1980 xs making knocking noises under throttle! HELP!

[xHolepunchx]

Last night I had my 1980 xs650 on the highway going about 70 for about 20 minutes. It started making somewhat of a strained noise, on the right side, kinda like a scratchy squeal and the piston hits were becoming more audible even over the highway noise.
I tried to make it to an exit to check some things, but before I could make it that far the bike briefly lost power and bogged. I went from 70 to 45 and couldn't get the throttle to respond with anything more than a feeble pull from the engine. I pulled off to the side, and shut off the bike for a few minutes.

I started it back up and it seemed like it ran fine after a brief cool down but the idle was about 2000 opposed to the 1100-1200 it usually runs warm. I hopped back on the interstate and it was good for a couple min, and then by the next exit was still making a bit more noise out of the right cylinder, so I pulled into a gas station.

Recently the bike had been making a light popping in the exhaust until warmed up on de-acceleration, so I thought maybe that cylinder was running lean and causing an overheat issue. I re-set the mix on the right side to a slightly richer setting and checked the plugs (both looked fine) and started her back up. Running at idle, no unusual noises. Revving in neutral, no unusual noises.

So, now off the highway, I rode it around the gas station parking lot and could hear the noise a lot clearer, it sounded like a hard knock coming from the top of the right piston, but only when moving in gear and when pulling on the throttle. I had to drive it a few more miles and as I drove it i went very easy on it. Even at low throttle it doesn't make the noise all the time, but at takeoffs and acceleration it would become very audible. If i pull the clutch and roll it stops, if I let off the throttle and let the bike coast with the clutch engaged, it makes no added noise (even at higher rpms, in lower gears).

It will also make the noise if while moving in gear I pull the clutch and then roll the throttle, but wont when the bike is in neutral just sitting still and I rev. This is not leaving me with a very definable situation to look into, any old pros ever run into anything like this. I have the biked garaged till I can figure it out out of fear of blowing the engine even though she seems to run just fine aside from this noise. Any help troubleshooting is most appreciated, and I thank you in advance.

 

[xHolepunchx]

...also, the only thing that has changed was I had to put 93 octane in the bike because the gas station near me didn't have 87 or 89 the day I filled up. I know usually higher octane gas is used to AVOID knocking, could that have any bearing? I'm going to re-check the cam chain tension and valve clearances AGAIN tomorrow if there's a possibility that that could have anything to do with that.... thoughts?

 

[bdholsin]

On a not about the octane...ever notice that our bikes (mine at least) calls for leaded gas?

91 or 93 octane would be fine. That's what I put in my bike. The higher octane is an "equivalent" to leaded gas.

 

[xHolepunchx]

ok, so its not the gas i put in... anyone have any other ideas

 

[jamesgs4]

tear it down and find out, or ride it around until it fails catastrophically.

 

[ReycleBill]

You're right, higher octane isn't a problem.

Spark knocks are usually more like a hard ping than a knock. I'm assuming on an '80 you have electronic ignition so any timing issues would affect both sides of the engine and not just one side. Noises as you described and the fact that the engine lost power is a definite concern and a knock on one side suggest possible internal damage.

Drain the oil (both drain plugs) and look for shiny stuff. (Shiny is bad.) If you refill it make sure you are running a motorcycle or diesel oil as automobile oil won't do.

Pull the spark plugs:
White or tan plugs suggest lean overheating. Lean engines run hot and hot engines run lean-- it's a viscous cycle.
Oil soaked plugs suggest damage.
Plugs soaked with gasoline indicate too rich-- a condition that will wash the oil off the cylinder walls, cause excessive wear, overheating and eventual engine failure. If you have a stock ignition system then that probably won't be a problem as these bikes tend to foul plugs and quit running before cylinders get ruined. But an aftermarket ignition system might fire hot enough to clear the plugs and melt down the engine.

(I'm not saying aftermarket ignitions are bad but that they might be too good if the mixture is too far out.)

High idle suggests stopped up pilot thingie in carb.

PS. If your engine has points then check the timing on both sides.

 

[xHolepunchx]

Ok: its stock, electric ignition. Plugs look a little tan on both sides, no signs of oil on the plugs. Airbox and mufflers are still stock. I'm gonna try changing the oiland straining it tonight or tomorrow. Looking into the spark plug holes looks like valves and everything are moving correctly. Haven't had the valve covers off yet to inspect clearences yet since this incident. Could a rocker or cam chain tension issue possibly cause a noise only under throttle and in gear? I would imagine that those would make noise anytime the engine was running in general... Seems strange the times that it actually makes that noise. Thanks, I really hope to isolate this without a blind teardown.

 

[ReycleBill]

Tan plugs indicate lean/hot. If the engine were liquid cooled I'd aim for tan plugs but on air cooled engines I go slightly rich to be safe. Also, do a compression test.

Cam chain too tight might cause some of your symptoms but I've never seen it happen. Cam chain too loose will cause timing problems and be noisy.

