Cam won’t rotate when heads torqued

[r lane]

If either the heads or cylinders are machined, the chain boxes have to be as well.

[mike sampsel]

Originally Posted by Ken911

Ok so did you install the camshaft retainers and the gears? Sometimes if everything has been resurfaced, it will rub on the side of the camshaft retainer (93010519600). Because now the chain box is slightly too long for the new stack height. the cam will spin fine in the tower but not once the cover and gears attached.

Interesting thoughts, so I put the retainer on with the chain box too and no issue, all turned well. Did not do the gears, but it seems the retainer tolerance is key.

Happy so far

[Walt Fricke]

If just a few thousandths are taken off the heads or cylinders - a clean-up job - the rubber O ring around the cam retainer part (3 6mm bolts hold it)will accommodate the difference. At some point (like guys running longer rods)it won't.

If more is removed, you can get it back with the cylinder base gaskets.

The issue here seems to be that tightening everything down caused cam bind, and that pretty much has to be due to some unevenness in the heights, however caused.

[Jonny042]

Just curious, you have your cam housings bolted solid to the heads, before torquing the head studs?

I'm sure there's a 40 page thread on the very subject, with at least 4 different ways of doing it, but I figured it would be better to have the heads tightened to the studs first, then put the sealant on the cam housings and torque to the heads with the 8mm bolts at 18 ft/lbs.

Is it possible you have an uneven amount of sealant between the heads and the cam housing, causing it to distort?

[mike sampsel]

Yes, I’ve gone the assembly route with housing bolted to heads. It’s a preferred method of two gentlemen who have built a lot of engines. So I went this route.

I think there is no chance uneven sealant (between housing and heads) could cause this, why would the cam spin freely with assembly at rest? Also, the sealant does not cause one of the cylinders to be taller than its neighbor.

I put a thicker case/cyl gasket under number 2 today, installed cylinder over rings and bolted up to 11# and the cam spins free as a bird in flight. Thinking I’ve got it so far.

[Richey]

The case is probably warped . #2 cylinder runs the hottest and the coresponding case cylinder deck is usually relatively low . So I guess a thicker cylinder base gasket is one way to fix the problem .

[Jonny042]

Originally Posted by mike sampsel

I think there is no chance uneven sealant (between housing and heads) could cause this, why would the cam spin freely with assembly at rest? Also, the sealant does not cause one of the cylinders to be taller than its neighbor.

I put a thicker case/cyl gasket under number 2 today, installed cylinder over rings and bolted up to 11# and the cam spins free as a bird in flight. Thinking I’ve got it so far.

If the sealant was uneven, one head could be farther from the cam carrier and the sealing surfaces of the heads would not all be in the same plane. Given that the clamping force of the cam carrier to heads is relatively low I see this as a potential problem area. Easy enough to check with a straightedge.

I would be surprised if you are able to fully rectify this using varying thickness base gaskets. If you put a .50mm gasket on one cylinder and .25mm on the others, that's 10 thousands of an inch height difference. In relative terms, that's a mile.

Look at it this way - Porsche went to the trouble of grouping cylinders by height, with only .007mm difference between the groups. That's 35 times smaller than a .25mm base gasket. Now perhaps Porsche were putting a finer edge on it than really needed, but there is no way you are going to "make up" more than a thousands of an inch (maybe 2) simply by tightening things down.

In fact, I wouldn't even torque things down like this, you are liable to permanently deform something.

Better to find out where the problem lies and fix it properly, you are much more likely to be successful and will have fewer problems down the road with cylinder to head sealing issues, etc.

Either the case is warped, the cylinders are of varying heights, or the heads have been machined in varying amounts.

Hope this helps!!

[mike sampsel]

Maybe you’ll be surprised, because with 0.5 gasket under number 2 cylinder and torqued per the spec sheet, the cam is spinning freely. Calling it done.

Again I’m ruling out your speculation on the cam housing sealant. Why? Because I could measure a difference with a straight edge between cylinders 2 and 3. Noted about 0.25 mm, part of which was due to the difference in thickness of the VR gaskets, the rest perhaps due to difference in the used 98 mm cylinders.

Maybe the case is warped after 115 miles (an SC with a warped case?)? Don’t know, don’t care. I wasn’t planning on touching this engine because it was fine, but well the wife wanted me to paint it, so I pulled the engine to paint, then do the valve guides and head studs (none broken) and it ballooned from there. So if the case was warped before I started, it did not effect performance any.

[Jonny042]

Originally Posted by mike sampsel

Maybe you’ll be surprised, because with 0.5 gasket under number 2 cylinder and torqued per the spec sheet, the cam is spinning freely. Calling it done.

Again I’m ruling out your speculation on the cam housing sealant. Why? Because I could measure a difference with a straight edge between cylinders 2 and 3. Noted about 0.25 mm, part of which was due to the difference in thickness of the VR gaskets, the rest perhaps due to difference in the used 98 mm cylinders.

Maybe the case is warped after 115 miles (an SC with a warped case?)? Don’t know, don’t care. I wasn’t planning on touching this engine because it was fine, but well the wife wanted me to paint it, so I pulled the engine to paint, then do the valve guides and head studs (none broken) and it ballooned from there. So if the case was warped before I started, it did not effect performance any.

Well that's great - glad you got it sorted. Onwards and upwards!