piston problems

[stretchedscoot]

pulled my motor apart to do the 54mm big bore and found a surprise.

the weird thing is it wasnt running bad and still showed 130psi compression.

guess my motor was running lean before i upgraded the carb.

[bootscooterboogie]

:stars:

At least you found it before it actually started to cause performance issues.

[2strokd]

The rings were holding it together.. China standard safety design.


Lol, glad you spotted it. Could have ruined the whole longblock.

[skuttadawg]

Did you do a plug chop to see if your lean ? What size carb and main jet ? Airbox and stock exhaust ? Run premium gas ?

I had a " secret 63 " put in 87 gas by mistake , rode a mile to a store . Left there and got on it hard and poof the piston cracked . This was day 2 with less than 100 miles on a brand new scooter . I drove it to my dealer as it lost power but still ran . He said he would remove the egr hose on the valve cover to run a test which he looked for smoke . Well it smoked so he said it would be a long time to tear it down , inspect and rebuild which he did for FREE . I had a meltdown as I was so thrilled about being back in the 2 wheel world after having so many of them when I was young and NEVER had a piston crack on any of them .

He said the BBKs of any size will have higher compression than the stock bore and should ONLY use premium gas to prevent damage like mine did in such a short time . I have seen car pistons that were damaging from preignition and 87 gas but took thousands of miles to damage since the pistons are not made from recycled pot metal and butter like mine was lol . I had it crack again after 6 weeks as I babbied it to avoid another meltdown . Took it back in my truck as it was DOA this time the piston was in pieces . I said alot of bad things I can not post here and said I did not want another POS piston . I had someone suggest Air Sal 50mm BBK which he had just gotten in that day . So he sold it to me at his cost and installed and rejetted for free . A year later which another owner it still runs and the owner owner replaced the belt and a bulb .

Air Sal is made in Spain ( correct if mistaken ) as I insisted no China engine parts . The Taiwanese stuff like Hoca or NCY are they way to go unless you can afford the better Italian goodies .

Stock head ? If so get a 50mm or bigger head as the 49cc the compression chamber is small and compression will be high . These are designed to use for light duty and not racing quality . An extra base gasket or shim will help reduce having too much compression that can damage the piston and also give more valve to piston clearance

[stretchedscoot]

i think the problem happened when i first did the 90cc swap.

i was running the stock 49cc carb with a drilled jet but maybe it was to small but i will never know cause it never ran any different even when i went to a 21mm carb.

like i said it ran good and had 130psi compression so i never even looked at it until i was going to do the big bore.

[katastroff]

Nice siamese twin pistons engine

:laugh: