Rebuilding me engine after a bigend failure and found out my heads are shimmed and don't have hydraulic tappets. In my stupidity I failed to mark them in order from where they came from.

So I realise it is a git of a job, but what do I have to do to measure them and put them back in?

Any information would be appreciated.

 

I assume putting the shims in and then positioning the cam and using feeler gauges to check?

Or am I way out!

 

are they over bucket or under bucket shims ?
Gary

 

Over I think.

 

98 UK Heads

 

Anyone?

 

Not done an Impreza but have done a solid lifter 16V Vauxhall engine so theoreticallly:

Build it with no shims. Measure clearances (with valve fully closed). Calculate required shim by: measured clearance - required clearance = shim required. Repeat for each valve. Mike up the shims and you should find you have one measuring the required clearance for each valve. If (when) you don't, divvy them up amongst the valves so they are as near as poss but always oversize, get some oversize shims for the missing ones, then grind to the required thickness. Strip, rebuild with the required shims. Measure again. Repeat until all are in tolerance.

You'll find this a really tedious repetitive exercise. To cheer you up a) Ducati desmo engines have both open and closing shims (no valve springs, finger followers both open and close the valves). You need zero clearance on the closing ones so you build with deliberately undersize shims, then, once you finally get everyting spot on you have to strip and rebuild again with bigger shims. b) Some racing jags have 5 valves per cylinder on a v12...

 

Ok, sounds like fun!

Are the tolerances I posted earlier correct?

 

It used to be inlet 0.20 and exhaust 0.25
On the latest update from subaru they use now inlet 0.20-0.25 and exhaust 0.30-0.35
But i would stick with the old tolerances

 

Right want to make sure I get this right.

Do you check the clearance between the silver bucket type shim and the cam lobe or where? Only used hydralic tappets before you see.

Do you do it whilst the valve is closed yes which is technically 'off-cam'?

 

Yes and yes