holed piston :( so angry (now with pics)

[tonydevon]

good call about leak down, will have to find out how to do that and the costs.

[servetakid]

There was guide on how to do it a few issues back in scootering, it showed you how to make your own tester.

[corrado]

Darrell has made a kit to do just that.

http://scooterotica.org/forum/viewtopic ... 12&t=26427

[scooterslag]

Alright Tony, sorry to hear about your engine blues, can't offer any real teccy advice to you as I've aways ran standard Lammies but don't get too disheartened, stick with it chap. All the best Paul

[tonydevon]

ok, sorry to be a pain, but took photos of the parts last night, forgot the spark plug, but its ashen grey, like its been in a fire, its alloy deposits on it. looks like a part thats had that aluminised spray stuff on it

can anyone maybe shed any light or comment on anything that they see? I havent a clue, checked for obvious things, no sign of gasket failure etc

what about the dish in the head, is that about right, or obviously wrong?

the marks in the bore look far worse than they are, NONE of them can be felt, the light I used with the camera really showed them up

underside of piston doesnt show signs of buildup or discolouring like I have read about with normal lean running??

[bristolmod]

I had an identcle "blow" albeit on a standardish engine, and that was down to running too lean.

Open mouth carb on M5 Northbound up the hill from Clevedon to Bristol- bike was really flying then silence- piston damage was the same.

I'd look at jetting and plug (correct heat range plug??)

Chris

[tonydevon]

B8es plug

Jetting I havent a clue about what to tweak, thats why I had it dynoed but guess its time to learn and and or pay someone to do it again.

same fuel/oil mix and heat of plug that was used for dyno.

mine just the same, uphill on the atlantic highway, flying along then pop pop silence

open mouth carb PHBH26, Av266, X3, 53 pilot, 40 slide, 102 main, 70 choke

I have confidence in the jetting as I checked with plug chops myself, and Simon that did it is very good bloke

tap is fast flow and flowing well on both ON and RESERVE

checked the carb etc and all clean.

[Ricko]

Also done the same..........weak running being the culprit again, choke check maybe, when the motors running again, to make sure no area of throttle is running weak?
Rick

[nelson pk]

As long as it hasn't lifted the nicasil lining you'll be ok. Just lightly wet and dry to remove any ally deposits that have been left from piston and then give the barrel a good wash in petrol or soapy water.
Best way to check compression is to fill combustion chamber with oil from a syringe and measure how many mm it take to fill it (1mm = 1cc). Also if you measure from top of barrel down to top of exhaust port in mm someone on here will be able to work out rough geometric compression and corrected compression and this will tell you if thats ok.
Check your fuel flow at the same place/height that the pipe enters the carb banjo and that will give you a realistic reading. You should be geting a pint (or very close to) in 60 seconds.
What size float needle/inlet is in the carb?

p.s If you do decide to measure the combustion chamber as described only fill to the squish band because if you imagine your engine complete, the crown of the piston will slightly portrude into the combustion chamber losing a minimal amount of cc, yet on the other hand your squish between the outer of the piston crown and head will cause you to gain a minimal amount of cc so if you only fill to the squish band it will counter act this effect if you see what i mean.
Hope this helps.

[tonydevon]

thanks Nelson

your comment regarding float valve is interesting, I put a 300 in the 28mm carb that it was fitted with when I dropped it off for tuning

just opened the 26mm carb up and its a 200 float valve in that one.

will swap that anyway as I cant see it doing any harm

I should add that its normally got a 9 plug in it for the long runs, I swapped back to an 8 as I been commuting on it and only short fast runs, nothing prolonged.

filter in the tank is clean, and the filter on the carb had minimal tiny particles, but close to nothing.