Valve adjusters

.... it certainly seems that deeper investigation is needed.

The cam chain is fine, no jerk when the snap occurs.

I had hoped not to have to split the engine, but it looks like I will have to.

Maybe the previous "builder" put in a 'special' cam

Thank you for your advice. The cam chain is correctly set, no unnecessary slack.

The cam seems ok, no sharp edges, smooth surface all over. The push rods are as noted in the AN website - 7.9 and 7.4

Is anyone able to tell me the sizes of the valve springs, the outer diameter of each, the inner diameter, the wire thickness?  I suspect maybe binding springs may be responsible.

...I mentioned is from the valve springs. Somehow the valve is being held open while the cam surface drops away, and then the valve suddenly is released resulting in a loud snap. It's regular on every rotation, both cylinders. Even turning it over very slowly, it is there as the valve is closing

Some investigation today:

 - There are no marks on the the pistons, valves, head suggesting contact. Anyway, such contact would not give the very distinct snapping noise.

 - When I turn the engine over with only the inner spring in place there is no problem, no noise.

 - Turning it over with the outer spring only in place, the problem is there.

 - The valve guides have a very small shoulder on which they locate on the head. Difficult to measure, about 1/2 to 3/4 mm wide (dia = about 14.1mm, valve guide 13.1mm). Much smaller than shown on the AN photo. So the spring bottom locating washer (inner diameter 18mm) is not  fixed in a specific position, can be off center by 2 mm depending on how it lined up in installation.

 - The spring bottom washer has a flat inner surface on which both springs rest, no raised surface to hold the inner spring radially in position. This is as the AN photo, but I am surprised as it allows the springs to touch and rub if not ideally located during assembly.

I need to think about this, but I am beginning to think it has incorrect valve guides which don't locate the springs properly. Somehow something is catching and snapping loose. It may be solved by simply turning up new bottom locating washers (inner dia 14.25 mm which would hold the springs centrally around the valve guide shoulder (I would then include a ledge the hold the inner spring central to the outer.)

Thank you all for your comments and help. I will send a photo of my piston/barrel situation. I don't know what pistons they are, I look more closely in a few days.

springs are wound in opposite directions.

The id of the inner spring is 19 mm. The od of the guide shoulder is 14 mm, so a large possible misalignment gap, the cup washer could be 2.5 mm off center.

Dave, could you please tell me the id of the spring seat washer?

I'm anticipating having to strip it down but I don't want to do that if I have no idea of the problem.

Thanks

Richard

... I'm going to have to strip it down.

Two reasons:

   - the sharp noise as the valves are coming off their peak (which can only be from the springs suddenly being released)

   - why the exhaust valve adjusters are screwed out so far that the tip hardly protrudes from the rocker at all (maybe 1/2mm), and the inlet adjusters are screwed so far down that the locking nut at the top has almost no thread to grip on. The push rods are the correct length for the 500, (inlet 201mm, exhaust 178mm)

To help me check what's going on, will someone please tell me the cam measurements (peak across maximum lift to base circle and base circle diameter)?

Also just to make sure, the length of the cam followers. 

This is what happens when you buy a bike with an engine which "you don't need to worry, it's been rebuilt by a professional." Ha!

Thank you for your help.

Richard

It certainly looks as if I will have to strip it down.

Two factors:

-what is causing the noise. I suspect the lalrge clearance in the base washer to the valve guide allows the bottom of the springs to be not correctly located.

- why is the such a difference/error in the position of the rockers when it has the correct pushrods.

I need to investigate further before I pull it apart.

Thanks again.

I decide that before I pull the engine out and split it to try to find the cause of my problem, I would do a cam profile measurement to see if there is anything in the profile to cause the sharp snap when the valve starts to close.

See attached plot of the profiles and timing. This was done by fitting a dial gauge to the top of the pushrods.  The profiles are smooth with nothing to cause a sudden jerk in the valve motion. There  is no unevenness or drag turning it over by hand with the head off. So I don't see any reason to strip it.

Judging by the photo and info from Russell and David, the engine has been fitted with high compression pistons - see photo below.

Regarding my problem with the rocker position (adjusters either too long or too short despite the cam and the pushrods being correct), I see that Norvil list two rockers for the Dominator. Could it be that the wrong rockers are fitted - which would result in the valve end being too high or too low? That would explain my problem. 

Thank you Philip, this is interesting.

My pushrods are 7.1 mm diameter, and don't look to me as if they are the fatter type. However, I'll look a little more closely at how they fit into the tunnel. See photo attached.

Regarding the rockers, they seem to be original as they fit well into the head and the valve end is positioned correctly. The width across the shaft axis is 39mm. The depth of the screwed end which holds the adjuster is 11.5 mm. I could solve my problem of the rods being too long or short by removing about 3 mm from the top face or the bottom face as needed. There shouldn't be a problem as this is strong material and the force to push down the spring is relatively low. If I can't find out why this strange situation (of the rods being too short or too long for the rockers) exists, maybe I'll end up doing this.

Regards Richard

..... I don't quite understand. My photo (Pushrods 7.1 mm dia, 7.0" and 7.9"  - 178 and 201mm), do you think they are correct for the early 500 ? Mine is about 1956, it is a dynamo engine. I assume the head is correct but I don't know for sure. What I do know for sure is that the pushrods are the wrong length, too long for the exhaust, too short for the inlet. 

I would guess they should be about 173 and 207 mm.

