'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.

 

That also is serious work in progress..

 

What are these rings in my cylinders and how do I get rid of them? They almost seem like carbon or dirt. It's raised off the surface rather than cut in like a deep scratch should be. Was it a piston ring issue? I'm gonna get these honed if I can. Maybe honing will do the trick. The cylinders are around 65.20-.25. Should be in spec

 

I think those look good. Nice pics by the way, hard to get the light in there. I wold guess those are just stains from the piston and rings sitting there for so long. I don't see any damage or issues with those cylinders.

 

Hey guys. I was putting back together my engine and I noticed the Haynes manual telling me to make sure the seal is on the middle gear drive. I don't remember taking off a seal when dismantling the engine, and if I did, it would be a large part, I doubt I would've thrown it out.

I see two shims behind one of the bearings and I'm wondering what are the shims for? They aren't pressing up against anything, they just free-float up and down the shaft. I looked up pictures and videos. Sometimes I find the middle gear with a seal and sometimes the middle gear doesn't have a seal. I can't remember exactly hat it looked like since I dismantled the engine during the summer. I lost all pre-dismantle pictures when my phone broke. So, I'm in the dark. What's, the deal, am I going crazy here or does the XJ750 Seca not have a seal and just these two shims?

 

Have a look at this exploded view. Part 9 is a thrust shim and 19 is for the helical gear back lash clearance. There is an oil seal number 14 on the output shaft flange.

https://www.partzilla.com/catalog/yamaha/motorcycle/1983/xj750mk/middle-drive-gear

 

Hey guys,

Anyone know the torque spec for the crankshaft bolt in the timing plate?

 

Quite daring to be undertaking an overhaul like that without having a factory manual.
Doesn't the Haynes manual have the spec?

Yamaha manual has the hex cap screw for the timing plate as 17 ft./lb.

Tony

 

Haynes doesn't always have the specs :\ unless I'm missing them somehow. I just ordered a Factory manual but it shouldn't arrive until Feb. I just checked the gear lash for my middle gear drive and am ready to torque back up the bolts but Hayne's stops at "tension up the bolts", however, they never say the torque specs. Anyone know the torque specs for these bolts?

 

18 lb./ft. with locktite.

Assembly will definitely go a lot quicker when you get the manual.

Tony

 

Hey guys, putting the clutch pressure plate back on with new springs and bolts. Torque specs are 7.2 foot lbs but... the bolts keep spinning. It shouldn't be difficult to hi the torque spec. I'm afraid any more and the bolt heads will snap off. Any tips on how to get this clutch pressure plate on successfully?

 

What range does your torque wrench have?

 

Haynes has all the specs. Some are wrong, but all of the torque values are correct.

 

+1.
If you are within 20% of either end of the range of the torque wrench it will not give a reliable reading,

 

This is the one I have and I have not used it yet.

https://www.drapertools.com/product/72623/1-4-3-8inch-Sq-Dr-Push-Through-Torque-Wrench-(5-35NM)

 

Got the torque wrench for £10 off eBay so at that price it was worth it if accurate enough.

 

Hey guys,

I have this Tekton 3/8 10-80 ft lb wrench:

https://www.amazon.com/gp/product/B00FMPKAD0/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1

Although, the torque value for the bolts is 7.2, I've torqued up the other bolts on the engine with this wrench at 7.2 without an issue. I heard using a 1/4 might be best.

How risky would it be to guess the torque I put on the bolts? I've heard of people riding a bike with 4/5 clutch bolts to a shop. Might be my last resort in case I snap a clutch bolt off like a clown.

 

I would not guess the torque, on my machine and the range of your wrench is above the factory torque for the clutch bolts. You don't want to damage your clutch hub.

 

You're right. I'll just take it to a shop. Last thing I wanna do this far into the build is F something up

 

Buy the apporporiate torque wrench. It'll cost you less than a trip to any shop, and you'll know the job was actually one right.

 

i've found 7.2 is about as tight as i can make it with a screwdriver type handle with my left hand, i'm right handed
that's quick and dirty, don't use it for anything important

 

Hey guys. Final stretch for engine rebuild. Then its on to just waiting for Spring and putting her back together.... though I lost some reference photos so I gotta do it by book , memory and videos...
Anyways, anyone got any tips on how to pull these two sprockets onto the camshafts? It's a brand new chain so it's super taut and getting them both on at the same time is extremely difficult.

