Will a 1979 Honda XR185 Piston work with my 1983 ATC 185s?

[Bernard3rd]

Hello All,

I have recently purchased a 1983 ATC 185 s which is very clean and in overall really nice shape. I want to do some mild mods, and have found a Vintage Supertrapp exhaust and have a K&N air filter. It is still possible to get a +1mm 1979 Honda XR185 piston and rings which wold bump the displacement to an actual 185cc's (185.94 to be exact) and would bump the compression up a bit from 8.0 to 9.2 to 1.

Are the Heads of the 1979 XR 185 and the ATC 185s interchangable or the same except for the compression release? If so, it would seem that the XR piston should work with the ATC heads Would there be possible clearance problems?

Thanks so much for any and all pertinent comments/information.

Bernard

[YTZ drew]

Yes, the heads are the same, and yes, the piston will work. I have a complete 79 XR185 top end on my 200X, except for the cam. I'm using an XL185 cam.

[Bernard3rd]

Thanks so much YTZ drew - I really appreciate your input. Why did you go with the XL Cam rather than an XR? If I understand correctly, the XL is better for low to midrange, and the XR is better for mid to top end?

[YTZ drew]

Your understanding is correct! The XL cam has a tiny bit more duration than the 200x cam, and the XR is greater still. I saved the XR cam for another engine I will eventually build. I love the combination of the XR piston (10:1 comp) and XL cam, very snappy response and lots of torque. Roll on wheelies are a piece of cake, and it's great in the tight woods.