#5 rod bearing is worn and not other rod bearings??

[Sboxin]

We have the engine case split and are wondering why the #5 rod bearing would have so much wear and not the others??

1992 964 3.6L thought to have 115K miles

Thank you,
Roy T

Photos --

[Steve@Rennsport]

The very last place for oil to reach in a 911 engine at higher RPM are the #2 & #5 rod journals so when they fail, oil starvation is usually the cause. If this was a stock engine that would have never seen 7K, its more likely due to hard running with low oil level.

Naturally, each case gets judged on its own merits and some detailed forensics should be done to see if this is the case here. One would need a LOT more information to offer anything further.

[Sboxin]

Steve,

Thank you for the excellent review -- we really don't have a lot of information on this engine.

We will take the time to thoroughly check/clean the oil passages and pump.
The main bearings are good except for the rear main has some wear.
We will replace all the bearings and micro-polish the crank.

Regards,
Roy T

[Steve@Rennsport]

Originally Posted by Sboxin

Steve,

Thank you for the excellent review -- we really don't have a lot of information on this engine.

We will take the time to thoroughly check/clean the oil passages and pump.
The main bearings are good except for the rear main has some wear.
We will replace all the bearings and micro-polish the crank.

Regards,
Roy T

Don't forget/overlook a thorough cleaning/scrubbing of the oil tank, thermostat, and all lines & fittings as thats where metallic debris gets lodged.

[AlfonsoR]

Steve W,

If you do the crank mods to the #2 and #5 and groove bearings as well, do you also recommend upgrading the oil pump to ensure adequate flow to the new orifice or is that not necessary?

Thanks.

[Steve@Rennsport]

Originally Posted by AlfonsoR

Steve W,

If you do the crank mods to the #2 and #5 and groove bearings as well, do you also recommend upgrading the oil pump to ensure adequate flow to the new orifice or is that not necessary?

Thanks.

Your stock oil pump is adequate up to 7500 RPM. Beyond that, I'd be using a GT-3R pump for its much improved scavenge capability.

[Sboxin]

Thanks Steve, you are always a really big help on this forum!!

[Walt Fricke]

If you use the GT3 pump, consider two things:

1) With the 964 engine case, you may not have to relieve the case for the pump, because it has a big pump to start with. But good to check. And also for rod/crank throw clearance. For sure, if you use an earlier case you will have to do some work. See the post "oh-oh" for the problems a little crank/pump clearance caused.

2) For reasons I don't fully understand, in order to have oil pressure build beyond about 30-40 psi as RPMs increased on my 2.8 motor with an early turbo/3.0 case, I had to shim the oil pressure setting spring. Porsche did this, and there is a part for it, in the GT3 and Cup car engines. The spring, piston, and other parts are the same as they were on the 3.2s and later.

[Sboxin]

Thanks Walt for your comments on the oil pump and pressure.

Yes, I did see the "oh oh" thread and will check on the spring related pressure.

Right now we are thinking of staying with the existing 964 oil pump - mostly because we plan to limit RPMs to under 6800. If, in the future we redo this engine for big HP and RPMs we will find a GT3 pump and make some other suggested modifications.

Regards,
Roy