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 Piston Broke!

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mjpowell

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Number of posts : 1074
Localisation : Lincoln England
Registration date : 2006-12-09

PostSubject: Piston Broke!   Sat May 26, 2012 10:20 am

This piston finished race 2 at Cadwell but only just! I thought it had trapped the ring
in the grove as in race 1 but it was more serious -as pic shows, really struggled on
the last half a lap...



JB whats your diagnosis??

ps i know the answer....
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john bass

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Age : 88
Localisation : Bensberg, Germany
Registration date : 2006-12-06

PostSubject: Got a bit warm I think!!   Sat May 26, 2012 8:58 pm

Got a bit warm -- I think!

I´ll leave it to later `cos I am a Rodney Dümmkopf when it comes to diagnosis and for sure Derek will know what it was...

Was that a flywheel I saw next to the gudgeon pin?

Cheers!

Rodney D...

PS -- The evidence of first failure is destroyed by the running on afterwards -- you should have stopped as soon as the piston edge crumbled, attributably to ....???

It really is amazing how an engine keeps running with such damage. We had similar happenings with an air-cooled diesel: a glazed bore had the ring not transferring heat to the barrel wall which led to local overheating, such that the top land crumbled -- but nothing looking so bad as this. THIS IS NOT MY DIAGNOSIS OF YOUR MISFORTUNE MIKE I am just telling of a happening with an aircooled diesel where we were able to see the bore glazing. Obviouisly that would be destroyed too by your selfish attitude to finish the race and not contribute further to science!!

Knowing you never read more than two lines of long replies I know you won´t have read that bit about being selfish so I feel sure we are still friends??????????? .

JayBee for John-Boy!
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Derek

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PostSubject: Re: Piston Broke!   Sun May 27, 2012 5:00 am

listen John can you just get over the Rodney jig its peeing me off,

John but at last your talking ,absolute sense for a change, yes I do know its quite clearly the ring has trapped in the grove more importantly why though ?

I think i can see why? tell tail.!

regards Derek John Betts ?
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john bass

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PostSubject: You started it...   Mon May 28, 2012 10:06 pm

You started it Derek -- remember? way back. That was long before you said -- just a few days ago -- that I should not be taken notice of -- and you were going to educate me, the Rodney. I am waiting for the reply to 4 apples making a pound ...?
Otherwise I have no wish to be part of the offensive nit-picking?

And on this particular failure you address me and say, "... yes I do know its clearly the ring has trapped in the groove..." when I NEVER MENTIONED ring-trapping at all. And what I said was something to do with my experience of a particular air-cooled diesel engine.

Tell us all then -- as you the educator of the Rodney -- what Mike´s Piston Broke is all about?

Either you did not comprehend what I said or you are just nit-picking at me....

Whichever it is Derek let me assure you now -- I have no intention of carrying on with this nonsensical slanging match -- you seem to enjoy.

Ende!

PS. No point to it -- is there?
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Ned

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Localisation : Rayleigh Essex
Registration date : 2007-01-11

PostSubject: Re: Piston Broke!   Tue May 29, 2012 4:25 am

mjpowell wrote:




JB whats your diagnosis??

ps i know the answer....

Come on then Mike what caused it ?

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john bass

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PostSubject: Derek will tell...   Tue May 29, 2012 4:46 am

Derek knows....

But since Mike addressed me on this and HE SAID -- it was NOT ring trapping as it was in the first race -- something could have happened with a new ring for second race.

The ring trapping in the first race may --- MAY, I say -- have caused some bore glazing which Mike did not see which would have the new ring not sealing properly. In these cases the bore becomes devoid of oil and things get worse...

OR the new ring did not bed-in properly and the area of overheat resulted -- maybe with bore glazing and maybe not.

Or did Mike make another change -- besides just changing the ring....? That also includes something changed before the meeting which caused the 1st ring to get trapped? Change of petroil mix to less oil than earlier? Ignition timing or carburation change-- or some mechanical change ...??

A new ring in an already highly polished bore, from previous running, can be as bad as having a glazed bore but by what Mike has said -- the way he said it -- there is something else -- not a wrong size of ring surely??

Cheers!


Last edited by john bass on Tue May 29, 2012 5:15 am; edited 1 time in total
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mm_tribsa

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PostSubject: Re: Piston Broke!   Tue May 29, 2012 5:03 am

Big air leak I think !! Ring nipped in race 1 and total destruction caused by not sealing the bottom of the motor rushing to get out for race 2...
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john bass

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PostSubject: Good idea MM...   Tue May 29, 2012 5:23 am

Good idea MM ... you are saying overheating was why the ring got trapped in the FIRST race? Are you suggesting the air-leak is the same one for the second race?

