Next Engine, please

[trbig]

You might be able to set it up on the center stand, run it, and use the rear brake to put it under a load.

A loose primary chain sometimes slaps around, but it's usually only going to do that at idle with carbs un-synched.

As many problems as I've had in the past with the crank bearings on these, that's always my innitial thought when I start hearing those noises. But a crank knock sounds deep in the motor, not a chain noise. An evening to pull the motor and pull the bottom case off to check on that may save you an engine case and crank. A spun bearing will ruin both. BUT.. usually you will get an oil leak out from around the crank seal before that happens.

I have no experience with a piston clip coming off, but don't really see how that would cause a constant knocking. The pin could contact the cylinder wall and rub, but there shouldn't be any constant lateral movement to speak of. The pin would stay inside the piston.. but I guess constant forces too far on one side of the piston could wallow out one side of the hole. If it was a constant and sounds up higher than a crank bearing, then I might look at that or possibly the rod bearings. Were those replaced in the rebuild? If so, were they replaced with the correct size according to the rod stamps? Those "Correct sizes" only count if there's no wear to the crank. Putting in the "Right sizes" when the crank is slightly worn, will let there be some movement in the between the rod and crank. It would last a little while, but then start knocking more and more. I had one that I replaced all the bearings on to the correct size, and 2500 miles later, they were junk.

So, if you deplete all of your non-invasive ideas about timing and such, you might look at the bearings. Just a suggestion. You could also run the motor and get things stirred up, drain it into a screen, and see if there's some copper looking shavings that don't sick to a magnet.

Tod

[petejw]

jat,
with the rev range your describing,
that might indicate something with the mid range
circuit of the carbs (lean or rich) you could try
turning the mixture screws half turn either way and take it for a ride
and see if there is any difference, it could also help rule out detonation.

[Crazcnuk]

I don't think it's rod or main bearings. The sound is not 'deep' enough. This noise sounds like a nut bouncing around inside an aluminum case, just a little more steady.

Also, the noise is not constant. It does not occur under 4000rpm, until I have revved up to 4000. After that it will sometimes occur down as low as 2500rpm, but it kind of has to be 'broke loose' first. Sometimes I can't make it do it at all, and other times it won't go away anytime I am adding throttle. It never occurs on decelleration. after 5000rpm or so it goes away.

I don't know what a loose wrist pin (missing retainer) would sound like either, but I reused the old clips, and have read that is not good.

Like I said, to me, it sounds like a bad hydraulic lifter. It makes no noise until you give it throttle, then the lifter gets flattened and you have a relatively light valve train rattle.

My first though was a loose valve, as I had set them on the loose side when I did the rings. So I took it apart and checked. I went one size thinner on all 4 intake, and 2 exhaust shims. This made no difference to this particular noise.

I have 2 seperate noises. Right now the valve train is really noisy at idle, especially when cold. This quietens as the motor gets hot, but is still noiser than it should be even when hot. This noise I wqas able to quiet by adjusting the cam chain, but it came back a few days later, and now adjusting the cam chain does not help.

Then I have the 'under load' noise. I don't know if they are seperate issues, or related.

[Ivan]

Are you sure it isn't the knock sound described in the TSB that had a different advance pod for a fix? Can't get that part now anyway, but the TSB says it won't hurt the engine. The old engine in Red did that, and it was off and on like you describe, and always from 4-5000. I learned to live with it. Red is one cranky SOB.

[XSokieSPECIAL]

Have you checked for exhaust leaks?

Kinda sound like it might be a cracked head pipe.

[Crazcnuk]

Derwat was thinking exhaust too, he came for a ride with me to listen to it. However, I can't find where or how it would be making this noise.

You have to remember this just started, I've got 30,000kms (on two engines) on the bike so I know all of the 'normal' wierd noises.

If I can get the 78 running nicely with no untoward noises, I will probably move all the touring stuff onto it, pull this motor out, take the head off and put it on the 79 Special (bent valves).

[petejw]

"This noise sounds like a nut bouncing around inside an aluminum case"

thats what pinging sounds like,
if you dont wanna try playing with the mixture screws
try running a higher premium fuel.
or if its an engine with adj timing, retard it a cpl of degrees.

