Can anyone please explain the differences between these two engines?
Is everything the same except for the tuning (carbs, cams, etc...)??

Also, will a XL600 ('85 or '87) fit into an '84 XR350  frame?

My XR350 engine is in need of a "freshening" and I have an opportunity of purchasing either an '85 and/or an '87 XL600 engine which also needs rebuild.
I was thinking that if the large bore engine will fit into my frame then I may as well add some CC's to my ride.

Your thoughts.......???

I had an XR600R 84', 89', 94', XR600L 86' and a XR500 84 and a XR350 I think it was an 83?  If I remember right the difference between the XR600 and XL600 was the cam, piston carburation, swingarm and a few other small things. I had the XR600R cam and piston, carburation put into the "L" when I rebiult the "R". I know that the XR500 engine fit's into the XR350 but, Maybe the XR600 also. I never tried that, they all looked the same. That was a long time ago! I was real fast back then and in a few more years I will be even faster back then! If I get old enough I will be the fastest that ever lived! Man the stories will be great when I get into the old folks home!

This is purely rational speculation.....

My dad has an '84 XL600 and except for the head and induction, it is the same as my '95 XR600. He just rebuilt it and the gasket set that he got was for an XR500 or 600 and the only difference was a handful of washers and a head gasket, so that that would lead me to believe that the XR500 and XR600 cases are the same and if a 500 will fit in a 350 frame, then a 600 will too. It makes sense but I make no guarantees.

Thanks for the responses guys!
My '84 XR350R is a wet sump model.
Would you happen to remember whether the XL600's of those years were wet or dry?

By the way BWB63, I didn't think you were fast at all, all those years ago. I seem to remember that I was much quicker....although it just might be one of those delusional things happening since I've been on those Alzheimer drugs. I think.

hilift said:

My 83 XR350 was a wet sump.  My 86 XL600R is a dry sump.

The old 350 was a very well balanced machine.  I wouldn't change it.

IMO I would stay with the XR350.  I had one that I put a big bore kit from XR's only in it and it ran great.  The  oiling system hookup for the XL600's would be a pain because the frame has no provision to hold oil.  Also depending on where you ride the extra weigh would not be good either.  I have a XL600R that is great but it is heavy in the woods.  By the way the XL is forsale.

Well, I've decided to stay with the 350 as it'll be more work that it's worth.
I had already picked up a first over Wiseco piston in 10:1 and a woods grind Mugen camshaft for it anyways so that made the decision that much easier.
Too bad I couldn't bore 'er to 500 or better tho!!! LOL!
Thanks for all the advise and tech info guys!

hilift said:

Where'd you get that? Mugen is a big tuner out of Japan for Honda cars, but I rarely hear about them doing anything for the bikes....and one that old to boot. Most of their stuff costs a heap too.

I picked up the cam from an English contact who used to race the XR350's in European ISDE.
Yup, cost a heap too!

You've made the right decision. In my opinion, the XR350 was the better all round bike than the rest of the XR range in that era as it avoided the starting/engine problem hassles of the XR250 and was much lighter and better balanced than the 500. Something I found thats amazing too is that it is frighteningly close to a stock XR400 in power so you wouldn't say that it's a slug either! Rebuild the "donk" and enjoy!

headtrauma, Mugen which means unlimited in japanese is owned by the son of Honda and made all the trick works bike parts in the late '70's early '80's. Do an internet search on Johnny O'mara he was mugen's best rider.