This bike has really been put together with bits and pieces from all over. I wonder what the PO was thinking - if at all!

I have found that the engine has the incorrect valves, inlet too short by 4.3mm, exhaust too long by 2mm. This explains why the adjusters were out of position.  In addition, the exhaust valve head is too large (35.7 mm vs 33.3 - AN). To correct this the valve seat must be changed.

The shoulder on the valve guides is much narrower than it should be so the bottom cup washer could be 2-1/2 mm out of position.

Regarding the snapping noise as the valve moves off peak lift, I've decided to remove the camshaft. Can anyone tell me if it can be taken out from the timing side without splitting the case?

The cylinder head has a casing number on it (T2225). Can anyone tell me if this can identify which model Dominator it came from?

Maybe, considering all the things found incorrect, it will be better to pull the whole contraption apart.

Thank you for your help.

... I'm going to start by getting new bottom cup washers made which will hold the springs in their correct positions.

I'll certainly get the correct valves. Then I'll check what happens.

If the noise is still there (it's definitely the cam follower slapping down on the cam as the valve starts to close, not at tdc) then I'll certainly have to take the cam out. Can it be done without splitting the engine? 

I was hoping the cam could be pulled out the timing side.

I'll split the engine now as the cam is almost certainly to be in a poor condition judging by the other parts.

The followers are ok, they have been ground with a very slight curved surface - by a cam specialist company!

I'll need new valves, valve seats, bottom cup washers.  I'm hoping main bearings and big end shells are ok - the previous "specialist rebuilder" surely got something right!

How on earth do I remove the half time pinion from the end of the crankshaft?

It's all very well to tell users to contact the service department (60 years ago!) but not helpful when you live in South Africa.

The triangular washer behind the pinion leaves very little recess (2-3 mm) to get the lip of a conventional gear puller in.

Does anyone know how I can do it?

Oh dear, another unpleasant surprise - I hope not.

I've now got the engine apart and found what gave me a nasty fright - but I'm not sure.

The attached photos show what looks like a crack right around the camshaft boss. However it doesn't travel through the flanges, and doesn't appear at all on the outside of the case.

Is it a casting mark? Please say yes!

Thank you Robert, I can breath again!

For those of you who are still following my convoluted story, I have made more progress.

I bought four new valves and then found that the SPO (s....d previous owner) had fitted an inlet valve in the exhaust port, the seat had been machined out to suit. So I had new seats put in the exhaust side (the fact that the machine shop fitted the new seats on the inlet side and fitted the new exhaust valves there and so had to do it all again is irrelevant here.) I also had new spring cup washers made which take into account that the valve guides have a very narrow shoulder (only about 2 mm bigger in diameter than the guide) so the springs are now located in the correct position relative to each other and the guide.

Anyway, the correct new valves, seats and cup washers went in and the engine partly assembled on the bench. I turned it over slowly to make sure that the new valve setup  didn't create any piston /valve contact and nearly cried when the snap is still there. No difference at all.

It is definitely coming from the cam follower hitting the cam sharply with the valve spring force driving it. It happens as the the cam is coming off its peak, turning the engine clockwise or anti clock wise. To try to identify what is causing it, I took all the valve train pieces out, (rockers, push rods and cam followers) for 3 valves leaving only one valve and its pieces in place. The snap is still there.

There is nothing else that it can be, but the camshaft/ follower. The cam looks in reasonable condition, but may be from some other bike. 

When I started this restoration, a long time ago, I noticed that the valves were not opening in a smooth movement. I found that the surface of the cam followers were worn in a wave type shape. I had the contact face of the followers lightly ground by the cam specialist. He put a very large radius on the face - very slight curve. 

I now suspect the cam/follower shapes are causing the problem. I'm going to take the cam out and send it together with the followers to the specialist to check. He specializes in designing and making racing cams so hopefully he will see if they are not compatible.

Could someone tell me if the 1956 88/99 should have flat or slightly convex followers?

Also, if someone has a profile drawing of the cam, that would be useful too.

Thank you

Thank you for this information.

The lift on my cam is measured at 0.29" - as David Cooper said the standard cam should be.

Russell gave me the following valve spring data:

Outer: 32.77mm ext, 24.87 int,  3.25 mm wire, length 40.68mm

Inner: 23.79 mm ext,17.6 int,  2.32 mm wire, length 36.9mm.

Mine are:

Outer: 31.8mm ext, 24.7 int,  3.6 mm wire, length 52.8mm

Inner: 24.0 mm ext,18.7 int,  2.6 mm wire, length 44.0mm.

So the diameters are correct, but the wire diameter and lengths are very different. If Russell's figures are correct, then the springs in my engine are vastly too strong, probably up to 100% additional loading on the cam and the followers.

Can anyone tell me which spring data is correct for the 88/99?

Thank you all.

I have the correct length springs, but I would like the wire thickness confirmed. I have seen one comment that mentions thicknesses a lot less than mine.

I have reached the point now where it can only be the cam/follower interface. The cam profile is what I suspect.

Today I removed the cam drive chain and turned the cam only - using a large spanner. The result was the same, as the valve started to close - just came off the peak lift - the follower snapped down on to the cam face. This happens turning the cam clockwise or anti-clockwise..

It looks like I will have to get the cam/followers checked and maybe reground to a regular profile.

I think I am getting to the source of the problem slowly. It's obvious that this engine is such a mix of parts that I can be sure of nothing.