Xj750 Maxim motor tear down

Starting a thread to post progress on this as I'll inevitably need some help along the way.

The brief recap: this is a motor I picked up with unknown history, never heard it run. I have the original motor for my 750 project and decided to swap this one as it seemed to be in better condition from an external appearance. The original was pretty badly corroded from sitting outside.

A small alternator seal leak led me to examine the starter chain oiler, and then the starter chain guide itself. Turns out the guide was chewed to bits, along with one of the metal mounting tabs which made for some small metal debris in the pan, and no doubt circulated through the system.

At this point I've decided to disassemble it the rest of the way, lap the valves, make sure there's no broken rings and hopefully find the cylinders aren't chewed up.

Otherwise it'll be a low budget clean up, reseal, regasket job. I will replace starter clutch pieces and starter chain guide at minimum.

I've found a couple cam journals that have some grooves. Not pretty, but I think I can clean them up. One crank bearing shell is badly grooved. If I can identify the size and find a replacement, I will. The crank itself doesn't seem to be damaged.

Question... Where do I find the bearing "code" numbers? I see the photo in the Haynes manual, and I've looked all over but don't see them. I can't tell for sure which spot on the case I should look from the Haynes photo.

While I'm in this deep, is there any other problem areas I should examine or address? The starter chain and cam chain both feel decent, but I don't know the original chain pitch to measure stretch, and don't even know if that's an accurate check.

Of course the original motor for this bike might be in better internal condition. Hoping not to have two of them exploded simultaneously, but it's an option.

Some photos:

The crank bearing shell that looks the worst. Other half looks good as the scars line up with the oil groove.



The cam bearing that looks the worst. Definitely had some metal chunks go thru the system. Good reminder to change your oil and filter often.



Cam looks ok I think? Needs some spit shine and emory.



Searching for the bearing code engraving. Where should I be looking here?

 

See pages 8-15:

https://www.xj4ever.com/catalog/frame-engine-id.pdf

 

One upgrade worth the money and COOL factor is the spin on oil filter from xj4ever.

 

Thank you, Len. That helped immensely. I was thinking they were stamped inside the case for some reason.

So now that I've found them, I can't read them.

Does that say 45455 ? Funny looking 5's if that's what they are.

 

Yes, that is what I would interpret them as saying..........being that they're "handwritten", they can be very neat or very sloppy.

 

Finished pulling the rest of the motor apart. Pistons and cylinders look very nice, but haven't started measuring anything yet.

Then also decided I needed to have a look at the original motor, because why have only one torn apart in a shop that's already full? The original motor I never have ran either, although I did crank it and compression test and got it to cough a little before realizing the carbs needed a complete rebuild, which ultimately led to every nut and bolt on the bike coming apart. Funny how that works.

Took the oil pan off and it looks really good inside. Starter chain guide still intact, no debris in the pan. Maybe outward appearances were deceiving.

Now I'm in a quandary. This is the numbers matching motor that I'd prefer to have on the bike. I might talk myself into doing a crude cleanup on this one just to get the bike running again, while still doing a more complete rebuild on the spare motor.

 

Did some cursory measurements to make sure I still had usable parts. Everything is looking pretty good so far.



Bores measure 65.02-65.03 parallel to the crank and up to 65.06 perpendicular with service limit at 65.10. No ring ridge is detectable with the calibrated finger tips.

Ring end gap around .45-.50 with service limit at 1.00 mm.

Ring groove clearance on the top rings was at or slightly beyond specs, with the second rings still ok.

All and all I'm pretty happy with the condition. I don't think this was a super high mileage motor before it fell victim to the chain tensioner problem.

Still need to disassemble the head, but did a little clean up and don't see any obvious problems yet. The carbon encrusted stage of the project isn't the most fun....

 

The wear on the worst cam bearing is horrible, and the cam needs to be spray-welded and re-cut. Get another head.

What do the crankshaft journals look like?

Replace the alternator chain guide, and rebuild the starter clutch while you're in that deep.

 

Yah it's not pretty for sure. The crank journals look good. I haven't tried polishing the cam journals yet, but I'm hoping there's enough good surface surrounding the deep grooves. Guess I'll cross that bridge when I get to it.

Already planning on the starter clutch and chain guide.