964 3.6L Engine Parts Evaluation

rothaus · 10-10-2022, 02:27 PM

I posted earlier about the condition of the pistons and cylinders of the 3.6L engine I working on, and I thought it would maybe helpful for others as well to start a post for additional parts as I go along.

The question about the Piston and Cylinder is located here:
3.6L Piston and Cylinder dimensions

Today it's about the camshafts of that engine.

The camshafts have some areas what looks like pitting.

My question, could this be there from the factory all the time ?

Below are some pictures of the cam lobes with the pitting. I also have a second set which has also some of these spots. So the pictures are from both sets.

The rockers actually looked very good, which makes me think that these spots on the cam lobes were there from beginning on. Below is a picture.

Any input is appreciated.

Thanks
Engelbert

prschmn · 10-11-2022, 06:09 AM

Your post may start yet another oil thread! The cause has been a subject of debate for a long time. Some/many blaming it on reduced Zinc. I am not a proponent of that though.
Found an article years ago from an industrial site stating that what was found was that the hardened surface was actually popped off by hydraulic pressure forcing oil though micro cracks which seems quite plausible to me. Soooooo-yup they may well have been there a very long time.

Peter M · 10-11-2022, 01:11 PM

Most of the spalling appears to fresh and clean to be there from the factory.
If it was an oil issue there would be other evidence of distress and more lobes would be effected.
Fix the problem now as it will only get worse.

Neil Harvey · 10-11-2022, 02:11 PM

These cams are cast. They use a type of mould called a chill, in difference to sand casting. Drop one and find out how brittle they are.

Crappy base material full of nasty inclusions. Many just under the surface. In your case exactly. With the contact stresses involved and poor oiling in these engines to remove the heat, the surface material breaks down and the inclusions appear.

Can be repaired but check all other part involved to make sure they are all good.

safe · safe's Garage

Good news!
You get to upgrade the engine with spicier cams!

If you look where the defects are, they are mostly on the high load areas, not the base circle, that should give you a clue to if they were there to begin with or not.

rothaus · 10-12-2022, 04:05 AM

Thanks to all for your input. So these cams are basically trash, or maybe repairable ? What would be my alternative. New cams are expensive.

Thanks
Engelbert

dannobee · 10-12-2022, 05:16 AM

Those cams can be welded and reground to whatever (reasonable) specs that you want.

Dougherty Cams, Web Cams, Elgin, etc.

rothaus · 10-12-2022, 09:01 AM

OK, great, there is hope. I will check with these companies.

Thanks again for all the input.
Engelbert

gled49 · 10-12-2022, 03:51 PM

New or reconed cams, u must use new or reconed rockers.

Sboxin · Sboxin's Garage

We used Web Cams for our 3.8L race engine a few times now - - great turn around time,
excellent customer service, etc. . . . did both cams and rockers . . . pitting is sometimes
due to cold start warm up procedure, i.e. don't idle to warm up - too little oil on cams
causes wear, etc. . . .

Wish you the best on your project,
Regards,
Roy T

PS: Also, we use Amsoil race oil 15-50 . . .

Bill Verburg · Bill Verburg's Garage

If you have the cams remanufactured, go to ss spec, It will really wake the 964 motor up

safe · safe's Garage

I can recommend these:
https://www.fvd.net/us-en/100105964002/camshaft-964-993-street-sport-right-mra-21-mm-tdc-49mm-brg.html

Makes good power, comes in like a freight train above 4000. Dyno tested before and after in a friends 993 3.8, 300 vs 330 hp, same dyno, different day (different year actually).

i got those too in my car.

RSstop · 10-29-2022, 10:08 AM

Yes, welded lobes can be done but it adds about 3-6 weeks turn-around time right now.
New castings are faster delivery but cost a few hundred more.
Sometimes there is still enough base circle left to just re-grind those fretted cams with a mild upgrade.
You would probably need to sent to one of the grinders mentioned above to evaluate. Neil Harvey is providing new cams for us now too.

RSstop · 10-29-2022, 10:16 AM

Mark, I like your explanation on hydraulic pressure causing the fretting.
It is usually just on one side of the lobe which is usually loaded more than the other side. Hard to get rocker and cam faces parallel. Porsche usually didn't from the factory.

harrydarwen · 05:56 AM

Sometimes there is still enough base circle left to just re-grind those fretted cams with a mild upgrade.

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