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Hey, if you have read my other post, the crank on my R recently blew up. Today, at work I measured my cylinder bore. I guess it wasn't as trashed as I thought it would be. The top of the cylinder measured a 2.8755" near the exhaust port it was a tad bigger (relieved?) at 2.876", and down near the bottom of the cylinder it was a bit smaller at 2.8745". If I get a new 73mm piston (measures at 72.95 or 2.8720") would that be tooo much piston to cylinder clearance? Its a a total of .004" at the exhaust bridge area and at .0025" at the bottom, and .003" at the top. Do you guys think this is too much? I heard that with a forged wiseco you need a little more clearance because of thermal expansion? Also, I used a three point type mic because that is all we had so I do not know whether or not it is out of round... I really don't want to go to the 73.5mm bore because that would put me on the last bore before I would need a resleeve!!! Thanks....
 

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i aways try to run between .0025 and .003 on my pistons
they are wiseco forged but i am only at 68mm.
the piston are eliptical from wiseco so when they epand they expand in to a circle.
 

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i aways try to run between .0025 and .003 on my pistons
they are wiseco forged but i am only at 68mm.
the piston are eliptical from wiseco so when they epand they expand in to a circle.
Are you sure they are eliptical? I've looked at a Wiseco before, and it appears they've been finish turned in a lathe. Typically, when something has been machined in a lathe and it's out of round, it's not supposed to be like that and there's an issue with the machine accuracy.
 

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If you measured the piston on an X and Y axis, you'd get different numbers. They're larger front-to-back, and smaller side-to-side, across the wristpin area. More metal in the wristpin area, and when it heats up, it gets bigger than the other areas of the piston. There's just more metal to heat and expand there.

No lie...
 

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Hey, if you have read my other post, the crank on my R recently blew up. Today, at work I measured my cylinder bore. I guess it wasn't as trashed as I thought it would be. The top of the cylinder measured a 2.8755" near the exhaust port it was a tad bigger (relieved?) at 2.876", and down near the bottom of the cylinder it was a bit smaller at 2.8745". If I get a new 73mm piston (measures at 72.95 or 2.8720") would that be tooo much piston to cylinder clearance? Its a a total of .004" at the exhaust bridge area and at .0025" at the bottom, and .003" at the top. Do you guys think this is too much? I heard that with a forged wiseco you need a little more clearance because of thermal expansion? Also, I used a three point type mic because that is all we had so I do not know whether or not it is out of round... I really don't want to go to the 73.5mm bore because that would put me on the last bore before I would need a resleeve!!! Thanks....
if you ask me the more clearance the better ! .005-.006 no problem.. matter of fact it will make more power @ looser clearance... never have any problems running loose but running tight on the other hand can cause problems.....some of the giant motors i build will be at around .010 after break in.....looser is better...imo
 

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if you ask me the more clearance the better ! .005-.006 no problem.. matter of fact it will make more power @ looser clearance... never have any problems running loose but running tight on the other hand can cause problems.....some of the giant motors i build will be at around .010 after break in.....looser is better...imo

You talking about a 4 stroke, right :eek:

If you got to run 0.010 on a 2 stroke piston, theres some serious issues going on somewhere with those engines.
Neil
 

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You talking about a 4 stroke, right :eek:

If you got to run 0.010 on a 2 stroke piston, theres some serious issues going on somewhere with those engines.
Neil
with a reply like that its obious you dont know what your doing! any one who has any experiance with big motors will tell you that .010 is better than .005
250r motors....with a 97mm bore and big porting you wont get any less than ".007 fresh" to not stick.. after break in you have about .010... btw lots of motors come from the factory with lots of clearance especially watercraft and outboards.... seen as much as .014 on a merc.

as a general rule you can take wisecos recomended clearance and add .002-.003 to it and itl be about right... the reccomended clearance is only for stock porting and compression! wiseco will even tell you that..
 

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:p :lol: :lol: Ok, I read your reply :huh: & I tell you what, you keep on building yours how you want & I'll keep building mine like I do or like I have in the past 36 years.
Oh, & since I dont know what I'm doing,,,, well never mind, I'll just leave it at that.
Neil
 

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with a 97mm bore and big porting you wont get any less than ".007 fresh" to not stick.. after break in you have about .010...
So, you're saying you're losing 3 thou just on breakin?... In piston-to-cylinder clearance, you're losing 3 thou for a breakin?
 

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:p :lol: :lol: Ok, I read your reply :huh: & I tell you what, you keep on building yours how you want & I'll keep building mine like I do or like I have in the past 36 years.
Oh, & since I dont know what I'm doing,,,, well never mind, I'll just leave it at that.
Neil
you have been messing up peoples motors for 36 years !? i havnt been building for quite that long just since 1990...
question for you though how many 100+ hp 250r motors have you built ? wait i know the answer to that. ZERO !!!!!!
how many 250r motors over 450ccs have you built ? ibet i know the answer to that as well. NONE!
lastly how many prox motors have you built that have lasted over 300 gallons of fuel ? once agin i bet i know the answer to that one too...

as far as clearance goes
the needs for an alky burning drag motor are quite diffrent that a motor that is going to plink around on a mx or flat track ! the fact that my big motors will run through damn near a gallon of fuel in one pass and actually freeze the carb , intake and intake bridge in that short time the added clearance is a must ! the man that makes the cytlinders will even tell you so ! try this somtiime measure a piston then heat it up to about 1000degrees measure it agin.. its going to be alot bigger.. you add that to a cylinder that is colder than ambient temp and its gonna get tight on you fast !

heres my reccomended clearances for gas

64-68mm .0035
68-72mm .004-.0045
72-78mm .0045-.005
78mm-85mm .005-.0055
90+ mm .006 .0065
97-100mm .006 -.0065

on alky you can add a thou or so to all those numbers..
 

