Suggestions for rebuilding an XJ700 block

I'm posting to tap the knowledge base here. I'm pretty much a noob at modifying bikes, but I have hotrodded some auto engines, and I've been wrenching on my own rides for 30+ years.

I've got a bone stock 1985 XJ700N as my current ride, but I also have a 1986 XJ700N parts bike that's complete except for carbs, exhaust, tank, gauges, seat, and a few odds & ends. My skills as a DIY fabricator have improved to the point where I'd like to build a vintage look cafe bike out of the parts bike and sell the stock ride.

The parts motor has low compression on the number 1 cyl., and I don't have a set of carbs for it anyway, so I was considering boring it out to 750cc (or possibly more - I'm open to suggestions) and mating it to some 750cc carbs.

So, is it feasible to bore out a 700cc to 750cc, and if so, what do I need to do? Should I change the stroke while I'm at it? Any recommendations for pistons? And what carbs should I look for to mate up to my new motor? I don't intend to race the new build, but I wouldn't hate a quicker bike than my stock ride.

 

i'm not possitive,...but i think i read on the site somewhere that the only
diff in the 700n and 750 is the stroke, but i'm not sure.
but bore away if thats easier/cheaper then a used set of heads/arms.

 

Welcome Jfenn !!

http://www.xjbikes.com/Forums/viewtopic ... tml#184747

Read thru this thread, and follow the link for more info about your motor.

Making a "cafe" from an '86 poses the problem that the overall lines of the bike are more "cruiser" than an earlier XJ. The forks look too long also.

 

Thank you for the reply.

You are quite correct about the fork length and the lines of the frame not being conducive to a cafe build. I've been pondering that for awhile. I have a solution in mind for the forks, but the frame will require a lot of hacking. I'll consider some earlier frames before I start.

 

If my refference material is correct, the bore and stroke on the XJ700N should be as follows. (bore 65.0, stroke 52.4). That being the case, boring would make very little difference.
With those spec, bored out .60 would only bring it to 708.4cc.

To increase the stroke, I believe you would need to change the crank to one from a 750 (or aftermarket), as the deciding factor for stroke is going to be BDC to TDC of the crank journal, not the rod length.

Using the above numbers, if it was stroked to match the 750 (Stroke 56.4), and bored .60 over, then you would have a 762cc

If I remember my engines, putting a slightly longer con rod would only increase compression, and maybe take out a valve