Head Gasket changed, motor won't rotate, need thicker head gasket?

slam

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Do I need a thicker head gasket?

Finally tore down the head to fix a leaky head gasket. Had the head resurfaced and valves redone. Reassembled everything, torqued the head down, but now the motor won't turn by hand back to TDC (we had moved it off TDC to clean the block surface). It's shy by about 4 maybe 5 teeth when looking down through the flywheel window. I can use a mirror to see the TDC mark just out of reach.

One of the pistons seems to be hitting on a valve. We know this because if we loosen the cam shaft caps (slowly, so as not to warp the cam) then the motor will rotate free and easy to TDC and beyond. Tighten the cam back down and lock the cam to TDC and the motor sticks again before the motor can get to TDC.

The head resurface took off 0.005" which comes to 0.127 mm. I replaced my original 2-hole head gasket with another 2-hole gasket. Would moving up to the 3-hole fix this issue? Are the tolerances really that tight or is something wrong with a valve or shim that's keeping a valve slightly open?
 

schultp

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Someone else recently was rebuilding an engine and posted that they had the cylinder head resurfaced. IIRC they seemed to have some data on using the thicker gasket based on some data....maybe it was CrazyQuantumMan?? it was within the last month. Do a search and perhaps you could send a PM to this person and get some info.

...couldn't find the post I had seen, but here is another one with some interesting info:

http://forums.tdiclub.com/showthread.php?t=318262&highlight=head+shave
 
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schultp

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My guess is that JFettig is indicating that your timing is somehow off so that even though you have locked the cam, another component involved with timing is off (IP, crank).

It wouldn't hurt to check since this would be the easiest, cheapest scenario...only requires a little effort.
 

slam

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I don't have the timing belt on. I can't put it on if I can't get the motor to TDC.

My IP is not set to TDC, but how would that matter if the belt is off? I can set it and lock it when I go back in today but I don't see how the IP could relate to the cam or pistons without the belt on.
 

JFettig

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I must have missed that part. Are you absolutely sure you didn't go past TDC? lift the cam caps and let the valves shut and find the mark on the flywheel.
 

slam

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100% sure I didn't go past TDC. I painted it with yellow paint and it's impossible to miss. Plus like I said above I can put a mirror in the flywheel view port and see the yellow mark about 4 teeth away from TDC. And the crank will not move further. It's 100% hitting something.

I did life the cam caps. When I do the crank can rotate to TDC freely. If I put the cam caps back on, then I cannot get the motor to TDC.
 

slam

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Ah I found out the head gasket thickness is entirely about the piston protrusion. Head resurfacing doesn't matter at all.

So something is causing a valve to stick out.
 

RIP TDI

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Did the machine shop check valve stem heights before grinding the valves and seats and then heights checked and shortened/corrected after grinding?
 

Vince Waldon

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At TDC for #1 there are valves open for other cylinders... ie... there is no place in the cam's rotation where all valves are closed. So, if you've got the cam bolted down you won't necessarily be able to rotate the engine, no matter where the cam is locked. This is why something always gets pranged whenever the timing belt breaks.

One solution is to unbolt the cam, which allows *all* valves to close, rotate the engine to TDC, and then bolt the cam back down. :)

If after unbolting the cam you still have valve interference something is jamming a lifter or a valve, but you've at least eliminated the cam from the equation.
 
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whitedog

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I'm confused again.

You have the head on and the cam is bolted down. There is no belt on the engine and you are trying to turn the engine? If so, Vince has the solution.
 

onlyn8v

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Ah I found out the head gasket thickness is entirely about the piston protrusion. Head resurfacing doesn't matter at all.

So something is causing a valve to stick out.
Doesnt seem to 100% true. If you mill a head, it isnt as thick. Its the same as the piston coming up higher in the head.
 

Vince Waldon

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Except that our heads are perfectly flat already... the piston "comes up" into the gasket only... so milling a flat head just makes it flatter. :)

People used to gas engines are used to changing the thickness of the head gasket after milling the head because part of the combustion chamber is in the head itself... on our engines all of the combustion chamber is in the depression machined into the head of the piston...so again, milling the head has no effect.

