BannedCR500Riders.com

I tore down the top end on my 500 after the compression was noticeably dropping and found the piston and cylinder to both still be in spec. My original plan was to send the cylinder off and have it plated, but that turned out to not be in the cards just yet.

So yea, the question is in the poll.

if piston is still fine why would you buy new one of the same size ?

How many hours on your top end? Rather than go through the expense of just re-ringing or using the same size components, I think I would just go for the next size piston and rings and get the cylinder bored.

100hp honda wrote:if piston is still fine why would you buy new one of the same size ?

A guy I race with recommended I do so. I wanted to see what you guys thought. My original thought was to just re-ring it.

JBaze wrote:How many hours on your top end? Rather than go through the expense of just re-ringing or using the same size components, I think I would just go for the next size piston and rings and get the cylinder bored.

If I had to take a wild ass guess...at least 60.

Since everything is still in spec I'm hoping I can keep it on this bore for a while longer.

Alot of the bike shops will bore a cylinder for like $20 or $40. Piston kit will cost what it costs whatever the bore it's on. I would just go ahead and do it.

if it ain't broke why fix it?Hone,re-ring or throw a new piston kit in,depends on how much cash you got to burn I guess

You are saving the cost of a piston kit, re-bore and shipping for the expense of second gasket set and your labor taking the head and cylinder off. Replace the rings and do the honing....

I voted " Ring It".

Me too.

The only reason I have for a complete rebuild is, On my 91 500 had the same thing happen, so I just re-rung it and put it back together, every thing looked good. I went to a race the next weekend and the piston came apart on the start straight. So I am paranoid about that kind of shit.

In my new Smokey Yunick autobiography.... there is a interesting story on honing.

Smokey invented allot of stuff we take for granted, like torqueplating.

"If the cylinder is round, the rings are seated...... period!"

One day he got the idea to use such fine stones, the cylinders gleamed like chrome.

AFTER running the engine for some time, when dissasembled, the cross hatch was visable....

WTF!!!

He ( correctly) summised that the final "honing" was really just folding the peaks of the cross hatch over, like folding a box closed.

He revised his honing schedule, to remove these peaks, instead of folding them over... and " Plateau Honing" was born....

This was like in 1966 mind you...



Thanks Smokey!!!

If you inspected the piston and it looks good, within spec even as you mentioned. I don't believe you are going to have any problems running it for another season, maybe two?

My top end has about as much time as yours. In the next couple weeks that's all I'm doing is putting new rings in it. I know the piston won't be as tight as I'd like it...but what the hell. If the piston looks sharp I'm not going to replace it. I'm just not ready to do the full rebuild like I have in mind...

AlisoBob wrote:I voted " Ring It".

me to now get to it

I say ring it !!

XR250rdr wrote:

100hp honda wrote:if piston is still fine why would you buy new one of the same size ?

A guy I race with recommended I do so. I wanted to see what you guys thought. My original thought was to just re-ring it.

i cant see anybody giving that kind of advise, especially since you said your piston is just fine. if you bought a new piston, theres no way to know for sure what its going to measure. it may be looser than the one you have now, or it may be too tight. theres also a chance it may be exact size you need

Thanks for all the input. I'm going to hone and re-ring then reassess things when racing takes a break for summer. I'm getting tired of riding the couch.

100hp honda wrote:

XR250rdr wrote:

100hp honda wrote:if piston is still fine why would you buy new one of the same size ?

A guy I race with recommended I do so. I wanted to see what you guys thought. My original thought was to just re-ring it.

i cant see anybody giving that kind of advise, especially since you said your piston is just fine. if you bought a new piston, theres no way to know for sure what its going to measure. it may be looser than the one you have now, or it may be too tight. theres also a chance it may be exact size you need

There are all sorts of different schools of thought. He said he had good luck doing it that way but it didn't make total sense to me.

Did anyone mention to check the cylinder for taper? Obviously the piston to wall clearance in the case of taper out of tolerance will change at different points of stoke causing the ring to constantly flex and eventually break......

XR250rdr wrote: If I had to take a wild ass guess...at least 60.

Since everything is still in spec I'm hoping I can keep it on this bore for a while longer.

I voted Rings however, with 60est., if its a cast piston I'd think I'd get a new one, I don't trust them.

Just re-ring it and be done with it, my AF has probably the lowest compression of everyone on this board and still runs tits

I voted for replacing top end, but I like spending other people's money...

I like spending other peoples money too. It's fun. I still voted ring and ride it!

britincali wrote:Just re-ring it and be done with it, my AF has probably the lowest compression of everyone on this board and still runs tits

Says the white man that don't jump.

Hey aren't you suppose to be in Dudemont?

mega491 wrote:Did anyone mention to check the cylinder for taper? Obviously the piston to wall clearance in the case of taper out of tolerance will change at different points of stoke causing the ring to constantly flex and eventually break......

I checked that too. It was within factory spec.

EDIT: found a set of rings

So to drag up an old topic to give closure.

I re-rung the piston and the bike ran strong (except for some low throttle jetting issues surrounding a PWK swap) for two races. The next time I rode it the left crank bearing apparently had developed some play and it sucked air past the seal. It started to run away on me then stuck the piston about a mile from camp and I had to push it back.

I guess I'm glad I didn't throw a brand new piston in it.