Hitchcocks Forum

Hi all... As I don't want to hijack Creaky45's piston thread I start my own on broken pistons. Mine broke last week... Bike 2003 500cc Bullet Crown piston CR 7,4:1 (19000 km) Mr H's tuned head Mikuni TM32 runing to the rich side free flowing intake/exhaust... In the morning after only 2 km and at 50 kmh I heard some metal brake and when pulling over to the side the engined died as I pulled the clutch. Is it a production faillure? Or something else, serious or not? Please have a look at the pictures I let me know your opinion on this. And please feel free to upload your own pictures and personal stories about your broken piston... regards Jacob

Sorry Jacob, can't see the photos, seems to be the curse of Photobucket again. Time to find a better photo host!



A.

Sorry to hear that Adrian. The photos are visible when I visit the forum on my own computer. Maybe some of the pix wizards can help?

The pictures work for me. Ugly though they are... A case of bad luck Jacob? Hope you get it sorted.

It may have been a casting or heat treatment flaw? But Detonation (over advanced ign timing) can cause gudgeon boss's to crack/fail...




What brand is the piston? I dont recognise that one???


Crown to Gudgeon support is minimal. Rings seems to have sealed Ok. Burnt oil under side of crown, she had been running too hot. The crown has been running Hot enough to contact burn oil


Did you measure the combustion chamber capacity? Or is the 7.4 - 1 a nominal figure?

Hi Guys--------- I'm with TIM on this...The rings look free and normal contact seems to have been made on the barrel face...The close-up underside view clearly shows the much-preferred type of crown construction when compared to the OEM Bullet piston ie}--- solid all the way around with radial oil holes for evenly placed oil distribution onto the mating barrel face....Excessive temperature on the crown has conducted through to burn the oil mist and give that classic "yellow" look....Clearly huge Physical forces allied with ( as TIM mentions ) a poor design around the Gudgeon pin ( Wrist Pin for our across the "Pond" friends !!) has resulted in this scenario.........The cracks would seem to indicate a pure linear force at play eg}--- just coming onto IGN. and TDC. rather than a failure after throttle shut-down at high RPM.......I've no practical experience of a TM32 carb but the read-up says "Faster and smoother air flow through the venturi"..so if you jetted as per an equivalent round slide then that would give a weak setting.. .Could you post an image or two of the crown please ??

The TM32 is used very successfully by our American friends on their tuned Bullets. A.

Jacob, in your description you say Crown piston (19000 km) is that the total distance with this piston?

First of all thank you for all replies... Exile, yes it will get sorted, but not untill winter comes around... Tim, it'a an Indian piston (the brand is Crown); rings move freely around in their grooves and no damage to the ring lands; CR 7,4:1 is a nominal figure; no blueing of the gudgeon pin... Gwilly, yes 19000 km is the total distance of this piston... I'm runing rich (too rich!) for two reasons: the bike runs super nice on the mixture and I'm sort of scared of runing too lean. A new load of pictures to answer some of your questions will come as soon as photobucket starts to act nice again... regards Jacob

Pictures coming up...