1000 questions (ytm200k)

[jagerlager]

Hello all!

*I pulled the motor from my ytm 200k before I did a compression check... is it accurate to test compression with motor disconected from muffler pipe and carb?


*Tonight was my first time setting valves and It was interesting to find top dead center. There are three marks on the flywheel if I am correct, the "f" timing mark, the "T" line for tdc, and a line before those two in rotation. pretty much ... the valves had play simultaniously anywhere within these marks ... the valves themselves "play" seemed to tell me tdc at different points on the flywheel... randomely any one of those marks. is this normal? the flywheel and timing chain sprocket are aligned at tdc.

*typically one would adjust the valves when the space has become too large, correct?

*I have been mulling over whether to pull the head and inspect the cylinder... tonight I inspected somewhat through the spark plug threads with a flashlight. It all looks relatively good, some carbon on the piston.. the cylinder wall on the side I could see looked clean and smooth. I did see , however, a hole in the top of the piston. a small hole maybe 3/32 wide and deep. looks pretty symetrical...almost punched or machined, couldnt tell if all the way through perhaps 3/32 deep. Is there a machined dimple in these pistons from the factory???

*the valve stems and flats look pretty badly carboned, is this normal ? will it burn off or correct itself with normal operation? Or does it need to be taken apart and cleaned?

Thank you for your advice!!!!

[jagerlager]

long winded eh?

[thefox]

OK, let me take a stab at some of these questions.

1. I don't know, personally I would say it is ok but I am not sure on this.

2. Remember that the arms are only tight when the valve is being opened, with that said they should be loose most of the time. Do you have a book? It takes 2 turns of the crank to spin the cam 1 time. With the T mark lined up feel both rockers, now turn the crank once so the T is lined back up, now one of the rockers should be loose but the other one is tight. Set the valve spec when both rockers are loose.

3. Yes if the rocker gap is not in the specified range then adjust them so they are.

4. The pistons come with an indent for the intake valve, I don't remember if there is an indent for the exhaust valve or not on the stock piston. I will attach a picture of an aftermarket 200 piston, your indents are a lot smaller but it gives you an idea of what is in there.

5. The whole valve area will get carbon buildup on it, it is normal. It is a good idea to clean as much off as you can. I don't take an engine apart just to clean the ports (4 strokes anyways) but I do scrape off what I can if the engine is out of the frame already.

[jagerlager]

Thank you!
that was a big help, cleared some of the gray area.

One of my concerns is having any carbon I clean from the valve areas fall into the cylinder head.

I am pretty sure now that the hole is supposed to be there, Its in the center of the piston, just like the pictures in the manual.

As far as valve clearance.... I was wondering if they are ever too tight ... or if they always wear to a bigger gap and this is why one would need to adjust.

thanks again!