Maintenance & Technical > KX500 Aluminum Frame Conversion (AFC)

Bad experience with Wossner pistons...

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Motorrad:

--- Quote from: cobbs on May 06, 2012, 08:11:12 AM ---make fun of forged pistons all you want I don't think some of you understand metallurgy at all so I guess you wouldn't understand why cast pistons are better for non nitrous motors.....

--- End quote ---

I have a degreen in mechanical engineering.. is that enough?

Foxx4Beaver:
I have a great sense of humor....I made a joke about cast,and then you said "I don't think any of you took classes in metallurgy."....basically saying none of us know what we're doing.I don't need to take a class....I have enough hands on experiance and have seen too many catastrophic failures with cast,and none with forged in the last 32 years.
I felt your words were a little harsh,so I gave back.....sorry if I upset you.

cobbs:
well thats why i said "i dont think" not i know plus didnt say that untill you TOLD me that "ALL the proof ANYONE needs is right here" basically saying what others know is wrong if its different from your "proof" and i said that because everyone i know whos educated in metalurgy will not use them  and ive seen many failures myself and out of prbably 30-35 failures ive seen only 2 were cast failures both were rider/owner error all the rest ive seen were forged and like i said before 90% of piston failures have nothing to do with the piston but i have most certainly seen forged pistons fail just from expanding and locking up and then taking out the cylinder, con rod and crank i have even seen a case destroyed because the rod bent so bad so lets agree to disagree and i will never bring this cursed subject up again ohh and Motorad you know your more than qualified thats why im confused with your preference well then again its probably because your one of the VERY FEW guys who can achieve 10'000rpm so i guess i see why you would

Foxx4Beaver:

--- Quote from: cobbs on May 06, 2012, 01:00:49 PM ---all the rest ive seen were forged and like i said before 90% of piston failures have nothing to do with the piston but i have most certainly seen forged pistons fail just from expanding and locking up and then taking out the cylinder, con rod and crank i have even seen a case destroyed because the rod bent so bad so lets agree to disagree and i will never bring this cursed subject up again
--- End quote ---


Haha...agreed.

The main reason guys have problems with forged "expanding and locking up" as you say,is because guys set them up way too tight.I bring this up because you said you're running a Wossner...I am too.On the box,Wossner says recommended tolerence is .0028....that's way too tight!!.I e-mailed one of the guys on this forum that deals with Wossner and builds motors...(he knows who he is)...he said they set them up at .004,and that makes them "happier".I went in between at .0036.After 1 hour of run time,I pulled the motor and inspected the cylinder for any signs of over tightness of tolerences...all good.I did the same thing at six hours,and still good.I'm at just about ten hours now.It is a snug fit,but if I had gone with Wossners tolerences...it very well could've been bad.Hopefully you did'nt go with the .0028.

RoostiusMaximus:
I'm going back to May 7/11 from when I started the official complaint to Wossner on the cr500 pistons also.
I was working direct with John Noonan

I also added more clearance than the box called for (btw, the old boxes show a tighter spec than the newer)
I ran the first one at .003" and stuck it, ran the same piston again, swiss cheesed with lube holes at .005". The afternoon that I stuck the first one I installed my spare cylinder with a vertex and ran it for a week or more, wfo. hillclimbs, bush, field and didnt fail it, eliminating exactly what I'd faught the wossner dudes about, the tune.

another engine I set it up at .0035", leary after the other sticking and stuck this one also.
during the time it took to get that motor installed i'd built a motor for a customer the same, .0035", he also stuck it.

I ran the .005" one in the winter, on the lake and stuck it once more, but i had a good reason for it that time  :-D
I got it back together at .006-.0065", (depending on where you measured it, it was pretty scarred up) and ran it another 10+ hours until i sunk the dome trying some evil ignition timing this spring.

I failed 6 pistons, some had an intake window cut, all had .020"-.022" ring end gap (these single ring ones need more)

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