3.0 Rebuild Q's?

KoenigsTiger · 10-03-2009, 02:16 PM

Hey Guys!!!

My first Porsche eng rebuild, I've done a top end on a VW before...

Anyway. One cam is shot and six rockers...

I was thinking of going with 964 cams. Obviously if I get a reground and hardened cam I have to get a set of rockers to match... I want to stick with CIS for now.

One of the cylinder holes has a bit of wear on it from a broken stud. Its just look a bit worn, no noticeable metal removed.

I was hoping to go with 9.8 CR Euro spec pistons, but they are pretty rear. Does JE even make 9.8? Wayne's picks mentioned JE 9.8. Now I see 9.5 and 10. Is there much of HP difference between 9.8 and 9.5? The OEM ones are better then JE, because the have a swirled top?

Thanks guys!!!

Gene

Steve@Rennsport · 10-03-2009, 02:35 PM

Your camshaft damage is typical for what I see these days. Its due to insufficient ZDDP in the oil as well as clogged spray bars.

Your compression ratio will depend on what octane fuels you will use. In such cases, "less is more".

KoenigsTiger · 10-03-2009, 02:42 PM

It's probably the clogged spray bar. The other cam is fine, has no pitting. The bad one has 4 pitted lobes...

I am thinking I'll go with the 9.5 JEs...

lucittm · lucittm's Garage

It is hard to tell from the picture but it looks like the damage on the cam is on the round part of the shaft where there is little or no real pressure from the cam follower. I would suspect galling (from low levels of ZDDP) to be on the lift ramp or "nose" of the cam lobe where there is significant friction and pressure. Also, notice the cam bearing surface looks superb except for very light scratching.

Due to the pattern (not symetrical across the face of the cam surface) I would almost suggest galvanic corrosion. This could occur if the cam stopped in the position where the cam follower was resting on the cam and moisture was present. That seems unlikely. The only other explanation would be porosity in the original cam surface that wore down on the surface and exposed the pitting. Almost like a weld that looks good until you hammer off the slag and see the pinholes.

Thoughts?

Mark

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Steve@Rennsport

Your camshaft damage is typical for what I see these days. Its due to insufficient ZDDP in the oil as well as clogged spray bars.

Your compression ratio will depend on what octane fuels you will use. In such cases, "less is more".

Steve,

How do you check the spray bar? I have disassembled my 3.0 liter engine and very much interested to know how to check it before sealing the case. Thanks.

Tony

prschmn · 10-04-2009, 04:57 AM

Another theory to ponder is flaking or spalling of the surface hardening. Subsurface cracks can develop due to stress then some may come to the surface
where oil can be pushed into them with hydrostatic pressure which then pops the hardened layer off. hard to tell from the picture and clogged spray bars are all
too common as well. Either wayit's expensive! Seen a lot like this over the years.

KoenigsTiger · 10-04-2009, 07:57 AM

I haven't cleaned the spray bars. Can they be removed? Or just carb cleaner sprayed out? The odd thing is that, the other cam does not have any pitting... This one has 4 lobes shot.

camgrinder · 10-04-2009, 09:46 AM

This camshaft have lobe taper. The rocker arm was riding on one side of the lobe. Very common on right bank 3.0 litre cams. Looks fixable, but I would have to have them in hand to know for sure. And as already mentioned, the lack of zinc and clogged spray bars will also accelerate the wear.
I also see very worn rocker arm bushings with cams like these.