125-200cc Exhaust valve clearance

Hi everyone, I received my cr-w125 from Bills and am in the process of checking it over. (torques/loctite). (Need to narrow handlebars). Considering it was put together more than once, it came through the process better than I thought it would. I was inspecting the 144 cylinder that came with her and when I slide the exhaust valves in(without linkages) and they hit the limit of travel,(I am assuming they are the limits to travel) one side looks to have about .060" clearance to the bore and the other is much closer. Estimating .010-.015" at the bridge. My question is (hey Walt) with the linkage hooked up is there another mechanism limiting the travel or is the end of the machined slot the stop for the valves? I also measured the depth of the slot and one side is machined deeper.The valves are about the same dimensions as expected with mass produced parts, that is minor, the mismatch is from the difference in slot stop machining depth.

Marc,

The power valve throw is limited and determined by the collars with the pin through it and the washers/cups that sit into the machined slots on the cylinder. The bore slots should not be the limiting factor as the valves should never bottom against the end of the machined slots on either side. You have to mount up the valves with the washers, collars, and shaft. Then bolt the washers down and you can now accurately measure the gap from the power valve face to the ring. If either of the collars isn't sitting flush with the washers and the valve is being held up by the bore holes then you need to remove metal where there is contact until you have clearance.

Hi Walt, pardon me for not responding sooner. Thanks to your expertise I am relieved I can work with these parts without much difficulty. Upon further inspection I see that one valve is contacting the bridge support limiting the travel. It is not actually touching what I thought was the stop.The opposite side of the support had some hand grinding performed for clearance. I will match what was done there. I found a workshop manual online and see a spec for the '09 125, page H 25 for .4-.5mm ring to valve clearance. Can you tell me what is the spec for 144? Or where I can get 144 info. Also how does one determine the valves are faired into the exhaust port roof at high RPM? Reference marks after setting it up statically and throttle winging in neutral?

Husky may say the spec is .4 to .5mm but I have yet to find a stock valve that is within 1.0mm and some are as large as 1.5mm. Lots of variables that come into play with cast semi-mass produced parts. You can get a better ring to valve clearance with the stock valves by machining down the retainer collar width. If you go that route you need to be very careful with the collars as they are hard and fairly brittle. You also need to keep them within a couple of thousands of each other and min and max collar width.

Walt, thanks for that info. I know a lot of that came from many hours of study and I appreciate that. I have not been able to make time for investigating the linkage arrangement, and it sort of looks like I need to raise the front of the engine to remove cylinder. Also the valve cover, unless it has very short fasteners.(very close to downtube). I'll take a look at it later, not a big deal.