Valve clearances again..

[Robbie693]

Before I took the head off for it's new gasket and cam bearings I measured the valve clearances and bought the shims to correct them.

Having fitted the new shims I find that the clearances are not in the middle of spec as I expected.

I now have:

Inlet - .006(tight) .007 .005 1/2 .005 1/2

Exhaust - .009 .009(tight) .011 .011(tight)

I noticed when checking the new shims that they were sometimes out by 1/2 a thou from what they were supposed to be. So the question is, am I chasing my tail trying to get these exactly in the middle range and should I have another go or leave them be?

Cheers

Robbie

[andyelan]

Robbie

Although you can get the clearences to mid range, it will almost certanly take 2 or 3 attempts to do so. My advice is that once they're within tolerence, leave them alone.

One important point to note however, if you have the head off, is that the clearence will change by 2 or 3 thou when it is re-fitted (especially on cylinders 1 and 4). So, don't set the valve clearences with the head on the bench and then expect them to still be correct once its been re-fitted and torqued down. Be sure to re-check them.

Regards
Andy

[CBUEB1771]

I agree with everything Andy says. I have had the same experience with valve clearances changing after installing and torquing the head down. This baffles me because it suggests that the head deforms quite a bit however the camshafts seem to turn freely in either state.

[stuartgb100]

Mind that if the head/cams are inherited from PO etc that there may be unknowns.

Best to back off the cam caps and then re-torque to the correct figure in the right sequence.

Best also that all other related work has been finished: new bearings etc.

Then take your measurements last.

Regards,
Stuart.

[ppnelan]

I have had the same experience with valve clearances changing after installing and torquing the head down. This baffles me because it suggests that the head deforms quite a bit however the camshafts seem to turn freely in either state.

I think it is not deformation of the head but the timing chain pulling the sprockets & camshafts down that changes the clearances.

Matthew

[rgh0]

Robbie

Your new cam bearings will have altered the shims required by a little assuming your old cam bearings were worn. If the cam shaft could move a little in its worn bearings it may be a little higher or lower before bearing replacement compared to after the bearings were replaced depending on which cylinder you are measuring as the cam is pushed around by the spring loads of the other cylinders and the drive chain.

You also do get some small changes in clearances each time you bolt down a head as they do distort and compress a little until the bolt loads.

If you have enough shims and patience you can get them to the middle of the tolerance range once the head is installed if you want but really no need.

cheers
Rohan

[Robbie693]

Thanks everyone, I'll leave 'em be then.

Cheers

Robbie