how to fit FJ600 top end on XJ550 bottom

First post and it is a complicated one. In the past i raced a XJ550 that o updated with FJ600 front end and wheels, full body work, TZ20 tail and jet kit and 4-1. When i was done racing it i road it around on the street for a while. I eventually tried putting a FZ600 head and carbs on the 550 motor. Worked OK until i dropped a valve and destroyed it. I think the larger valves didnt match the piston cut outs on the smaller 550 pistons. Also i think i had LOW compression from the large 600cc combustion chamber and small 550 piston.

So the other day i was cleaning out the house to move. Came across a bunch of FJ600 motor stuff and a complete XJ550 bottom end (from my blown up motor). So i have a XJ600 top end complete with Arais high compression big bore pistons, head, cams, carbs, jugs and more. I was getting ready to get rid of it when i called my friend to see if he wanted it. He tells me his friend has a clean XJ550 with a bad head and low compression in two cylinders. He made a call and we were told "come and get it" (free). So i am thinking a budget scrambler type bike or a cafe racer using a FZR600 front end/wheel and a matching rear GSXR 17"and Al. FZ600 swing arm i have laying around. I really need to be getting rid of stuff not taking new project on. My wife is going to kill me if i do this.

So i would need to put the FJ600 top end on the 550 bottom end. I know a good bit about these motors but hopefully someone here knows more. My big issue is that the stroke is longer on the 600 motor. I dont have a 550 jugs in my hands yet. But i think they are a few MM shorter than the 600. So if i just bolt the 600 jugs, pistons, head and cams on the pistons on to the 550 bottom end i think the piston tops at TDC will sit too low. One option would be to deck the cylinders to the height of the 550 cylinders. Has anyone done this? Did you cut from the top or bottom? Any idea what your final height was?

This brings questions about rod length and gasket thickness. Are the 600 and 550 base and head gaskets the same thickness? If not it would be another factor to figure. What about rod length? If the 550 had longer rods the the right amount then it could run the same length jugs as the 600. But i dont think that is the case. Are the rods the same part number between the FJ/FZ600 and 550?

Then piston thought. If the wrist pin to piston top is the same on the 550 and 600 then i could just bore the 550 jugs to the bore i need for the Arias pistons. SIMPLE!!! But i dont know if the 550 sleeves are thick enough. What would be the min thickness on the sleeves that would be acceptable? Also I would run 600 base and head gaskets. If they were thinner for some reason then clearance would be tight. lots to consider. Anyone know about sleeve thickness and how much i can bore a 550 jug? pistons are 59.5mm i think.
Third option would be to find a used 600 crank and rods on ebay for CHEAP. Then stick it in my spare 550 bottom end. If it fits then the 600 pistons, jugs, head, cams should all go right on. i think the 550, Radian, FJ600,FZ600 are all the same case. Anyone know if it will all bolt in? I have not done a motorcycle crank before. I figure i would need new main bearings and inspect/plastigauge rod bearings if it comes as a unit?

Simple in concept but the minor concerns are technical. Any help would be great. I have so many projects, 94 CR125, RZ350, RC51 (not project) and my on going FZJ80 Land Cruiser. i need to be down sizing not growing. But if this can be simple maybe i will make something fun and ride it for a while before selling it. Other wise all my parts and his non running bike will eventually just end up in the trash, you know how it goes.

 

It is, I overbored my XJ550 using XJ600 pistons and sitting side by side they were the same, I think from looking at bits from both motors the 600 crank was a longer stroke but it ran shorter rods

550/600 stuff is all basically the same with a few little differences

 

go to
www.yamahapartsnation.com

when you look up the part for the 550 or fj 600 click on the part number and it will tell you what other bikes it is used on
none of the parts cross referance not even the gaskets or valve cover
are you thinking 600 to 650 ?

 

Thanks for the link to parts nation. That will be a a good resource. I do mean the XJ550, Radian, FJ600, FZ600. All those motores are basically the same but with internal differences. This gives some options for swapping them around and making different motor combinations. But since they are different they should have different part numbers on many of the parts. Some times the difference might just be the color.

Kickaha, Thanks for the info about the pistons. If the 550 used longer rods that would be nice. Maybe i can try to measure if i have them side by side.

 

valve cover gasket is the same, My guess would be there are suttle differances between the head gaskets (larger dia pistons) so that part of the gasket would be different as long as the bolt holes line up.


whats wrong with making it a short stroker ?
the Arais high compression pistons may compensate for the differance

 

xj 600
bore and stroke
58.5 x 55.7 mm

xj 550
bore and stroke
57 X 51.8 mm

does this help any?

 

I've got both 550 jugs and 600 spare at home. I thought they were the same height but I'll double check. Also I think
the liners are thicker on teh 550s so as kickaha has done - they can take teh bore-out.

J

 

A100man. if you could check that it would be great. What do you guys think would be min thickness on the sleeves if I bore to fit my pistons?

 

for the fj 600 the max oversized piston is 1.0mm over stock
for the xj 550 it is also 1.0mm o/s

so you could bore out the 550 jug to 58 mm
thats not to say you could not go more but that would be the spec

 

I think I was told 60mm was the max I coulds safely take the 550 out to before the liner got to thin but I dont remember what thickness that left it, mine was at 58.5 for stock 600 pistons but I have a set of new 1mm o/s 600 pistons for the next one

 

my guess would be it all depends on the machine shop and their willingness to go past what ever the max spec would be.

 

Ok placed them side by side and took some pics that I will try and upload. height is spot on the same. Viewed from top the liners look thicker on the 550 and a rough measurement confirms this (550 approx 8mm, 600 approx 7.3 mm), but they are stepped so at teh bottom the protruding liner looks to be 3mm on the 550 and 2.7mm on the 600. Even so going from 57 - 58.5 doesn't seem to be much of a problem as the liner at the bottom will still be 2.25mm..

Cheers

James

 

I know them so they will do it to whatever I tell them, my problem if it doesn't work

 

So i just cleaned up my 600 jugs and looked at the cylinders. This is the cylinders that match my 618cc Arias pistons. Cylinder one has a good groove in it from a wrist pin walking out. I found the piston and the wrist pin slides out over the circlip. Either the clip is bad or it sits too deeply in the groove to effectively retain the wrist pin. I will have to see if it is a piston defect. But at this point i wont be using the 600 cylinders. So that has me looking back at taking the 550 cylinders off of the bad motor and boring them to fit my Arais pistons. I like this idea for a few reasons but i need to get a accurate measurement of the 550 sleeves. If anyone has 55o cylinders around and a good micrometer could the measure to OD of the sleeves for me? From there i can measure my pistons and bad FJ600 cylinders and figure how thick the sleeve would be after boring.

 

Chacal sells the 550 sleeves. Start a conversation and ask him for the wall thickness. Xj550 says max os for 550 pistons is 58. Kickaha says he had them bored to 58.5 for stock 600 pistons.

Gary H.

 

Thanks. I will look into that. I think my pistons are 59.5 or 60mm.

 

Hey kid, what kind of cams do you have and are they for sale?