Loss of compression post head refurbishment.

[volvo-express]

Hi all,

I had reason to replace my cylinder head and I had a spare...so I had it sent off to local machine shop. Got it back and fitted it with a new MLS gasket and bolts. Set up timming as per green book perfectly and when started it ran like a dog.

I double checked all timming and ok....did a compression check and on average each cylinder is 17 bar.

As part of head refurbishment the shims were to be replaced with thinner ones. I've last night quickly "as it was raining" on cylinder 1 exhaust clearance and I was expecting 0.40 and it's more like 0.25.

Question is.....if the machine shop ground the valves and the seats but just used the old shims again would this cause the loss of compression?

I will check the other valve clearance and write down the results .