motor blew up

[EPApolice]

Here you go Ken

[ken007]

thanks Pat, have sent PM, ken

[ken007]

finally got computer to work , heres s a couple of photos, anybody seen this before, ken

[JonW]

ooof! nasty!

[ken007]

i read on the internet that the reason for most pistons breaking apart at the bottom like that is the barrells bored to big?

[hybrid]

If the bore is too big it can allow the piston to rock too much and the skirt can hit against the bore, so that's a possibility, yes.

[Stankflapper]

Hi Ken, I have just read this posting now. that is terrible news mate and to have it let go on you so soon is not going to make you love the RD much. I hope that you can get it back together soon. the guy I used to rebuild my RD400 Cranks was just outside Toowoomba, but now I am lead to believe that he has shifted to Darwin or there abouts. I hope you can find a crank rebuilder closer.

[Stankflapper]

After looking at the pics, my guess would be the little end bearing failure, then the needles rolling over eachother causing the small end of the rod to split in two.

[ken007]

thanks for your thoughts on this, the crank rebuilder has moved to darwin, ive tracked down a bloke here in brisbane who is going to take care of the barrells and the crank, thats interesting about the small end bearing failure, at 1st i thought that myself but couldnt back it up, there was a couple of small marks in the dome were a needle or 2 got hammered, on another site a chap said maybe a possibility that i used a rod thru the small end to lock the crank to tighten up the nuts on the end of the crank which i did, anyway its been a steep learning curve and sometime in the new year it should be up and running,, ken

[fred99999au]

Even with the amount of damage you have, I think you should be able to get an idea of the piston clearance in the bore to either rule in or out the oversize bore problem. Have a check for damage around the port edges as well to see if any part of the piston had hit here.

[L.B.]

Interesting comment about the rod through the little end to tighten crank nuts. Ive used same to undo but not to tighten. Even then i used the old bearing n pin in the con rod.
CSR - Graham is still in buisness in N.T. Got a crank on its way to him now for rebuild.
Good luck with it Ken. Keep us updated.

[ken007]

heres a photo of the exhaust port on the damaged side, i got the good piston from the left barrell and put it in both barrells and i reckon the right is looser ,you can slightly wiggle it and makes a rattle sound, my caliper has a flat battery at the moment but i doubt i could get an accurate measurement,,i think i am going with this fellow. ron russ,to do the crank repair, hes in here under serco in the rebore and crank section at the top.anybody used him in the past?
http://auction.netbikes.com.au/vjmw.php?page=resources

[hybrid]

Looks like the skirt could have got caught in the exhaust port.
But that could have happened after the breakage.

[ken007]

yeah im starting to think that unless you were in the motor when it happened i will never know 100%,but i do appeciate all replies, hope it doesnt happem again

[DuncanB]

The skirt catching and stopping the piston in it's tracks would explain the destruction on the top of the conrod.