Quick question, will a 1980ish 450 engine bolt right into an early 425 frame....

[tkent02]

Or would there be fitment issues?

Pondering my next project.....

[JRHemmen]

This thread might prove to be helpful. It looks like they were discussing a 425 engine in a 450 frame, but they mention compatible parts.

http://www.thegsresources.com/_forum/showthread.php?102495-GS450-(81-)-vs-GS425-engine-differences

Also, here's a chart of general comparisons between the different engines from the 250 to the 500.

http://www.eurospares.com/gsfaq.htm

[pete]

As far as I know it's a yes Tom, the 400/425/450/500 bottom ends are all interchangeable mount wise as far as I'm aware.

[John Park]

I haven't done it, but I remember someone saying you need to use the appropriate front brackets.

The carb spacing is a little different [narrower?] so the fit to the air box could be off.

The 425 frame is different around the coils and is not braced like the later frames. Not hard to put a gusset at the base of the top tube.

I have fond memories of many hours spent with my face in the instruments of my 425, howling through the Mexican night.