Hey guys new to the forum. I just picked up a older Yamoto Im trying to get running. In the second pic there is a ??gearbox?? on the rear axle with a dipstick, does anybody know what this gearbox is and what type of oil doe it require. TIA!

 

Looks like a copy of a Yamaha 80/90, I suppose the clue is in the name. I would go for SAE 80/90 gear oil. Smell the stuff on the dipstick, if it has that gear oil smell, it will be gear oil. Officially that is a bevel drive gearbox, most people refer to it as the "diff" (though it isn't really).

 

Ok got that taken care of now to get it to start. New Carb I have fuel,spark. I adjusted valve and used starter fluid and still no go. The timing Chain cam it correct and in time. I'm starting to think the rings are shot. I can hold my finger over the plug hole and hold all the pressure in. I am trying to locate a compression gauge but I don't think it has very much. I want to just rebuild the top end but can not figure out what kit/part to buy. Anybody have any luck rebuilding one of these?

 

First be very sure you adjusted the valves correctly 0-003" clearance at TDC on the compression stroke. The engine again looks like a copy of the 80cc/90cc Yamaha. If it is down on compression, it will need new rings, or may need a rebore and oversize piston, but you won't know until you get the top end apart. Get a manual for the Yamaha if you can, as it will have size limits and torque values in it. Though I think Yamahas always used 50cc, 80cc or 90cc versions of that engine on ATVs, so finding gaskets, rings and pistons may prove difficult.

 

Thanks! I was looking at rebuild kits online and the motor almost identically matches kits for the early Honda's Is it possible the motor is a Honda Clone?

https://www.ebay.com/itm/Cylinder-He....c100005.m1851

 

Yes, could well be a Honda clone, they are much more commonly copied by Chinese makers, not entirely sure Yamaha didn't do a bit of copying themselves when they changed from two stokes to four on small engines, but on close examination, Yamaha used two exposed small bolts to hold the cam sprocket cover on, yours seems to have the through bolt, like Hondas. However, no point buying a full kit if all you need is a head gasket and rings, take the cylinder off and check what you need.

 

So I got a compression tester and it has 45 PSi in the cylinder. I'm pretty sure that is low for these engines. Could that cause the engine not to start given it has spark and fuel?

 

Yes, 45psi is useless, take the cylinder off, check for scoring and a wear ridge, more than about 003" and you need either a new cylinder kit or a rebore and oversize piston.

 

Ok got a piston and ring kit, changed them out and it started right up and running great! Thanks for the help!!