[Crazcnuk]

Heh, you'd have to go and read about 100 pages of what we've done with the carbs to know that playing with mixture screws is minor.

I don't think your getting the picture. I KNOW what the normal 4000rpm ping sound is, and this new one drowns it out by about 30 decibels.

This noise is audible to people riding beside you on Harleys with Monster oval pipes and it makes them think the bike is about to handgrenade all over the road.

[petejw]

relax, ive read your previous posts,
is this the bike that has the float levels
2mm under stock?
i wasnt refering to the normal 4000rpm knock, pinging can happen at
any rev range under load,
i was just trying to give you a cpl of cheap and easy
options to try out.


if it was a loose circlip, it wouldnt last too long
in the engine before it was chewed up and spat out,
the noise wouldnt come and go.

[Crazcnuk]

Yes, this one's floats are down 2mm. Mains 120 (up from 110) stock pilots, MikeXS adjustable needles w/ matching tubes.

I replaced the rings and cam chain last spring. I read that reusing the wrist pin retainer circlips is not a good idea, if you can get new ones. That is why I was wondering what that would sound like.

I don't mean the clip bouncing around, I mean the pin hitting the barrels occasionally.

[petejw]

if your happy that you put the circlips in place
securely they wont pop out, ive done many over the years
and never had a problem.
ill send u a pm.

[kjohnson]

i don't know if it would be the same kind of noise, but when i first got my XJ, it made a kind of knocking noise under load. it turned out to be the tip of the primary chain guide had broke off and was getting tossed about with the oil. not sure how it broke as the primary chain didn't seem to touch the guide at all. removed the piece via removed oil pan and it was happy again, until i threw a rod. po really didn't take care of it at all.

[Ivan]

Heh, you'd have to go and read about 100 pages of what we've done with the carbs to know that playing with mixture screws is minor.

I don't think your getting the picture. I KNOW what the normal 4000rpm ping sound is, and this new one drowns it out by about 30 decibels.

This noise is audible to people riding beside you on Harleys with Monster oval pipes and it makes them think the bike is about to handgrenade all over the road.

That has to be and awesome feeling, making the Harley guys annoyed with all the ruckus. Sure you want to fix it?

Wrist pin area noises have a unique sound in about any engine I have ever heard with that problem. It is kinda like a heavy engine knock but different. Hard to describe, but if you find this to be the problem, for sure you won't forget the sound. I wish I had dealt with that in more recent history, so I could give a more concise description. If it is that loud, and comes and goes in that way, its very possible that you could have a wrist pin problem somewhere. Has any foriegn object been introduced into the cylinder(s) lately? You discription somewhat sounds like a compressed skirt from the piston hitting something on one side of the cylinder and smashing the other side skirt using the wrist pin as a fulcrum. It allows the piston to rock and makes all kinds of racket at different times. I learned this from a pop rivit that got in under the carb on a minivan I was working on. A 15 minute job that turned into a 3 day ordeal.

Hope you find the solution. Sounds like it isn't going to be easy, and with that level of noise, I'd bet you have a trip into the cases. The good news is that its about as simple as anything else on the scoot. My adolescently bumbling 12 year old and I had my engine out and split for inspection in about 45 minutes. Not sure if he was help or hinderance, but he sure tried to help.

[Geezer]

It could be a cracked piston skirt or perhaps a piece has broken off. With a noise of that magnitude, it warrants a tear down.

Geezer

[Crazcnuk]

Well, it's moot now. Thi engine just entered the 'paperweight of the year' contest.

I took the iridium plugs out and put some regular ones in. Took it for a trip.

The rattle was the same. When I got to Edson, about 50miles, a new noise hard started. Lower int he rpm, and lower in frequency and tone.

The bike also started stalling at intersections.

On the way home the noise(s) were drowning out the normal engine function sounds.

It was also losing power. It could keep 120kph on flat stretches, but lost speed on hills.

About 5 miles from home, it made a couple of nasty noises, and a mile or so further, it let loose. The rod punched 4 holes in the crankcase and took the side out of the piston.

The broken rod bolts are in the bottom of the case.

Strangely enough the crank looks fine. I can only assume that the detonation finally beat the rest to the point of failure.