Compression & Cylinder Shims

[supradan]

Hi Everyone,

I've started on my 3.3 rebuild.

After inspecting my pistons, I noticed that a few pistons have two slight groves located where the valves would line up (see pics below). This leads me to believe that the previous owner might have run too much boost at a high compression ratio.

Furthermore, when I removed the cylinders from the case, I discovered 3 cylinder shims (2)@ .25 and (1)@ .50.

Is this normal to see this kind of markings on a piston on a boosted 3.3 motor?

Thank you in advance for your help and input, sincerely appreciated.

Regards,
Daniel

[Steve@Rennsport]

Hi,

Those little "smiles" show piston-to-valve contact. Its most likely that either someone missed a shift and overrevved the engine (probably on a downshift) or the cams slipped. Turbo's usually have plenty of clearance due to the low mechanical compression ratio, but I'd see what cams you have.

The base gasket stacking displays the efforts made to adjust deck height. Boosted engines should never run more than one base gasket since multiple ones makes everything more prone to leak. This is more prevalent on engines running 1 bar or more.