HT Piston Problem

[Irish John]

I have a 70cc HT about 5 weeks old which has only done about 800 kms including the 500 kms running in. I notice when I wheel the bike backwards with the clutch in there is a grating noise like a piston ring scratching on the cylinder and there is resistance in the cylinder. It's barely noticeable when I wheel the bike forward but I'm sure it's a piston ring. Same thing happened my last engine after 1300 kms. Has anyone got any idea what this might be? The last engine was repaired with new rings and the cylinder was honed where it was scratched by a misfitting ring - I got the rebuilt motor back today but the cylinder has been put on backwards so it will have to be taken apart again.
I am heartily sick of getting these problems with nearly new motors. I only have one bike working now and that's a week old and has only done 180 kms. It feels like it's a better motor but I'll be taking the motor out this week end to put in the 50cc 4-stroke. The kit came from Bicycle Engines. com and the bolts and studs all have to be replaced with proper steel ones before I can start assembling it. I'm surprised they bother to sell these kits with chinese bolts in them it's such a drag replacing them all but not to would be downright dangerous. Anyway I need help to diagnose this grating sound in the HT.

MBC EDIT: THIS THREAD HAS NOW BEEN MOVED TO FRAME MOUNT SECTION

 

[Large Filipino]

Try squirting 2 stroke oil thru the spark plug hole then see if it still does it. Maybe with time it would wear so that it won't do that again.
Take this advise with a grain of salt. This is just off my head.

 

[BSA]

What oil ratio are you running it on?

BSA

 

[Irish John]

Oil ratio

I ran 16:1 for first 500kms and 20:1 for last 400kms. I use fully synthetic oil although I read here that ordinary oil is better when running in. Not sure about that.

 

[BSA]

Well it hasn't partly siezed due to lack of oil then. By the way, 16-1 oil ratio is very good. A lot of people will say that you only need 20-1, I say the more oil the better, so long as your willing to clean out the engine every 500 miles or so. Use standard oil for the rest of break in, and then change to synthetic.

 

[Irish John]

I used to run my 55cc HT on 30:1 and sometimes 35:1 and it went longer before seizing than any other HT i've had. It also ran smoother but I run 20:1 after break in now. I think the important part is the fully synthetic oil more than the ratio. This is just my feeling which is not necessarily right. I don't really like to use non synthetic during break-in as suggested by people on MBc. When you've had as many HT motors as I've had you occasionally get a good one that is noticeably SO MUCH better. You can tell from its first start up. I wonder what day of the week the good ones get made and what time of the shift on that day does the quality improve?