Vibration is driving me insane... guess my vibration?

[CrazyCabbie]

Could a rotten muffler cause vibration? Like hand-numbing, mirror-blurring vibration?

My 82 Seca ran glass smooth even at 120km/h 2 years ago, but somewhere along the line it started vibrating the handlebars and pegs like a metal engraver.

I've replaced everything from sprockets to tires, bearings, swingarm bearings.
The steering head has no play... Valves are close to spec, it runs great in all weather, and starts easily even in cold weather. Idles fine.

I pull out the clutch at any speed and it glides smoothly, but revving it up with the clutch still in, it starts trying to vibrate the teeth out of my head again as soon as it hits around 3000rpm. Wondering if anyone could offer any suggestions...

It also has a slight knock when starting sometimes...

 

[Scorpio1963]

Im not completely sure on this but I beleive the pipes are double walled and baffles do come lose and vibrate but you would hear noise if its the exhaust sytem.Is your exhaust system rubbing on your frame anywhere?That could be a possibility.If you have a loose chain that would cause vibration.Dealing with vibration issues myself these are things I have been noticing.My problems with vibration were not caused by 1 issue but quite a few different things.Air pressue in the tires or wheel bearing are also things to check.

 

[markjs]

Eww, that sounds to me like possibly a piston rod issue...? I sure hope not! How many miles on it?

 

[Scorpio1963]

Gosh I must be blind I did see the part about the knock on start up.Yeah thats not good.Your either going be taking your engibe apart checking the crank for roundness and replacing the bearings which arent very cheap.
Alternitive # 2 replace the engine.

 

[CrazyCabbie]

Crap... I was afraid of that... I knew I recognised the sound of rod knock when it did it... Had a Camry that died that way... I just don't want to believe it
There are almost 70,000km on the motor...

Thanks for the replies.

I replaced the chain and checked for any rubbing parts too. Was really hoping that the sprocket replacements today were going to kill the bad vibes...

I guess I'd better search for a cheap spare DOHC motor/bike before it dies... I'd like to rebuild this one, but even tracking down the parts could take a long time...

Would parts come flying out and kill me if out let go, ya think? Or just die/seize?

 

[markjs]

Not likely but oil burns and a back wheel lock up at speed is no fun. Try turning the engine over by hand with a wrench and see if you can notice anything (not sure if that would work but without tearing stuff down it might confirm the worst). It isn't that hard to take apart this engine and you probably could tell without splitting the case (get the top end and cylinders off, if it's vibrating that much the play will probably be obvious from the top).

 

[Scorpio1963]

Just get a mechanics stethiscope and put it down on the bottom of the engine,Then listen.The engine might be easy to take apart if you have done it before but to somebody whos new to bikes well..........

 

[devdg]

Check your clutch for broken friction material or broken springs. Also check the bearings on the clutch for excessive wear that would cause bad vibration. Rod or main bearings make a very noticeable noise and it will sound like you have hammers in your engine not rods and pistons.

 

[Scorpio1963]

I definately hate hearing that sound.

 

[CrazyCabbie]

Thanks devdg and scorpio! I will definately check the clutch and clutch bearings out!
I don't have a stethoscope available, but I appreciate the suggestion. It reminded me that a steel rod held to my ear and on various motor surfaces will also work in a pinch. I'll have a closer listen.

It is starting to sound like a hammer in the right cylinder

On the upside,I'm moving into a ground floor apartment May first, so IF I MUST, I'll finally have the ability to carry an engine into my kitchen to dissect, lol...

 

[devdg]

if one cylinder is making the noise more then the other also try checking to make sure your carbs are in sync because one cylinder will do all the work and the other one will just float and that is very hard on any multiple cylinder engine.

 

[Scorpio1963]

That doesnt sound very good I hope that it isnt hammer time on the crank and bearing.If it is have you chose the option to dig in or r$r

 

[CrazyCabbie]

The procedure doesn't seem THAT expensive (2-300 bucks?), or even terribly hard (a month?) providing there's no scoring on the crank or case... Am I being too optimistic? I've done thousands of jobs on cars, but never bottom end work...
I think my next step will be gathering tools and buying assembly lube while I'm still mobile... Bearings and gaskets can be mailed cheaply, lol.

I'm still trying to figure out the best tool to measure the microscopic clearances of the crank and big end of the rod... Thinking digital calipers... There are several mentions during the (shop manual) procedure of Yamaha 'special tools' as well... My biggest worry at the moment is that I might not be able to find or afford something, once it's torn down...

 

[devdg]

Sucks that it is bottom end work, I would stop riding the bike now since it only gets worse.

Best tools are a inside and outside micrometer set, most can be had cheap enough at napa or other parts stores. A caliper is not accurate enough to get proper measurements for the clearances on a crank.

Normally once a rod bearing goes it takes out the crank as they tend to gouge the journal for the rod. Unless your bearings are installed wrong, I have only ever seen three bearings where they spun in the rod versus taking out the crank. Hopefully you don't need to replace your crank because you caught it soon enough but expect that the crank will need to be replaced and hope for the best.

I know not good news to hear

 

[CrazyCabbie]

Thanks for the info! even bad news I'd better than not knowing, lol...
Okay, after I move across town tomorrow I'll park it :'(
And now I know to get an inside outside micrometer set.

I notice there are two cranks for sale on ebay at the moment... If it comes to that.
What about having it machined? Or do you mean it might be beyond that?

Coming soon: The XS400 DOHC amateur teardown thread.

 

[Scorpio1963]

rod bearings can be hard to find and expensive for our bikes,I think your best option unless you just want the expereince of tearing down the engine.

 

[CrazyCabbie]

Yep, rod bearings are discontinued... Aargh!
I can find balancer and crank bearings no problem...

Seems the only ones I can find still in stock in North America are the 12E-11656-20, which I understand to be 20 thousandths 'undersize'... Does this mean I can use those if I have the crank ground down to fit?

I have no other vehicle to get a motor or bike, so repair is pretty much my only option...

 

[Lou Ranger]

... I appreciate the suggestion. It reminded me that a steel rod held to my ear and on various motor surfaces will also work in a pinch. I'll have a closer listen....

42 years ago, Dino my old Italian mechanic at the local SHELL station, used a wooden yard-stick and his ear to pinpoint and diagnose a bent connecting rod in my Morris 1100 (single carb). I had water flood in the carb while it was running
He said I could spend 100s of $$ to install a new rod or live with the knocking as it wouldn't hurt anything. He was right, I drove the car for 4 years without a problem - with the connecting rod that is.
Being a sterling example of British blacksmithery, the Morris had more than its share of other problems ...

 

[Scorpio1963]

Crazycabbie dont you have a buddy that get you rides to pick up an engine if needed?Under the circumstances you might just be better parting out the bike or looking for a replacement engine

 

[devdg]

Take your crank to a machine shop and they can measure and turn to match the bearings you can find, I will look around with some of my vintage suppliers and see if they can locate STD bearings.

If you can find a whole engine or a parts one that would be the better option. typically you can transfer over your working parts to fix one that has running issues.

Have you ruled out a broken valve or spring. Normally a broken valve will punch through the piston and thats the end of the noise unless the spring is broken then it will keep being hit and hammered into the head.