Is a performance oriented rod bearing the solution to 944 rod bearing failures? Well, I won't go that far, but a good rod bearing is a huge step forward in addressing this painful issue.

First, a little pertinent history: Years ago early 911 racetrack oriented engines started having rod bearing issues similar to the 944. An investigation revealed that Glyco had changed the bearing material and structure to something more appropriate for the perceived intended purpose - street driving. The failures continued until Scott McPherson at Auto Associates in CT (860-693-0278) commissioned a race quality bearing from a major bearing manufacturer. He made them available to the performance community and the issue went away. Thank you Scott! Fortunately there's a large enough market in the 911 world to justify that investment.

The 944 OEM rod bearing (also Glyco) is another street design, and usually does its job in that application. On the race track or when used in performance applications, however, it's out of its element. The bearings won't survive the distortion of the connecting rod big ends at high RPM, and the material is way too soft for severe service. What's needed is a performance oriented bearing like Mahle/Clevite's 'H' spec bearing. Here's their description:

Mahle/Clevite H - Series Bearings
These bearings were developed primarily for use in NASCAR racing, but are suitable for all types of competition engines. H series bearings have a medium level of eccentricity, high crush, and a hardened steel back. They have a precision wall tolerance of +/- .00015" with strong, extra thin overlays to withstand high loading and resist flaking.

I've used the 'H' bearing many times in the 944, but had to machine the crankshaft rod journals to a smaller size and use custom connecting rods. Since this is a relatively complex and certainly expensive solution, a simpler approach would make the modification more suitable for the typical 944 racer. It turns out that there's a Clevite 'H' bearing that can be made to fit a modified 944 connecting rod. We've built a dedicated fixture to machine the rod, and the wimpy Glyco rod bearing gets replaced with a performance oriented H series bearing which fits the standard Porsche 944 crankshaft. The result is an inexpensive upgrade to any of the existing 944 rods. The process includes fitting the 'H' bearing, re-machining the rod's big end to ensure concentricity, setting proper oil clearance, checking the pin bushing and balance. The rods get returned with a new set of the Mahle/Clevite 'H' bearings. Life is good, or at least better….

The 'H' bearing conversion can be performed on any cast or forged 944 rod. The 'H' bearing may be even more important with cast rods since the big end tends to deform more at high RPM than the forged pieces. The eccentric design of the 'H' bearing addresses this issue and prevents the bearing from 'pinching' the crank journal.

This modification shouldn't be considered a complete nor perfect solution to the 944 rod bearing issue, but it's certainly a major improvement to a serious problem. It should be strongly considered for any performance oriented or race 944. The basics still apply: maintain proper oil level, use an appropriate grade and weight oil, and monitor oil temperature and pressure.

Photos show (1) an unmodified rod, (2 and 3) rod modified to accept 'H' bearing, (4) new bearing installed in the rod.

 

Hopefully this is a great improvement on the current bearing failure issue.
Tanks for sharing.

Bookmarked for next rebuild.

 

It sounds like you are suggesting that you can just send in your rods for modification. How do you set proper oil clearance if you don't have the crankshaft to check it? Is there normally no wear to the crankshaft journal so it is irrelevant?

 

Very interesting, I have been wondering about a solution to the #2 problem for my next engine build.
Do you have a ballpark cost for parts and machining a set of 4 forged rods?

 

Maybe this could be applied to 944 block:


http://www.amicale928.org/forums/vie...t=7951&start=0

http://jenniskens.livedsl.nl/Technic...arings%202.pdf

Looks like it could be part of solution to the problem:

 

The Porsche cranks are tough, and wear is minimal even with very high mileage. I've measured many, many 944 cranks and they are surprisingly consistent; be they old, new, 2.5, S2, or 968.

 

Yes. My understanding is $350/set gets you the machining to fit the bearing, make the rod big end concentric, set the proper oil clearance, check the balance and check the pin bushing, and includes a set of the 'H' bearings.

 

Sounds like a deal. How many racers know about this. And, who is it that you send the rods in to get them remachined, etc.? It isn't clear to me who actually does this work for us.

 

This is new, so at the moment relatively few racers are aware of it. At the moment it has only been announced on RL.

I'm retired. I also don't have a sponsor rating with RL. However, I'm close enough to this process and the shop to stand behind the quality and the professionalism (we go way back). This is a service to the 944 world.

 

Interesting. What's the bearing length for these bearings? The reason why I am asking is that the 928/944 pistons and rods are heavy compared to modern engines, and I am curious about the bearing area.

 

Tuomo, I thought I send you possible bearing options in PM message while back already. There are several. We have two sets of 928 rods currently in machine shop ready for pick up which have this modification done. Clevite bearing we use seems little difficult to find in STD size but we have enough for now for our own needs. Based on pictures in #1 message its different bearing since it needs lock groove cuts into different position. Its almost within mm same width as stock Clyco so its difficult to be worse than factory stuff.

 

Erkka -- Yes, your bearing choice for the 928 is long, almost as long as the 928/944 stock bearing. I was wondering if Michael Mount's bearings were as long as stock, as well. Using the relatively new 52mm journal bearings that Clevite makes for Subaru would be nice because of the wide availability for the infinite future, but those are significantly shorter than the 928/944 stock bearings. Not that it would necessarily be any problem, but maybe one would want to do some computations before using the Subaru bearings.

 

Specs on rod mods? Part # and supplier for the bearings? Any shops in 'merica offering this mod for $350 mentioned cost? Sorry if I missed this info else where.

 

There's only one place doing it. Here's where to send your rods:

BPMS
Attn: 944 Rod Mod
5210 Minnick Rd.
Laurel, MD 20707

$350. includes the machine work and a set of the 'H' bearings. Payment via PayPal. You can contact me if there are any concerns/issues.

 

This could be done to a 944 Carillo rod, right?