Forum

[Charlie]

At 700 miles on a new ally barrel and piston from our hosts my 51 Bullet engine was just about run in, then 1/2 a mile from home disaster. Engine note changed and oil started coming out of the breather (that's never happened before). Got the head and barrel off to see that a piece of the piston skirt had detached from one gudgeon pin hole to the other!! The bore was fine, so no indication of seizure, unfortunately the piece of piston that came off got minced by the crank so it was impossible to check its surface.
So learned readers please tell me, what may have happened to hasten my pistons demise an what should I replace it with?
Oh and while I'm here, a warning to anyone considering not stripping the engine fully after a piston failure, think again! Pieces of piston were so firmly wedged in the scavenge pump oil way that I had to use a hammer and punch to get them out!

[Mark M]

Indian piston? Had one badly crack at similar distance, oil consumption made me strip it which is when I found the crack. I could push it inwards with light finger pressure so total failure not far off. Contact our Hosts, I think they may be interested....

REgards, Mark

[Leon Novello]

It is so prevalent in Australia that someone always carries a spare piston on long rides so it can be changed at the roadside.

[Leon Novello]

Don`t know what happened, trying again.

[Tim NZ]

Failed 350 pistons are not common.


Failed T Slot, split-skirt over-reved high mileage pistons are legion. If you plan of riding fast (not advised with a pre 56 350 with its narrow con-rod) fit a forged or solid skirt piston.


To have died so young there will have had to have been a major stress riser at one or both ends of the Slot machined in piston directly behind the Oil ring. Square Cut terminal ends to T Slots and split skirts are acknowledged sources of major stress risers; skirt failure...


Crappy After-market Local market pistons are frequently encountered very badly machined and finished. Typically H does not sell such junk.


Alternative cause will have been as a result of impact damage to the skirt, as in being dropped from a height; fell off work bench for example? T-Slot Spilt-skirt pistons are fragile!


Did you verify piston/bore clearances at at both Top and Bottom of skirt? Skirt Taper is critical! Probably did not, but it is always advised to be recorded and to make sure that clearances are within spec.




Smile nicely, explain the situation to the parts man and ask for a super friendly price for the replacement piston...


One task you must not overlook is reseating the oil pump discs...

[Tim NZ]

Leon: Not Fair showing High-Comp Preigniton holed pistons; that can happen to any bike.


And the first pic, of one of my shattered pistons; was pulling +5500rpm in 3rd gear when it exploded.

[Leon Novello]

I like making people nervous, Tim.

[Charlie]

Good information guys. I should have measured skirt clearance new, just to make sure the piston hadn't been bounced. Forgot to mention piston was manufactured by Goetze is it Indian? Skirt was not split type but slotted vertically above gudgeon pin and horizontally under the oil control ring. Luckily none of the bits had reached the oil pump, but I've lapped them in anyway. Cheers

[papasmurf]

They are Indian:-
http://www.goetzeparts.in/,
http://www.goetzeparts.in/contact-us.html

[Charlie]

That's interesting, but just because it's made in India doesn't mean it's NG does it? Mark M do you know if your cracked piston was also Goetze and what did you replace it with please?