What have I done?

Hello, new guy here. Sunday, I was perusing the forums I frequent and found an 83 XJ900 for sale for $200. Seller had JUST updated thread, "Free, come get it." It was raining, I was bored to the point of watching golf... Before you get too excited, it's a bare frame and a bunch of boxes. Engine is intact, has a couple of studs broken off on the carb side. Everything is bagged and tagged, seemingly pretty well.
Side note, I'd never heard of this bike before Sunday.

I'm an old fart, spin a decent wrench, but I'll admit once I got it home I'm a bit intimidated. Where to start?
I need to make sure the motor spins, stupid question; which way does the driveshaft turn? Will it hurt anything if I spin it backwards? I plan to check the valves before putting in frame. Anything else?

Second attempt, first try w/pics failed.

 

Welcome! After you post 5 times, you're allowed to post photos here. You could alternatively, post elsewhere and link to them before that.
You've come to the right place! As you know a picture is worth a thousand words, so we'd love to see what you have and I'm sure we can set you on the right path!

 

Thanks, I figured it was something like that.

 

Welcome! I've only been immersed in XJ's for a couple years, having started with some solid mechanic knowledge, but none related to these bikes. Here's what I've picked up along the way.

A free bike isn't free! Although parts are still relatively available, these are antiques. If the project is a hobby (and keeps you off the streets or away from other expensive, dangerous pursuits like golf) then its a good use of time. If the hope is to assemble a free bike for free, just box that sucker up now and pass it along.

Get a good manual and read it for fun, again and again!

Do the same with a wiring diagram. Little systems like interlock relays are baffling until that light bulb moment of understanding.

Don't be afraid to screw up. Do some research, then plunge in, make some mistakes. They are the finest education.

Likewise, don't expect perfection from the bike or yourself.

There are tons of other guys on here more technically savvy than me, ask lots of stupid questions!

Click that "XJ4EVER, supporting vendor" link and there is a parts catalog, then lower down some must read pages on carbs, electrical, etc.

And then from a more practical standpoint, I would rig a battery to the starter, whether the engine is in the frame or not, and check compression, and also cycle through the gear shift, to make sure you don't have major issues before commencing. Enjoy!!

 

Thank you! I truly understand free ain't really free. And thank you for the hints.

 

Let' see, about me. Mid 60's, been riding again since 2010. Probably average 12k miles a year. In 2010 I bought a 2005 FZ1. Along the way there's been a 13 Super Tenere, a couple of KTM 450 EXC's, 2018 BMW R1200 RS, 2016 BMW S1000XR, KTM 390 ADV, 2020 KTM 890 Duke R. Probably a few more. Present stable is a 22 BMW GSA, 21 KTM 890 Duke R, 1985 Honda Nighthawk S, and a 1985 Yamaha RZ 350.
I do most/all my own maintenance and like quiet walks along the beach and puppies.

 

I know it's generally frowned upon to post for no reason. But this is #5 and I'm anxious to post pics. I promise I won't do it again, at least not to reach #5 .

 

Frame

engine

boxes

wheels, exhaust

 

That looks like a surprisingly good condition pile of parts. If it is complete, you should be in good shape. Did the seller give you any history on why it had been dismantled?

 

Shine a torch in the tank - 90% of the issues with these is rusty fuel contaminating the carbs, jamming the float valves open etc.
The frame looks good - check the bottoms of the lower front rails for rust. Spinning the engine on the starter is a good idea if it turns over with a spanner. Then valve clearances and put it in!
Looking forward to pics of a complete bike..

 

It was his buddy's who had parked it years ago. His buddy offered it to him, he decided to restore it. The he decided he'd rather ride bikes than put them together. My real guess is his wife wanted to park in the garage.

Wasn't aware of the tank corner rusting issue when I looked, but the top of the inside of the tank is pristine. I'll check more closely, thanks.

Looking forward to pics of a complete bike. Me too!

 

It is looking good now, looking forward to you getting it assembled and running. Remove the plugs and left crankshaft round cover. You can turn the engine anticlockwise with a 19mm spanner to check it. Check you can change the gears. Once you do a compression test and check and adjust valve clearances, best to repair the studs when the engine is out.

 

Thank you!

 

Welcome to the fold! I would throw in that this would be a good time to make sure the starter clutch (it's internal and you do have to split the cases to get to it) is good.

You'll fall in love with these bikes.

 

Yes and the alternator starter clutch chain guide and new bolts if he splits the cases.

 

Sounds like I've got some research to do. I wasn't planning on going that deep. Any other common problems I need to know about now instead of later? Thanks for the suggestions, keep them coming.

 

Nooooo.
Put the engine in, if it runs and is anywhere as good as it looks it will be fine. Splitting the cases to inspect the starter clutch is daft. 99% certain it will be fine, and if not, then you know what do do. If you split this now we'll be seeing an ad for bits on here in a years time...

 

After sleeping on it, no splitting of cases. Originally the plan was not to proceed if motor is locked up. I see no reason to change that idea. I'm just not willing to go that far. Thanks for all the comments, keep em coming.

 

Motor spins freely, thanks Franz.

 

Now, don't cock up drilling out those studs - you can use a left hand drill, left hand tap even, but m4, or max m5 is the limit. I would drill 3mm with lh drill first...

 

If I'm doing the valve check correctly, lobe pointed straight up in relation to the shim, every valve is tight. Something over 58k miles on this bike, does that sound right? You guys have me worried about pulling them one at a time, since I have to do every stinking one of them.

