Holed Piston, Any Ideas Why?

[soulsurfer]

Some pics of my holed TS1 piston and cylinder head, open to suggestions as to what may have caused it. Can't see any sign of inlet, exhaust or cylinder head leaks






Fortunately the cylinder was ok

I understand the crank may need to be removed and cleaned up, but what else would I need to check or replace, bearings, seals gaskets etc.?

[sean brady scooters]

looks to me that maybe the head gasket was pertruding into the bore and causing pre ignition/detonation.............

[soulsurfer]

looks to me that maybe the head gasket was pertruding into the bore and causing pre ignition/detonation.............

No Gasket but dowelled head.

[sean brady scooters]

ha ha.........that blows that theory then.....

[teamsequipe]

What mounting rubber did you have on the inlet manifold ? and how easy was the carb to remove when you stripped the engine ?

[Ian Hepworth]

What were the circumstances in which it happened (i.e. thrash on a really hot day)? Just filled up from a petrol station you don't normally use?

Had you changed anything recently (carb, jetting, timing, ignition) - I know you like to tinker.

[cezeta]

looks identical to mine, i found my head was leaking and so was my jl3.

the jl3 slip joint had got baggy so was leaking. i normaly silicone them but having been told there was no need i didnt on this one.

chaulky at replay calls the jl3 "the piston holer" aparently they can cause a wqeek spot that is hard to get rid of so quite often it stays waiting for the right circomstances to do damage.

[drunkmunkey6969]

chaulky at replay calls the jl3 "the piston holer" aparently they can cause a wqeek spot that is hard to get rid of so quite often it stays waiting for the right circomstances to do damage.

Can you expand on this? Sounds interesting.

[J1MS]

The only thing I dont like in the pictures (besides the destruction) is how far the sparkplug protrudes into the cylinderhead.... the heat path for the plug is surface contact with the head, the less the surface contact the hotter the plug gets if it glows too hot it can cause pre-ignition.... Not saying its whats happened on yours but it is somthing that can happen.... I can see from the pic that the head has had material removed to lower compression... Ive done this a few times myself and have in the past (sometimes depending on the head) removed a little more from the depth then fitted a short reach plug with the correct heat range.... rather than have the tip protrude into empty space... But I could be well wrong with my guess work... and its somthing completly diffrent maybe re angled transferes failing to cool the crown (Thats if the barrel has been ported) or maybe one of a dozen other things or a combination of two.... Hope you sort it so that it dosnt happen again... All the best...

[soulsurfer]

Okay, It's an LTH manifold with a Mikuni plate rubber mount.

It was a warm sunny day at cruising speed of 65mph/6.5k rpm. It had just been dynoed and with EGT guage a 700 degC spike at this speed which, on a TMX30, I tried to jet out without success. I'd previously opened the throttle or slowed to cool the spike but now I was reassured that this wasn't something to be concerned about and would be okay and possibly due to the Devtour pipe holding the temperature as it's stainless steel. Within 13 miles of leaving, this happened after about 10 minutes at said speed, by the time I realised it was pinking, POP!

The cylinder head is a MB Indian low comp head. The cylinder head was noticed but not identified as the cause, CC = 23/24. An AF head has now been recommended.

The cylinder is a standard 225 MB Road Tune.


On inspection, it was deemed inconclusive as to what caused it, what with the melting around the edge and the hole combined, but that it happened very quickly.

I'm not sure I'll get to the bottom of the cause but would like to eliminate any possible causes for the future.

Thanks for your replies thus far