Which engines are chain drive and fit the xj550

I am going to buy an engine and just want to know which chain drive engines are a direct bolt on for the xj550 maxim frame.
My bike still has a decent motor with around 15 or 16k so I am not looking to swap yet. And the size isn't as important as the deal I can get so want to have a broader range of choices than just looking for a 550 engine. All I care about is if it is chain drive and will fit the mounts on the 550 maxim frame. I want to try an engine rebuild and don't want to do it to my perfectly good motor (which I hope to be putting to good use in a few days).
I want one that is chain drive and fits my bike, though, so that if I do a successful restoration on the engine I can use it in my bike. But it won't matter if I trash it. Anyway...

 

if you just want to practice a resto then maybe get a beater off craigslist for a couple hundred bucks and "go through the motions" to get some experience? unless you are looking for something to eventually wind up in your bike then i don't know.

 

I believe the xj600 engine will fit directly as it is based on the 550. The model was called an FJ 600 in the US. The only catch might be the fact that they use an electronic tacho and I am not sure which type the 550 used.

 

I do believe the 550's all had a mechanical tachometer

 

Fact: The Radian used the 550 Maxim frame. That will widen your scope a bit...

 

Excellent. I know the 600 motors are the same as the 550 with top end modifications. But electro tach or mechanical (as all the 81-83 550s have) I have eliminated the stock tach anyway.
As far as getting another bike, etc... whether or not the motor is on the bike or not, I am going for the cheapest, money-wise. The condition of the motor (unless there is serious damage to the case, head, or block, as would happen, lets say, if someone dropped it off a cliff or got ran over by a semi) isn't too important.
I am rebuilding the motor from top to bottom when I get one. There is going to be a lot to learn... hahaha.

 

I have a Radian motor in my Seca, same as the FZ600.

 

Sorry to pee in your cornflakes, but you probably won't be; for the same reason Thrasher has a Radian motor in his Seca.

You will have a nearly impossible time finding rings, pistons and main bearings in any oversize sizes, or even stock. You CAN spend cubic $$$ to get pistons and rings made, but spending over $1000 to rebuild a motor when you can get another one for $200- $500 (or less) and just DROP IT IN makes no sense.

Which is why there's a Radian mill in Thrasher's ex-racebike.

If you really want to rebuild a motor, pick any old Yammie that was popularly raced, like the XS650 or the XT/TT/SR 500. THOSE motors have tonnes of parts available, in every oversize you can imagine.

Or buy an old Triumph (same reason.)

 

I suspect that the pistons and rings from the later Seca2 600 will be compatible, once I have some spare cash I will buy one and find out

Does anyone have the bearing journal sizes to compare from the Seca 2 vs XJ550/600?

Spend $1000 and you know exactly what you've got or $200-500 and take a chance on getting something better than what you got

 

So a Radian (YX600) lump will fit?

Any chance with a Seca II or FJ600 engine? (I'm assuming these have completely different frames from the XJ550 and may run into more complex problems)

 

YZ/FZ/FJ600 motors all will fit, the Seca 2 I wouldn't think so as the block is more inclined towards the front of the bike

 

Well, the rebuild is more for the experience but want it to be able to fit my mounts. It doesn't have anything to do with replacing my engine.
And if I am able to rebuild, and even add performance or make some kind of beefy engine out of it, looks like i'll have a rare motor then. I have spent way too much money already on this bike. Over $3,000. I am not interested in stopping because of cost. I pay my bills and work 55 hours a week minimum. The price of custom or hard to find parts isn't really important to me. It is whether or not I succeed that is. I don't know. Maybe I can start out on just a top end rebuild or something.
I don't want to go too far out. But if I rebuilt a motor successfully and spent $1500 on doing it, I would have spent about what the shop would charge for just a regular stock rebuild