Top end questions
 

Hey guys first post so go easy on me please. Doing my first top end on a 09 ec250. Seems to run ok but kinda want to start from scratch with hours on the top end and it?s cold so good time to tinker. So I have Pulled the cylinder and cleaned her all up than scotchbrite on the cylinder walls but I can feel a lip up near the top. First off is it possible to get a shop to hone the cylinder with a diamond hone and will that work with the Nikasil coating that is currently on it? My second question is does anybody know the clearence tolerance between piston and cylinder if I install a Forged pistons vs a cast on or does it matter? Manual states .055mm to .1mm clearence I believe if I have her right. Or should I just slap a C piston (66.35) in it and not worry about the barely discernible ridge as the rest of the cylinder looks good with crosshatching and feels smooth?

C size & send it is what I'd do.
How many hours on cylinder?

Thanks shawbagga, that?s exactly what I think I will do than. As far as hours,no clue but I believe lots.

You can run it this way but make sure you use the same thickness base gasket or slightly thicker. You do not want the new piston and ring running into the cylinder ridge.

A diamond hone used to finish size the plating will also remove the ridge and true the cylinder but you will need the larger piston.

Just to confirm, is the original piston and cylinder sized for a B piston?

Yes Zman, the piston jug is marked b and the piston I removed was a b piston as well. Thanks for the reply, I just was not sure if I could get the cylinder diamond honed and keep the nichsel coating so thanks. Also it makes sense to throw a bigger or thicker gasket on the base of the jug in order to keep the new piston rings from contacting the ridge at the top of jug. Honestly I did not even think of doing that so thanks again man.

The downside of a thicker base gasket is that your squish band will be higher than before. Most of these engines have too big squish clearence. Do you know if the head has been reworked to reduce the squish?

I agree that going with a significantly larger base gasket will be a problem as well.

Thanks for the info guys. So if I understand correctly, I can get the cylinder honed by a shop with a diamond hone to remove the lip at top of the cylinder provided I have enough plating left todo this correct? Or do I need to get the cylinder re coated and than get her diamond honed at which point I may as well go with an A piston size? Much appreciated guys, thanks!

A machine shop that deals with plated cylinders can hone it. Check first. They will tell you if it needs replating.

Yes that is correct.

If the cylinder is worn too much they may tell you to replate it.