A while ago I wrote an article about the 944 Oiling System, with some ideas about #2 rod bearing failures. http://newhillgarage.com/2013/06/25/...tem-explained/

Last week I replaced the rod bearings in my track car. I wrote a fairly comprehensive article that I've posted on my website here: http://newhillgarage.com/2014/12/29/...g-replacement/

I know there is a lot of angst out there about rod bearing failures. And a lot of ideas about the causes. I don't think there really is a definative way to find a true single cause simply because there are so many variables. Age of the engine, maintenance history, usage, oil type/brand, oil change interval, etc. But based on my recent bearing change here are a few more data points.

The bearings in my track car have been in there for about 25 track days. Nothing but pedal to the metal, high rpm usage. Hard usage. I run R-comp tires so lateral G loadings are typically greater than 1 G. I run mainly at VIR and Road Atlanta. Its gets hot. The engine is a stock N/A engine with the exception that the balance shafts are disconnected and I have a later model oil pan (the one with the oil level sensor). I use 20-50 Valvoline Racing full synthetic oil and Mann filters. I change the oil and filter after every other track weekend. As noted in the article, the "trap door" device in the bottom of the pan had come loose so was not active for some unknown period of time. My crankshaft is not crossdrilled. There have been times when I came in from the track and found the oil to be almost a quart low. I don't like to let it get that low but the back straight at Road Atlanta really seems to suck the oil out of my engine!

I'll be the first to admit that I don't have much experience with used rod bearings but to my eye the bearings I took out looked to be in good shape. There was no appreciable difference in the appearance of the #2 bearing.

So to what do I owe my good fortune? Beats the hell out of me. I'm sticking with the policy of using a good motor oil with low foaming properties. And changing it at conservative intervals. I'm sure the later model pan helps as it has obviously different baffles and also crank scrapers. So there's my update. I wish everyone a Happy New Year and also Happy Motoring!

 

I think quality and level of oil has a lot to do with #2 failures.

I always wondered what is the point in welding metal around pickup mesh, how should that help picking up oil..

 

Zinc!

 

It keeps the suction focused on the very bottom of the oil pan, as opposed to the sides of the pickup tube, which is where air would be sucked in first from extreme oil sloshing.

I have a theory about another contributor that people don't talk about - the bearing fit and/or the big-end of the rod going out of round. First, the big end of the rod will stretch a little over time, especially at high RPMs, and elongate the round opening. Once a little gap has developed, two things start happening: the oil runs out faster (larger space) so the oil film preventing metal-to-metal contact isn't as efficient, and the crankshaft journal starts "hammering" the bearing at the transition of the crankshaft pushing the piston up, and the combustion pushing the piston down. Think of it this way: if you're trying to hammer a nail, the further you wind up your swing, the harder you can hit it.

Second, this picture below is from a bearing from a race engine which had about a year on it. I remember building that engine, and the #3 bearing was a bad fit (Glyco) - it protruded above the ends of the rod cap. I filed it down until I thought it was a good fit, but, in reality, that should have been a red-flag not to use it... For whatever reason, whether is was still too large and put an unusual force on the crank, or if it was too small and allowed for an excess gap, it showed extreme wear *and* it fell out of the rod cap when I took it apart - it had no more "spring" holding it in (thus the hammering was evident).

 

Hi Van, the issue that the stock bearing we are using are too hard. They are meant for high milage use. Race bearinngs which they dont make for 944's are softer which will take more abuse from lack of oil/pinging/air in oil. Thats why the "H" bearing setup. Properly baffled larger oil pan, modified rods/bearings, proper warm up before racing also helps. my 2 cents worth.

 

Good to know!

Happy New Year, Ernie!

 

Pickup tube already picks up oil on the very bottom of mesh filter since it is shaped like that and oil pan has a bulge to go even lower on the spot where pick up is.

In this picture the pickup is at the same level as the end of added metal belt , so it really does not extend it, what it might do is trap air instead.

I would really love to see a proof that this is working, but I doubt it.

 

michaelmount can re-round them for you

 

an interesting read http://www.bhjdynamics.com/index.php...page=page&id=4

 

Yes. And he does!!

 

Gents..so as a newbie to P-cars..and wanting to build my engine for street use only..should I stick to the Glyco bearings or go with the H-bearing set up?? My engine is apart right now and I have already bought the Glyco bearings...main & rod...need input please..Thanks

 

We run glycos in our all of our race cars. Change them every 30 hours of race time, so after every 2nd race (15-16 hour race weekends). Always look good coming out. Good preventative maintenance. They will be just fine for your street motor.

Every spun rod bearing I have seen in the 944s, the car has been a quart or more low on oil....every time.

 

I think Glyco bearings are fine for the crank. I use the Michael Mount rod bearing setup now.

 

It would have been more interesting than doing a visual inspection if you had the clearances of the rod bearings when installed compared to after the 25 track days. I would curious to know if there was any difference of the wear across all the rods, especially between rod #1 and rod #2. Maybe next time.

 

The thickness of bearings can be measured with a ball micrometer so you can compare old and new. It's a great tool. Here's a good example for the hobbyist;
http://www.ebay.com/itm/1-Dual-Ball-...item35de35e56d