3500 rpm rattle part 2

I removed the top end this past weekend to check the valves and replace the piston rings trying to solve the mystery rattle at 3500 rpm, when the bike is being ridden. It does not do it while in netural. I had previously swapped out the carb set which did not resolve the problem. I took the stock exhaust system off and installed a MAC off my other bike which made no difference either. I have not checked the valves as I am going to install a spare head that I had just gone through. The cylinders showed no wear at all. No scuffs on the pistons or ring groove wear. All the rings were as they should be except for one cylinder that had the gaps all in a line on the compression rings. I measured the cam chain and it is in spec. The front guide showed some wear but not excessive. No wear on the rear guide. I am going to replace both guides and the adjuster springs.

The cylinders cleaned up very nicely with the glaze breaker hone. No abnormal wear noticed. Neither the wrist pins or rods showed any abnormal loosness. I did not remove the lower end to check the main bearings. I hope they are ok. This bike is fully dressed and has only been used for road travel so it has not been beat or ridden hard. The parts will be in Friday so I hope things go together ok. Compressing 4 pistons full of rings is a pain but I have been there many times before. Too cheap to buy a 4 cylinder ring compressor......I hope this cures my rattle problem.....chris3

where are you hearing the rattle noise?

It sounds like an exhaust valve leak, but a compression check does not substantiate it. The engine runs great up to the 3000-3500 rpm range then the rattle/knock starts. It seems to fade away as the rpms go higher. You can make it come and go with the throttle. I don't see any obvious exhaust gasket leaks nor any leaks in the head gasket. I don't have a leak down tester. When I did a compression check the readings were 140,120,140,140 dry and 190 across the board wet. I had replaced the clutch springs and did not notice anything odd with the clutch assy. Maybe a weak exhaust valve spring. One other thing, the rattle does not start until the engine is good and warm. The bike has 41000 miles on it........chris3

Let me guess, you give it throttle to accelerate at around 3500 rpm, and the rattle starts? Then you reduce the throttle and the rattle goes away?

Those are the classic characteristics of detonation, AKA spark knock.

Common causes:

Timing excessively advanced
Carbon buildup in combustion chamber causing increased compression.
Bad fuel (ie: not enough octane)
Oil mist in mixture
Overheated motor

And just possibly, a overly restricted exhaust, as in carbon buildup plugging it.
Not common though, usually that just causes reduced performance.

The timing is not adjustable, that I know of. I get my fuel at several different stations and running hi-test does not make any difference. There is very little carbon buildup on the head/pistons. The spark plugs indicate a perfect burn. I did a valve job on the bike 3000 miles ago with new stem seals. The bike uses oil because the base gasket leaks. However, it seems oil is blown out somewhere, I just cannot tell where it is coming from. It only blows out on my pants leg while riding. Could be a connection somewhere. No back pressure in the exhaust because I changed exhaust with no help. I have three of these bikes, 82 1100s, that I brought back to life. I have had 4 cyl Kaws since 73, and this one is the only problem child of the bunch.....chris

As far as overheating goes, I wonder if the Vetter fairing is causing the engine to run hot? The air passages between the inner cylinders and the cam chain opening were clogged with dirt. I found this when cleaning the jugs after removing them. I am not a hard rider and mostly under 50 mph riding back and forth to work and errands around town. Because of this rattle, I do not ride at highway speeds. I would hate to have a major breakage of whatever this is. I don't notice any more engine heat vs the other bikes I have. They are all daily riders....chris3

We have pretty well established that's it's detonation, so what we have to do now is find the cause of it and fix it.

If you are still using the stock airbox, and the crankcase vent hooks to it, then it's possible that excessive blowby is putting an oil mist into the airbox, where it's sucked in by the motor.

It's also possible that something is wrong with the timing advancer or something else in the ignition. It's pretty simple to check the timing and verify that it's correct.
I'd start by putting 1&4 pistons at TDC and checking the timing mark to make sure it lines up, then I'd put a timing light on it and check the timing at idle and at 4000 rpm.

You have done a lot already, and you still have the problem, so now it's time to start with the very basics and work your way up till you find the problem.

I have been a mechanic of one sort or another for most of my life, and I couldn't begin to count the times I have had to start all over from the beginning and go one step at a time till I found the problem. Generally it's something weird that no one's ever run across before, sometimes it's something that's so basic I never thought to check it.

The faring on the bike will make you hear noises that you normally dont hear, and since it is at the rpm when the timing advance should be moving, just wondering if the springs are weak or there is some play in the unit causing erratic timing movement

Sorry I did not respond yesterday. I cannot log in from home.

You have a point there with the oil mist. As I said, oil seems to be blown out the left side of the engine onto my pants leg. The number 1 cylinder has the compression rings gap lined up which would allow blow-by. The number 2 cylinder had low compression, 120. The crankcase vent hose to the air box is in bad shape and I have trouble keeping it attached, so I don't think that is the problem.

When I got the bike, it had a somewhat sluggish accelleration. I discovered the mechanical advance was very stiff and I doubt it was working properly. I removed it and cleaned it up so it seems to be working ok now. It had never been removed before. In fact, this engine had never been apart before I got it.

So, when I get it back together, I hope the new rings will solve the possible oil blow-by problem. I can then check on the ignition advance and if it is giving me problems, I will swap it with the advance assy from my other bike.....thanks for all the help....chris3