kevin12973

How often are 944 owners changing their rod bearings? In particular, cars only (or mostly) seeing track miles. I know their are people changing them after every event but that sounds extreme. I would like to hear how long you can go safely between rod bearing changes. This will make my decision on the Lindsey 3 piece crossmember. Thanks, Kevin

PorscheDoc

We change rod bearings on the track cars every 2 years. Our chump car got them every 2-3 races (one a year), but that would be 2-3 events a year, anywhere from 12-24 hour races, so it was logging a lot more hours than the other track cars.

Eric_Oz_S2

In my S2, after 6 years of track use I pulled the bearing out and measured them. They were still towards the minimum range of specified clearance - ie like new. Even though I had new bearings I put the old ones back in as they were almost perfect. Total mileage about 155,000 km. I know most of the history of the car and it has always been very well maintained.

Perhaps the S2 with the improved oil pan insert and different block profile and windage makes all the difference. The oil also gets changed every 3rd or so track day and I only use 20W60 oil.

So I think there is no clear answer to the question in terms of optimum replacement interval. It is probably more reasonable to suggest that if you don't know the history you should change them.

I suspect a lot of failures are related to poor maintenance, oil spec and oil level.

VirginiaF1

Welcome Kevin..

Although not a track car, my 260k daily driver has original engine and while I've not measured tolerances, the last 2 oil analyses still showed virtually no metal wear.. ( @251k & 256k)
Shell Rotella T6 5W-40 plus a wee bit o' ZDDP from Rislone.

Cheers!

harveyf

Based on nothing more than I can do it myself and I don't go to the track in the winter, I have decided to change the rod bearings each winter. There is a post on my website about my recent bearing change out and pictures of the bearings after 60 hours of track use.

Note that the key to bearing life is maintaining that very thin film of oil between the bearing and the rod journal. The daily driver goes 300,000 miles on one set of bearings. If you miss a shift at the track and over rev, one possible consequence is that the inertia forces on the rod bearings shoot up for that very short period of time, the oil film gets squeezed to nothing, and kerblamo, you've got a failure. Run on a hot day with high oil temps, reducing the effectiveness of the oil and kefblamo, you've got a failure. Let the oil get too low and suck a few air bubbles and kefblamo, you've got a failure. I suspect that just replacing the rod bearings is not that effective in the face of other more dramatic factors but it is fairly cheap insurance.

BTW, I run Valvoline Racing 20-50 full synthetic and I change it every other track weekend. No real science behind that decision, just relatively cheap insurance.

Your results may vary.

kevin12973

Thanks for all the detailed responses. This is just what I was hoping to hear. I think I was being a little paranoid. I think as long as I dont hear any nocking I will leave it alone.

TexasRider

For track time I think before it was concluded ( some how another by experience and calculations and pure guess ) that more failures occurred arounf 100-120 hours. So the replace time became 80 hours. Then it became maybe 60 hours. So dependent on conditions and how you are set up maybe 60 - 80 hours all the way to 100 hours if you are feeling lucky and not at max rpm all the time.

TexasRider

Separrately my bearings were great at 26 years and 91,000 miles on my 1986 951. But I replaced them anyway.

dirtyTurbo

I don't think the problem is with the bearings themselves, there just isn't great oil flow to #2. Rarely will you take the bearings out and find they were just about to fail, its all or none. I'd be more concerned with oil cooling and flow.

This is just my opinion, I could be wrong.