Robins eh29c cylinder bore question

[Superx2]

Hello all, first off ,engine started rattling so decided to tear it down. Found a rod cap had broke in half. Cylinder walls and everything looks really good. Still has cross hatching. The pistons don’t have any oversize marks on them so seam to be standard bore but when I try to measure with calipers I come up with around 64.40mm. Ring gap seems to be .018. It did smoke a little bit. So should I just put a new rod and a set of rings in it or have it bored. It ran fine before this happened. Gps speed with full governor was 14 just a couple days ago so don’t think it was down on compression but never got a chance to test it. Thanks

[Fairtax4me]

If the cylinders still have the cross hatching, I’d just pop some new rings in it for good measure. Don’t bother with honing or even trying to “de-glaze”.

[Superx2]

So being a little over sized you don’t think will hurt? Do all oversized pistons have a .25 etc. stamped on top? Is .018 ring gap to much? Not sure why it would smoke a little unless it was valve seals. Sry for all the questions but I’m pretty mechanical but never really tore an engine all the way down. Thanks

[CP241]

I'd agree. Get a new set of rings, new rods and a gasket kit. You'll have it back up and running in no time, and it wont cost you an arm and a leg :)

Theres 2 "sets" of rings on there. There are 2 rings on each piston that control compression. These are the important ones that make it run.

Below that there are 2 really thin oil control rings. These can get stuck, break, etc. These are what will cause it to smoke, but have no impact on compression.

Personally, I will always run a home quick through the cylinder when I put in new rings. Some choose not to, if theres no scoring in the cylinder its personal.preference. but .018 isnt really bad. .008-.016 is spec. New set of rings will probably put it right back where it belones

While it is apart, I'd check the intake valves closely.for wear. They're common to wear out and if you're gonna replace it, now would be the time :)


Also, remove the oil pump from the engine side cover before reassembling it. Pay particular attention to the o-ring that goes between the top of the side cover and the block. This o-ring is important! If you leave it out (and may not have even noticed it was there) it wont leak externally, but the seal between the oil pump and the head will not be good and the head will starve for oil. Then bad things happen... And get a new gasket for the camshaft cover or it will leak like crazy. No need to replace the valve cover gasket unless it was leaking before. They're thick rubber and seldom leak.

[Superx2]

Thank for your guys help. Hopefully I can get the stuff and get it back together by the end of the week.