Mike must be asked about the changes he made before the racing began and what he actually did after finding the ring trapped after the first race? If he put the same ring back after freeing it off it could well have overheated enough (duiring the 1st race) to loose its temper, radial pressure and ability to seal.
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mjpowell

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PostSubject: Re: Piston Broke!   Tue May 29, 2012 8:02 am

Right here goes.... reed valve motor used, went out to see if it worked as untested on a Dellorto34 - set up for last years piston valve motor(there i've used it again) seemed a bit lacking in performance - too rich. Went to start in paddock - would not start? lack of compression - stripped top end quickly with help from Tom and Arthur (My Seeley 7R & G50 supplier) Ring stuck in groove, freed ring refitted ring re-built top end but in a hurry and snagged the base gasket resulting in an air leak and picture of a ruined piston you see!!

Mike Mc ... did we have a conversation post 2nd race strip down?? If not well guessed Shocked

JB thanks for your input ... you can always pm me if you like?

Regards Mike
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Derek

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PostSubject: Re: Piston Broke!   Tue May 29, 2012 8:48 am

I dont think so Mike, Clearly Mike Mcdonald can see what I can, or he is as you say telling porkies and discussed it with you.

regards Derek
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john bass

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PostSubject: I was right...   Tue May 29, 2012 4:35 pm

I was wrong -- Derek was right -- as was MM -- but I did say, "... it got warm..." -- dinn I?

No Mike, I have tried sending PMs and my PC doesn´t seem to want to cooperate.

3rd line -- but doesn´t PeeEmming members PeeEmming each other suggest a secret society operating within the ranks??

John-Boy -- still a learning apprentice albeit slowly.



PS added later --- Why did the ring get trapped in the first race (place)? Is it a common thing? I ask because I never experienced such with racing 2-stroke engines and wonder if trapped ring occurrance comes from engines running at higher speeds now than they did 30-40 years ago.

Cheers!


Last edited by john bass on Wed May 30, 2012 4:08 am; edited 1 time in total
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john bass

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PostSubject: Interesting topic ...   Tue May 29, 2012 5:26 pm

Piston failure must be the prominent failure in 2-stroke engine racing so I´ll keep it going...

The 250 had an air-cooled head and water-cooled barrel and didn´t seem quite right carb wise so Andy got the Gardner bloke down to Brands with me on the Wednesday before Snetterton and we spent a lot of time doing Plug-Chops. The only change made was the carb needle and after the Gardner expert had settled the notch position on the needle I did two fast, 30min sessions (well they felt fast -- and a couple of watchers said the bike looked very quick...). Nothing was changed after that... Weather conditions at Snetterton on Sunday were similar to Brands on Wednesday. Warmed up the 250 and went out to practice. It was really flying -- passing everything in sight -- and again in the Norwich Straight, which was very long in those days -- about 1/2way along -- it seized and put a hole in the piston.

Why? when the Gardner expert had installed a new needle, set its position and I´d done an hour of hard riding at Brands did it seize at Snetterton?

Then there was Icarus-2 Bantam that revved to 11,000 -- and more*** rpm with a sort of sordid unreliability. There was a dreadful tapping noise in the last minutes of a race at Lydden. Head off showed the piston crown had been contacting the head. I´d gone from 40thou to 30thou `bump clearnce´ (i.e. piston-crown-to-head clearance measured with soft solder). Straight away I jumped at the conclusion too little Bump Clearnce was the cause. So I found a bit of ten thou shim, cut it out and refitted it under the head just in time for the next race. Wo & behold! The noise was less but strangely still there. Then after a while more so at higher revs. Icarus-2 kept going, strangely with not much less acceleration than earlier but the noise got worse and I had to give in and stop....

What was it, do you think? and why did the piston contact the head like that?

*** the rev-counter was already in bother at 11,000rpm.

Cheers!
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john bass

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PostSubject: Oh come now ...   Fri Jun 01, 2012 5:17 am

Oh come now ... don´t let this one die.

Brands Hatch circuit is 400ft ABOVE sea level and Snettertion only 85ft above sea level ...

So it cannot be anything to do with height above sea level weakening-off the mixture at Snetterton `cos its the wrong way round and not enough difference in pressure anyway. Nothing was changed on the 250 except the new needle in the Gardner carb...

And what was it with Icarus-2? -- not just piston expansion, surely???

Cheers!
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