Cylinder wall clearence for 310

[Honda 250r 001]

this winter im goin for a new piston and bore for my 310, but i know that you have to run more tolerance with a bigger piston because more metal can expand more and since this is my first time i dont know how far to go.

On my stock cylinder with a 68m piston i was running 3 thousandths, but should i run more with the 310? I want reliability and i break my engines in for at least 3 hours before running hard.

I like to run forged but if you guys think i could get more hours out of a cast piston then i will give one a try.

[hondamancbr03]

Whatever piston you choose will have the clearance requirements required....Forged pistons need more clearance since they react more to heat, where as cast does not.

I leave my clearance requirements up to the machinist and the piston manufacturer not a forum.....That's just my two cents.

[Honda 250r 001]

well what do you run? Thats what i want to know. Some people run 3 thousandths to start off and others run 8 thousandths. Im my own engine builder so i need a lil help.

[croat1]

you are an engine builder? or do you just assemble the motor?
you have a cylinder boring machine?

like hondamancbr03 said the machine shop will bore to the correct size. who's 310 motor do you have. i would first ask them.

just my opinion

[Honda 250r 001]

so no know knows what they bore their cylinders to?

[hondamancbr03]

Many things come into factor when having your cylinder bored...It's not a black or white selection, go on www.wiseco.com if you really need to know (if you run their piston).

My drab Banshee is close to .0035 Niks plated
My Play Banshee is close to .004 to .0045 Niks plated
My Honda was together when i purchased it and only have had the head off to change compression and check port timing, can't say what it was set at......

As i stated above...MANY factors need to be considered and unless you have a boring jig i would leave it up to the machinist.

I myself have never walk into a machine shop and started telling them how to do their job.

[86 Quad R]

dont take this the wrong way but, apparently you personally havent built/assembled very many engines to date.......... reason i say this is because just like jetting, every engine will be different from one another as to what it needs and is dependant on how its run/where its run, what compression it will be set to and what rpm range it will spend most of it time in ect ect... not to mention the piston type in relation to bore size, who's gonna be riding the machine ect ect ect. most engine builders will take all this into consideration when tolerancing one. the pistom manufacturer has a recommended P to B tolerance and is nothing more than a "safe" guide line and is generally based on your typical grade of the final hone. some "engine" builders will do a "micro" hone (ready to race) for those cylinders and can be setup with an even tighter tolerance out of the box so to speak.

i personally have 4 R's and a blastee and believe it or not i've set each one up differently. my personal R is always set up loose.

i hope some of this babble makes sense to you.... :cool:

[hondamancbr03]

Originally posted by 86 Quad R
every engine will be different from one another as to what it needs and is dependant on how its run/where its run, what compression it will be set to and what rpm range it will spend most of it time in ect ect

X10 on that...........Well put!

[2-330s]

3 to 3.5 any more and they start to rattle and tend to crack skirts

[Honda 250r 001]

ok, im running a steel liner and a forged piston, this is going to be a mx machine and duner. I hear three thousandths is a tad on the tight size. so thirty five thousandths?

[2-330s]

i have steel in all 3 of mine. when my sparks motor came it was at 28 my lrd was at 3 and my ftz was at 3. i flat track. when i have them redone i have them set at 35 for ice racing. my sparks motor didn't make it at 28 stuck at every port. they told me it wasn't intended to run that cold open it up to 3 i run forged in all mine as well. in a bind i ran one at 4 it cracked the skirt. it rattled as well

[Honda 250r 001]

Originally posted by Honda 250r 001
ok, im running a steel liner and a forged piston, this is going to be a mx machine and duner. I hear three thousandths is a tad on the tight size. so thirty five thousandths?

i spend a lot of time wfo and i run around just under 200 comp...

[2-330s]

sparks is 220 lrd 210 ftz 260

[hondamancbr03]

Originally posted by 2-330s
3 to 3.5 any more and they start to rattle and tend to crack skirts

Forged pistons can run with more room, they tend to bend the skirt long before they break, cast piston are set with a tighter tolerence being they don't expand as much and when they get to the point of rattle they tend to break off skirts, cast doesn't bend much at all, it breaks.

Honestly, how can you state a bore size without knowing all the rest of the required information? What if he's running higher compression? Is it a standard or larger bore?

I wouldn't suggest .003 to anyone unless plan on racing and trying to get all you can from the motor.

[Honda 250r 001]

Originally posted by hondamancbr03
Forged pistons can run with more room, they tend to bend the skirt long before they break, cast piston are set with a tighter tolerence being they don't expand as much and when they get to the point of rattle they tend to break off skirts, cast doesn't bend much at all, it breaks.

