Valve Clearance Checking After Re-Shimming

[William2]

I am in the process of changing some of the shims to get correct tolerances.
Camshafts have been removed and all parts laid out on the bench. I have also kept the tension on the timing chain by using a bungee hooked over a garage crossbeam above the engine.
My question is concerning the best way of re-checking the valve clearances knowing from past experience that no matter how accurately you measure the replacement shims you won't necessarily end up with the correct valve clearance the first time round!
Is it best to do one camshaft at a time and rotate it with the timing chain still removed from the sprocket using a spanner on the sprocket bolt, in which case I guess you have to rotate the crankshaft from the TDC position to prevent valves hitting pistons? Or is it better and safer to do both camshafts and put the chain back in position, re-tighten chain and then turn the engine over manually.
If I did have to rotate the engine with the chain still removed from the sprocket, how far does it have to be rotated. What I don't want is for the chain to slip off the crank or jack shaft gears and lose my ignition timing.
Thanks for any tips and advice on this matter.

[lotusfan]

is it better and safer to do both camshafts and put the chain back in position, re-tighten chain and then turn the engine over manually.

That is by far the safest and really, only, option.

[Foxie]

This is how I do it.

Set the crank at TDC compression on cyl no. 1

Undo the chain tensioner.

Remove the inlet sprocket only, and lift the timing chain off the exhaust sprocket. No need to remove the exhaust sprocket.

No need to tie up the timing chain, just drop it into the timing chest, it will hang on the water pump casting. You will lose the ignition timing, you will have to reset it when you're finished.

Replace the inlet sprocket.

Unbolt all the cam bearings on one side or the other, and let that cam lift, closing all the v/vs on that side.

You can then rotate the other cam with a 3/8" socket/spanner, measure the clearances, adjust shims and replace as required.

Release the bearings on that side, allowing all the v/vs to close.

Repeat for the other side.

Replace the cams in the TDC position. (No 1 in & ex cams facing out)

Remove the inlet sprocket and refit the chain, with the cams aligned to their marks. You most likely will have to rotate the inlet cam slightly with a vice grips to get the sprocket aligned to its timing mark to mate with the dowels.

Refit the chain tensioner

Carefully rotate the engine by hand, and check the cam timing. Repeat, and check again !

Reset the distributor timing, it will most definitely have been disturbed when the chain was removed and replaced.

Not to be rushed !

[Concrete-crusher]

Hi I'm curious, I get the valves won't hit each other with this method but won't they hit the piston crown at TDC on number 1 and 4?

Steve

[rgh0]

This is how I do it.

Set the crank at TDC compression on cyl no. 1

Undo the chain tensioner.

Remove the inlet sprocket only, and lift the timing chain off the exhaust sprocket. No need to remove the exhaust sprocket.

No need to tie up the timing chain, just drop it into the timing chest, it will hang on the water pump casting. You will lose the ignition timing, you will have to reset it when you're finished.

Replace the inlet sprocket.

Unbolt all the cam bearings on one side or the other, and let that cam lift, closing all the v/vs on that side.

You can then rotate the other cam with a 3/8" socket/spanner, measure the clearances, adjust shims and replace as required.

Release the bearings on that side, allowing all the v/vs to close.

Repeat for the other side.

Replace the cams in the TDC position. (No 1 in & ex cams facing out)

Remove the inlet sprocket and refit the chain, with the cams aligned to their marks. You most likely will have to rotate the inlet cam slightly with a vice grips to get the sprocket aligned to its timing mark to mate with the dowels.

Refit the chain tensioner

Carefully rotate the engine by hand, and check the cam timing. Repeat, and check again !

Reset the distributor timing, it will most definitely have been disturbed when the chain was removed and replaced.

Not to be rushed !

In general I do it similar to adjust the clearances once the head is bolted down on the block as some shift is normal when bolting down the head and compressing it with the bolt loads.

By measurement and calculation I can normally get the shim selection right within a couple of thou and do a setup up on a head that will be right for most of the valves allowing for a small shift when bolted down. However I always find a couple of valves that need adjustment once bolted to the engine generally on the exhaust side

One day I will set the head shim clearances by bolting it down on a empty block for the shim setting before setting it up on the actual engine to avoid the clearance shift.

cheers
Rohan

[Foxie]

Hi I'm curious, I get the valves won't hit each other with this method but won't they hit the piston crown at TDC on number 1 and 4?

Steve

Steve,

You are quite right. I omitted to mention the you need to rotate the crank around 90 degs to give max clearance for all the valves. All the pistons are then half way down the bores. You will need to lift the timing chain to seat it on the crankshaft sprocket when doing this to avoid jamming loose links.

You will of course need to return it to TDC before final fitting of the cams in their TDC correct positions.