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

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.

 

Yea, you're right! Makes sense. Guess I'll just follow this chart for any nut or bolt that doesn't have specific torque value. Hopefully I don't bugger anything up so close to the end

 

Hey guys,

Been having some trouble with these bloody cams :\ I've turned the crank to TDC, put the Exhaust and Intake cams in correct spots, bolted on the cams and turned them so the dot aligns with the arrow.

Now comes the trouble. The sprocket bolt holes do not align cleanly with the cams when the cams are in the correct spot. The sprocket bolt holes are just maybe a few millimeters off... I can try to +/- the teeth so I can fit the sprocket bolts in and align the dots as close as possible . I'm able to get the sprocket bolts on but then the dots aren't perfectly aligned with cams. I heard if they're just barely off it's no big deal but doing this gives my chain some slack. So when I turn the crank over, the cams don't immediately move causing them to be out of position when the crank is TDC. With the slack, turning the crank over maybe 1/4th of the way causes it stop turning. I'm guessing this is from the chain slackening and tightening up again, perhaps jamming up so the crank stops turning clean. Obviously something not wanted.

I've read a few threads and I checked if the pistons were truly TDC with the straw in the spark plugs technique. All good there. Crank turns free when cams are off, also turns free when cams are bolt on, so no binding there. I'm thinking maybe it has to do with sprockets? I have a brand new chain but old sprockets. I just ordered new sprockets. If that's not it then I'm stumped. I'm at a loss on how to lift the sprockets onto the cams with little slack and have the bolt holes line up.

 

This might help.

https://xjbikes.com/forums/threads/1982-xj750-cam-timing-pictures.48419/

 

Thanks :^)

Yea I've been checking out multiple threads. The manual states gives some nice clear steps. I'm thinking it's just the sprockets atm. New chain is probably too taut for the old sprockets and thus can't align sprocket holes with the cam bolt holes. New sprockets should be coming soon and I'll try again

 

I fitted a new cam chain on my old sprockets. As the crank sprocket is smaller than the cam sprockets l would need another crankshaft if l wanted to change it. Theoretically it should wear more than the cam sprockets with half the number of teeth. I haven't seen worn cam sprockets even on high mileage engines. Your engine should be fine with the sprockets you have.

 

Ahhhh I think I figured it out. I'm a clown.

Re-reading the instructions in the manual. Only one bolt should be fitted onto each sprocket. Then automatic chain tensioner should be fitted on C mark and tensioned up then rotate the crank so the final bolt can be fitted on the sprockets and tightened. I was making the mistake of trying to rotate the crank to fit both bolts on the sprockets and then put in the tensioner. I'll try this later today and see how it goes.

 

Yes that is the way l fitted the bolts.

 

Hey guys,

Still having some issues with turning the crank. I've gotten both sprocket bolts on. Tensioned up the chain nicely. But there's still this issue of turning the crank. There's resistance when turning it 1/4th around. I've checked no valves are clashing pistons, no binding of pistons. It's all good until I put the sprocket bolts in and tighten up the chain. I have no idea what it could be. I'm thinking maybe the chain is getting caught on on of the chain guides? It's either I didn't set the back chain guide in nicely enough or the front chain guide isn't fully in the slot. The back chain guide should be pretty loose yes? I made sure it the inner bolt lightly touched the chain guide then I set the locknut. The auto chain tensioner should do the rest. As for the front chain guide. Does anyone have a picture of how far in the slot it should go? It sort of bounces a bit if you push down on it. Maybe it needs to sit firmly. Not sure. Though it might not be much help, I'll see if I can record a video.

 

The exhaust side cam chain guide should not bounce. There is a pocket the guide goes into. Not getting it in the pocket is an easy error to make. Try turning the engine more than a quarter turn clockwise with the tensioner in place to see if you get the same resistance. The back chain guide ( I assume you mean the tensioner side should not be loose when the tensioner is set correctly). The chain should be taught.

 

do you think the chain could be half way off the crank?