There *is* a tiny pocket in the head created by the valve shrouds... and if you're a serious purist you may sink the valves a tiny bit after milling the head.. but if you do the math it's very very small potatoes and most people drive more, worry less.
 
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whitedog

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I may be thinking wrong here, but if the head is milled, aren't the valves now down farther towards the piston? I think Frank has mentioned that he ensures that the valves sit the correct distance from the face of the head.
 

Vince Waldon

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Yup.. that's what I meant (however poorly worded) here:

There *is* a tiny pocket in the head created by the valve shrouds... and if you're a serious purist you may sink the valves a tiny bit after milling the head.. but if you do the math it's very very small potatoes and most people drive more, worry less.
Dunno at what point one worries about it... 2mm shaved, 5mm shaved? Frank will know. :)
 

Seatman

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Is there any chance that the mark on the flywheel is just a random one and not the actual tdc? With a head skim they don't take off mm just a few thousands of 1mm, I can't see that causing the problem at all. The worst it could be wrong is just higher compression surely? If the valves and pistons are hitting it's timing, there's no other reason for the valves and pistons to hit pressuming the correct valves have been fitted and the head work was done properly. I would slacken the cam caps and rotate the crank very slowly to double check there's not another mark somewhere.
 

FOG

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I may be thinking wrong here, but if the head is milled, aren't the valves now down farther towards the piston? I think Frank has mentioned that he ensures that the valves sit the correct distance from the face of the head.
When you have our heads milled the valves would be .005" closer to the pistons but doing valve job will sink them back in the head. I think the shop that did the job sank them too much and when you install the cam all of the valves are open a little. Somewere in shop manuel there is speck for from how much you can sink the valves. On the Porsche that I worked on it was from the valve cover gasket seat to the top of the valve stem. If it was too high you had to trim the valve stem to get it in speck. Our TDI engines have all but 0 overlap. If the cam is at TDC #1 then #4 is at overlap #2 & #3 are at BDC.

Fog ;)
 
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whitedog

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Now things are getting really FOGgy for me... :)

Aren't the HLAs going to take up the difference in valve stem height? Or can they only do so much and after a certain point, they can't collapse anymore? I was thin king about stem height too, but then I got to thinking about the HLAs so I didn't mention that. but now y9ou come along to FOG things up for me again.
 

slam

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Did the machine shop check valve stem heights before grinding the valves and seats and then heights checked and shortened/corrected after grinding?
That I don't know. I suspect not. The tops of the stems show slight spidering consistant with normal wear. If they were ground I'd expect them to be mirror-clean and polished.

We're going to call on Monday morning to check.
 

Luskavarna

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Actually the valve to piston clearance comes closer together. but that clearance is like .030 to .045 and you cant possibly take that much out of the head. usually a milling will remove .002-.005, nothing. Your solution is shown above.

But listen to this. . . Did you make sure that the intake and exhaust ports were clear upon head install and that a bolt or something like it was not left in a cylinder???
 

slam

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Lots of excellent questions, thanks. Let me try to recap and clarify:

  • Cam off, crank can spin to TDC. Cam on, crank cannot spin to TDC.

    This means that when the cam is off, the valves are all out of the way of the pistons. It's likely all the valves and valve seats are okay and the springs are all working.

    This means that when the cam is on, the contact path is this: cam, hydraulic lifter assy, valve stem to valve head, piston top. Clunk, crank won't spin. Cam and pistons seem to be good, so I'm guessing the problem must be in the lifters or the valve stems are too long. Lifters were good when I drove the car into the shop.​
  • Gasket is same size as original.
  • I am 100% certain the cam is at TDC, #1 lobes near the sprocket are up, cam lock plate is in.
  • I am 100% I know where the TDC mark is on the flywheel. I marked it with yellow paint, it's impossible to miss, and I confirmed it when the head was off because #1 and #4 pistons were protruding. When the crank locks up by hitting something I can put a mirror in the flywheel viewport and see the TDC mark 4 teeth away.
  • I am not trying to get full flywheel rotation with the cam in. I understand some valves must be open at all times. We are mounting the cam with the flywheel maybe 10° off TDC, then trying to rotate to TDC.