Honestly, how can you state a bore size without knowing all the rest of the required information? What if he's running higher compression? Is it a standard or larger bore?

I wouldn't suggest .003 to anyone unless plan on racing and trying to get all you can from the motor.

what do you suggest?

195 compression

100ll fuel

i love to over rev the **** out of it.

forged piston

steel liner

72mm piston

thanks!

[2-330s]

it seems fairly common on any of the 250r bb cylinders. read back a little his comp under 200

[hondamancbr03]

Originally posted by Honda 250r 001
what do you suggest?

Honestly, and I don't want to sound rude but I suggest you call a shop that builds them everyday for a living and give them your info and let them tell you....Don't take what any of us say as fact. Since I’ve been on this forum I’ve seen so many people give out opinions that they call fact.

My bikes run, they usually give me around 4 good seasons (except my drag bike), they run and last because I listen to people that deal with 100's of motors and different types of people per month.

Call Arlen with LED, he's my local guy and he seems to enjoy sharing his years of knowledge with people like us.

I don't want to see you take bad advice and stick a piston.....

[hondamancbr03]

Originally posted by 2-330s
my sparks motor didn't make it at 28 stuck at every port.

Do you really want to tell a guy to run .003 after you stuck a piston running .0028?

[86 Quad R]

man!!! as suggested, you need to pic a builder that does this for a living and follow his lead as to what needs to be done.fork the doh and get it done RIGHT. as i've stated, there are so many variables it aint funny. you cant necesserially go by what someone elses is set at. hell i've set some up as tight as .0015 and as loose as .006 that dont mean you should. :cool:

[Aceman]

The last time I rebuilt my 310, I used another teflon-coated Pro-X piston, which they mentioned lets them bore it pretty tight. I didn't ask the bore specs, but it makes 237 psi and runs like a champ!

Ditto on the "ask your engine builder."

[IcutMetl]

Originally posted by Honda 250r 001
I hear three thousandths is a tad on the tight size. so thirty five thousandths?


No matter if you're an "engine builder" or not; for God sakes, learn how to use a decimal point when talking about tolerances and machine work. "Three thousandths" (.003) is a whole lot different than "thirty five thousandths" (.035"). Perhaps what you meant to say is three and a half thousandths, or three and five tenths (.0035"). I am definitely not a motor guru, but at a bore clearance of "thirty five thousandths," that would be like throwing your hot dog down a loose hallway!

I had the same questions as you when I had some motor work done. I've done all kinds of general machine work...which applies to a lot of what goes into these, but I don't know dirt when it applies to engine building and bore clearance. I bought a piston, and sent it off to someone who knows a lot more than me.

[2-330s]

if you all know more than the people that build my motors then why the f**k aren't you building motors that beat them? please take their advice call a GOOD motor builder. arlen (led) jon(ftz) or curtis sparks (good luck!) and ask them.
icut if he is going to do his own work i would think that you would give him the credit due.

[2-330s]

ps the sparks motor that stuck was at 9 deg F if you dune at that temp let me know!

[Honda 250r 001]

Ok+obiously+people+dont+understand.+Im+just+wonder ing+what+you+guys+are+running+for+clearence+but+si nce+everyone+insists+on+bashing+me+this+thread+war +useless

[86 Quad R]

no where in my posts was i bashing. i gave you straight up experienced advice and it carries alot of merit as i have a personal relationship with each builder/individual that i use to assist me everytime i build an engine. whether its the porter, borer, dome profiler or crank builder. reason being, they need to know your riding habits. i inturn pass this along everytime i build an engine for others. the goal is to build an engine around the person for whom its for. and my freind includes tolerancing a piston aswell.

in your posts you seem to want others to make a decision for you by giving you a magic number.

if i came across as bashing, thats simply the way you took it......

goed day :)

[Aceman]

Originally posted by Honda 250r 001
Ok+obiously+people+dont+understand.+Im+just+wonder ing+what+you+guys+are+running+for+clearence+but+si nce+everyone+insists+on+bashing+me+this+thread+war +useless

What a slap in the face your response is. You took it as bashing when the folks on here gave you a reasonable response to your question. Instead of thanking the ones that tried to answer your question and taking it as advice learned from their experience, you instead call it bashing.

I'll keep that in mind next time I think about responding to one of your questions...

