'82 Seca 750 Refresh Project: Now Scooby's Bike

Hey guys. I could use some help . I can't seem to find any guide on disassembly of drive shaft. And the Haynes manual just touches lightly upon it. I was taking everything apart since the gears looked gunked up and I toss em in an ultrasonic bath. And I came across this oil seal on the housing bearing for the drive shaft. Looks like there's a small hole in it so I wanna replace it. Blueprints show it should come off but I have no idea how to remove it.

Also, there's this self locking nut inside the gear coupling. But I dunno how to remove this either. I'm afraid to brute force it.

 

OMG. Why did you think that the final drive needed to be disassembled?! Gunk is no reason. Gunk can be flushed out.

You now need to make a special tool for reassembly.


In future; ask before doing.

 

I have no problem with that. It was my intention to tear this thing apart, replace bits and bobs and rebuild.

 

Which special tool is required?

 

The tool that holds the output gear in place, and a tool to hold the input shaft.
gear-lash-tool.53249

 

Cheers k moe so it to prevent excessive wear in the gears by keeping oil between them. Learned something else .

 

K-Moe has a valid point. Disassembly simply for cleaning, especially disassembling things without knowing what you're doing can get expensive and often irreversable. Highly recommend reading, nay-- STUDYING the service manual prior to disassembling any major components. Too easy to paint yourself into a bad corner if you don't know what's lurking...

You came right close to shooting yourself in the foot here; next time you might not miss...

 

Finishing cleaning up and rebuilding the final drive. Anyone know the torque spec on these nuts and screws?

 

2.3 m-kg

You really should have a service manual on-hand so you don't have to wait on answers about torque specs.

 

thanks man, Yea the Haynes manual. from what I checked, doesn't give any specs on them as it says to inspect for wear, no disassembly info, and leaves it at that. I torqued the nuts to your specs but now the shaft doesn't budge by hand. It should move freely should it not? As if you put it into neutral, the shaft would spin free with the wheel.

 

That spec comes from the Yamaha factory service manual. Did you make sure to put the shims back in the correct order and location? Did you measure gear lash and set the input shaft collar correctly? Taking the final drive apart is not reccomended unless the gears need to be replaced, precicely because final setup is critical to it functioning properly.

 

Fixed the final drive. just took it apart, double checked and reassembled it. Works perfect now.

Pulled out the old swing arm bearings and seals since they were pretty worn. Got a new set. I bought a piece of PVC pipe and used a dremel tool to make it just small enough that I could knock the collar down into the slot. However, the issue before I can do that is getting the collar passed the lip of the swing arm slot. I've seen people use custom press tools but the issue with this swingarm is it doesn't run straight through to the other side that I could slip a bar through for a custom press. Any ideas on getting these bearings in?

 

Freeze the bearings. They'll drop right in.

 

What's the extent of damage a piston can take and still be used? I was gonna replace the rings and noticed a few kinks in one of the pistons. Rings aren't cheap, neither are pistons... so I'm hoping not to replace all the pistons as well... luckily this is the only one with noticeable damage. Should it be replaced?

 

Wow, looks severe.
Repacement I would guess.
Did the engine ran without oil or got it way to hot/seize?

 

+ 1 surely combustion gases will flow past that damage and lower psi a little in the combustion chamber instead of getting behind the ring and forcing the ring against the cylinder. Top picture really bad. I wouldn't use them if it were my engine.

Perhaps you could get a good set of pistons, rings and cylinders from one of the XJ community because l doubt that damage can be repaired (bearing in mind l am not an engineer).

Or just replace the two damaged pistons using the existing rings might be an option? That way the same rings are in the same bores.

 

Not sure what happened. Previous owner was having carb issues. Bike couldn't run with choke otherwise it'd stall out. Not sure if this piston also contributed to his problem.. But this engine hasn't been opened since.. who knows when Since the gaskets were baked on good.

Yea I figured it would need new pistons... I'll def buy new rings for all 4. I hope I can get away with 3 used and one new piston with no issue. Is it alright to use 40k mile used pistons like this again? I assume if they aren't damaged, its good to go.

 

I would expect 40k pistons to be scrap, but a lot depends on kind of use, how well it's set up and driven.
Get new rings and check how they sit in the grooves - if the grooves arent parallel and square the rings won't sit flat in them, causing galling of the bores, overheating, loss of compression. Waste of time in other words.
If the ring grooves are good, as well as the thrust face and gudgeon pin bore, then they're usable.
What I allways say when someone tries to persuade me something like this is Ok - "are they going to improve with use?"
Obvious answer is no, they will get worse.

 

great advice, thanks. Yea, was trying to not go overboard on buying all new parts for a rebuild but if there were a problem with the pistons down the road. tearing down the whole engine again would be a big pain in the butt. Best to replace with new parts now to avoid any bigger headaches in the future

 

Well I didn't say you had to buy new, just no point in buying worn out used stuff. You just need to learn to inspect stuff - feeler gauges, micrometer, magnifying glass are all tools to use - having a good unworn item to compare can also be useful.
For example I'm collecting parts to build a new vmax engine (the knackered one that was in the trike when I bought it). I bought a used block and pulled the liners out of it, I bought a set of low miles pistons and a used crankshaft. I fully expect the engine will run as good as a new one.