Overbored 1756cc needs another bore

[SeventySix124]

wow - quite a read there Beek.

Good info there, though. As I was reading that, I got to thinking about how the head gasket that I pulled off when I tore this engine down didn't measure round. At random, it measured about 85.14 mm at the widest and down to 84.82 in some places. I was originally attributing that to the bulge from the head bolts but as I think of it more, the machinist did say that I had a barrel shape in my cylinder bore. I want to get clarification from him now on what he meant by that. I was originally thinking that the center of the cylinder was wider than the top/bottom. Now, I am curious if he was talking about it being out of round.
This only makes sense because it was the thrust that dumped on me, allowing slop in the stroke. Then, he told me that I needed at least an 84.5mm bore. I'm SO confused!

I couldn't be happier to be experiencing this and learning about all of this with a Fiat!

Thanks again guys.
More to come - I should get the bearings in tomorrow and they can put it all together and check the tolerances.

[BEEK]

sorry to bore most people to death, but i am a machinist.... who loves fiats

[sgkent]

Inspect the replacement engine to be sure that there are no areas that have deep rust. Have it checked for water jack cracks. If it is good, and you are able to use it, you will be on the first overbore if you use it. You cannot assume that someone took the head off just because they needed it, unless you see some piston to valve marks or something like that which might imply a broken timing belt. Most 124 blocks look similar with subtle differences so look it over carefully before deciding what it is.

On the other hand. if you decide to use the old block to the last overbore, have the machinist bore it after the pistons arrive so he/she can match each bore clearance to a specific piston. Use rings designed for the new piston size. Do not use standard rings in an overbore situation. You will need to measure ring end gaps, and ring land gaps to be sure they are correct.