Camchain Noise: A Solution


Ok, major work.

I have always had a very noisy engine, the cam chains particularly on the right hand side or rear cylinder make quite a bit of noise. The dealers mechanics could never eliminate it or pin it down. I have opened it up a few times myself trying to figure it out.

Recently I was just passing the bike on the way to get into the cage and whilst staring at the thing I was idly fiddling with the starter button, just pushing it enough to get the engine to turn over but not to fire. Yes it’s a stupid thing to do but… stupid is a stupid does. Suddenly it back fired and something didn’t sound right when it did.

I started it up and now there was a totally new loud and very worrying valve type noise going on?! Something was definitely not right.

The thought of having to go back in was a bit irritating but, along with fixing this new problem I was determined to find out once and for all what was causing the clatter. As I got into the valves I realised that the front cylinder cams were completely away from where they should have been at TDC. AHHHHH feck! This could be really serious!

This is what I think had happened; when it backfired there was no oil pressure to keep the cam tensioners tight and in turning backwards the chain had slipped a couple of teeth. When I ran it straight after what I could hear was the valves running totally out from where they should have. It was possible that the chain may have slipped enough to have the valves hit the top of the piston. So to check this I had to take the head off. This was turning out to be a lot more work than I had anticipated.

It was at about this time that I decided that if I was going to go this far in I might as well check the lengths of the cam chains too. I really do not believe that my motor is just a “noisy one” and decided that I was going to replace my cam chains and cam chain guides and to try to see if I could not figure this irritation out.

That got me to here. No damage to the piston or valves, I was lucky.

To get the cam chains out you have to take the balancer shaft out. That’s the shaft above the flywheel/rotor.

To get that shaft out you have to undo this nut on the other side.

It is impossible without locking the engine with the locking bolt. Once that is off there is a special little torture test getting the two woodruff keys out of the shaft to get the balancer and cam gear off.

Once I got those off, I finally found what I believe is has been causing the clatter that I get from the engine. This is the left balancer; you can see the rear cylinder cam chain has bitten into it. The wear is all the way around the balancer – deeper where it picks up the chain and less as it turns.

The guide for the above balancers’ chain is the one on the right; you can see that the chain, unlike the one of the left, does not run straight down the guide. There is very slight play in the bearing of the guide (but the play is the same for both).

The locking screw for the balance shaft bearing on the right side of the motor has also seen some wear from the cam chain;

The cam chain for the other side has also worn the balancer although not as bad;

I did check the cam chain tensioners and the length of the spring that regulates the oil pressure. All were in spec. Ultimately what happens is that for some reason the cam chains operate very close to the balancers. The balancer clips the chain and causes the perpendicular flutter that cannot be damped by the tensioner and causes the cam chain clatter that can be heard at lower revs. It also sets up some horizontal movement that then bites into the bearing retainer screw.

I consulted with the head of technical services for KTM in South Africa. He was pretty helpful and suggested after chatting to the propeller heads in Austria that the balancer shaft bearing may be at fault and I need to get them out. They think that the shaft has more play left and right than it should have and the left hand bearing is supposed to prevent this.

How do you get the left balancer shaft bearing out? Good question. That’s the one next to the worn screw in the above picture. There are some expensive solutions that call for splitting the cases or bearing pullers but a simple method is…. A broom stick! The left hand bearing... the one above the crankshaft here

has a bigger inside diameter than the right (the one I wanted out) and amazingly I happen to have a broom stick that happened to be the right diameter to fit through the above bearing yet not the right and I could drive the right hand bearing out from the left hand side. A word of caution though…

This left bearing has a race in it that has a lip on the engine side of it that prevents the race from falling out.

There is a retaining lip on the inside of the case that stops the race from coming into the engine. This retaining lip does not run the whole way round, it is a half moon. When I drove the bearing out the race got stuck on the broom stick. I didn’t see this as a problem as all I had to do was now drive the broomstick out the race. What I should have done was pull the stick all the way through and pull off the race. But I just gave it a few taps. The race came off the broom and promptly fell into the crank case. This happened because the case lip does not go the whole way around the case. The race once it came off the broomstick, fell into the case. So there I was swearing that I had a race sitting somewhere deep in the bowels in-between the cranks somewhere. It is a very depressing predicament to be in. Fortunately for me I had already taken the front cylinder head off. So I was lucky in that by turning the front cylinder to TDC and pulling the barrel up a bit I could see the race nestled at the bottom of the crankshafts and it was easy to hook it out. You don’t want to have to do this.

The bearing had quite a bit of lateral play in it. So I think that the balancer shaft was able to move laterally, this causes the balancers to catch the cam chains and causes the clatter. What I think is the cause is that the bearing had not been pushed in far enough and had not seated properly. this allows the race too much play and thus the shaft can move too much and causes the cam chain flutter when the balancers nick the cam chain.

Those bearings are expensive. But then anything with a KTM sticker is. In hindsight the old bearing is fine, it just needed to be driven in a bit more. Ahh well I now have a new bearing in there.

Now that that had been changed, to the cam chains

Old vs new one. Interestingly I couldn’t find any wear marks on the chain from hitting the balancer. They both are markedly longer than the replacement ones.

Rear cam chain with replacement

Front cam chain with replacement

I also bought a pair of the longer tensioner bolts, they are about 5mm longer, sorry I didn’t take a pic of them.

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