XJ550 First Motorcycle Project (Shifter Drum Question)

Hey all,
I bought an old 1982 xj550 as a project. I know little about motors and I'm using this to teach myself. The engine is not locked up [though it may have low compression], I'm waiting on some gaskets so I can reinstall the cleaned carbs. I noticed the clutch seemed sticky on the release so I read up on this forum. I've pulled the clutch plates to refurbish and am buying some new springs. I haven't removed the basket, it seems fine (I'm thinking someone already did a rebuild on this one just based off of the plates as well).

My question is should the shifter bar be able to rotate the shifter drum with the clutch basket still on? Do I need to remove the clutch basket to determine this? I would think since it is in neutral that it is irrelevant. When I press the shifter pedal, I can watch the shifter assembly move against the shifter drum wheel; but it does not rotate the drum wheel. Is this indicative of the broken spring that I have read about? Or do I need to remove the clutch basket to truly see if this is the case.

Thanks in advance and sorry if I've posted in the wrong area.

 

You need to pull the shifter cover and look for a broken spring. I think that you'll find one.

FYI this is the correct place to post questions.

 

Because it is a sequential gearbox, it will stop (and act as though something locked) if you try to shift through the gears without moving the rear wheel. With the bike on the centerstand you can get through the entire 6 speeds but it will take constant rotating/moving the rear wheel to do so. The gearbox is connected to the rear wheel; the clutch separates the motor from the gearbox. The clutch is not involved with shifting other than disconnecting the motor to allow shifting.
Why are you worried about being able to shift gears? I always find it a major pain to find neutral again if I've "dead shifted" it into a higher gear. But if you want to, that's the only way it will work.

Quick note: having the carbs off the bike makes doing an accurate compression test even easier. If you suspect the engine has low compression, find out now before you sink a bunch of time and money into a lost cause. Things like new pistons are absolutely not available for the 550s; rings are but they are not cheap.

 

Not in a 550 he won't. He's looking in the right place; on the 550s the shifter shaft crosses over and the mousetrap is on the right side behind the clutch. If you want to completely see (or replace a spring) then yes, the clutch basket needs to come off. However, mousetrap or shifter return spring breakage is uncommon in the 550s; if the bike can be shifted in the manner I described above, then there's no need to pull the clutch basket to watch the mousetrap work.

All you find behind the shifter cover on a 550 is the front drive sprocket and a whole lotta chain lube grimy YUCK. Oh, and the poor neutral light switch.

 

Thanks for the responses both of you! I've looked into that mechanism and it seems that the springs are there and doing what they should.. They could be weak (worn out) but I'll leave them be for the time being and move towards doing a compression test. I should be able to borrow a compression gauge tomorrow.

Like I mentioned, I'm very new to this mechanical stuff. I just graduated so I have a lot more free time now that I'm not working and going to school at the same time. I thought this might be an interesting hobby to spend my time on.

It looks like for a compression test I allow the starter motor to turn the engine over while the gauge measures compression produced by the piston? And the fact that it's the starter motor allows it to be performed with the carbs and gas tank off? Or would it be better to crank the engine by hand for this?

Once again, thanks for the responses; it means a lot to me being new to this.

 

Compresson test should be performed with the starter motor doing the heavy lifting, and the throttle fully open. The gas tank can stay in place, unless you need better access to the sprk plug holes.

 

Which is why you get even better results with the carbs off the bike (no having to hold throttles open.)

Yes, a compression test is performed by spinning the motor over until the gauge reads the most it will (usually not more than a couple dozen revolutions) then record the results and move to the next cylinder. You can't spin the motor fast enough by hand to get a good compression test.

BE SURE TO unplug your TCI unit (ignition "black box") so it doesn't try to fire spark plugs that are not there. That can damage the unit.

Compression specs for the 550 are 121 psi "standard", 100 psi minimum and 135 psi maximum. Overall numbers, as long as over 100 and under 135 psi, are not as important as the differences between cylinders. You should not see more than 14 psi difference between cylinders. Don't assume anything bad if you find a "soggy pot" you may need to check valve clearances and re-test. In a perfect world, the valves would be in spec and the motor slightly warm before testing; but getting a basic reading now will help you understand what you may have to do.