XL/XR200 cam identification??

[shanefromnz]

Can anyone tell me if there is a way to identify an XL 200 camshaft from an XR200 one?

I currently have an 83 XL200 that I am looking to do the standard XR cam and piston upgrade etc. I have looked in the manual and it gives the cam lobe height for all models other than the XL125 & TL200 as: 31.675-31.875mm (intake) 31.279-31.479 (exhaust). I know for a fact that the XL200 and XR200 do use a different cam so can assume that it is the width and grind that is the difference. Are there any hidden numbers or measurements that identify the difference?

I have a box of bits that includes a cam, I am just unsure if it is off another XL or is the XR cam I am after.

Also, does anyone know if the XL200 would run with an XR200 piston but keeping the same XL cam?? I know the XR has a 10.1 compression with a raised piston. Would running the XL cam hit the valves??

I'm sure someone out there knows these motors back to front.

Thanks

[Chuck.]

The reason for the same values for the cams is the lifts are the same but the valve timing occurs on the sides of the lobes.

Because the XR cam is the most aggressive of the 2 valve cams I think using an XL cam with a XR piston should be OK for valve clearance. The other issue is the high compression XR piston with the mild XL cam will create more compression than a XR combo but these engines were designed for unleaded regular so if you run pump premium you should be OK. I run 11:1 on pump premium but I limit total ignition advance to 29 degrees.

You can check the cam using a dial indicator and a degree wheel, the timing specs are at 0.040" of valve lift.

[shanefromnz]

Hey thanks very much for that. As its an older engine i would worry about pushing the compression past 10.1 so will either just bore it out to 66mm and use an XL piston or find an XR cam and use the XR piston. Thanks again.

[Chuck.]

I think you'll be OK with the higher compression.

As far as ignition timing I bought a used 90 XR200R that ran very good. Original engine but the ignition timing was at 34 degrees, for how long I don't know but it is on the original rings and the compression is still good.

Inlet valve closing is the start of compression and Honda used late closing on the XR cam with a 10:1 CR, other models use earlier inlet closing with 9.2:1 CR. As I mentioned I've been running 10.5:1 with the XR cam for years without issues, and 11:1 with a Powroll Torque cam that has earlier inlet valve closing, both on pump premium but the later with total timing limited to 29 degrees. My XR Owner's Manual say to use unleaded regular 86 (R+M/2) octane fuel (91 Research octane), switching from regular to 91 octane premium gas lets you run about a point higher compression ratio.