A couple of 350x topend questions...

[Liquid-Darkness]

Which topend compression and overbore should I go with a 350x?


Also was wondering I thought I read years ago that piston to cylinder clearence was supose to be .0025 for cast pistons and .003 for forged pistons. Reason I ask is G & H said they would bore .020 over with 10.25:1 and use .002 clearence from piston to cylinder wall..

[RIDE-RED 250r]

I would only bore as much as necessary to bring the cylinder back into spec for taper, diameter and out of round. 99 times out of 100 if your engine is currently running, the next size bore from where it currently is will be all you need.

As to piston, decide on what piston you want to use, and have the bore matched to the piston per the piston manufacturers specs.

Unless you want to get into running race fuel, stick with the 10.25:1 piston.

And on a side note, make sure you check and adjust ring gap as necessary per piston manufacturers specs as well. Most times, the ring gap does need to be adjusted. Too tight of ring gap will make quick work of ruining your new rings and bore job

[Liquid-Darkness]

Alright thanks for the input! I ran a 10.25:1 before. It barely made it on 91 premium fuel. I mean after running it hard, I would predetonate a little bit after 3/4 throttle, jetted of course.

I may just have to go with a fresh set of rings, c-clips and a honed cylinder. I could get the topend gasket kit and just break the glaze on the cylinder my self. That way its a fresh topend. Then a rebuilt carb, new chain, and performance exhaust maybe a new clutch and I will have a trail monster for sure!! Those stock 350x's are quick though.

[RIDE-RED 250r]

Sounds like a good plan, but I would measure that cylinder up and make sure it's within spec before committing to just a hone and new rings.

[barnett468]

Alright thanks for the input! I ran a 10.25:1 before. It barely made it on 91 premium fuel. I mean after running it hard, I would predetonate a little bit after 3/4 throttle, jetted of course.

If your timing is adjustable you can retard it slightly. this will reduce detonation.

I would only bore as much as necessary to bring the cylinder back into spec for taper, diameter and out of round. 99 times out of 100 if your engine is currently running, the next size bore from where it currently is will be all you need.

I may just have to go with a fresh set of rings, c-clips and a honed cylinder. I could get the topend gasket kit and just break the glaze on the cylinder my self. That way its a fresh topend. Then a rebuilt carb, new chain, and performance exhaust maybe a new clutch and I will have a trail monster for sure!! Those stock 350x's are quick though.

Sounds like a good plan, but I would measure that cylinder up and make sure it's within spec before committing to just a hone and new rings.

This is where most people make a mistake. they look at the cyl and say, "Hey there are no visible signs of wear in my cylinder so I'll just deglaze it and it will be fine."

It must be measured with the proper tools. If either the taper or out of round is more than around is more than around .0017 it will likely smoke because the rings can not seal properly. Also if you add up the ampount of taper and out of round and it addss up to .00175 or more it may smoke.



FORGED PISTON CLEARANCE - As far as this goes the statement that they need more clearance than a cast piston is out dated. With the use of new materials and mfg processes some forged pistons can be run just as tight as cast ones.

[Liquid-Darkness]

Alright yeah before I go and slam a new set of rings in a topend, I will bring the piston and cylinder to my local bike mechanic and have him mike+ it for specs. I have brought him topends before and he checked them out and let me know if I could just re-ring them.

[RIDE-RED 250r]

Just make sure you have the specs for your engine to give him.

[Liquid-Darkness]

Alright I will.