holed piston :( so angry (now with pics)

[Speed Demon]

Just going on to reserve can weaken the mixture enough to hole a piston if it happens at full bore. Also there is a problem with the rubber washers in some of the fast flow taps deteriorating and blocking flow because they are not resistant to ethanol. I'd check the tap flow again if I was you, and also that the breather in the cap isn't blocked.

If it ran fine and the plugs looked fine when chopped then it sounds like fuel starvation or an air leak.

[Toddy]

Bad Fuel ??

[tonydevon]

ok thanks guys, at least theres some hope in that it was possibly the running out of fuel while near on full chat.

others seem more smug or intent on saying there was obviously other problems, but the motor was perfect, I know it was good, I took boxes of new plugs out and had chopped it at 1/4 1/2 3/4 and full throttle, all perfect colours, and full throttle runs were slightly rich, I did this out of interest, as it had been dynoed and I have total trust and faith in the guy that set it up.

I did a fast 70 mile run a couple of weeks back and she never missed a beat.

its been mentioned elsewhere that some muggy heads weren't correct? will look into that once its apart.

cant afford rebuild it sadly, and now lost just about every penny I had on this but would like to try and find out what caused it.

I tried to do it right by using good parts and not cutting corners, and it looks like running out of fuel ended it

if anyone wants a gp125 with holed piston for easy project then let me know LOL

[mick1]

Mate holed a TS piston on the way to Cleethorpes the other year. Got AA to campsite (Friday). Saturday (on the campsite) we dropped the cylinder, gave it a quick clean, tried washing crank with petrol, picked up a new piston from Beedspeed, fitted it back together, never missed a beat since.

If you can afford a new piston, you might be lucky.

CamLam advertise a warning light on their fast flow taps, (as opposed to a reserve). They warn against the risks of going onto reserve when giving it some. That's probably the likely cause in this case

[Donnie]

others seem more smug or intent on saying there was obviously other problems,

Can you clarify?

[nelson pk]

ok thanks guys, at least theres some hope in that it was possibly the running out of fuel while near on full chat.

others seem more smug or intent on saying there was obviously other problems, but the motor was perfect, I know it was good, I took boxes of new plugs out and had chopped it at 1/4 1/2 3/4 and full throttle, all perfect colours, and full throttle runs were slightly rich, I did this out of interest, as it had been dynoed and I have total trust and faith in the guy that set it up.

I did a fast 70 mile run a couple of weeks back and she never missed a beat.

its been mentioned elsewhere that some muggy heads weren't correct? will look into that once its apart.

cant afford rebuild it sadly, and now lost just about every penny I had on this but would like to try and find out what caused it.

I tried to do it right by using good parts and not cutting corners, and it looks like running out of fuel ended it

if anyone wants a gp125 with holed piston for easy project then let me know LOL

Hi Tony

Did you retorque the head after 50 to 100 miles. If you don't do this (especially on a new build) it can come loose and cause an air leak. I would also retorque exhaust nuts too and and use high temp sealer on the exhaust gasket too as this is also a problem area on lambrettas.

I always run on reserve setting on tap for the reason discussed and advise anyone i do engines for to do the same thing. A mate of mine who i told this to didn't take this advice on his kitted motor and guess what......just as he was switching to reserve while he was cruising along at 60, it seized badly.
If you do a fuel flow test at 1/2 a tank and then one at 1/4 of a tank or just above reserve the difference in flow can be very different indeed.
I think the Muggy heads you refer to were a batch of 225 heads that didn't have enough cc's in the combustion chamber 2 or 3 years back as i had one. I dont think the 186 heads were affected and this was only one batch back then.

Its a p155 off for sure but calm down and put it in the back of the garage until your ready to look at it again.

[tonydevon]

well at least Im not totally wrong, locally Im being told that the piston wouldnt hole just from running out of fuel, and that it was obviously a long term underlying problem, I think its more of an axe to grind with my dyno guy as they dont seem to like him, I know 100% that the motor was fine and that the dyno setup was spot on

to go from perfect to dead at the same time as running out of fuel was too much of a coincidence.

head was retorqued down, minimal tightening occured but it was later than that in mileage (about 250), I wonder if that might have been a contributary problem?

however its done about 100 miles since then without issue, always the same no matter what, fuel tap on, choke on, put lid and gloves on, one slow kick just to make sure everything working ok, then sharp prod and it fires into life, choke off within 2 seconds and it sits at happy idle.

time to try and price up a piston to at least get an idea, didnt want to sell the numberplate from it, but now it might be my saving grace, unless I can get maybe £1700 for it with holed piston which I seriously doubt

[tonydevon]

ok so I know it needs a 66mm piston

but found mahle ones at 50 quid, cam lam list the muggy 200 piston at 100 quid or MB do one for 150 quid

HELP LOL

currently just trying to price it up while praying the barrel has survived, may be able to borrow from family to buy new piston and gaskets, but if barrel buggered then Im not buying new kit etc, deffo scrap then.

[Adam_Winstone]

It could be down to the issues already touched on but it may well still be down to over-advanced ignition timing. 17 degrees is what I've recently had to set a number of iron barrelled motors to in order to stop them from overheating, these were not very high compression motors and with very minor road tunes. 16 dbtdc was the static figure for a standard T5 and I would put money on your motor having higher compression and revving harder with the PM pipe.

I recently had to reset the timing on a mate's Mallossi 210 (with long stroke crank) as he had holed the piston, after having it dynoed and it running very well for some time. He holed his piston the first time he took it on a fast A road and held it at speed for a decent length of time.

It should be noted that CamLam now recommend that their kitted motors are set at a starting point of 21 degrees when using an Ancillotti clubman and 19 degrees when using an expansion, which would see the timing dropping to well below your 17 degrees static timing.

NB: If you are using plug chops as an indicator of jetting/running then you need to perform it at each and every stage of throttle progression; 1/4, 1/2, 3/4 and full, after accurately holding it at this marked throttle position for a number of miles before getting a true plug colour. Checking plug colour a hundred times at 3/4 throttle will tell you nothing about how it is running at 1/2 or full throttle.

Good luck with finding the cause or making your money back by splitting it.

Adam

[tonydevon]

thanks for taking the time to reply Adam,much appreciated, as is the input of everyone else

17 degrees was what I beleive that I read from camlam sheet online, and was suggested by several places/people

should I get it running again then I will change that and see how it goes.

the chops were performed at set stages, from info I learnt on here, maybe one of your posts? marked the twistgrip and used a local straight section of road, about 1 mile.

I really dont beleive jetting was an issue.

I have about £2700 in this scooter and reckon I be lucky to get £1500 back on it, so one hell of a loss, but maybe it can be rescued.

waiting to ring camlam and ask about pistons and prices etc