Rogue Piston?

[lateracer]

So I'm tearing down my Craigslist-special b25 motor and notice that piston #1 is completely different from #s 4-5. Not just the piston, but the rings and con-rod too...at least it's a Mahle...



The other pistons appear to be stock. It looks like this rogue piston ran for a while without any real problems (carbon deposits on piston top and chamber appear uniform with the rest of the motor). The #1 cylinder looks comparable to the rest as well.

I'm building this motor for my track car on as tight of a budget as I can reasonably manage, so how should I handle the black sheep piston I've found?

At this point, I'm thinking that I should weight balance it with all of the internal assemblies (rod/pin/piston), measure it to make sure it's the same size as the rest, put new rings and rod bearings on and pretend it never happened.

Anything else?

[Aptyp]

show a pick of the the top.

[Van Westervelt]

Likely a broken tb at some point with contact on that piston, hence replacement, and at the time they likely cleaned off the surface of all the pistons. Should be a-ok.

[nando]

as long as they're all i pistons/rods you should be ok. I notice the skirt is different, it could be a later short skirt i piston vs the earlier long skirt pistons. in that case I would also check the weights of them all and have them balanced together. same with the rods.

[lateracer]

Thx for the responses. I'm pretty sure the top of the piston is the same as the rest of the others, but I'll check to be sure.

I noticed the different piston has (what looks like) weights added to it on the inside, so I'm hoping it's balanced already...we'll see.

What about rings? It uses different rings but "looks" like it could use the same as the others. Can I order one type of ring for all of the pistons or do I need to do a 5+1 type of thing?

[jlevie]

I'd get an M20B25 piston and replace that. I'd also make sure that the rod has the same center to center distance as the other rods. I don't know where that piston came from, but it obviously isn't what should be in the engine.

[nando]

there are two different B25 pistons though, early/late.