Bigfoot928

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Bigfoot928

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ptuomov

Getting a set of completely stock cams is a good idea to see if they rotate freely in the heads. If the cams are stock regrinds from cams pulled from these heads, then I’d guess that the cams need to be straightened. If they are on some other cores, I’d mike the journals first and try rotating them with just one cam cap fastened.

Rob Edwards

Looks like everything is being fitted dry. Why is the exhaust cam in the intake position and vice versa in post #193?

Kevin in Atlanta

I cannot say enough about the support I receive on this forum. Thanks to everyone that has added to this thread.

Cam caps are correctly oriented and match the number between the exhaust ports.
Yes, the cam lobes are unfinished.
I do have a set of stock cams.
I have a dial indicator.
I don't possess a micrometer. I found a digital one at harbor freight - will that suffice?

So, I will buy a micrometer.

First order of business is to put the stock cams in the heads and retest.

Kevin in Atlanta

What an idiot I am - you are right. Off to test again. ROFLMAO

ptuomov

Good plan.

Thinking about it logically, there’re two reasons why the center can caps can bind. First, either the cam bearing journal is too large for the bore or the cam is not straight. I don’t see other possibilities, since the center caps don’t have any thrust bearing involved.

jcorenman

Edit: I wrote this before the last few replies. I'll leave it for the numbers:

Kevin, It's unlikely that the bores got smaller than when Porsche machined them, so pulling the cams and checking the journals would be the logical first step.
The spec for cam journals is 1.1002 to 1.1008". (28mm -0.04/-0.055 per tech spec book). And for bores is 1.1024-1.1032" (28mm +0.021).
So minimum clearance would be 0.0016", that is a max-size cam journal and min-sized bore.
Plastigage will confirm that it is too tight but not tell you which part is wrong and by how much. I am thinking that it is has to be cams that are oversized.

ptuomov

The factory spec is on the large side because one can’t guarantee the straightness of the cams, either statically or in a running engine. Normally, I’d think that 0.1% clearance would be good for journal bearing. However, the factory spec is 0.145-0.27% which by logic is on the wider side because the cam isn’t and doesn’t stay straight. With higher acceleration (usually meaning short duration for the lift) and stiffer valve springs, I’d want to stay on the wider side of that factory range. Not much experience here, just thinking it out loud.

I’m thinking that it’s pretty easy to adjust the clearance down by sanding the caps down on a block a little bit. Ghetto or not, that will get the bearing bore eccentricity to be more correct than a round bore.

Kevin in Atlanta

So, here we are... each of the caps except #8 added a little of resistance. Torque #8 and cam will not turn without serious effort. Notable this is one of the cam journals where the bushing was MIA.

My analysis is that there is an issue with both the #8 cam's journal and the cap.

Off to Harbor Freight for a digital micrometer and then....

I'm going to put the stock cams in and see what I see.

Strosek Ultra

Believe you mentioned WEB-Cams. Those are welded cams on stock cam cores. Welding cams do make them warp, the camshafts have to be straightened after welding.
WEB-Cams do not do anything to the journals so they must be within specs.
Åke

Kevin in Atlanta

Tossed the intake 1-4 cam from the 89 the heads came from - and the cam locked as soon as I torqued the #8. For grins I swapped the #6 for the #8 cap on the stock cam and it was looser.

The bridge cap is definitely tight and needs to be looked at, but #8 is the real culprit. Now, there's no way the '89 engine ran like this before. So, something changed.

Need a bore gauge. I can lap the cam journal or pull the head and get it line bored.

Kevin in Atlanta

I have three pairs of 87-88 heads I had rebuilt sitting on the shelf. I may pull a set down and dry fit the new cams in them. Hoarding has its advantages.

ptuomov

Those were good buys at the time, prices were good as the market paid a premium for later casting versions.

Kevin in Atlanta

So, I think I have figured it out.

I slapped the new cams in a naked 87 head, torqued down all the caps and I can spin either cam with the tip of my finger. The intake cam is a tad tighter.