wiley0717

I had to make a repair to my crankcase and tore the engine down completely for inspection while I was at it. Now reassembling, the cam has a dot on it, could someone tell me the orientation of this dot, up seems to be tdc on compression stroke. I cannot find any info on the web.

Thanks
William

Troy Newman

Its in these forums from past posts....


But the the timing is set this way.

The rear of the crank as a dot on it....This dot goes down at 6 o'clock....this is as the piston reaches TDC....its just a little bit before...like 11:45 if you wanted to be critical....

But the crank dot goes down.

Then the cam dot goes up at 12 oclock...actually by the time it twists into the spiral gear it ends up being just a hair past 12 oclcock like 12:30.....

The sprial gear is course enough that if you are toth ahead or a tooth behind you will not even be cloase to the 12 oclock position..


So go over it again in summary the crank dot down, and the cam dot up.

Before you button the enigne completely up[ re-check the tappet valve clearances.

Troy Newman
Team YS

wiley0717

Ok, go reassembled, now......low compression! valves are not stuck so I am guessing ring. Can i just replace the ring or do i have to replace the cyl as well?

Troy Newman

The top of the piston has some little notches in it. These are gas porting slots in the piston. You need to make sure the piston ring is not aligned in the middle of one of these slots.

Also of note. When the engine is dry and not heated up it will sometimes not show much compression this is normal.

But if the piston ring is properly aligned to not have the ring gap on one of those gas port slots then you need to run the engine and get it "wet and lubricated. Then the compression will come back when flipping by hand.


Troy Newman
Team YS

wiley0717

willl fire it up and try it tomorrow see if it improves. If not, can I just replace the ring or do i have to replace the entire head (does the liner come out? possibly)

Troy Newman

Liner is not something you can replace. but the ring is an easy fix.

YS parts and Service I believe has a tool that can remove the liner. However this is not something that you and I can do easily. Also they don't sell just the liner.


I would make sure the ring gap is not directly over one of those gas porting holes.....If its not then put it togteher and run it. Compression on the ringed 4 strokes is not always a sign of a healthy engine. Often times compression will seem very very low while the engine is cold. When it heats up it will come back work fine.

This is common with all glow 4 stroke engines. If they get a little dry the compression will feel very soft yet when they get wet and the heat starts to expand the parts the compression comes back.

Troy Newman
Team YS