KE70 engine piston diameter

watt4 · May 1, 2018

Hi i own a ke70 engine that needs repair (broken piston ring). Piston diameter on the top is 72.65mm on the bottom 72.9mm , cylinder hole on the top diameter is 73.1mm in the middle 73.15mm on the bottom 73.05mm. Should i replace only the piston rings or hone the cylinder and install oversized piston?
Thanks for the answers and sory for bad english.

bigdeano · May 1, 2018

Welcome to the board.

I'm not an expert, just a retired machinist and I've rebuilt several engines. With those measurements and if the cylinder wall isn't scored I'd just put in new rings. You'll have to roughen up the cylinder with a ball hone or something similar so the rings will seat, or it will burn oil.

To put in an oversize piston you'd have to have the block bored at a machine shop I would think. I don't see the need for it if the cylinder is smooth.

ericm979 · May 1, 2018

I'd look at the factory specs. They'll have specs for piston size, cylinder, etc. If you're out of spec, then buy oversize pistons and ring and get the block bored to match them. But .015mm on a 73mm cylinder does not sound like it's worn out.

If one ring broke and you don't know why it might be worth replacing all of them.

watt4 · May 2, 2018

I cant find factory specs. Does enyone knows specs?

dantnz · Sep 19, 2018

Is that what you need? I have a similar problem, lack of compression, but I suspect finding oversize pistons will be impossible for this engine.

Let me know how you get on.

IH3444 · Sep 19, 2018

If my math is right looks to be about 0.0098 inch taper. That's quite a bit of taper from top to bottom. Rings subjected to that amount of flex are prong to breakage. You can try new rings, but they may break again under use. I would seriously consider a proper boring job, 0.020" oversize, 0.5mm. I am not a fan of honing to size. You are following the taper and not machining to a new perfectly round straight bore. I bored a diesel rabbit block to 1mm oversize, 0.040". A piston kit was about $200.00 USD. Came with 4 pistons, rings, wrist pins with clips. Did a 15hp cast iron Briggs engine, 0.020" oversize. Factory parts were not expensive either.