Fj1100 installing 1250 big bore.

[rexsk8er]

So, i bought a fresh 85 fj1100. The bikes came with a new paint job, and a blown motor. Dont ask. Anyway the bike came with a 1250 big bore kit. I actually work at a motorcycle shop, and the boss is who sold me the bike. So, I finally got some time to get this thing put together. I got the pistons on and slid the block down on the pistons, but once i got to slide the sleeves into the block it became quite apparent that the new sleeves in the block were to big for the cases.

So getting to the point, obviously the cases need to be modded, can this be done in the frame by removing the head studs and pistons, covering up the crank with rags and tape, and just use a dremel tool to take a few mm off the cases. Does the engine have to be completely dis-assembled? I have no qualms about doing that, but I'd rather save time and just do it by hand if possible, if its only a small amount needed to be removed. I hear that you should under-cut second and do some clutch work. But, the only mod done to this bike will be the big bore so I figure it may be ok to keep the bottom end stock.

[andyb]

You'll very probably break second gear if it isn't already rounded off.  To do it right would be to send the trans out and get it undercut (do first while you're in there if you have any intention of launching the bike hard, also) and replace the shift forks with the later forks (which are stronger and prevent the issue).

If you decide to clearance the upper crankcase by hand, go ahead.  Remember that even the tiniest bit of grain is undoubtedly going to end up in the oiling system, though.  If nothing else, pull the oil pan off and wash things downwards with oil once you've got it to dry fit successfully.  It's not doing it properly, but you know that.  Probably it'd be a good idea to clean the oil pickup anyhow, and probably again at the first oil change once it's running.

You know the rules, either pay now or pay later, y`know?  If you're desperate to get it finished now, go for it.  If you want things really done well and utterly trustworthy, you'll want to strip everything apart.  Odds are a camchain, starter chain, starter chain guide, and a whole mess of gaskets will be important as well.  If nothing else, call Randy up and get some good advise on the build while it's apart.

How'd the motor let go?  Are you dead certain that the bottom end is in decent shape?  What's the head like?  You're really only limited by your timeframe and budget, but it's a shame not to do a valvejob, better valvesprings, set the quench precisely, new bearings, bulletproof the trans, etc.  If you're okay with tearing it down at a later date with possible damage from something you missed, go for the cheap and dirty to get it running sooner.

[rexsk8er]

Ok, so it is do-able.

I guess I didn't explain totally. The situation is, I have a shop with 3 FJ1100s, 4 motors and about 5 heads. I have plenty of parts, Cases heads ect. In fact the 1250 had a ported head. The one that blew was one that was in the frame, they swapped in another complete bottom end. So thats how my boss got the bike. He also had the 1250 block and head pistons and rings, that was a throw away from some legend racers that wanted bottom end parts. So when I started working there I had cash, wanted the bike but couldn't settle for a price until he threw in the stuff for the 1250 kit. He also said I had pick of any of the parts he had, as long as he has enough to build his bike. So theres enough to build a whole motor, after I have this bike on the road.

About 2 years ago I put a turbo on my honda civic. I actually got it used on trade (helped my neighbor swap a rb20det into a 240 for it) fabbed up the manifold and pipes and got my tune right, and as you said you either pay now or pay later. Sure enough the turbo started smoking.  I was planning on a new turbo when i first built it, but ended up getting laid off at work. So I had to move and what not and that all went on hold, the car sat while I skateboarded everywhere until I had a job to afford insurance and what not.

SOOO since my car needs to be torn down I'd like to get the bike running, and as I've done alot of shade tree wrenching I know how easy it is to destroy a motor with one bad measurement or tiny peice of scrap. Not that I like to cut corners but in a pinch I've even gone so far as to straighten up bent valves on a drill press.


I tend to ramble a little but the point is I'll be doing a full build once I have my car fixed. I just need my FJ running for the next few months so I can put back and forth to work and the skatepark and around town.

Future plans!
Fzr1000 Forks and maybe swingarm. Still doin research. Maybe even built bottom end and power adders. I've been known to fab up a sick turbocharger system.

Thanks for the help, this is quite a good site!!!