this for very long as has been documented.
That motor is on an engine stand. It's going to go back into a street car that I'm putting all my spare parts into and then sell. Will be quite a nifty little thing...but will check the bearings out before it goes back in just in case. Shall report any unusual findings.

BTW: What are the downsides to Accusumps?

blown 944

Having spun a couple bearings in the past, I can only give my experience.

One was from over revving due to traction loss. It happened the third time I was taking off aggressively one night.

The other was from being low on oil and getting on it around a long curve.

To contrast. I have ran my latest engine up on the rev limiter in the water box over 60 times this last year (not a good idea, I know). The coating on the bearings are still perfect. I will be updating my thread with photos shortly.

lart951

never spun a bearing ran the car up to 23psi & 6500 rpms but iam a firm believer of 2k miles oil changes and friction modifiers

refresh951

Thanks Lart. Can you give more detail on "friction modifiers"?

lart951

btw my oil of choice is 20w50 castrol and duralube or slick50, in summer when temp hits three digits i use 1/4 of lucas just for the extra protection

lart951

i yet to feel what a spun bearing feels like (knocking on wood) lol

lart951

of the few cars that I have dissected and if you noticed my pattern (compared to other parts sellers)over the last ten years i dont sell motors together, I take them apart completely (weird) of those who had rod bearing failure dirty oil and sediment was a common denominator others, had some coolant on the oil probably a blown gasket and the milkshake was left too long in the car or the engine ran with milkshake for sometime.

Dirty oil was a factor on scored 944S & S2 camshaft & bearings as well.

on a few a broken or cracked oil pick up as well

User 52121

Good discussion... subscribing.

I know I've read a few of these threads in the past and it always seemed like the discussion came back around to RPM levels. It's one of the (few) reasons I liked my 26/6... I had no benefit to spinning the motor past 6000rpm. Just one extra little "safeguard". With the new turbo I'll probably lower the rev-limiter just to keep me from getting greedy, even if it means leaving some of the curve on the table.