[John Witd]

Working on a 1999 Honda foreman 450 s does this piston gap look right? It was smoking bad but found issues with valves and it had 100psi of compression. Guy i got it from said it has a new wis. Piston and rings

 

[retro]

Piston clearance and ring gaps have to be measured while the cylinder is off the motor & before the piston is put on the rod.

What did you find wrong with valves? Stuck, bent, bad seals...?

Welcome to the forums!

 

[mac102004]

Need to remove piston and jug to check ring gap. Remove the rings off the piston and place them in the jug to measure. If it's a fresh top end the first thing I would check is the placement of the ring gaps. The Gaps should be about 120° apart.

Here is a link to the Wiseco instructions to set the ring gap since it's a wiseco piston. The "4825M09000" stamped in the piston is a Wiseco part number. 450 Foreman 90mm bore.

http://www.wiseco.com/PDFs/Manuals/RingEndGap.pdf

 

[John Witd]

Intake side was very clean but exhaust side was not

 

[retro]

It looks like the valve seals were shot.

 

[John Witd]

I ordered a whole new cylinder with valves 200 bucks not bad at all it was smoking horribly it would smoke out my whole property do yall think it could be the rings with 100psi of compression fyi it idles good and runs good

 

[John Witd]

This is what im unsure about i have built many atvs but never seen them have this much gap is it normal for a foreman? Sorry for all the questions im just puzzled ?

 

[misterclean59]

I can see the piston leaning off to one side. That is way too much piston clearance. You need to bore to the next sized piston.........perhaps two sizes? Others here have shop do the whole job for you. Just mail the cylinder to them and they send it back bored with the correct piston and gasket kit. Shadetree, Jeep, Fish, Retro etc.... should know some suggestions. I just have my local shop do it for me where for others doing it thru the mail is cheaper and easier.

 

[retro]

G&H does a good job:

Cylinder & Head Machining Service - G&H Discount ATV Supply

Or you could just buy a new OEM cylinder since the new Wiseco piston you already have appears to be for a standard bore. Its your call...

 

[misterclean59]

G&H does a good job:

Cylinder & Head Machining Service - G&H Discount ATV Supply

Or you could just buy a new OEM cylinder since the new Wiseco piston you already have appears to be for a standard bore. Its your call...

Great idea to keep the same piston if it's not worn and the original size.

 

[John Witd]

So update i got a new 90mm oem cylinder now heres how the rings are the top ring is 90.25 bottom ring is oem 90mm does the 90mm ring gap look to big still?

 

[shadetree]

So update i got a new 90mm oem cylinder now heres how the rings are the top ring is 90.25 bottom ring is oem 90mm does the 90mm ring gap look to big still?

oh yeah...lol, that bottom ring gap is wayyyyyyyyyyyy too big !.

 

[shadetree]

are these the old rings ??, if they are ?, and you upsized the cylinder ?, then you have to start with fresh new rings to match cylinder, as well as a piston to match rings AND CYLINDER !.

 

[John Witd]

Its a oem 90mm cylinder i have a wiseco 90mm piston and rings which is the bottom ring

 

[shadetree]

Its a oem 90mm cylinder i have a wiseco 90mm piston and rings which is the bottom ring

well, I can tell you this, those rings won't work. If you had this cylinder bored over, and bought this piston kit ?, surely you bough the piston to match the bore...right ?. when I have a cylinder bored over, I always have the correct piston kit on hand to match cylinder. those rings wont work, which tells me the piston won't work, because it does not match your cylinder.

 

[retro]

Are the rings squared up in the bore? You can use the piston crown to push them down the bore a bit... to square them up. Then use feeler gauges to measure the ring gap for the top ring and then repeat the squaring/measuring process for the 2nd ring. Write each gap down.

Is that an oil ring scraper in your photo? If so, you needn't measure those... just measure the top ring and 2nd ring gaps.

You may be able to lower the bare piston into the bore and measure the piston-to-cylinder clearance (at the skirt, 90 degrees from the wrist pin bore) using feeler gauges if you have a narrow-bladed set handy.