XR200 / XR200R Camshaft

[Weldangrind]

Since the question has come up a couple of times, I thought I'd share the cam specs I found today. My son and I were tearing down another donor engine for his '83 XR200R that's under construction, so we took some measurements.

We measured a 1980 XR200 and a 1983 XR200R cam, and found that they were within 0.001" of each other. The cams measure 0.0270" intake and 0.0255 exhaust at max lift (I don't have a degree wheel for duration measurements).

It seems that the only difference between the two engines is the high compression piston in the XR200R. Guess which piston we'll be using? :wink:

Maybe this info will benefit a Lifan China Rider.

[katoranger]

Maybe I should take the lifan engine apart and measure its cam.

Allen

[2LZ]

Originally Posted by katoranger

Maybe I should take the lifan engine apart and measure its cam.

Allen

That's a marvelous idea! I think I may know where I can get my hands on one if it fits!...and is a better cam timing arrangement!

[Weldangrind]

I should add that I'm not certain if the cam in the '83 XR200R is correct for that year; it had a plain XR200 head on an otherwise XR200R engine. All I know is that one of the cams I measured is from a plain XR200, and the two cams are virtually identical.

[Weldangrind]

Kato asked about the measuring process in another thread, so here's how I did it. I used a dial indicator and magnetic base, and I set the zeroed dial indicator tip as close to the centerline of the cam base circle as I could. I cycled the cam in both directions to ensure consistency, and I didn't disturb the adjustments when I swapped in another cam for comparison.

Dial indicator:



Magnetic base (I had a hard time getting the magnet to stick to the aluminum, hence the clamp ):

[katoranger]

So I will need to pull the valve cover off this engine and get some details.

Allen



I can do that. FIY, I found an 86 xr200 needing an engine. :wink:

[TheRealWorld]

That is some remarkable work! And very interesting. How can a different piston change the compression?

[TurboT]

Originally Posted by TheRealWorld

That is some remarkable work! And very interesting. How can a different piston change the compression?

It is the shape of the top or dome that squishes more air and fuel creating more compression. They are usually a different metal material to be able to handle the heat without melting as well.

[TheRealWorld]

OK, sure is interesting!

[Weldangrind]

Originally Posted by TurboT

It is the shape of the top or dome that squishes more air and fuel creating more compression. They are usually a different metal material to be able to handle the heat without melting as well.

To expand on TurboT's comment, the dome shape of the piston top squishes the same amount of air / fuel into a smaller space (vs. a flat top piston). The more the mixture is compressed, the more energy is released when it's ignited.

[TurboT]

Originally Posted by Weldangrind

It seems that the only difference between the two engines is the high compression piston in the XR200R. Guess which piston we'll be using? :wink:

Hey D,

I seem to remember a burnt valve from one of those motors? Was the burnt valve from the HC piston motor?

I'm not sure, but if you went with the HC piston you may want to ensure the valves were the same and not a different material or design. (More heat)

[Weldangrind]

Nope, no burned valves in these motors, in fact the valves on this latest motor look really good. Since it was a matched set, I'm gonna run the new head, cylinder, piston and valves.

You might be thinking of an old Toyota I had.

[TurboT]

Originally Posted by Weldangrind

Nope, no burned valves in these motors, in fact the valves on this latest motor look really good. Since it was a matched set, I'm gonna run the new head, cylinder, piston and valves.

You might be thinking of an old Toyota I had.

Hmmmmm..... I could've swore I saw a bad valve in a Honda head over in your shop. Perhaps I've just been sniffing too much glue of late. :P

No matter, I'm sure you have your engine rebuild well under control, I can't wait to race Sam on the newly built W&G + Son Honda. Yamaha will prevail. Go Team Blue! 8)

[suprf1y]

Originally Posted by Weldangrind

We measured a 1980 XR200 and a 1983 XR200R cam, and found that they were within 0.001" of each other. The cams measure 0.0270" intake and 0.0255 exhaust at max lift (I don't have a degree wheel for duration measurements).

The duration of the XR200 cams should be 220 at .050" lift.

[Weldangrind]

I was waiting for your input, suprf1y. I don't think that we have any other cam grinders on here.

Have you ever played with the mechanical advance mechanism on an old XR200R? I figure that I should be able to connect my timing light and check the dynamic behaviour.