BannedCR500Riders.com

ok drilled the hole is the piston. exactly to wiseco specs. however for some reason they give you a range for the size of the holes. .06-.09 so i went .075. my next question is do i really need to relieve the bridge or are the holes good enough. if they are ill just throw it back together sad save myself a few bucks. i never mad it to the machine shop today. the booze hound got ahold of me bad last night. hahah

Yea..relieve that sucka.... Its not an option.

AlisoBob wrote:Those are pretty big...

That's what I thought but Glen had a good reason. I just forgot what he said.
There was a pic somewhere of a piston that had holes drilled all over the dang thing.


Pencil holder you funny Justin

AlisoBob wrote:Also, primary compression is going out those holes too.

I don't understand this statement......... shouldn't the compression be above the piston rings not below?

that was brits piston with all the holes

Primary compression is when the piston it traveling down, the reeds close, and air is pumped up the transfer ports.

Those holes look big enough to allow primary compression to blow out the exhaust port ( around the bridge)

AlisoBob wrote:Primary compression is when the piston it traveling down, the reeds close, and air is pumped up the transfer ports.

Those holes look big enough to allow primary compression to blow out the exhaust port ( around the bridge)

Damnit Bob I hate it when you make me think!

why dont they drill them at the factory?

aloha450x wrote:why dont they drill them at the factory?

You dont drill cast pistons...

why not? someone break this whole piston thnig down for me. which is better and why?

You just opened a big ol' can of worms..

Basically?

Cast: Long lasting, but structural failure is common if left in too long.

Forged: Dont last as long, but dont shatter and take out the bottom end either.

what would be too long?6mo at 6hr a week?

I've seen 10 year old CR500 motors run great with with oem pistons.

Its all about the cylinder wall to piston clearance. When it gets too big, bad things happen.

My current cast piston is about 3.5 years old. I've ran the crap out of it, but I keep an eye on it too.

It will be its last season, no matter what happens this year.

$150 / 4 years is $38 in piston costs per year.....pretty cheap.

I've seen allot of cast pistons fail ( as in come apart)

I've also seen allot of Wiesco's fail ( as in seize or score badly, or have tons of blow-by)

Like I said.... its a real tug -o -war. You need to make your own decisions.

ok one more question. what is the correct piston to cylinder clearance and what is the proper way to measure it?

Cast is about 0.0025"

Forged is about double, 0.004"

You probably dont own inside mic's to measure the bore, so take it to a machine shop and have them do it.

well the best i could get with some calipers is 3.560 for the cylinder and 3.538 for the piston

Like I said .... inside mics, or a bore gauge...



or

I've been running almost 2 years on a forged wiseco at .004" and still have foot breaking compression. The forged pistons REALLY need to get warmed up before you get on it. Before the piston expands it rocks a lot and that is when damage that will throw your bore out of round occurs. It is also a fine balance. you CAN run them at .003, but if you over heat the thing at all it WILL seize. Cast pistons are the definite choice for a stock bike that doesn't get the snot reved out of it. At the dunes I will keep my bike WFO for long periods of time and have a lot of work done to my bike, so the added piston stength is worth more to me than a longer lasting tighter bore of a cast piston that could frag and destroy my bottom end.
Its all a toss up based on application. If you are running supermoto and plan to rev the snot out of it, I would recommend the forged, but only if you plan on building the thing up. if you plan to keep it stock, a stock motor with a cast piston will last 10+ years when well taken care of.

dannygraves wrote:if you plan to keep it stock, a stock motor with a cast piston will last 10+ years when well taken care of.

Yup, especially if you only ride twice a year like Danny or Clyde...shit, that thing would last 100 years!!

I ride almost every weekend, almost 90% sand dunes (hard as hell on the motor) and on top of that I beat the crap outta my bikes. Lots of drag racing, jumping, crashing, I love it all!! Granted I havnt rode my 500 much since the 450 came about, but thats only been the last year or so. In my application, a cast piston isnt an option...

M.F.D.B. wrote:

dannygraves wrote:if you plan to keep it stock, a stock motor with a cast piston will last 10+ years when well taken care of.

Yup, especially if you only ride twice a year like Danny or Clyde...shit, that thing would last 100 years!!

I ride almost every weekend, almost 90% sand dunes (hard as hell on the motor) and on top of that I beat the crap outta my bikes. Lots of drag racing, jumping, crashing, I love it all!! Granted I havnt rode my 500 much since the 450 came about, but thats only been the last year or so. In my application, a cast piston isnt an option...

yeah, just keep talkin shit! Some of us have JOBS and have to miss a few rides! HAHA

dannygraves wrote: yeah, just keep talkin shit! Some of us have JOBS and have to miss a few rides! HAHA

Dont be HATIN!! Ninja please...

I beleive if my brain does not fail me that Rossco said his seizco is in at 28 with no problems.

But the great piston debate lives on,

P.S. I put holes in my pistons just because they are dam sexy.

yeah, I think you are right. And they will run fine like that as long as you never over heat it, or run lean! He rides gnarly trails where you would be lucky to hit 3rd gear, so I don't think he gets the piston as hot as dune riders do.

well i grabbed a inside mic at work so ill post what i got when i get home. the engine is beautiful and just rebuilt but i dont trust anyone elses work. esp since i dont know who rebuilt it. so im going back threw it. it has a wiseco and didnt have holes so i drilled them and the exhaust bridge isnt recessed. thanks for everyones input and help

dannygraves wrote:yeah, I think you are right. And they will run fine like that as long as you never over heat it, or run lean! He rides gnarly trails where you would be lucky to hit 3rd gear, so I don't think he gets the piston as hot as dune riders do.

I would disagree....

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

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.