Pro-X piston clearance

[teton]

today I did some calling around but got a million different answers so hopefully someone can help me out
I am re-boring a 61x cylinder from stock to 82.5mm and am going to run pro-x pistons, what should the cylinder wall to piston clearance be, i heard everything today from 45 thousands of an inch to .45mm which as I'm sure you know is a huge difference.
the cylinder has some light porting and i do plan on bumping up the compression from stock

 

[teton]

make the second number above .045mm
my bad

 

[CG Racing]

.0045" is what you are looking for.

 

[teton]

so in machinist speak that means "45 thousands of an inch" right?

 

[PancakePete]

I dont know.. depends.. Recently I have seen .015mm.. (ducking)
Um.. I think .02mm is a bore and depending on piston... .003mm to .005mm is good clearance.. Just learing myself here !

That is probly way off though !:Banane37:

 

[CG Racing]

.0045 = 4 and one half thousandths of an inch

.045 = 45 thousandths of an inch.

1st decimal is tenths .0
2nd decimal is hundredths .00
3rd decimal is thousandths .000
4th decimal is ten thousandths .0000

 

[Matt_E]

I dont know.. depends.. Recently I have seen .015mm.. (ducking)
Um.. I think .02mm is a bore and depending on piston... .003mm to .005mm is good clearance.. Just learing myself here !

That is probly way off though !:Banane37:

Yes, it is. :biggthumpup:

0.005mm = 0.0002 in, or 2 tenthousands.

Instant seizure.

 

[teton]

so does everyone agree that .0045" or four and a half thousands of an inch is good piston to cylinder clearance for pro-x pistons, i originally told the machinist three thousands of an inch or .003
but this was just an average of the millions of answers i heard from riva,wamiltons,magoos and various other sources

 

[robertg]

I thought the spec in the Yamaha manual was 0.0028"-0.0032". I haven't looked at it in a while. ProX pistons are cast like a Yamaha piston so I would assume you would use the same clearance as OEM.

I believe a modified engine might need a little more piston clearance.

 

[keefer]

Everything that I have ever had setup for cast pistons is like everybody here is saying .004 to .0045 is good.

 

[Phill]

so does everyone agree that .0045" or four and a half thousands of an inch is good piston to cylinder clearance for pro-x pistons, i originally told the machinist three thousands of an inch or .003
but this was just an average of the millions of answers i heard from riva,wamiltons,magoos and various other sources

Thats what I run mine at.....

 

[Mark44]

Be sure to check ring gap also.

Mark44

 

[feartheride]

Be sure to check ring gap also.

Mark44

Yes check the end gap,I had one that was way off last year.

.004"-.0045" is a good range to shoot for,you could go tighter if it is stock.

I would have someone else double check the finished size if you know someone with a bore guage or inside micro. or telescopic guages.

 

[IceRocket1286]

it should say right on the piston box, unless you want a little tighter tolerance.

 

[hondamxracer]

I'm having my 61x cylinder with mild porting bored tomorrow to fit a set of 82mm Pro-X pistons (01.2510.100).

I found a couple of different ranges:
-> Owners manual: .0028'' - .0030''
-> Pro-X: .0035'' - .0050''
-> This post: .0045''

Is .0045'' still the recommend clearance?

Pro-X Instructions: http://www.pro-x.com/media/downloads/Piston%20Kit%20Instructions.pdf

 

[augustaf]

ProX pistons seem to be made by the same manufacturer that makes the Yam oem, The Yam specs are a bit scary, suggest you furnish a piston to the machinist and request .0035- .0045".(they like to check it with their own micrometer) Anything larger than that just causes needless piston slap. Had good luck with these specs for the last 23 years.

 

[Philip Clemmons]

Stock clearances are only good for 100% stock skis. We rarely keep things stock . Adding heads, pipes, etc requires more clearance due to more heat. Some of the bigger pistons run up to .006", but .0045-.005" is a safe range for our normal use with bolt ons.

I'd assume .003" is a seizure waiting to happen........

 

[Nuklear6]

.0045 is a good number for cast pistons. Could go a little tighter but no need. Forged pistons I like to see .005 or a bit better. As far as having piston slap if over .005, I've pulled engines apart with .008 clearance that didn't slap and ran pretty well. Closed loop cooling systems can survive tighter clearance. The micro sprint engines I build can run as tight as .002 but tend to cold seize easily at end of the year races in very cold weather. I opened my clearance up to .0035 lost no power and never cold seized again. The owner of the nikasil plating company I use argued with me first time I asked for that clearance, next off season after my stuff ran a well as it did at national race he was telling everyone .0035 was fine.

 

[JetManiac]

.0045 is a good number for cast pistons. Could go a little tighter but no need. Forged pistons I like to see .005 or a bit better. As far as having piston slap if over .005, I've pulled engines apart with .008 clearance that didn't slap and ran pretty well. Closed loop cooling systems can survive tighter clearance. The micro sprint engines I build can run as tight as .002 but tend to cold seize easily at end of the year races in very cold weather. I opened my clearance up to .0035 lost no power and never cold seized again. The owner of the nikasil plating company I use argued with me first time I asked for that clearance, next off season after my stuff ran a well as it did at national race he was telling everyone .0035 was fine.

.0045 is a good number for cast pistons.

X2

 

[wanderer1]

.0045 is a good number for cast pistons. Could go a little tighter but no need. Forged pistons I like to see .005 or a bit better. As far as having piston slap if over .005, I've pulled engines apart with .008 clearance that didn't slap and ran pretty well. Closed loop cooling systems can survive tighter clearance. The micro sprint engines I build can run as tight as .002 but tend to cold seize easily at end of the year races in very cold weather. I opened my clearance up to .0035 lost no power and never cold seized again. The owner of the nikasil plating company I use argued with me first time I asked for that clearance, next off season after my stuff ran a well as it did at national race he was telling everyone .0035 was fine.

Are you talking per side or total difference from piston od to cylinder id? probably want to specify for others. Also been a little debate on where to measure, top of piston-bottom of stroke or top of piston top of stroke?