 

Ah never mind. I think I might know the solution. I haven't torqued down the cylinder head yet. Those few millimeters might help mount the chain on easier. I haven't installed the cam chain tensioner yet so thats no issue. Gonna torque down the head and see how it goes.

 

Yes torque the head get the crankshaft on the TDC mark and fit the exhaust camshaft and sprocket making sure there is no slack in the chain and your timing mark on the exhaust cam is lining up. Then follow the same process with the inlet camshaft. You should be able to fit the chain on the sprocket with the tensioner off the engine. Double check the timing marks if satisfactory fit the tensioner and rotate the engine anticlockwise to make sure pistons and valves don't come into contact. You won't have any problems if your timing marks are spot on.

 

Hey again guys. So I'm just about ready to time up my cams. But I'm trying to be super careful of course. So TDC for crankshaft is when Pistons #1 and #4 are at topmost position correct? So if I line my my camshafts so the dots match the arrow on the cam caps. It looks like the only valve that should be open is the Intake #2, Bottom Near Left valve. So it should be good to keep pistons in TDC, Torque on cam caps and carefully put the intake cam on time so the only valve open wont clash with Piston #2 right? I drew a little crappy diagram to explain my reasoning. What do ya'll think?

 

Your piston cannot hit inlet valve No 2. I keep the crankshaft on the TDC mark and install the exhaust camshaft first. Then the intake. The dots on your cams lining up with the arrows are right. It is not possible for your inlet valve no 2 to hit your piston with the engine in the TDC configuration. TDC on the compression stroke is No 1 piston but No 4 is at TDC too you are right No 2 and No 3 are at BDC.

Have you got a manual, follow the process in that and when you have it all set up properly turn the crankshaft anticlockwise four revolutions to make sure there is no contact between valves and pistons . Then double check your timing marks.

 

Remember when your timing marks are exactly right turning the crankshaft 360 degrees one revolution will mean the cams have moved through 180 degrees. You need to turn the crankshaft through two revolutions 720 degrees for the dots and arrows and crankshaft timing marks to line up.

One stroke from TDC to BDC is 180 degrees but the cams move 90 degrees.

 

Hey guys,

Just replaced the steering head bearings from some I bought from XJ4Ever. The tapered bearings. The Haynes manual says a torque of 18 ft lbs is required for the steering torque spec, however, that is for ball bearings, it might be the same for tapered bearings. The instructions I got from XJ4Ever says the bearings can withstand a torque spec between 15 to 25 ft lbs. I know a lot of guys just tighten it up with a drift and a C spanner but since I'm a newbie at adjusting steering, and I don't wanna death wiggle at high speeds I figure I'd just stick to the book. Anyone try torqueing up tapered bearings to a specific torque or is the general consensus people just do it by "feel"?

 

the bars should flop to either side, just barely. don't worry too much now, you should do it again in a few hundred miles. they will loosen up the first time

 

Hey guys,

Spring is here! Well, just about. It's time to bring the frame out of the basement. I'm not familiar with the names of exactly every part on the bike so sometimes I see a torque spec but not quite sure what part it goes to. So I found this general torque chat from the XJ750 supplement. And I've been wondering how correct it is. As the nuts on the final drive to the driveshaft are about 14mm. So the torque should be 22 lb fts? Doesn't that seem a bit excessive? I've also been looking for specs on kickstand nut and centerstand nut. Which according to the chart I think was 40 lb fts. I'm not sure how accurate the chart is. But those seem a bit high or even low for the 6mm and 8mm bolts

 

22 ft lb is not excessive. You do not want the final drive to have any flex or wiggle where it meets the swingarm.

The actual value from the XJ750 Suplementary manual (page 48) is 30.4 ft lb.

I do not recall seeing, nor can I find, a torque spec for either stand. I have always just cleaned the fasteners, applied blue Locktite, and tightened them until I felt they were tight enough.

It may be in the original FSM, but mine is sitlll in a box....somewhere. Sigh.