Are you sure the noise came from the right side?

PS. Only in gear and moving suggests a seized/trying to seize bearing(s) in transmission but don't go there yet.

When you strain the oil:
Black plastic is from cam chain guides.
Aluminum is most likely from cam chain guides.
Steel is bad, very bad.

Use a magnet to test metal: Sticks to magnet = steel.

 

[irristeve]

sounds like youve siezed a piston,had simular on my old engine,was running flat out 2 up for about 10ks when it lost power sudenly,upon next start up had clacking noise,rode it around a bit after that,keeping revs low etc.eventurly pulled it down,left piston had bad scouring on skirts good luck

 

[xHolepunchx]

Well this am I changed the oil. It looked clean, no noticable rubber/plastic or metallic shavings, just a very little amount of non magnetic powderish metal scattered sparingly in it, but nothing worth noting really. I checked the valve clearences, they were loose a little on the intake side for both cylinders, but not by much and I re-adjusted them to specs. I made sure the cam chain tensioner was cool and it was. I removed the right exhaust pipe and no metal shavings present in the exhaust side of the head. Pulled the spark plug and looked inside the cylinder. Piston looks ok, what I can see, and moves smoothly in the bore. Valves are moving smoothly. But, I fire it up and it knocks near the top of the right cylinder when I pull the throttle while in motion. I did try pulling the right plug, with the plug out of the hole the engine runs and the noise is gone. I did notice that the plug was sooty this round, suggesting rich mixture, which I had previously adjusted for... Is it possible my mix or cab balance is so far out that it could make some goofy noises? I'm about to tow it to the local yamaha dealership to have them take a listen. Shitty that its beautiful weather and 4th of july weekend...

 

[ReycleBill]

Non magnetic metal suggests cam tensioner worn out.

Piston pin? Rod bearing? Cam bearing?

But before you go there, check for weird stuff. I once had a loose bolt on my fairing that sounded like an engine noise under acceleration. Pipes sometimes rattle and sound like a knock. Look for anything anywhere that is loose or broken.

Have you done a compression test?

Another test:
Pull 1 plug wire
Pull spark plug.
Hook plug wire back on plug.
Figure out way to clamp spark plug to ground (This is important as an ungrounded plug will fry electronic ignition.)
Crank engine on one cylinder, ride and listen. Will run like a 50cc mini bike only worse.
Put it back together and repeat for other side.

Rod bearings and piston pins are usually quiet when cylinder is dead. Crank bearing still knocks.

And I can't stress this enough: make sure plug is grounded.

 

[xHolepunchx]

yeah, I pulled the plug today as a run down of the troubleshooting steps Ive been trying and it doesn't seem to make that noise with the plug out and run it with one cylinder. I had it grounded to the fins, seen coils go boom before! Put in the plug and fire it up and its there. I'm noticing its not consistent at middle rpms, it comes and goes, but its in the engine, I definitely looked high and low for something loose/vibrating in hopes for something simple... Seems to not be AS prevalent when I lean out the fuel mixture... but still there through most of the power band. Or maybe Im just grasping straws on that one. I'm assuming riding this thing as it is is a ticking time bomb huh?

 

[ReycleBill]

yeah, I pulled the plug today as a run down of the troubleshooting steps Ive been trying and it doesn't seem to make that noise with the plug out and run it with one cylinder. I had it grounded to the fins, seen coils go boom before! Put in the plug and fire it up and its there. I'm noticing its not consistent at middle rpms, it comes and goes, but its in the engine, I definitely looked high and low for something loose/vibrating in hopes for something simple... Seems to not be AS prevalent when I lean out the fuel mixture... but still there through most of the power band. Or maybe Im just grasping straws on that one. I'm assuming riding this thing as it is is a ticking time bomb huh?

I'm certainly no expert but if it were mine I'd be pulling the engine from the frame at this point.

 

[xHolepunchx]

OK, took the bike to a local Yamaha specialty shop, and one of the guys there had been selling/servicing xs's since they first came off the line. He said it was mid-cylinder knocking, eliminating cam and valve related things and lower end. Hec checked the cam-chain tension and poked around a lil bit. He suggested it was possibly looseness in the wrist pin. I know to crack into the top end I'll need new gaskets, and might as well put in a new cam chain (he said mine was getting to a stretched point) and I would imagine that I need the the wrist pin sleeve and clips. I wanna make sure while I'm in there I check everything still, out of fear that the top of the con-rod would be worn not the wrist pin itself. How do I go about checking proper tolerances to ensure that the bottom end and con-rods are set and to ensure that when I re-assemble I find and re-new any/all the worn issues. Gonna be fun as I like to tinker, but I really wanna do this right the first time. I have a manual, but there are still things that I dont knwo what Im looking for. Anyone been here for this issue before?

 

[XSLeo]

Your repair manual will tell you how to check for worn parts. Read it.
Leo