XJ/FJ/FZ/YX 600

Are these all basically the same motor? ( I dont care about the rest of the bike)

 

Yes, no, sorta? Pretty much, yes. Things kept changing especially into the nineties and they started changing the angles on things, like the cylinders to the block.

A couple of them are pretty much the same as the 550; a couple of the others LOOK like it but like I said, angles changed. I think there is some additional interchangeability between things like heads but I don't know for sure. I didn't dig too deeply, I was exploring drop-in upgrades for a 550 Seca. I can't tell you which was which, sorry.

 

Exactly what I am doing

I know the original XJ600 stuff is direct bolt on, even the engine mounts are the same but we didn't really get the FJ/FZ?YZ over here but I see a bit of stuff on ebay

I have just bought XJ600 pistons, stock are 58.5mm so 1.5mm over a XJ550 which will take it from the stock 528cc to 557cc, what I want is a set of 1mm oversize XJ600 pistons which at 59.5 will make it 576cc and can be bored with the stock 550 liner

If I could find some 60mm or 60.5mm pistons would be even better as I could make it 596cc as we have a 600cc limit

Supposedly the 600 has bigger valves and more lift and duration on the cam which is also what I want for my next motor

 

I saw a beautiful FJ on Kijiji here a while ago, if I had the cash in hand,.........

 

I have an XJ600, which was marketed as an Fj in the US. The XJ is rated at 72 bhp.The FZ was a more sporting bike, with liquid cooling and 90bhp!

I think my engine is very close to that of an XJ550, although it does not have YICS. Reading the forum, things like the regulator and CDI look identical.

 

The early FZ600 (1986) is listed as aircooled

Apart from bore x stroke the engines are basically the same

I have seen later 600cc engines with what looks like the casting for the YICS on the barrels and heads but it hasn't been machined

 

So I found myself a FZ600 (2HW) motor, a quick measure shows the intakes ports are 2mm bigger than the 550, now I just need to strip the head off to measure valves and cams

One thing I did find out though was that even though the FZ600 was more of a sports bike than the XJ/FJ600 it had smaller carbs 30mm compared to 32mm (both of which are bigger than the 28mm on the 550) supposedly this was because of the available space in the frame for the airbox

 

http://www.xjbikes.com/Forums/viewtopic ... crank.html

Hey Kickaha,
check out "worldsfastestxj" 25 posts. Wont take you long.

Knife edge your crank, advance your timing, polish and shot peen your rods, raise compression, 3 angle valve job, adjust cam timing for high RPM running, jet a little rich, and cross your fingers !!

 

Yeah I've seen that but for roadracing my requirements will be somewhat different, it's not all about peak HP it more about useable HP, but I will be doing some of that.

I am restricted to 600cc if I want to stay in Post Classic junior though

As far as timing goes I will be fitting a programmable ignition

 

Just stripped the cams out of the FZ600 motor I have bought and compared them to the XJ

Measuring from base circle to cam nose
XJ550 exhaust 35.08mm
XL550 Inlet 35.55

FZ600 exhaust 35.78
FZ600 Inlet 36.26

so it looks like .7mm more lift, but I will get them into a cam shop and get them measured properly as that way I can check the duration as well

Valve sizes

XJ550 exhaust 26mm
XJ550 inlet 30mm

FZ600 exhaust 27mm
FZ600 inlet 31mm

exhaust and inlet ports on the 600 head are about 2mm bigger as well

Now I need a XJ600 head to compare as they ran 2mm bigger carbs than the FZ600 so it would be interesting to compare them as well