An odd Rattle...

The sound is more like a chain rolling through teeth, like the sound you get when walking a bike backwards, except louder. It is coming from the lower end. Not from inside the generator cover, just pulled it off and found everything pristine.

Compression shows an even nastier imbalance than before; Right side 155lbs, Left side 95lbs. Bad ring? When I pulled the left plug out I saw a bit of smoke (ran the bike a couple of minutes before to check sound location) but the exhaust only occasionally sputters out smoke, and typically only during start.

Its very tough for me to adjust the carb balance without replacing the crabs because one doesn't have a mix screw anymore, just a wad of trashed brass inside. I've attempted several methods of pulling it, with no luck. I can try to set the one carb to be equal to the stuck one. Both plugs show the same color of dark tan.

When I set the timing chain tension, I didn't notice much movement in the pin, only about a millimeter in and then back to flush, should there be more inwards movement?

TeK9iNe wrote:
"With the compression numbers you already posted - I would tear that thing down and start inspecting the cylinders - if no seriously noticable improvement in compression after vavlve adjust."

Robwolf:
"Compression shows an even nastier imbalance than before; Right side 155lbs, Left side 95lbs. Bad ring? When I pulled the left plug out I saw a bit of smoke (ran the bike a couple of minutes before to check sound location) but the exhaust only occasionally sputters out smoke, and typically only during start."

Time for a tear down, probably a wrecked piston from wrong Ignition timing, to far advanced. Pull it out, and apart. Bummer! But it will all be good again when your done.

Well thats too bad. You cant run with the compression that far off, you'll just wreck the rest of the motor over time.

Pop a couple teaspoons of oil in each cylinder thru pug hole, and turn it over a couple times with starter to disperse oil. Then repeat compression test.

If compression in a cylinder comes up sharply, (much higher compression like 160+) the rings/piston are suspects for replacement.
If the compression only rises marginally (like 20-30psi), then it could just be a leaking/warped valve or damaged valve seat.

Good luck.

Anyone want a 79 kz400 with bad motor? Just kidding. Guess the real fun starts tuesday. Gotta get my vulcan back in road shape so I have something. It only needs solenoid and magneto. Got one need to order the more expensive. I'll be sure to post pics of the kzs ugly guts when they come out. Also would like new[er] carbs suggestions? Street use commuter with highway in route.

Compression came up to 145 almost 150 with the oil in the cylinder. So valve perhaps? Working on getting the head off now.

Hunting down the broken parts. Got pictures of the process so far. Partly to document the procedure, partly to remind myself how it looked as it came apart, and partly to let you all judge the condition of the engine. Enjoy.

Now with the head off...








The "trouble" valves ^^^

The Cylinder block off...




"Trouble" Piston and rings ^^^^

And the block back on...

Improvised chain keeper ^^^

So as far as the fun meter goes its just about pegged out at 11! While I'm in here I'm going to try and at least clean things up a bit. Replace gaskets of course. Next step is getting the valves and their keepers out without loosing them in the nearby lake or taking one through the skull. I'll need a spring compressor, got one but it doesn't work with a bike motor, so it goes back to the store. I'll keep you up to date on all the fun as I go, though I'm sure many of you have experienced this before. I'll just say this is the first time I've gone below the head (That just sounds terrible!!) on any engine.

Definitely looks like the piston is Toast. Is that the side where you had the Rattle? The Piston to bore clearance is probably excessive. Hows the other side? Do you have any measuring tools?
You'll need to re-bore that set of cylinders, get new over-sized pistons and rings, then a valve job, gaskets etc. Thats just the Top end. It'll add up quick. Maybe shop around on Feebay, you might get a decent used set of pistons with the matching block. Then get a new set of rings for those ones. Still the head work will cost a bit, depending on the parts needed.
Are you going to pull the cases apart? Check the bearings for the Rods, clean out the Sludge etc?

Yeah I'm planning on working down into the bottom to check the bearing since nothing from the top has made its way into the bottom, seeing that it's all in place. Maybe I should just try to find a whole new motor, perhaps take that 500cc one off the Vulcan behind the bike? (It has its own trouble though).

Motor Head wrote: Definitely looks like the piston is Toast. Is that the side where you had the Rattle? The Piston to bore clearance is probably excessive. Hows the other side? Do you have any measuring tools?

The other side had good compression, and wasn't making much noise, so it's probably fine, but...

Motor Head wrote: You'll need to re-bore that set of cylinders, get new over-sized pistons and rings, then a valve job, gaskets etc.

If I'm going to do this, I'll obviously be trashing it too. I was wondering if Bikebandit.com part #761041 PISTON,0.020",O/S OPTION or #760913 PISTON,0.040",O/S OPTION was what you were referring to as "over-sized pistons." If so they aren't terribly expensive, and I'd just need to find a local shop to measure and bore out my cylinder block.