Will XJ650 Cylinder - Pistons fit an XJ550?

I'm used to XS bikes. Learning fast on XJ's ... and doubtless someone has asked this question before.

Will the Cylinders, Pistons, top end from a '81 XJ650 fit onto a '81 XJ550 engine case? Or is it more useful to do the overbore / oversize piston route?

Anyone who has succeeded in this parts swap / install?

thanx

 

I think (and we have a couple of former club racers with 550 experience, I'm not one) that the hot setup is a top end from an FZR600. Why would you even consider tearing into that low mileage motor? Do what I plan to do: find another motor, "build" it to the teeth and then swap 'em. Actually I was thinking of getting ahold of an FZ600 motor to build.

 

Its more of a "what if I could get some hotter engine bits" question .... future changes and all that.

Need more time actually riding this bike to get an idea of its real world performance.

thanx

 

I have built a FZ 600 motor and put that in the seca 550. They are the same cases, so it will bolt right in. I built the crap outta that thing, putting in a wiesco 652 kit into it along with some porting of the head. It pulled like a freight train and I wound up coming into the pits a couple of times wondering if I had all 6 gears. It was pulling so hard in top gear that I thought I was still in 5th. I need to get that bike street legal just to drag race the turbo with it. Bet the old racebike would win

Just a word of caution, I do not know if the FZR 600 stuff will fit since it was a watercooled engine however the pistons,cylinders, head and will bolt into the 550. It would be easier to get a FJ,FZ or Radian 600 motor.

Sean

 

dino,
What year FZ600 are we talking about?

 

Specifics, man specifics. I had read comments that the Radian mill didn't necessarily fit. If you run certain 550 part numbers, like the clutch basket for instance, thru the Yamaha parts fiche the FJ's it fits go up thru 1985, FZs thru '88. I also ran the front engine mount plates and they match the Radian up thru 1990. But we're just guessing, so please share...

 

Why wouldnt the Radian mill fit? isnt it the same cases from the fj and fz 600 motors? the only xj 600 motor that wont fit is the seca2's from the early 90's. If I am wrong someone please tell me but I was under the impression that all of the fz fj and radian engines were essentially the same minus different ignition and cam timing, maybe different compressions but the basic motor is the same??? I know for a fact that the FZ or FJ engine fits right in. I can take pics let me know.


Sean

 

dinoracer - Can you post some pics? I sure would like to see an FZ600 engine in a xj550 Seca frame.

Right now I'm leaning toward grafting an air-cooled xj650 engine minus the bevel gear (converted to chain drive) into the '81 550 frame since it makes 70 hp in stock form. OK it's a fantasy....

Failing that I'd go for an xj600 air-cooled 10:1 comp head mated to an otherwise stock xj550 Cylinder & case, use pods and a 4-2 exhaust for reliability & economy. What year xj600 big valve head fits the air-cooled xj550 engine?

What the advantages of using Keihin FCR carbs on either engine xj550 or larger? What carb sizes do the pre 82 class racers use?

 

I doubt the xj600 heads will fit. On the seca2's arent the cylinders canted forward, if so then the carbs will be angled so that they lay horizontal. Now when you put that head on the xj 550 you will run into problems. However the FJ and the FZ heads will bolt on. For pics I will have to clear off some crap off of the bike bench and take some pics later today or tomorrow.

Sean

 

I thought the Radian mill would fit too, but someone had posted a while back that it wouldn't. I would think that if the engine mount plates have the same part numbers it would. The main reason for getting away from CV carbs for racing is the tuning difficulty, is it not? I thought building an FZ600 motor with smoothbore slide-valve carbs and pods and a 4-2 exhaust with modern carbon-fiber cans would be neat to drop into my '83 at some point in the future, and save the stock motor.