engine rebuild

I have an 81 xj750 seca and ecently I pulled the motor an I am looking to rebuild it. wondering if anyone knows of any aftermarket parts such as forged pistons, aluminum rods, anything of that sort that are available.

 

is there a reason you are rebuilding the motor or you just want to?

 

I found metal shavings in the oil. im rebuilding it because i want to find this problem as well as i just want to instead of buying another used motor. its only a 15,000 mile engine

 

That’s barely broken in. A new motor will always shed metal as the parts mesh together. You wouldn’t have believed what I found in my current KLR’s 1st oil change. There was a 3” diameter shaving from machining the oil filter housing missed by their QC.
Also may KTM ate it’s electric start gears and I was pulling complete gear teeth from the drain plug. This bike has 4 oil filters/screens so it’s still running solid after fixing that.
Having said this you can use XJ900 components with some custom machining, something I’m working on myself.

 

well. i have it out and off id still like to dive in and rebuild it. just wondering about aftermarket performance parts. thanks for the heads up on the metal shavings though

 

The aftermarket performance parts manufacturer’s direct their attention to the new bikes being raced as this crowd will spend big for any advantage. Is some cases older bikes being raced. It’s just not good business stocking big bore and performance cam kits they’d need to list for more than the value of a 750 Seca. You might be ready to spend large but not enough others are, not enough to support this.

 

hmm, ok. thanks. ill keep my eyes out but until then itl be a stock rebuild i guess!!

 

There was a big bore kit available for the 750… Not easy to find though

 

Is this the one?
https://www.google.ca/url?sa=t&sour...FjABegQICRAB&usg=AOvVaw2SJVXbG5tceDcTsOSFJYp5

Or this one?
https://www.google.ca/url?sa=t&sour...FjADegQIBxAB&usg=AOvVaw3OQGP1mU10RImKBxWPBi6B

 

Looks like it

 

Both of those kits use a 68.00mm bore......3.00mm over the stock size. I've never understood how they will work well with the stock cylinder liners, the max. O/S that Yamaha recommends is +1.00mm. Although there is enough meat in the cylinder liners to actually bore them out that large, those walls be getting awfully thin at that point, and I'd be a little concerned about long-term reliability of such a set-up. For racing purposes, doing things like that is okay/common, but so is doing periodic full engine rebuilds.........up to and including replacing cylinder liners!

But, like they say, there is no substitute for extra cubic inches in the horsepower game.....

 

to be honest i probably will not do a big bore kit for that exact reason. i am planning to use this bike as almost a daily driver and dont want to risk blowing through a wall.

 

Hey thanks for posting that Matti, I may need that later for my project. Haven’t seen inside my 900 motor yet.

 

isn't there something about a 900 cam fitting a 750 ?

 

The ultimate result is going to be spending money that doesn't need to be spent.

The most reasonable courses of action are:

1: put the engine back in and tend to all of the other things that actually need to be done at this point in the machine's life.

2: Split the cases to replace the alternator chain guide before it grenades, and rebuild the starter clutch while you're in there. Then put the engine back in and move on to option one.

 

That's a maybe. I don't recall that anyone has done that and reported about the results here.

 

I know that at least one of the kits (not sure if it's one that is curently available) requires boring out the case to accept larger diameter liners.

 

well, i just got in after getting tearing into and off the top end, turns out the metal shavings was a blown connecting rod. now im really stuck, can this still be repaired??? what are the steps that need to be taken. thanks for any help

 

Explain further please............spun bearing, snapped rod, spit off the cap?

 

one bolt blew off the cap and came off, busted part of the skirt off. the upper and lower case look scuffed but not punctured as far as i can see. these are the best pictures i could get as of now. I will be splitting the case tomorrow with more pictures

 

Yep, that's the first step.............

You need some new jugs at least, a rod and bearings, and perhaps a crank..........in which case, you might want to look for a replacement engine.

Sucks. Did you ever hear this engine run b4 tearing it down?

 

nope. i wish I would have though. i got a screamin deal on the bike so im not super bummed. i would like to do all I can to rebuild this one because of the fairly low miles on it. im willing to buy a new crank, set of rods, as well as new jugs for this motor. only main concern at this point is case being too damaged for comfort I believe.

 

Gee, I wonder why

 

f***edy-doodah,,

 

Well.....that's different then.

Remember, step one of buying a vehicle is a compression check.

 

the guy stored it for 20 years in my grandpas barn, he said he put it away after it quit running and thats all he remembers. i bought it from him for a hundred bucks....im not super worried about putting a little money into it. just gotta figure out what i gotta do

 

You're on the upside no matter what you do with it.

 

I would save that engine for parts and buy another one from your local MC junk yard. Most MC salvage operators are MC enthusiasts themselves
and will at least check that the engine spins freely before selling it. Some of them will test compression. I'm starting my 4th xj650 maxim build
and am almost done with an xj750 seca. I found that most of the used engines I hunted up in New Mexico had 20 to 30 k miles on them. Most
of those still had pretty good compression and I found I could improve that by squirting a 50/50 mix of atf and acetone down the plug holes
and letting it sit for a few days before changing the oil and testing again. Clean the carbs, reshim the valves and synchronize the beast and it should
be a good runner. The funkiest one I found was an 81 650 maxim roller with a dirt encrusted engine for $100 bucks. It ended up being the best runner.

 

This won't work, as the 900 cams ride directly in the head at four places, while the 750 cams ride in only three.