My son (poor college student) and I are rebuilding his 77 245DL with a B21F in it. I am bone new to Volvos, I looked under the hood of one for the first time ever Saturday morning. I was measuring the cylinders and pleasantly surprised when they were round and not tapered (about at wear limits, which is good enough for that car). I was disappointed when I looked up the specs and found the block is a .015 overbore. At least it doesn't need bored again.

It got towed here so I couldn't run block tests (compression, differential pressure or leakdown) with it warmed up and oil flowing through it. Just out of couriosity, after it was on the stand, I removed to cam so the valves would all be shut, engine ice cold, not running in 24 hours (it quit on the way here), I used a differential pressure test (leakdown, I used to have a plane so wrong terminology). I expected the dynamic seal (rings) to be poor, maybe even 50% at 100psi but was going to squirt oil through the plug holes to seal them firmly and test static seal (valves, head, block, head gasket).

They leaked 100% without oil (I only did one without oil). I added oil and got nothing, rolled it to TDC (remember cam out, valves always closed) and got to maybe 20% on the leakdown, but all of the oil quickly was blown out of the bottom of block onto my feet. I have never seen a dynamic seal just blow oil out!

I am now, having found the .015" overbore, assuming they are the original pistons with .015" over rings. This leaves 3 main questions:

1. How do I tell which piston (OEM, AE, Mahle, or KS maybe some are the same) and if the piston is the stock size. I don't have a good divider set to measure the outside of the piston with my 6" calipers. I could measure it only at the top.

2. Can I run stock size pistons with oversize rings.

3. I only saw .010" (.25mm) and .020" (.50mm) overbore rings browsing some web parts pages. Can I get .020" overbore and just file down the end gap until the gap is in spec?

If he's going to drive it back on Sunday night (this is Monday night), I need to get this straightened out. I could sure use some experience in the matter. If you just know of a knowlegable parts place that could give good advice or a manufacturers web page that describes this, I could use that too.

Thank you in advance,
Mark Cantrell