There's no way I am going to put the flywheel at TDC with the cam off, then put the cam on and torque it down. This is just wrong. If there's any valve-piston contact I'll be torquing my camshaft against a valve that is hitting a piston. This seems like a horribly bad idea to me. Something will break and it will probably be my budget.

Some other info:

• Head shop paperwork says they took 0.005", which is 0.127mm.

• Franko6 says, "There are few heads that clean up at .005". It's more like .010". It's hard to comprehend them surfacing enough that the valves are holding open and will not shut all the way."

• Franko6 says "We did recently replace a whole set of CRAP valves that had .050" projection and caused the problem you describe for yours. We normally set our valve projection around .020" below the head gasket surface."

• Maybe the head has been resurfaced before?

• We swapped some lifters from #3 to #4 because one of the #4 lifters seemed stiff, but the issue is the same.
 
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slam

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When you have our heads milled the valves would be .005" closer to the pistons but doing valve job will sink them back in the head. I think the shop that did the job sank them too much and when you install the cam all of the valves are open a little.
Fog ;)
How far the cams sink when seated won't matter at all for this issue. With the cam out, and the cams all sunk, the crank rotates fine. With the cam in... clunk. I hang up on something hard. The only difference is the cam is on... so the cam must be pressing on a valve, which is hitting a piston. Valve seat depth would have zero effect on this.
 

slam

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Actually the valve to piston clearance comes closer together. but that clearance is like .030 to .045 and you cant possibly take that much out of the head. usually a milling will remove .002-.005, nothing. Your solution is shown above.
If by solution you mean setting the flywheel to TDC first, then bolting in the cam, no way. Not until I am clear I don't have valve to piston contact. With the cam in, I *should* be able to rotate freely +/- 10° from TDC and back without issues. If I can't it's because something is in the way.
But listen to this. . . Did you make sure that the intake and exhaust ports were clear upon head install and that a bolt or something like it was not left in a cylinder???
It was a two-man job so I can't say 100% for sure that nothing fell in. BUT, it didn't happen when I was watching, and my cousin is a 10+ year BMW mechanic and lead guy in his shop, so it's not likely. And that would be an issue even with the cam out. Cam out crank spins free, cam in crank has contact. Must be valve contact. Issue is valve or lifter. Right?
 

slam

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Correct me if I am wrong, but at TDC shouldn't the #1 and #4 valves all be completely shut?

At TDC, only #1 and #4 pistons are up... so if the #1 and #4 valves are all shut, there should be no contact.

But I am getting contact.
 

White Crow

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If every thing is in time the only ones that can interfere are on #4 cylinder #1 is closed and 2 and 3 pistons are at BDC. Leave the followers out of #4 and see what happens. If you are off even a little bit #4 intake is starting to open so if it's a cam timing issue it will lock up again when #3 comes up.
 
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GTiTDi

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When you have our heads milled the valves would be .005" closer to the pistons but doing valve job will sink them back in the head. I think the shop that did the job sank them too much and when you install the cam all of the valves are open a little. Somewere in shop manuel there is speck for from how much you can sink the valves. On the Porsche that I worked on it was from the valve cover gasket seat to the top of the valve stem. If it was too high you had to trim the valve stem to get it in speck. Our TDI engines have all but 0 overlap. If the cam is at TDC #1 then #4 is at overlap #2 & #3 are at BDC.

Fog ;)
you may have dismissed him, but my bets would be with his suggestion..I remember this being a critical measurement after upgrading my valve train to dual springs and 7mm valve stem valves and some porting...If you had any machining done this is a necessary dimension to check.
 
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