Just taken the head off my series 3 diesel, found a blown head gasket that was blowing on to a push rod chamber, push rod coated in a thick layer of carbon....

Nos 3 and 4 pistons have some play in them, Nos 1 and 2 dont, No 3 piston crown is clean No 4 is oily with a small amount of carbon, all cylinder bores seem fine no scores etc, small build up of carbon at the top of the bores which is pretty normal..

Now that I have the head and sump off, what should i do, replace pistons and rings, just replace rings, or do bottom bearings, pistons and rings. New head gasket etc will be fitted as a matter of course......

I'd say,
Clean the carbon from the head with a wire brush.

Replace the rings, and if the pistons dont appear to be worn leave them in.

Carl.

The pistons do tend to look pretty new, so will take your advice and just replace rings......

Am going to regind valve seats as the head is off anyway, plus new valve seals...


What is the best way of removing that carbon build up you get at the top of the bores? Dont want to damage the bores, or push new rings past it......

Get a honing stone. Hone all 4 bores> Remove compression ring from piston put down each piston measure gap at top and bottom of bore in each cylinder. if gap difference is over 8 thou.between top and bottom in any bore Rebore engine If not rings will do. Dont forget to use an old ring to clean grooves before fitting new rings to pistons.-----BB