2S camshaft

Previously wrote:

can anyone advise whether you fit heat insulating washers under the spring seats when fitting a 2s/combat camshaft in a 750 engine. regards alan

Hello Alan,

Good question.

Personally, I would want those insulating washers in place. I expect youâre wondering whether you would then have the valve springs coil binding, because of the extra lift of the 2S cam.

Do you have some workshop facilities and some experience working on these machines?

If so, the best course for you is to assemble your engine (including the insulation washers) and turn it over by hand, checking that each valve spring still has some movement left when thevalve reaches full lift.

You may have access to a copy of Paul Dunstallâs illustrated booklet, where he explains how to measure (with a DTI) then set each valve spring by adding shims, so that they all have the same travel remaining before coil binding.

If they are already coil binding, John Hudson recommended having the tops of the valve collet grooves machined 1/16â higher.

The trouble is, the Combat era came at a time when quality control at Nortons was hitting an all time low and machining of the head where the valve springs seat would have varied in depth.

Donât assume anything; but it may be that your engine was one of the good ones, or perhaps someone has already carried out some remedial work.

These motors need to be carefully hand-built. If you can do that, youâll have one hell of an engine.

There has been a lot of cobblers written about the Combat motor in the Classic comics, by journalists who donât have the faintest idea what theyâre on about.

Just remember that the glossy bike magazines are the source of more mis-information on Nortons, than youâll hear on the average club night!

I have heard of one owner who put more than 30,000 miles on his Combat with its original (non-Superblend) main bearings. He was a young lad and rode accordingly.

Paul

Previously wrote:

Previously wrote:

can anyone advise whether you fit heat insulating washers under the spring seats when fitting a 2s/combat camshaft in a 750 engine. regards alan

Hello Alan,

Good question.

Personally, I would want those insulating washers in place. I expect youâre wondering whether you would then have the valve springs coil binding, because of the extra lift of the 2S cam.

Do you have some workshop facilities and some experience working on these machines?

If so, the best course for you is to assemble your engine (including the insulation washers) and turn it over by hand, checking that each valve spring still has some movement left when thevalve reaches full lift.

You may have access to a copy of Paul Dunstallâs illustrated booklet, where he explains how to measure (with a DTI) then set each valve spring by adding shims, so that they all have the same travel remaining before coil binding.

If they are already coil binding, John Hudson recommended having the tops of the valve collet grooves machined 1/16â higher.

The trouble is, the Combat era came at a time when quality control at Nortons was hitting an all time low and machining of the head where the valve springs seat would have varied in depth.

Donât assume anything; but it may be that your engine was one of the good ones, or perhaps someone has already carried out some remedial work.

These motors need to be carefully hand-built. If you can do that, youâll have one hell of an engine.

There has been a lot of cobblers written about the Combat motor in the Classic comics, by journalists who donât have the faintest idea what theyâre on about.

Just remember that the glossy bike magazines are the source of more mis-information on Nortons, than youâll hear on the average club night!

I have heard of one owner who put more than 30,000 miles on his Combat with its original (non-Superblend) main bearings. He was a young lad and rode accordingly.

Paul

thanks paul, the reason for the enquiry is that i purchased a new 2s cam as part of an engine rebuild, the engine was rebuilt by a mechanic with more than 30 years experience in nortons, but after 250 miles of running in i took the bike back as it wasn't running as sweet as i thought it could. a pull down revealed the left inlet lobe had lost approx 1 mm of case hardening. the cam supplier has suggested it could be 1 of 3 things: lack of clearance ie "2s did not run with heat insulating washers under the spring seats to allow more clearance".,lack of proper lubrication or a faulty component. when i queried the clearance and lubrication points and why the rest of the cam lobes or followers weren't damaged, the reply was that the left lobe has a tendency to be the least lubricated. your thoughts alan

Previously wrote:

thanks paul, the reason for the enquiry is that i purchased a new 2s cam as part of an engine rebuild, the engine was rebuilt by a mechanic with more than 30 years experience in nortons, but after 250 miles of running in i took the bike back as it wasn't running as sweet as i thought it could. a pull down revealed the left inlet lobe had lost approx 1 mm of case hardening. the cam supplier has suggested it could be 1 of 3 things: lack of clearance ie "2s did not run with heat insulating washers under the spring seats to allow more clearance".,lack of proper lubrication or a faulty component. when i queried the clearance and lubrication points and why the rest of the cam lobes or followers weren't damaged, the reply was that the left lobe has a tendency to be the least lubricated. your thoughts alan

Hello Alan,

Sorry to hear of that fast cam lobe wear.

