Question about piston clearance!

weldpro · Post by **weldpro** » December 12th, 2008, 7:21 pm

I ripped apart my new to me 500 to inspect the top end etc. What I found was a OEM piston that looked to be in good shape, and a cylinder that was a stock bore also seemed to be decent. Compression test cold revealed 125psi so I measured out the piston, and ordered a new pro x in the stock bore size.
When I received the new piston the first thing that I did was to measure piston to cylinder clearance, and it was .009 so at that point I knew the cylinder was going out to GSS for a bore & hone job. I called Glen, and got everything down to him, and he did the work the very same day. I must say that for the $70.00 I spent on labor I feel like I got a bargain, and I am very happy with the job he did.
Today when the cylinder showed up the first thing I did was to measure the piston to cylinder clearance, and it is .008! Now I have used two different feeler gauges so it can't be the gauges! But I started thinking maybe when the torque plate is on there, and the piston is in the bore it is the .004 that Glen uses for the Wiseco pistons (I bought the piston from him too). It's that or I am a total idiot....which is definitely possible.

pstoffers · Post by **pstoffers** » December 12th, 2008, 7:32 pm

If you divide 8x2 you get what?

weldpro · Post by **weldpro** » December 12th, 2008, 7:43 pm

WOW. No shit. I feel pretty damn stupid. Thanks for the info......now I must go tell my wife so that she can laugh at me.
Richard

Post by **AlisoBob** » December 12th, 2008, 7:48 pm

Friggin' Welders......

(

)

weldpro · Post by **weldpro** » December 12th, 2008, 7:52 pm

She laughed, and even said that she thought that maybe that was it but did not say anything because well...she's a girl, and could not possibly know wtf's going on with my motor! I should delete this thread but hey I like humility!
Richard

Post by **AlisoBob** » December 12th, 2008, 7:54 pm

weldpro wrote: I like humility!
Richard

Were all very humble here, and have all "been there"......

pstoffers · Post by **pstoffers** » December 12th, 2008, 7:54 pm

weldpro · Post by **weldpro** » December 12th, 2008, 7:56 pm

AlisoBob wrote:Friggin' Welders......

( )

No kidding!!! People I know would really get a laugh out of this. I remember telling Glen before I sent it "Oh yeah it's got .009 clearance" his response "damn that's a lot!". I now know it was really .0045 before. DUH.
Richard

lewisclan · Post by **lewisclan** » December 12th, 2008, 8:42 pm

I CAN FEEL THE LOVE HERE

weldpro · Post by **weldpro** » December 12th, 2008, 9:06 pm

I have been thinking wtf why did I not know this!? I have all kinds of mics, bore gauges etc., and I have rebuilt motors before BUT I never checked piston to cylinder clearance. The reason why is because I would always mic the piston (which I did on the OEM one), and mic the bore then do the math.
I had my contacts in the day I measured the OEM piston, and it was hard for me to see close up so I did not even measure the bore as it looked fine. So I said F it, and ordered up the new std, size piston. It was only then that I went the easy route, and measured the cylinder clearance with the feeler gauge when the pro-x piston showed up. Nonetheless I still have to laugh at myself.
For those who may want to see what the idiot is building I have a build up going on in the Steelie section.
Richard

http://www.bannedcr500riders.com/board/ ... php?t=4874

robertg · Post by **robertg** » December 13th, 2008, 4:56 am

The piston diameter is a lot smaller where you are measuring it. The diameter of the skirt should be measured about 3/4 of the way down the piston. A feeler guage is not a very accurate way to measure the clearance between two round objects.

I disagree with everyone, if you have 0.004" clearance, it's not 0.004" per side. Hopefully someone that does this for a living will help here.

100hp honda · Post by **100hp honda** » December 13th, 2008, 7:01 am

robertg wrote:The piston diameter is a lot smaller where you are measuring it. The diameter of the skirt should be measured about 3/4 of the way down the piston. A feeler guage is not a very accurate way to measure the clearance between two round objects.

