Valve shims - head off or on?

[Mart1n95]

Hi all

I'm going to be doing the valve shims when I get my head back from machining in the next week or so

Is it better or easier to do the shims before the head bolted to the block?

Martin

[rbgosling]

Better - I can't see any reason it would make any difference.

Easier - If the engine is on an engine stand, I'd probably say marginally easier with the head mounted to the block, but really I can't see a lot of difference.

One thing I would say - it's not enough just to tighten the bolts and nuts down until they feel tight-ish. I was getting wildly inconsistent results on what shims I needed, until I appreciated that the cam carrier needs to be tightened down to the specified torque, consistently, every time you measure. That's the only reason I can think that it might be easier with the head fitted to the block, it'll be a little easier to get the torque applied without the head spinning round as you try and tighten.

Oh, and another thing - when you do try tightening up the bolts to the correct torque, there's a very high probability you will strip one, or several, threads. So have a helicoil kit to hand before you start, then at least you won't be held up by waiting to buy one when the inevitable happens.

[Mart1n95]

Better - I can't see any reason it would make any difference.

Easier - If the engine is on an engine stand, I'd probably say marginally easier with the head mounted to the block, but really I can't see a lot of difference.

One thing I would say - it's not enough just to tighten the bolts and nuts down until they feel tight-ish. I was getting wildly inconsistent results on what shims I needed, until I appreciated that the cam carrier needs to be tightened down to the specified torque, consistently, every time you measure. That's the only reason I can think that it might be easier with the head fitted to the block, it'll be a little easier to get the torque applied without the head spinning round as you try and tighten.

Oh, and another thing - when you do try tightening up the bolts to the correct torque, there's a very high probability you will strip one, or several, threads. So have a helicoil kit to hand before you start, then at least you won't be held up by waiting to buy one when the inevitable happens.

I actually read through your thread from a few years ago to try and familiarise myself and took note of torquing down the cam carriers properly! My concern would be trying to torque it down whilst keeping the head steady, and trying not to bend any valves in the process

Good point on the helicoils, I have a good kit handy already. However it would probably be better to drill out the threads with the head off to keep it as free as possible of swarf

The engine is still in the car, so not on an engine stand

[rbgosling]

The engine is still in the car, so not on an engine stand

Last time I did the shims the engine was in the car, so that's perfectly possible.

Valid point about bending valves - as you tighten the cam down a couple will be open, so you can't sit the head flat onto the table. Also, as I think of it, it may be pretty stiff to try and turn the camshaft between measurements, that will be easier with the head conveniently attached to something solid like an engine block.

[Mart1n95]

The engine is still in the car, so not on an engine stand

Last time I did the shims the engine was in the car, so that's perfectly possible.

Valid point about bending valves - as you tighten the cam down a couple will be open, so you can't sit the head flat onto the table. Also, as I think of it, it may be pretty stiff to try and turn the camshaft between measurements, that will be easier with the head conveniently attached to something solid like an engine block.

Sounds like you've helped make my mind up then, I'll do it with the head on the block in the car, so thank you very much for that!

[Marten]

The engine is still in the car, so not on an engine stand

Last time I did the shims the engine was in the car, so that's perfectly possible.

Valid point about bending valves - as you tighten the cam down a couple will be open, so you can't sit the head flat onto the table. Also, as I think of it, it may be pretty stiff to try and turn the camshaft between measurements, that will be easier with the head conveniently attached to something solid like an engine block.

Bolt it to a piece of plywood with an appropriate cutout and you can do it on the workbench instead of bending over trying not to drop stuff

[DavidOliver]

I see no reference to sealing compound between cam carriers and cylinder head.
I hope you are aware of allowing for the difference between dry assembly and compound assembly.
If you have had the head to block skimmed and not the cam carrier surface on the head skimmed, the original shims should fit, unless you have lost valve reference.
It is a pain to keep cleaning off sealing compound every time you re-shim.

Dave the cog

[Mart1n95]

I see no reference to sealing compound between cam carriers and cylinder head.
I hope you are aware of allowing for the difference between dry assembly and compound assembly.
If you have had the head to block skimmed and not the cam carrier surface on the head skimmed, the original shims should fit, unless you have lost valve reference.
It is a pain to keep cleaning off sealing compound every time you re-shim.

Dave the cog

I have seen to allow for the sealer, a thou if I remember right? I do have the correct sealant for it, from PNM Parts, so I'll probably shoot for the halfway mark knowing the sealant will take it up a little

I've had the valve seats cut with all new exhaust valves, so not far off starting from scratch unfortunately!