Loud clicking/knocking sound from cylinder head

Hi Peter, 

While the head and springs were off, did you check that the offending valve was free sliding in the guide? Could be lots of reasons for it not to be, from burnt on oil deposits, slightly bent stem, even not enough clearance between valve and guide (although the last one is usually a hot engine issue). 

Otherwise, are there any 'witness marks' on the pushrods? If you have the larger diameter 650ss pushrods, they can touch/jam in 99 barrels/heads. 

Regards, George. 

Peter,

My 650ss (With a none 650ss head) has the same issue.

I have covered over 2000 miles like this. Otherwise it runs GR8.

I wrote to the forum a week ago because I thought it might be cam bushes?

Al Oz replied and suggested cam followers and I think he could be right, barrel coming off at the end of the season. Before all this political nonsense kicked off, I had the head off and found a few witness marks but nothing much. All went back together and the noise was as before and remains.

Building my Dommie Racer, I never realised how easy it is to put the cam followers in facing the wrong way.  Just a point. 

Not failed to engage a push rod in either the top or even bottom cup?

When a cam is driven by the crank, any backlash in the timing gear is taken up. As a cam goes over the top of the lobe, the load from the valve spring now tries to turn the camshaft and all the backlash is suddenly reversed.

Any wear or slack in the timing drive train can cause a clicking sound as the slack is taken up. When the engine is running, this may not be noticed. 

Triumph twins and triples make this noise with worn timing gears. My pre war Norton OHV and BSA make quite a pronounced click if you turn them over slowly. 

Not necessarily.  When the inlet valve on one cylinder is closing the exhaust on the other is starting to open so the valve train is loaded.

When an exhaust valve on one side is fully open the piston on the other side is on the compression stroke so there is nothing to load the drive train, hence the noise.

Put the dodgy side on compression and pull out the exhaust rocker spindle.  Check this spindle for steps near to each end for wear that has left a small ridge or step.

If there is bad wear in the form of a step or ridge, this may be the cause of the click. This is not uncommon on low pressure return fed rockers. A worn oil pump leads to poor scavenging, which in turn leads to a poor rocker supply. Especially on a cold engine start-up. 

A  rocker that is not sufficiently lubricated will wear both the spindle and the rocker itself. See attachment.

Hi Peter,

My issues are the same as yours and have been since 2011 and over 2,000 miles.

Performance is excellent with 70 mpg and the wind drowns out the noise above 50 mph.

I started off by checking the head, since mine is none standard 650ss but an earlier single carb job. I changed the rocker spindles as advised and checked oil supply to the head etc, all well. I often wondered if the thicker 650 pushrods were the problem given a few slight witness marks that were dressed.  I don't think so. Tick over produced the most knocking.

I bought the engine as rebuilt so not had the barrels off yet.  I might find the same as you? One thing that did quieten things down a bit was tightening (Slightly) the cam chain. 

I'll keep an eye on this thread and I'm sure we'll get to the bottom of it as I have no such issues with my standard 99 or Mk 3 Commando. Have you asked Dale Middlehurst yet?  

Check the timing gears and sprockets fit on the shaft key, I cured a really noisy B40 by changing the crank timing pinion, the old one had a worn keyway and was moving back and forth depending on the spring pressure. Despite the crank nut being torqued correctly and the tab washer used the nut loosened enough to move. New keys will be needed too after the pounding they get.

John's suggestion is good..... anything loose, at either end on the crankshaft,  may be the source of the noise. Alternator engines are well-known for the rotor floating about.

The mention of a rebuilt engine can ring the alarm bells. An early engine with later valves might end up with a rocker thumping the top of the head. The wrong pushrods will definitely cause problems.  Is a valve sticking and touching a piston?  Are the pistons the correct way round?

Has this rebuilt engine got  rollers on each end of its crankshaft? Add a double speed oil pump to this and the crank can get pushed sideways. Generally this just causes a ticking noise like a loose pushrod end.

As Al says the problem could be a very worn follower or tunnel or both.

On barrels bored to +60" the left side piston skirt is perilously close to the top of the breather tunnel. Any sideways piston float and the two can touch.

If you firmly believe that the noise is definitely in the exhaust valve region then this narrows down the list of potential sources.

As mentioned before I would be pulling out that exhaust  rocker spindle and checking it out for wear along its length.. Early Dominator cylinder heads had a reputation for oil starvation causing the rockers to partially seize on the spindles. This promoted wear of both spindle and rocker. Cruicially, the spindle would also turn in the head wearing out inner socket end. This in turn allowing the spindle to move about when the pushrod operated and a clicking noise resulting.

Careful levering, of the inner spindle end with a rod or screw driver, might allow you to check for wear and movement without pulling the head apart.

I had had "clicker" once that ran fine and it turned out to be an inner valve spring binding on the inside of the outer spring.  I also had another "rattler" that was caused by loose ball-end on the rocker.  It also ran fine and was difficult to spot.  When the pushrod was removed the hydraulic effect of the oil kept it in place in the rocker but when it was running it moved up and down in the rocker and acted like a very fast toffee hammer - curious.  Peter, did you say that the heat insulation washers are in place between the head floor and the valve spring bottom cup ?  Good Luck ! Howard

HI Peter I had a loud clicking noise on a low mileage Commando that came back from USA.It was on the left hand exhaust. I found the rocker arm was being pushed to one side on the shaft and compressing the thackeray washer by the push rod which was rubbing against the tunnel in the cylinder head and the clicking noise was the rocker arm sliding back on the shaft and  striking the inside of the cylinder head, this could be seen by removing the exhaust rocker cap and turning the engine over slowly. The fix was to put a rotary file in a battery drill and ease the pushrod tunnel out to clear the the pushrod.This must have been like it when it left the factory. Ease fix but a buger to find. PS the pushrod was not bent.

Good luck with that, Peter.

I changed all of mine from scrolled to plain, didn't make any difference. Putting my finger on the return feed in the oil tank, with the engine running obviously, muffled the noise a bit (With excess oil) though oil was getting up there anyway.

I look fwd to hearing how you get on, when you have time.

Have you checked the valve guide. Domis have a habit of the guides being loose in the head.

For me it was the simply ball end of a pushrod not being in the cup properly.