I disagree with everyone, if you have 0.004" clearance, it's not 0.004" per side. Hopefully someone that does this for a living will help here.

i have to agree alittle bit with robert. sticking a feeler gauge in there certainly isnt a real accurate way to do it. on the other hand, building up a stock cr500 doesnt take the preciseness of brain surgery....ive used feeler gauge before with no problem because i dont have a bore gauge, hell the only tool i have is cheap digital caliper from harbor freight. the piston is egg shaped and should be about .0025 on cast piston, im assuming glen knows this and bored the cylinder accordingly. if you have a "true" .004 clearance with that OEM piston, thats way to big

97af · Post by **97af** » December 13th, 2008, 7:31 am

Hunt down a set of theses and there is no question.

And just as much important as the cylinder wall - piston spec, make sure your ring end gap is where its supposed to be too. DO NOT just slap them on the piston and call it good......Like a guy I know who does....

89 millimeter = 3.50 inch x .004 = .014 minumum ring end gap

Post by **AlisoBob** » December 13th, 2008, 7:50 am

I have never seen the Wiesco rings come anywhere near OEM tolerance...

No chance of those ever butting together!!!

97af · Post by **97af** » December 13th, 2008, 8:27 am

AlisoBob wrote:I have never seen the Wiesco rings come anywhere near OEM tolerance...

No chance of those ever butting together!!!

But someone knows what happens when its not checked!!!!

weldpro · Post by **weldpro** » December 13th, 2008, 10:10 am

The OEM piston I was referring to was the one that was in the bike when I got it (that was the one with .0045 piston clearance)! After ordering a new one (prox std size), and it had similar clearance (but I was thinking .008 not .004) I freaked, and sent it out to Glen.
Since it went to Glen I figured I would buy the piston through him too. The new piston is a Wiseco, and it has a clearance of .004 which I am certain he had told me that is what he sets them to. Oh, and ring end gap is .018 bottom ring, and .017 for the top.
Richard

100hp honda · Post by **100hp honda** » December 13th, 2008, 10:45 am

double check the bridge is relieved (glen should of done that and he probly did). and drill the holes on exhaust side

weldpro · Post by **weldpro** » December 13th, 2008, 10:56 am

100hp honda wrote:double check the bridge is relieved (glen should of done that and he probly did). and drill the holes on exhaust side

Yup all that was done! Glen's work really is outstanding, and for $70 I feel like I got a gift.
Richard

south central hoon · December 16th, 2008, 10:27 am

i would never measure piston-bore clearance at the top of the bore. the pistons are tapered from the top. that is where there is the most material is and the most expansion at temperature. measure the skirt with the piston just above the transfers.

M.F.D.B. · Post by **M.F.D.B.** » December 16th, 2008, 10:19 pm

You need to be measuring the piston in the right place, 90 degrees to the wrist pin and at the midway point.

If you had 2 ring gaps one bigger then the other you should have put the larger gap on the 1st position.

Mad Dog · Post by **Mad Dog** » December 17th, 2008, 7:54 am

M.F.D.B. wrote: If you had 2 ring gaps one bigger then the other you should have put the larger gap on the 1st position.

Why?

97af · Post by **97af** » December 17th, 2008, 8:05 am

M.F.D.B. wrote: If you had 2 ring gaps one bigger then the other you should have put the larger gap on the 1st position.

Justin,
Bigger gap always in the second groove......

M.F.D.B. · Post by **M.F.D.B.** » December 17th, 2008, 5:21 pm

More heat in the top ring to close the over sized gap...

ISBB · Post by **ISBB** » December 17th, 2008, 8:28 pm

M.F.D.B. wrote:More heat in the top ring to close the over sized gap...

dont ya mean more heat in the top ring to close the undersized gap!

M.F.D.B. · Post by **M.F.D.B.** » December 17th, 2008, 8:48 pm

ISBB wrote:
M.F.D.B. wrote:More heat in the top ring to close the over sized gap...
dont ya mean more heat in the top ring to close the undersized gap!

You dont want them to butt!!

Honda has been using single ring pistons for quite some time, the second isnt needed...hahaha

BannedCR500Riders.com

Question about piston clearance!

Question about piston clearance!