I just started tearing down my brother's 1985 YFM200 to replace the head gasket. Everything is going well but I'm not sure what to do about unhooking the timing chain. I assume I am supposed to remove the timing tensioner on the back of the head first but want to be sure. The last thing I want is to do is have anything drop into the bottom end of the motor. I may have to put things on hold until I find a manual for it but I'd really like to get it apart today because it will take me a week to get parts if I need any.

 

Yeah if you unhook the timing chain tensioner 1st that will give you some slack in the chain to allow you to pull the timing gear off. You do have to be careful not to drop the chain down in the engine. I usually strap it up with some type of hanger or wire tie until I'm ready to put it back together. Stuffing a clean rag down in the hole will help, too.

 

Thanks. I have everything unhooked but don't have enough room to get the head off without pulling the motor. I'm trying to figure out where to separate the motor and crankshaft cover now. There are 2 places where it can come apart and I'm not sure which spot is right.

 

Well, I got it apart. I had to unbolt the rear differential and pull it back a few inches to get the motor out.

 

I meant driveshaft cover.

 

Wow I'm surprised you had to pull the entire motor. Usually you can take the head off, then the cylinder. The head has to be unbolted then lifted off the dowels, so usually you only have to raise the head up about 1" to get it off the cylinder. Then you can turn the engine so the piston is at the bottom of the cylinder and slide the cylinder off the piston. This can usually all be done with the bottom end of the engine in the frame.

 

The problem was getting the head up past the timing chain guides. At least with it all torn apart it'll give me a change to clean and paint the frame. I'm still looking for a manual for it. Does anyone know what the head and cam bolts are supposed to be torqued to?

 

You can buy this manual online. Some people don't like Clymer manuals but it's better than nothing: Clymer Yamaha YTM/YFM200 and YTM225 1983-1986

I actually still have a manual here from when I had a YFM200 23 years ago. The head bolts are as follows:
M6 bolt - 5.1 ft.-lb.
M8 flange bolt - 16 ft.-lb.
M8 bolt - 14 ft.-lb.

Sprocket cam bolt - 43 ft.-lb.

Cylinder bolts - 7.2 ft.-lb.

These numbers sound low, makes me wonder if the factory goes by these specs? You ever torn apart a machine that has never been wrenched on? It's like herculees put it together. Anyway, I hope this helps.

 

Thanks.
7.2 ft-lbs for the cylinder head bolts does seem low since the head bolts on my old snowmobiles is 16 ft-lbs and they certainly seemed to be a lot tighter than that when I took it apart.

 

No the head bolts are the M8 flange bolt - 16 ft.-lb.

There are 2 other sizes that hold the actual head on and all have different torque ratings depending on their size and type. The 7.2 ft.-lb. is for the cylinder bolts that hold the cylinder to the crankcases.

The head is only the very top piece that houses the valves and the cam. The cylinder is the piece that the piston slides in and out of. The cylinder (or some people call it a jug) is not considered the head.