The engine is supposed to be black with high-lighted fins? Someone has attempted to strip the paint off the head and the front of the engine needs some attention. Might as well do it now, any thoughts? I've searched, there's no definitive answer best I can tell. Frame touch-up the same.

 

58K miles and who knows when the last shim job was done. If the shim gap becomes nonexistant, the valves can be held open, not a good thing. Be thankful you have an airhead with only 8 shims which can be checked without pulling the cams. Every one needs to be checked with feeler gauges and the shim pulled to identify the size. Then you can figure out if some can be swapped and which need total replacement. Contact @hogfiddles for shim pool info.

 

Here's what I came up with


So, I need 4/ 2.75?

 

Looks like you are doing it right. And a stroke of good luck to be able to swap and reuse that many shims at once!

 

Interesting numbers. Here's what I found on my XJ750 with just over 36,600 on the clock. Clearances are in millimeters using measured feelers on a vernier caliper, compression is a Mac tools CTD300 digital pressure gauge.
Exhaust: Intake: Compression @ 60F WOT 6-puffs no plugs
1=0.164 0.014 142 dry 145 oil
2=0.168 0.012 145 dry 148 oil
3=0.158 0.011 145 dry 148 oil
4=0.154 0.015 141 dry 146 oil
Some ring wear but nothing bad from what I can see. Valves are on the tight end of the spec. Question for the experts is should I re-shim at this point?

 

That looks good! Tight end of spec is still in spec. It's hard to know if they'd been adjusted before, but I'm sure you'll check them again after a while. I don't recall how often, 5 or 10K miles?

 

Later this summer unless I get the itch to swap some with the shim pool and loosen things up. The cover has been off many times judging by the tool marks and stripped threads on the ends of the caps, a something to do in the future.

 

Exhaust #3 & #4 are out of spec (which is .16 - .20mm) You do NOT want tight exhaust valves, that's how they get burned, and then it's pull-the-head time for a valve job. Also, clearances do not "loosen up" on these engines, they get tighterover time. Compression numbers looks great.

 

I definitely need to add another few thousands for some margin of error. These are similar to the older VW/AUDI diesel motor valvetrain and they do much better looser than tighter, don't know what the shim numbers are at the moment but it's on the to-do list once the snow melts.

 

What's up folks. Picked up an 83' XJ750 with 17.9k miles for, surprise, $750. bypassed start circuit cutoff relay, blasted some starter fluid into the airbox opening and she ran! I had an 82' XJ650 about 9 years ago that washed away in the waves of life (bummer), so I'm moderately familiar with the steps required to make these things run well and road worthy. I ran a compression test before adjusting the valves (I know, I know; inaccurate. I barely trust the harbor freight compression tester i used anyways. I really just wanted a number to fret over, give me a break!).

All 4 cylinders read out at approx 120psi which really worried me that the cylinders/piston rings were done for, especially since i inspected the cylinders with a borescope and didn't see any notable signs of scoring on the cylinder walls. I attempted to measure the valve clearances tonight, valve train looked beautiful, cam lobes looked decent.

here's what i measured out with my "metric" feeler gauges:

intake: cyl 1- <.005 inches, cyl 2- minimum of .005 inches, cyl 3- minimum of .005 inches, cyl 4- minimum of .005 inches.
exhaust: cyl 1- minimum of .005 inches, cyl 2- minimum of .005 inches, cyl 3- minimum of .005 inches, cyl 4- minimum of .005 inches

I have some REAL metric feeler gauges that go down to .05mm on the way so i can redo these measurements more precisely and will promptly melt the ones i currently have into a paper weight out of spite. The SAE specs are .004-.006in intake and .006-.008in exhaust. based on that and my readings i can assume all 4 exhaust valves are tighter than spec, the intake definitely has at least one tighter than spec.

I'm going to remeasure everything again once i get my metric feeler gauges and will probably buy a Mityvac compression gauge so i can actually trust the reading.

With all that on the table, I'm still concerned about the 120psi. in all 4 cylinders. Being a mechanic that works on cars that all have self adjusting valves, I'm unfamiliar with how much valve adjustment can change compression, obviously if the valve has zero clearance and is stuck open there would be zero compression, but would bringing my slightly out of spec valves back into spec give me 5 psi? 15 psi? 20 psi? Has anyone seen a serious (I'm talking 15-20psi) jump in compression just from bringing slightly tight valves back into spec?

P.S. Just read in the Haynes manual that the compression test should be performed with the engine warm, i assume the engine will gain some compression just from pistons/rings/cylinders being at temp.

please ease my mind with sharp truth or soft stories, soothsayers.
Hope yall are having a good weekend and have some good weather to boot.
Dizzy

 

@dizzycow If the bike sat for years, shim your valves, do an oil change, get some heat in the motor and 50 miles on it before worrying too much about those compression numbers. Since they're all similar, and the bike obviously runs, that's at least a good sign. And did you remember to hold the throttle wide open also? I forget to do that half the time myself....

 

All 4 plugs out and throttle wide open. Thanks for the reassurance, i will report back with updated compression readings once i get valves shimmed and carbs rebuilt and tuned in.

 

Chacal I went back on my original notes, I fat-fingered the #3 & #4 numbers and they are 168 and 164 which are in spec but a little on the tight side.

 

Adapted an automotive engine stand to hold the Seca 900 engine. Some angle iron, assorted nuts and bolts and a little grinding to clear engine case.