Hi all,
I took a punt on a used 110cc atv (Model number is YB110 and the plate says made by Zhejiang Yongkang Easy Vehicle co), which became difficult to start then gave up completely. Cleaned carburettor out, then did a compression test which was low (around 50psi), and with the head removed, the valves looked coked / not seating. I picked up a new head unit rather than strip it, and have fitted it (can't seem to find a manual yet so good old you tube warrior research). The motor turns very freely on a ratchet on the crank shaft.
Anyone able to offer advice on whether compression should be seen when turning it by hand like this? It's now only around 25psi (by hand, with no oil yet added to the cylinder) but I'm not sure if that would be expected? Don't want to rebuild much further if I've got something wrong which needs sorted out. Looking at the moment for leads to wire the battery straight to the starter to test again.
Much obliged,
Ally

 

Did you take the cylinder off when you had the head off? If you didn't you were wasting your time and money. You do not fit a new head if it is coked, you de-coke it. You also check if the valves are seating properly and grind them in. Once the cylinder is off you take the top ring from the piston and put it in the cylinder, measure the ring gap Honda 90 is 0.012" maximum. My guess is you will be way over that. If you can, measure bore dia, if you have not got anything to do that, and it shows some wear, either get a cylinder kit or take the bore to a machine shop for checking. If the bore isn't worn or scored, but rings are worn, just fit new rings.

 

Cheers.
I did have the cylinder off. The walls looked ok, and I don’t have a little drill hone. I cleaned up the piston to remove the carbon but what I didn’t do was remove the rings and size them in the bore, I also had thought the valves in the new head may have been done already and that the unit would have been plug and play. Perhaps not as you say.
Bit more tinkering to do it seems. Thank you for the reply.
Al

 

Did you make sure valve clearances are correct? If you do take it off, ensure you know which way up that top ring is, so if it is OK you can put it back the right way up.

 

Thank you for replying. I did gap the valves, however if the valves are not lapped I suppose it wouldn’t matter. I’m just going to order a hone, new ring set and strip it to double check valve seats. I’ll be careful of removal and orientation of not only rings but valve springs and stem seals.

much obliged
Ally

 

Separately, would anyone say reinstalling this is ok since the scores are below the rings? I’m minded just to change it.