It Sounds Like A Spark Knock.. What is it?

[DJChrisp]

I have put about 45 miles or so on my HT and now for some reason when I lay into the throttle a little or when it is at a higher idle or going up a hill it is tapping or knocking. I have been following the break in procedures very closely with a few short sprints but other than that it has been running great since the knocking started. What could be causing this? Should I be worried about it or just keep riding? Any and all ideas welcome...

 

[MikeJ]

DJChrisp -

I know your condition well; it happened to me twice. The "tapping" or "knocking" will continue for a few dozens of miles, then the engine will run but you will have no drive to the rear wheel.

That happened to me twice: The screw holding the 20-tooth little gear is working loose. That tapping is a symptom. The loose screw allows the 20-tooth gear to slap around the 82-tooth gear on every cycle. If that screw gets too loose, the tiny half-moon woodruff key (under the screw head) holding the 20-tooth gear is getting beaten senseless and is being deformed a little and may fall out. Then you have no go power to the rear wheel.

Fix: take off the right-hand side reduction gear cover. Spread a large clean cloth under the engine, just in case that tiny half-moon key falls out. Don't lose it! If the key has not fallen out, get a big screwdriver and check the tightness of the screw. If it is loose, take it out and apply a little oil or grease to the threads. Then tighten down the screw as tight as you can. (I found that oil or grease works better than blue locktite.) To keep the gears from turning, jam a piece of wood into the gear teeth. Don't use a metal shim or screwdriver blade; you risk breaking teeth that way.

While you have this cover off, apply just a few little dabs of axle grease on the gear teeth. Or maybe a few drops of heavy oil. Go light; the excess gets slung inside the cover making a mess.

Reassemble everything and go riding! The pinging should be absent. Be aware that the looseness may return a few hundred miles from now. (I once lost complete power transfer while 60 miles from home. Good thing I had a set of select tools and cloth with me. I fixed a fallen-out woodruff key along side the highway!)

MikeJ
920 miles and counting

 

[DJChrisp]

Well MikeJ thank you but this was not the problem. As soon as I read your thread I ran out and checked the screw and it was incredibly tight. But thanks for the tip & I will be sure to check it regularly. I also started it & went around the block while I was outside so I could try to pinpoint where it was knocking/tapping (it's a tap at idle and a light to med knock while riding) & it seems to be in the area of the piston or under it. Does anyone else have any more ideas? Please Help!

 

[AussieSteve]

Sounds fairly ominous. At this point, I'd be removing the head and barrel for a closer look, if you're sure it's the motor and not a drive-train problem. ie. If it's not something like the joining link going over the roller etc. I'd also check the countershaft sprocket first as well, before pulling down the top end.
<edit>As an afterthought, it also wouldn't hurt to remove the magneto cover and check that the rotor is not loose and that the windings are screwed down tight and not rubbing on it.<edit>
Then, once the barrel is off, see if the piston is loose on the con-rod or if the con-rod is loose at the big end. (There may be some side-play, but there should be no noticeable end-play.)
Good luck.
... Steve

 

[MikeJ]

Oh well... Some days I guess right, some days I don't.

Here is a shot in the dark... Try a sample of high octane gas in your next tank. Half a tank will be plenty. Run the tank dry so low octane fuel does not contaminate the test. The compression ratio of these engines should allow the lowest octane fuel available to be run through them without pinging. After this, I am out of ideas. I hope someone has the answer.

 

[DJChrisp]

Now What?

I have checked and tried all of the above suggestions and everything is tight and solid. Drained the fuel (87) and ran it dry, tried 85 no difference in knock but a little spunkier then repeated above and tried 89 slight loss of power but still knocking! Where do I go from here?

 

[MikeJ]

Hmmmm.... Your observations make me wonder if my assumptions about the loose gear screw was correct. I also had the many hours of pinging you are hearing, and I had the very same concerns. I fully expected the cylinder to blow a hole or the piston crash into the bottom case. It never happened. I don't have any better a recommendation than before. Maybe parts are setting in? I will also note that after a hundred miles or so, I went to a full synthetic oil and have had little pinging since. After a total of a few hundreds of miles, the engine ran stronger than ever and continues to run great with no mechanical nor electrical problems. (Starting a cold engine takes some effort, though.)

I don't know what else to recommend... Hang in there? My latest ride of 127 miles cycled the engine over 1.2 million times. If it was going to break, it had all the reason in the world to do it on that ride.

 

[Al.Fisherman]

Let's start with....Have you made ANY mods to the engine what so ever????? Sometimes something so simple fails to be mentioned.

 

[DJChrisp]

Nope no mods. Still stock.

 

[andynogo]

Mine makes all kinds of terrible mechanical noises- these are simply noisy engines.

Of course it could be a bearing failing at the little or big end, but I doubt it. Have you tried the soundproofing mod for the clutch cover where you line it with cardboard or thin rubber sheet? That can quieten things down.

To be honest, I'd just keep on riding it. If you're really concerned, take the head and barrell off and have a look and feel for damage- doesn't take long at all to take it off and put it back on again.