[All250R]

Guys, I think he just wants to learn. It sounds like no one is willing to commit to defining some parameters to judge a clearance from. That's fine, but he should be encouraged to discover those parameters if he wants to learn, not just ask a shop what value to set it at. Not all machinists are created equal either, and a shop will often err on the side of wide.

[Ruf Racing]

Originally posted by All250R
Guys, I think he just wants to learn. It sounds like no one is willing to commit to defining some parameters to judge a clearance from. That's fine, but he should be encouraged to discover those parameters if he wants to learn, not just ask a shop what value to set it at. Not all machinists are created equal either, and a shop will often err on the side of wide.

I agree. The dude gave you his engine specs. and his riding style.
What more would a engine builder need to know? You guys make
it sound like it's rocket science. :ermm:

[IcutMetl]

Yea, you guys are right. Apologies if I came across as a dik. I shouldn't post when I'm having a bad day...haha. I'm sure bore clearance depends on a lot of variables that I'm not even aware of or care about.

[hondamancbr03]

Originally posted by Ruf Racing
I agree. The dude gave you his engine specs. and his riding style.
What more would a engine builder need to know? You guys make
it sound like it's rocket science. :ermm:

I can only speak for myself but he was asked if he had a boring machine to do his own work and he didn't answer, it would be understandable if he was boring his own engine for the first time and was asking for help.....The machine shop that does my work also specializes in two stroke motor building so when I drop something off I don't tell him what to bore it at.....All he had to do is go to the piston manufacture website, I gave him the link....They have the clearance specs for forged piston.

Someone told him to go .003 , that's great for a cast piston but that's a time bomb for a forged. Several of us kept telling him to talk to a shop that builds two strokes all day, all year...That seems like good advice.

[rsss396]

Wiseco states on my box for a 91mm clearance is .0030(0.076mm)

I personally like .0035

Warm up on a forged piston is very important! don't ride it until you feel a good amount of heat in the cylinder with your hand
(100 degrees)
If you don't like to be patient and do this increase the clearance to .004 to help cold seizing

or just run cast pistons, I run cast pistons .0015

[hondamancbr03]

Originally posted by rsss396
Wiseco states on my box for a 91mm clearance is .0030(0.076mm)

I believe what you are ready is the size of the piston, as in .0030 over stock bore.

This is copied right off the Wiseco website:
I went right to Wiseco website and found .004 piston to wall clearance stated from them. Not that i set mine to that but it's what they recommend.


I can also copy/paste MANY post on this forum where people had there pistons at .003 and stuck the piston to the walls.....But at this point my brain is worn out on this subject.

Go .003 on your bore, hell for that matter go .0025, that's where the power is:)

[rsss396]

looks like wiseco is a little confused itself :ermm:

here a picture:

[Honda 250r 001]

I can wait for motors to warm up, i always do. But i want the most hours and reliability out of a a cylinder and piston...

So whats the scary point on a cast piston for looseness?

[hondamancbr03]

Originally posted by rsss396
looks like wiseco is a little confused itself

Go to their web site if you question what i pasted.

Well just because i have one last ounce of care left on this subject i called the machine shop that does my boring and machine work...First question he asked was "Who's riding it and what for".....He said he wouldn't bore a wiseco piston at .003 for just anyone and wouldn't suggest it unless you want to chance sticking the piston. You HAVE to give the engine/piston extra break in time at that clearance.

Check through these post, there are many who have stuck fresh pistons at .003....From the begining i suggested that he go to a shop unless he's boring it himself. Maybe they'll set it at .003 for him on their suggestion.......This horse is dead, i'm done kicking it.

[86 Quad R]

Originally posted by Honda 250r 001
I can wait for motors to warm up, i always do. But i want the most hours and reliability out of a a cylinder and piston...

So whats the scary point on a cast piston for looseness?

typically a cast piston in a fresh bore can be set as tite as .0015 and as loose as .0035 with a max wear limit 0f about .006"

[Honda 250r 001]

Originally posted by 86 Quad R
typically a cast piston in a fresh bore can be set as tite as .0015 and as loose as .0035 with a max wear limit 0f about .006"

thanks, im going to call a few guys and see what they think but i believe i might go for a cast and go with .002.

[headache]

well since your running a 72mm piston that equals 2.8346" Bore the cylinder to that! or maybe .0002" .0003" bigger. Your piston will have the clearance built in it. But i always measure my piston before i bore a cylinder just to be sure that they didn't screw up and make the piston a little big or small. If your running a wiseco or other forged piston, ( i wouldn't recommend running anything else) shoot for about .002 to .0025 clearance. Just my .02 cents