So long old friend...

[alexh]

I was prepping my bike to go riding tomorrow and I had to change my jets from coming back from the summer at high elevation. So I also decided to take a look at the reeds and the piston to see how things were going. Here's what I found:



It was a Vertex. I had radiused the inside of the skirt before I installed it to prevent this sort of thing from happening, but alas it was not enough. Bob I don't know if you remember, but we had a discussion on the other board about this. Thinking of going to a Wiseco this time and having GSS do the work. Other than the crack, the rest of the piston looked good, no rub marks, only a little blow-by on the exhaust side. I'll probably strip it down tomorrow to get a better look.

Exhaust side:



It had been almost exactly two years of mixed riding since it was installed. I would guess about 75 hours, I dunno. Has anyone looked into nikasil or equivalent for the 500? I saw that US Chrome does this for iron sleeved cylinders, wondering if it was worth it.

[AlisoBob]

Yea.. cracked skirts are pretty common on cast pistons when the piston to wall clearence gets too big.

Scored pistons are pretty common with forged when the clearence is too small.....


Take your pick I guess.

My Vertex is getting pretty old. I'll inspect it pretty closely while the motor is out of the bike while doing the A/F conversion.

Most cracked cast pistons seem to happen after the first one has cracked, and a replacement piston is fitted without correcting the clearence issue.

Then its a cycle of crack, crack,crack... until the cylinder is bored, and the proper clearence is restored.

Two years of solid riding is a good lifespan, look at the "factory" maintenance interval, 20 hours or something like that.

If you buy a bike, the VERY first thing you should do is pull the reed block and pipe for an inspection, and count a top end into the price of the bike when you purchase, no matter what...even if the seller says its " Fresh"...

Ya, right....




Nikasil on a CR500 sleeve would be the hot ticket.

Do it!

[pstoffers]

Yea.. cracked skirts are pretty common on cast pistons when the piston to wall clearence gets too big.

Scored pistons are pretty common with forged when the clearence is too small.....


Take your pick I guess.

My Vertex is getting pretty old. I'll inspect it pretty closely while the motor is out of the bike while doing the A/F conversion.

Most cracked cast pistons seem to happen after the first one has cracked, and a replacement piston is fitted without correcting the clearence issue.

Then its a cycle of crack, crack,crack... until the cylinder is bored, and the proper clearence is restored.

Two years of solid riding is a good lifespan, look at the "factory" maintenance interval, 20 hours or something like that.

If you buy a bike, the VERY first thing you should do is pull the reed block and pipe for an inspection, and count a top end into the price of the bike when you purchase, no matter what...even if the seller says its " Fresh"...

Ya, right....




Nikasil on a CR500 sleeve would be the hot ticket.

Do it!

Spoken like a true HOON!!!

[alexh]

So today I finally got around to stripping the cylinder. Got the classic stop sign going on.





Piston comparison, old 89.5mm Vertex with new 90mm Vertex. Shows the smoothing work that I did with the casting flaws on the inside. Did it work, I don't know, but I think that it helped, considering that BOTH of the rings gapped at over .035 (biggest that my feeler gages go). I think that I'll be doing this again this time, since I don't think that it could hurt.



When Maxima says that the 927 has a long residence time, they're not kidding, there was a puddle of it in the bottom.

[britincali]

All two strokes have a puddle of oil in the crank case.

[lewisclan]

GOOD FRICKEN THING TOO

[bigpower]

A good bro of mine came up with this suggestion.

He seems to believe that a lot of the cracking problem in the CR's has to do with that huge intake port. If you've ever seen a Kawasaki cylinder, the main difference is the fact that the Kaw has a couple of bridges on the intake side. Bridges=support. It's not just the 500's that have this problem. He had a CR250 come to him in a box, blowed up, that suffered from the very same thing. Upon further inspection, one thing stood out....it, too, has a very large opening back there. He thinks that a couple of bridges back there would solve this sort of problem. An aluminum sleeve, with bridged intake, plated. The only problem, getting a piston off the shelf. We're talking custom, and that ends up costing a few dollars worth of beer money. I've been kickin around the idea of tryin it for a few now, but my lathe really isn't worth a shit as far as cutting something close enough. But I bet LA Sleeve could do it.
Than it would be a matter of getting a piston made, but that wouldn't be much of a problem in itself, just like I say, cost some $$. Than how would it effect performance would be the next question.
Still more cost effecient to check it every yr, IMO

[100hp honda]

never seen a wiseco crack yet

[ou812]

never seen a wiseco crack yet

Glen told me the old style pro lite ones do crack by the pin, he also said he talked to Wiesco and that is why they dropped the cut out around the pin area.

[alexh]

Sent it off to GSS today. $55 plus shipping and fast turnaround time, with a torque plate, beats the local guys' $50, no torque plate, 4 weeks turnaround.

[britincali]

Sent it off to GSS today. $55 plus shipping and fast turnaround time, with a torque plate, beats the local guys' $50, no torque plate, 4 weeks turnaround.

[AlisoBob]

with a torque plate, beats the local guys' $50, no torque plate, .

[iggys-amsoil]

never seen a wiseco crack yet

Glen told me the old style pro lite ones do crack by the pin, he also said he talked to Wiesco and that is why they dropped the cut out around the pin area.

Mine don't have them.

[100hp honda]

never seen a wiseco crack yet

Glen told me the old style pro lite ones do crack by the pin, he also said he talked to Wiesco and that is why they dropped the cut out around the pin area.

people also claimed to see bigfoot. ill believe it when i see it

[AlisoBob]

Glen says " Pay Up Sucka'!!"

[iggys-amsoil]

You know, if Glen knows about it, why does Brit have one?

[britincali]

You know, if Glen knows about it, why does Brit have one?

Ive never seen a cracked one personally, I'll bet the cracking is happening on nitrous/alky bikes or a bike that pinged badly.

[ou812]

If your pinging , somethings gotta give.

[dannygraves]

That pic is the OLD OLD one. 2 designs ago. thats why the more recent ones before the boat anchor were only cut in on one side, not both.

[dannygraves]

You know, if Glen knows about it, why does Brit have one?

Brit doesn't have THAT piston, he has the more recent design.

[britincali]

You know, if Glen knows about it, why does Brit have one?

Brit doesn't have THAT piston, he has the more recent design.

Nope the one I have is the old style wiseco, dont forget glen built that motor awhile back.

[dannygraves]

were talking about 3 generations of wiseco here, I have one like the pic that came out of my bike, lets just call that gen 1, the sides were almost flat like in the pic. The one you have is the next after that, lets call it gen-2 where the sides dip in, but only on the intake side, which is the same as whats in my bike now (not at risk of cracking) then the most recent is the boat anchor without any trimming on the side, lets call that gen-3. Gen-3 is a result of economics, wiseco trying to cut cost without lowering the price for us...they make more money. Gen-2 was developed to make up for craking gen-1 pistons...
Make sense???

[dannygraves]

see, heres your piston


and heres bobs pic, look at the exhaust side of the pin

[britincali]

Nice catch danny


I learned something new today!

[iggys-amsoil]

There must be a fourth gen in there cause mines like Brits except no pockets milled.

But like was said, NOS or Alky, most likely.