YetiSpec944

I bought a 944 Spec Race Car last month. The car is an 83 NA, w/ an 8v 88 motor and DME, and an Accusump oil system. I knew the rod bearings where nearing the end of their life, but being too excited I took the car to the track for a day before replacing them. I made it 3 laps before I got a knocking noise coming from the engine. I dropped the oil pan, thankfully the car has a 3 piece cross member, and found a spun #2 rod bearing. There was a small amount of metal on the magnetic drain plug, and a bunch of copper in the oil and oil filter. I replaced the bearings, oil and filter, and cleaned the pan out. The crank was in fairly good shape, but had a little bit of wear from the bearing. I smoothed it out very carefully with some emery paper. After installing new bearings, the car seems to run smoothly in the two blocks I've been able to drive it. I'm headed to the track for comp school this weekend and I have a few questions. Does anyone have an educated guess on how long it will last? I've been told by some fellow racers that it could last ten minutes or a whole season. I'd love to hear from anyone that has had the same thing happen. Do I need to do any type of break in before taking the car on track? Any advice on things I can check before or after my first session? I was thinking about taking a look at the drain plug to check for metal, as well as check the oil for copper. Any advice would be greatly appreciated. Thanx in advance.

Nick
#185 944 Spec

Van

A crazy guy? Seriously, the Mantis cars do well, Ernie has good advice.

I'm not sure how much this applies to just changing rod bearings, but my understanding is that break-in oils have a high ZDDP content and no detergents. This allows a small layer of protective zinc to build up on all surfaces - cylinder bores, pistons, lifters, bearings, etc. Once the zinc layer has developed, it's safe to run a detergent oil.

So, my gut feeling is that it might be wise to run a break-oil procedure on the new bearings. Does anyone with more experience have more to add?

YetiSpec944

Thanx for the advice guys. The oil runs thru a canton oil filter attached to the accusump system before the oil cooler. The old filter had a good amount of cooper in it, but no other metals. I'm hoping that copper being a soft metal, didn't do any damage to the rest of the motor. The oil filter does not have a filter bypass so hopefully nothing got by it. The oil in it is 15w-50 Redline, which has lots of ZDDP, or so says the bottle. The goal is to run it until I have an issue this weekend, and inspect afterwards. If it lasts, the motor will get a rebuild with a new crank and rods. I'm just hoping the block doesn't have to end up as a coffee table... Anymore suggestions/thoughts are greatly appreciated.

Ernie J

check the filter !

T&T Racing

Nick,

My research on the internet says that when the #2 rod bearing spins on the crank that there is a good chance that the piston wall and piston are scoured on #2 cylinder and also that the rings could be damaged or broken. The rotation of the crank flings the failed bearing material up into the cylinder and coats the walls.

Before going to the track, I would do a compression test to determine the CR of each cylinder. If they are all within say 10 psig of each other and no big discrepancy for #2, then you probably had luck on your side. Also a leakdown test would be a good evaluation if the rings have failed on #2. This takes about 1 1/2 hours of shop time by a knowledge technician.

But the cost to know will save you muchoo dollars later. More damage to the block means sleeving which is costly, the crankshaft has been probably damaged so the clearances are not tight so the oil pressure between the crank and the rod bearing will not hold the rod bearing from contacting the rotating crank journal.

The accusump will not save a rod bearing because it senses the oil pressure from the output of the oil pump not the oil pressure at the interface between the rod bearing and the crank journal. For what it is worth, the accusump will not prevent a #2 rod bearing failure. Check the threads on rennlist to see what is necessary to prevent the #2 rod bearing failure. Some of what needs to be done was suggested by Ernie J.

Better to be patient and right and not go to the track, spend all the money for fuel in the tow vehicle, the registration fees, etc plus possibly blow up the motor.

Those are my thoughts

YetiSpec944

Thanx Ernie and T&T. We did a compression test before swapping the bearings, and it came back with great compression across all cylinders. Hopefully that means the piston/cylinder is still in good shape. I'm going to pull the filter today to see if anything looks shiny, although driving around two blocks might not be enough to tell. I'm gonna check again after my first session on saturday. Unfortunately, I've already registered for comp school this weekend, and missing it would mean waiting until the fall before starting wheel to wheel. At this point all I really want is for the car to get thru the weekend. Should I be easy on the motor the first session for break in? Or are the bearings ready to go full bore?
Thanx,
Nick

s14kev

Agreed. I've never spun a bearing on a 944 motor but have on non-Porsche motors. Cylinder wall damage (even though minor in some cases) seemed to be a common result. I could be wrong but my thought is when the bearing is damaged it looses its ability to rotate. In effect the connecting rod "seizes" to the crank journal. As the crank continues to rotate this force is transferred as a side loading forcing the piston against the side of the affected cylinder resulting in cylinder wall/piston skirt damage.

Jamesr6967

Just a little side note, you can increase the zddp easily by adding some Risoline .

333pg333

You can have too much ZDDP so don't just add more without knowing what ppm that will make.

Oddjob

The crank condition is definitely a concern. The #2 rod bearing does have an oil supply problem, and the bearing/journal gap is somewhat critical to exposing this oil flow deficiency. The larger the gap, the more flow is required to maintain the oil film. This is why oil pressure is an indicator of bearing condition. What oil pressure are you seeing at hot idle and high rpm full load? When the crank journal is worn, or worse yet, scored, its likely more succeptable to future bearing failures.

If no machining was done (e.g. machining the crank for oversized bearings, re-honed bores, etc), some engine builders will say no break-in is necessary. I had one local reptuable 911 engine builder tell me he will immediately push a rebuilt engine hard to redline (mind you, I did not take that advice on my own rebuild, so take that for what its worth). Point being, you will probably get some varying opinions on this. But very likely would not hurt to run the car easy for a few hundred+ miles before putting on the track.

YetiSpec944

Well, with the car not being street legal, I wasn't able to put any miles on it. I warmed it up good before heading out for my warm up session. I took it very easy, but on the 4th lap I had to get by someone and put my foot in it. As soon as I neared 5500 RPM the knock came back and I new it was gone. My oil pressure dropped just after from over 5 bar to 3 bar. I shut the motor down and coasted into the pits. At this point I've hopefully found a new engine to put it in. I will then tear this one down and find out how bad it is. Thanx everyone for the help and advice. Luckily, I was able to rent another 944 Spec car to get me thru Comp School. The whole 944 group is a great bunch of people and I can't wait to start fighting for corners.
Thanx,
Nick