Holed piston - Mugello 200

[Dragbart]

Muggy 200
JL3 pipe
26 Delly
Varitronic
Camlam mapper box
Dyno'd by Charlie Edmunds so set up correctly 18 months ago

Went to Clacton Ride Out in Sunday and scooter running fine until the ride home.

Running at 55-60 two up, when engine backfired and coasted to a stop. No compression so took panel off and spark plug was clearly loose. When I got it out it was white as in the picture below. Just got out in the garage and it's clear theres a hole in the piston as per photo taken through the plug hole.

I've got a couple of questions:

1. Could the spark plug have come loose and created a technical leak turning the mixture lean and creating heat, white plug and blowing the hole?
2. The engine turns easily now and seems smooth. Can this be fixed by merely replacing the piston/rings etc?
3. Can the piston be replaced by dropping the front end and taking barrel off with the engine remaining n the frame?

Appreciate any thoughts as want to get back on the road asap

Sorry photo files are too big

[Warkton Tornado No.1]

1. Could the spark plug have come loose and created a technical leak turning the mixture lean and creating heat, white plug and blowing the hole?

Yes, most definately.


2. The engine turns easily now and seems smooth. Can this be fixed by merely replacing the piston/rings etc?

Hopefully, but you need to inspect the barrel fully.


3. Can the piston be replaced by dropping the front end and taking barrel off with the engine remaining n the frame?

More than likely, but I'd have a good look/feel of your crankshaft with the limited access whilst doing so.

[holty]

if i were you i would remove the engine and take out the crank to give it a good clean, especially the big end, you might be able to wash it out in situ, but any debris could damage your engine, when rebuilt i would do a leakdown test just to be on the safe side, also check your carb for any blockages, also check fuel flow rate from the tap, when up and running also do a plug chop to check your not running weak or get it dynoed just to be sure,
good luck ,
holty

[coaster]

Holty is right, the best way would be to completely strip the bottom end as it will be full of powderised aluminium from the hole in the piston which could find its way into the seals and cause you problems later. That said, I blew holes in 2 pistons on my Muggy 186 a few years ago and just flushed the crank case out with copious amount of WD40. I just kept spraying it in until there were no more particles in the liquid running out. I didn't have any more problems with that engine

[Dragbart]

Cheers for comments.

Coaster when you flushed with wd40 was the engine in situ or did you have it out the frame?

[CHRIS in MARGATE]

Copious amounts of WD40 means copious. In the past I have used old petrol and oil and finished off with more WD40.
I tell you something; just when you think it's all out, lo and behold a dribble more comes out. Keep spraying in and rotating flywheel. Don't proceed any further until you are 100% satisfied it's all clear. And wash the transfers out as well. You should be OK. Lots of us have done it.
When you rebuild you must check the spark plug colour regularly.

[Warkton Tornado No.1]

Feedback is appreciated by all of us, so images will always be interesting to see, especially the underside of the piston crown & bore.

As ever, caution should be taken with the bottom end, but if the piston is holed because of a weak mixture, the result is literally burning through of the piston crown.

Unlike a smashed piston, any debris will go out through the exhaust port/pepper the head whilst the burn is taking place. Only when the hole is established can any crap go through the crown toward the bottom end.

However, repeating myself:

3. Can the piston be replaced by dropping the front end and taking barrel off with the engine remaining n the frame?

More than likely, but I'd have a good look/feel of your crankshaft with the limited access whilst doing so.

[Dragbart]

Deffo gonna try washing it out. Will finish with wd40 as suggested but how did you wash with fuel, I'm thinking some form of teat pipette - or a bigger turkey Baster to spray it in/around??

[Warkton Tornado No.1]

Deffo gonna try washing it out. Will finish with wd40 as suggested but how did you wash with fuel, I'm thinking some form of teat pipette - or a bigger turkey Baster to spray it in/around??

Get yourself some of these:

Swab Sticks.JPG

(Medical Swab Sticks)

[Marty ULC]

On the way home from geezleweezle we cleaned up after my holed piston by using an oil bottle to slosh spare petrol into the crank whilst kicking it over vigorously.

[MickYork]

I'd do a leak test before stripping it down.

[Dragbart]

Thanks everyone for your help and advice. I'm off to Camlam on Saturday to pick up a new Muggy piston for the GP rebuild and some fork links for my old Jet that I'm playing about with .....then its garage time. When I get the piston out I'll put some pictures on here.

Cheers

Mark