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you have been messing up peoples motors for 36 years !? i havnt been building for quite that long just since 1990...
question for you though how many 100+ hp 250r motors have you built ? wait i know the answer to that. ZERO !!!!!!
how many 250r motors over 450ccs have you built ? ibet i know the answer to that as well. NONE!
lastly how many prox motors have you built that have lasted over 300 gallons of fuel ? once agin i bet i know the answer to that one too...
There's one in every crowd...
 

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There's one in every crowd...
since i dont see any reply from him i guess im right about all my questions ! lmao..


anytime this guy wants to have an engine building contest im in....he can pick what cylinder were gonna use... i donk care. but my designation will be unlimited though... such as a stock cyl but any bore stroke combo i want... or hell if we wants to play with more expensive setups i got a 561cc saber motor here with .010 piston to bore clearance that will do the job as well ! im sure he dont wanna spend 8k to loose though ! lmao

i know this dude is a mod but my concern for that could be measured in micro givashits .. kick me off the site or whatever.. he started it with "the motor that needs .010 clearance has some serious issues " comment... once agin wtf does he know about 500+++++ cc 250r motors ????????
 

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heres my reccomended clearances for gas

64-68mm .0035
68-72mm .004-.0045
72-78mm .0045-.005
78mm-85mm .005-.0055
90+ mm .006 .0065
97-100mm .006 -.0065
Ive been building race jetski motors for 15+yrs including world championship winning motors and theses numbers are 100% SPOT on with Wiseco in race watercraft. I bet every jetski world championship motor in the last 20 years that has had a Wiseco in it with an iron sleeve(all over 80mm bore) start out with these numbers exactly.
 

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you keep on building yours how you want & I'll keep building mine like I do
Neil
As long as your customers are happy, the sport benefits.

As long as you guys are building engines, the TRX250R benefits.

As long as we can all get along, this site benefits.

I guess I just don't get all the hostility. There's a certain amount of sarcasm and jabbing that takes place on this site...maybe some people haven't realized that yet?
 

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As long as your customers are happy, the sport benefits.
As long as you guys are building engines, the TRX250R benefits.
As long as we can all get along, this site benefits.
Some people haven't realized that yet?
The way I see it is were all headed to the same place. Each takes his own trail and finds different detours. Each detour presents a problem in getting to the place. Each makes a decision how to solve the problem. Some decisions are wrong and we learn to adapt. Some decisions are helpful and we take a step forward. Heading up the trail we happen along someone who made the wrong choice, give them some advice and continue on. In the end we all end up at the same place. Hopefully its to the top of the tallest dune at WinchesterBay Oregon! LOL!
 

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since i dont see any reply from him i guess im right about all my questions ! lmao..


anytime this guy wants to have an engine building contest im in....he can pick what cylinder were gonna use... i donk care. but my designation will be unlimited though... such as a stock cyl but any bore stroke combo i want... or hell if we wants to play with more expensive setups i got a 561cc saber motor here with .010 piston to bore clearance that will do the job as well ! im sure he dont wanna spend 8k to loose though ! lmao

i know this dude is a mod but my concern for that could be measured in micro givashits .. kick me off the site or whatever.. he started it with "the motor that needs .010 clearance has some serious issues " comment... once agin wtf does he know about 500+++++ cc 250r motors ????????

Reply, no, dont think I will because its a waste of time.

Far as you getting kicked off the site.
You have a small amount of right to talk to me like you want, & I'll except that, because I did respond probably not in the proper way to your reply, but, I'll be checking your post from now on & you will respond & act on this site respectfully to the other members on here.

I'm not the new member here, you are.
I have been here a good while & most any of the members on here know me for the most part & what I do at this site, so keep that in mind.

Kick you off, no, not me, not right now, you just keep replying like you already have & I'll let Bill & the other members decide & go from there.
Neil
 

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Any of you regular members think I'm out of line, please tell me so.
Thanks, Neil
Neil, you're nowhere near outta line...

Piranha, you need to heat a piston before you ever start a bore job. You don't measure a piston cold, then bore from there. No 2-stroke piston is ever gonna see, or live through 1000 degrees of piston temp, either - it melts at 1250, to molten aluminum; pure hot-ass liquid. You'll blow right through the top center of it well under 1000 degrees, so heating it to that temp for a bore job is useless.

Heat the piston up, measure it warm, use that measurement for your bore number. Bore to that, plus 3 thou and you'll be good. Never had one go wrong that way, ever. I heat them in my hands, for several minutes, just to make sure they're not cold from the start. 100 degrees of body temp is enough. No cold siezures, no hot lockups, and never any getting siezed by the ex bridge, which gets another 3 thou relief on top of the bore size. Figure out what you're doing, because somethings not working for you to lose 3 thou on a breakin. Something's not right with that, no matter what kinda motor combo you're running. Do whatever you want, though, and I hope it works.
 

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I guess theres some merit to what hes saying & I can understand needing that much clearance on a alky or jet ski engine.
You take those engines, like hes talking about, they are normally drag engines & piston life span not thought about much.
Take the jet ski now, the coolant used to cool that engine is what ever water its sitting in. Even if it has a thremostat inline to control the coolant heat, it will still see times the cylinder is colder than the piston because of when the thermostat opens & cold water rushes in.
I could understand those engines needing more piston to cylinder clearance.

The problem in all of this, would be the readers on here that own a 250R, Banshee or a 2 stroke dirt bike & think maybe on my next top end rebuild, I need to take his advice & add in the extra clearance.

The engine you guys have on here, I would say that probably 95% of you have, are not the type of engines hes talking about & dont need that much piston to cylinder clearance because your engine temps are more controled.

You have any questions on this subject, please fill free to ask.
Neil
 
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