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britincali wrote:The overall motor temp might be higher due to the slow speed but I'll bet cash money the piston crown doesnt get anywhere near as hot as at the dunes.

How many problems have you had with a piston crown?

Boiling the coolant at light loading helps piston to wall clearance.

Having a 700 degree piston ( WFO through the dunes) dosent.

Jerry Hall told me that under heavy loads ( Duning for example) the piston can actually be a press fit...

How does boiling coolant help clearance?

slomas wrote:
How many problems have you had with a piston crown?

Melted the exhaust side once.

It put a nice divot in the crown and melted off the top ring land, then smeared ally all down the bore and locked up solid.

It was a wiseco with no holes drilled, granted the meltdown was due to running lean but thats where it let go first.

britincali wrote:

slomas wrote:
How many problems have you had with a piston crown?

Melted the exhaust side once.

It put a nice divot in the crown and melted off the top ring land, then smeared ally all down the bore and locked up solid.

It was a wiseco with no holes drilled, granted the meltdown was due to running lean but thats where it let go first.

That doesn't count as it had a "Brit" tune

slomas wrote:How does boiling coolant help clearance?

Barrel expansion.

britincali wrote:

slomas wrote:How does boiling coolant help clearance?

Barrel expansion.

Cast or forged piston?
Standard or over bore?

slomas wrote:

britincali wrote:

slomas wrote:How does boiling coolant help clearance?

Barrel expansion.

Cast or forged piston?
Standard or over bore?

Either and either


The hotter the coolant is the bigger the barrel is (I know its only a tiny amount and not noticable)

boy am i fucked. hahaha bore is 3.562 and piston is 3.539 and best of all i checked the sleeve on the top looking down. way thinner on one side than the other. i didnt even mic it. lol looks like im just gonna scrap this cylinder and piston.

"Also, primary compression is going out those holes too."

The very reason I don't drill them and don't put the scallops back in.

slomas wrote:I would disagree....

Mountain riding is hell on clutches and due to the slower speed, you have less air going through the rads.

That altitude affect on cooling is negated by the less hp/heat produced, IMHO.

90% of the heat produced by the motor is LOAD based (I just made that satistic up, so I know its accurate) there is no load short of TOWING I can think of GREATER then sand doooning...

iggys-amsoil wrote:"Also, primary compression is going out those holes too."

The very reason I don't drill them and don't put the scallops back in.

With the proper sidewall clearance very very little (unmeasurable I bet) amounts of primary would be lost. Unless your holes where misaligned enough to "see" them from the exhaust port...

boy am i fucked. hahaha bore is 3.562 and piston is 3.539 and best of all i checked the sleeve on the top looking down. way thinner on one side than the other. i didnt even mic it. lol looks like im just gonna scrap this cylinder and piston

aloha450x wrote:boy am i fucked. hahaha bore is 3.562 and piston is 3.539 and best of all i checked the sleeve on the top looking down. way thinner on one side than the other. i didnt even mic it. lol looks like im just gonna scrap this cylinder and piston

Many of us, me included, have off center bores. I believe its do to core shift and come that way from Honda occasionally. Others blame the machine shop. Although it is poissble to bore off center if you "want to" its much easier to bore centered...

Just run it, mines been "off" for a LONG time, no ill effects...

nice but that still leaves the clearence issue right. that is too much right.

aloha450x wrote:boy am i fucked. hahaha bore is 3.562 and piston is 3.539 and best of all i checked the sleeve on the top looking down. way thinner on one side than the other. i didnt even mic it. lol looks like im just gonna scrap this cylinder and piston

I would double check and make sure you measured correctly. Where did you measure the piston? near the dome or at the skirt? I'm told the proper measurement is at the skirt, as it's a little larger than the dome... does someone know for sure? I'm not 100% on if thats true or not. By those measurements, it's time for a rebore, and you'll need to go with Wiseco due to the size needed, since ProX doesn't go bigger than 90mm I believe. Your cylinder is at about 90.48mm and your piston is about 89.9mm. Your clearance is about .023 which is a ton. Remeasure to be sure those numbers you gave are accurate.

fastkart wrote: I would double check and make sure you measured correctly.

And when you get done, check it 3 more times, drinking 2 beers in between sets...

fastkart wrote:Where did you measure the piston? near the dome or at the skirt? I'm told the proper measurement is at the skirt, as it's a little larger than the dome... does someone know for sure?

Skirt, 90 degrees from the wrist pin center line usually...

k took the piston off and got 3.563 at skirt and yes i tripple clecked the bore at 3.559 what do you guys make of all this. rebore? by my calucations thats .004 difference book says max is .005 should i just recess the exhaust bridge and see waht happens? haha

I'm going to take for granted you reversed the measurements in your post, otherwise your piston is .004 bigger than the cylinder.

Where to go from this is a tough call. You have one bore left on the cylinder... I'd be likely to pick up a new piston thats the same size you have now. Wiseco's generally like a little more clearance anyways. The other option would be to just have it bored for a 91mm piston and run it, or send it to be bored and nikasiled.

what kind of piston is it. if thats a wiseco, then you are good to go!

yeah its a wiseco. i spent quite some time measuring and remeasuring. it is so easy to slide the piston in the cylinder. give the rings a little squezze and its in. if i recall it's a little more difficult on my crf450.

check the ring gap. I can't remember for sure, but I think mine were .012. if you have too much ring gap, then your rings are worn.

dannygraves wrote:check the ring gap. I can't remember for sure, but I think mine were .012. if you have too much ring gap, then your rings are worn.

Shit im screwed, brand new my ring gap was double that!! LOL Thats my biggest complaint about Wiseco. They will give you a "recommended" side wall per your application. But they give you the same "prefit" rings in each kit. So if you have to run a loose sidewall then you get a huge ring gap...

Can you say FILE FIT?? HELLO SEIZCO??

mine were perfect out of the box! next time get the 2.00mm over bore ring kit and file down