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On the way back from Euro lambretta, I was overtaking a set of wagons, when I heard a high pitched whistle and then no power. Photo shows being loaded onto wagon 100 miles from Europort. At the time I suspected a leaking inlet manifold due to lots of oily matter around that region.

However, today, did a leak down test and no air leaks what so ever, but hole in piston. FYI carb rubber is OK and no sign of leaks at cylinder base or head.

Now at the rally, I bought a new TMX35 as my current one was worn and running too rich despite a 58 needle. Anyway, new TMX jetted with 56 needle, 2nd clip from top, 22.5 pilot and 330 main jet and 17 degrees static timing. Ran great, with good plug colour, till it went too hot and put a hole in the piston.

At the moment I'm scratching my head as i was convinced that the cause was an air leak.

Any ideas?

Plus, I note that there are now many piston for the TS1, but are there any benefits in paying more than the one that AF Rayspeed sell for around £100.00

What plug were you running ? What % oil were you using ?
What petrol were you putting in ?
G

Paul, I'd also be checking Ignition, I had a static one on once that popped 2 pistons, Strobed at 16 and advanced itself to 21/22 at high revs = bang.

Possible that an air leak occurs when the engine gets warm and something expands, which won't show when cold.

Timing could be a good call as well.

Paulnobodyimportant wrote:On the way back from Euro lambretta, I was overtaking a set of wagons, when I heard a high pitched whistle and then no power. Photo shows being loaded onto wagon 100 miles from Europort. At the time I suspected a leaking inlet manifold due to lots of oily matter around that region.

However, today, did a leak down test and no air leaks what so ever, but hole in piston. FYI carb rubber is OK and no sign of leaks at cylinder base or head.

Now at the rally, I bought a new TMX35 as my current one was worn and running too rich despite a 58 needle. Anyway, new TMX jetted with 56 needle, 2nd clip from top, 22.5 pilot and 330 main jet and 17 degrees static timing. Ran great, with good plug colour, till it went too hot and put a hole in the piston.

At the moment I'm scratching my head as i was convinced that the cause was an air leak.

Any ideas?

Plus, I note that there are now many piston for the TS1, but are there any benefits in paying more than the one that AF Rayspeed sell for around £100.00

I'm not surprised you thought it was an air leak,look at the colour on the top of your piston,it wouldn't surprise me if your spark plug was the same colour.That certainly looks like an air leak to me.

Looking at the top stud in the pic it shows that there's been a leak either from the base gasket or the head.Also, when you pressure test do you have a gauge connected to see the pressure drop?

Perhaps it’s just me, but my logic tends to presume the things that we change tend to cause changes...

Why else would we do it?

The piston is evidence of a lean mixture, but why your bike should suddenly spring an air leak precisely as you change carburetion would be a huge coincidence.

Sorry to sound cynical, but the carburetion has to be the prime suspect.

Paul,

So, am I right in thinking that you had done several hundred miles from the Euro site back in the direction of the port before this happened? The colour of the piston crown is SO extreme that I'd have thought it would have given up the ghost well before covering that sort of mileage(?). Did your route have you sitting at the same sort of speeds and throttle positions for long before this happened? If you followed the Rhine at different throttle positions, then got on the motorway shortly before this happened then IMO carb it is.

I agree with comments that swapping the carb out, with the associated jetting/component changes, is one heck of a coincidence if unrelated, however, the mileage covered might point towards this being a combination of elements. The question of fuel is a good one and it could well be that your carb swap resulted in it running weaker than before, which combined with a tank of hotter burning fuel pushed it over the edge (?).

Your bike was running so well on the way to Euro that I've no doubt that your motor was in generally good health... and wonder if we are not looking at a combination of factors? A think back to riding style/speed/route and throttle position (varying or just sitting at one) might help refine ideas on cause.

Adam

Just to answer some of the questions, before coming to my conclusion.

Journey there was using Exol fully synthetic, which I've used for a good few years and came back with Rock oil from team Francis, as I had run out of Exol and all at 3%. Plug was a 9. 10 miles before the holed piston, we had all filled up. Can't remember if it was 95 octane or super, but I put 8.5 litres into a 12 litre tank, but i don't think petrol was the real culprit.

Timing was 17 degrees static, but I take on board what GP240 says, so will check timing over rev range on re-build this Friday, which will include re-sealing inlet, exhaust and barrel. Then I'll do an air test which does have one of those blood pressure monitors as seen on SLUK.

As for cause, the good thing about forum feed back is that all your comments make you think. I was set on a leaking inlet gasket, but that proved not to be the case. So as Warkton says and he is correct, look at what you have changed, in my case a new carb, which I took for granted I had jetted safely.

And then Adam did get me thinking about speed and revs. So the first full day was spent on Autobahns and A roads, probably cruising at 60-65mph and overtaking at 70 plus. Now I've got to admit that on that first day, I did hear the high pitched whistle when overtaking. Of course, checked plug color at two fuel stops, I know that its not a plug chop, but colour looked OK and inlet manifold seemed tight.

Second day, the fateful day, whistling sound again on overtaking, which when the power went I put down to an air leak. However, I'm almost convinced that my jetting has caused the problem. When I was overtaking, I was not on full throttle, but probably still on the last part of the needle, with the whistling occurring. So my thought is that I was running extremely lean at that rev range and the whistling was my piston being torched.

Lesson learn't, do plug chops. So when i re-build, I will go to a richer needle and start from there.

Apologies for the ramble, but thanks for the suggestions.

maybe get it dynoed with the original carb' and see what it shows up ........then use the dyno to set it correctly (if wrong)

I had been reading this post.... then this happened to a mate at the weekend... having just filled up 5 miles before.... he was caning it tho....




First thing I noticed was an air leak going to top left stud.


re-assembled to check for any other leaks... he was worried about a casting mark at the bottom of the crank case that looked like a crack...




Small air leak at inlet....





big airleak caused by the plug not sealing properly... fitted a new plug and that leak went....


I deduce that his was caused by airleaks..... If thats any help


My question is... what do you do with the crank.... The big end bearing has just been showered in vapourised aluminium...

wow that sure is a nasty link to the images on photobucket.

I saw over 30+ cookies being downloaded as well as a piece of software being downloaded and installed called IF ? before I cut the connection
That site really is one to be avoided