Petals breaking.......

[Truls221]

I've spent the last six months fondling with the jetting for my scoot, got it quite good and then I changed to a new exhaust and the sympthoms showed up.

Thought it was the new exhaust all along (could still be a factor), but then it showed that one of the six petals had snapped in half lenght. Not good for fuel pump underpressure, not good when riding wide open throttle. :uargh:

But I didn't spoil the whole engine, just a twisted scamcrank as the victim of two races and some street driving. total running distance of 150km.

Do anyone have experience with their petals breaking after very short time? (it's a cr125 membrane)

Anyone have an idea why this happened?

thanks for any replies

truls

[gertax]

maybe the petal hit the engine case? Or it could touch the crank? Some petals tend to lenghten themselves a bit during running.

If you're running without air filter some small stones (ie Sand) could have come between petal and reed rubber... if the petal hits the stone it is mostly destined to crack, not immediately, but in most cases it doesn't take very long

[freibier]

Maybe the material, the petal is made of, is not strong enough...?!? Are you sure, that there is a thing, made of an material like a rubber, that the petal hits, wenn its closed? If not, they brake in this short time.

greetings, Ralf

[Lucifer]

I guess, Gerald's explanation is korrect!

Have you mounted the metal-reedstops too, which should limit the movement of the reed-petals? Exept Boyesen and V-Power, they are essential part of the whole reed-construction!

Another aspect: people tend to overtighten the screws holding the reeds on the cage, which may brake the reed-petal itself - or even ruin the cage! Usually it's a good advise to use Loctite screw-stopper (should not get into contact with plastic or carbon petals)! Lost screws taking their trip down the crankcase and cylinder isn't just a horror-vision of mine...

[karoo]

The stock CR125 petals i know are quite strong - and a Vespa engine is most unlikely to reach the high rpms of a CR125! Mine showed not even the slightest sign of wear the last time i checked them (after being run for approx. 2.000km)!

Or was it backfire that snapped the reed? Fluttering reeds wear mostly near the tips and usually don't snap... What is the condition of the 5 other petals?

But how should a snapped reed petal cause a crankshaft to twist? I don't see a connection there...

[Lucifer]

Correctly mounted petals don't wear so much!

Ususally they stand much longer than your whole other engine-parts....!

Personally I have just seen one completely destroyed Vespa-Motor during years due to a broken RD-reed-petal (steel) coming lose....! In this special case parts of the petal blocked the mainbearing (crankpin), causing the crank to stop and twist emediately at about 8000rpm. The driver was kicked of the bike like a rocket and severly hurted, the ensurance refused to pay.....so that the completely destroyed bike and the cause for all that shit became really negligible....

Plastic reeds don't tend to come lose that way and the consequences are usually less severe too! As Karoo pointed out above, they wear at the edges and sometimes become even porous, resulting in a drastic loss of power, enormous blowback, no primary compression anymore,...! A twisted crank ist really unlikely...., more the other way round: parts of the destroyed crank, piston,... more probably broke the reed!

Nevertheless, consequent inspection should be done periodically, dependant to mileage and stress! Most manufacturers recommend a change every year...

[Truls221]

Thanks for the replies.

The fact that the petals hit the crankcase could be the problem, allthough I can´t see any signs of it, carefully looked over with the petals bent manually fully open. I think therefore the reeds may expand a little more with the flex of the reedstop, this is the only thing I can think of. The other petals showed no signs of wear and is in perfect condition. The petal that broke was the one at the back, on the lima-side of the engine.

I know of course that the crankshaft don´t twist by this reason, but it seemed strange that this happend with a brand new crankshaft after so short driving distance, seems like I have to do some welding there.

BTW, does anyone know which year honda used the six-petal membrane, or were I can get new ones for replacement?

cheers

truls

[karoo]

I think mine was '96!