I think someone has posted a link to a website run by a DynoDave, on the subject of Heavy Twins cylinder heads. If you trawl through DynoDaveâs site, he shows some details of some extensive testing he did on cam lobe hardness. What was most interesting were the surprisingly poor results for camshafts supplied by one of the UKâs main Norton specialists. Very, very poor they were. Take a look.

As for the left lobe having less lubrication than the rest, this is where we need some input from some Norton experts. Dommie & Commando camshafts donât have any type of positive lubrication. They rely on âsplashâ from whatever is flung off the flywheel; âdrainâ from oil coming down the pushrod tunnels (then being metered by the close running fit of the cam followers) and also by the lobes dipping into oil lying in the trough under the camshaft, which was gradually reduced throughout the enlargement of the twins, with Commandos finally not getting very much. Now, I donât see where the left lobe has been left out in the cold with this system.

Running without the heat insulating washers is a bad idea. The heating of the springs will anneal (soften) them, so basically they will loose the ability to spring! I know leaving the washers out was a quick-fix solution to the coil binding of Combat springs; but it was a bad one. I never met anyone who fitted the shallower bottom valve spring seating cups, which were listed by Norton apparently to â...give the springs enough working clearanceâ either. Having measured a (standard) spring seat cup, I found its base was just under 0.050â. So just fitting a thinner one wouldnât give you the 1/16â (0.046â) extra clearance recommended. Having the valve stem collet recesses machined higher and fitting the insulation washers would be my choice. That might be a bit trickier to do if you have stainless steel valves fitted.

Anyway, I think itâs very easy (and very common, in the Norton world) for a supplier to blame you when their camshaft is made of inferior material and wears quickly. If you research the opinions and feedback of those who have fitted camshafts made by David Newman, in chilled cast iron, you may be tempted to use them. A mate of mine has just bought a PW3 profile from Newman and it cost him £130 + P&P & VAT.

David Evans wrote:

I'm not convinced that the temperatures involved in a Norton cylinder head are high enough to anneal spring steel. There are plenty of other manufacturers that don't fit heat insulation washers. (1/16" is 0.0625" by the way) Roy Bacons book says........

Thank you David, for correcting me, regarding 1/16â = 0.0625â. Although the Norton twin cylinder heads were one of the better designs of their era for cooling, the highest temperatures will be in the region of the exhaust valves (the exhaust lobes have less lift than the inlets, so there would be more room available there for insulating washers). Perhaps the thinner spring cups listed at the time were specifically for fitting under the exhaust springs to allow room for the insulators. As to whether not using the insulators may compromise the structure of the springs, there is a paragraph in the Service Notes where someone had experience of that happening when he left out the washers. Perhaps he was racing.

Where are all the Norton experts? Surely some of the old-school have internet access and are still NOC members!

One aspect of the Norton cylinder head, which would be worth discussing on another thread, is that there is a lot of potential lost from âthroughflowâ, where the incoming charge is scavenged or assisted by the closing exhaust valve. Itâs fundamentally a good thing; but as much as 40% of the incoming fuel & air can be wasted and burnt in the exhaust, especially if there are valve cutaways, or a dome on the top of the piston. Norton twins are prone to blueing of the exhaust pipes, so you can see the effect some of that wasted heat is having.

On the subject of the excessive wear on the left (inlet) lobe, Alan: If the camshaft was a good one, then there is another scenario which would lead to rapid wear. With the lobes getting most of their direct lubrication from oil draining past the cam followers, each followers (after 1970) should have one bevelled edge which must be fitted towards the front of the engine, so that the cam lobe gets the benefit where it needs it most. It might be worth having a look if you have access to your engine, to check the followers are fitted correctly. I think all the lobes would have worn in that case, however.

Paul

Previously wrote:

David Evans wrote:

I'm not convinced that the temperatures involved in a Norton cylinder head are high enough to anneal spring steel. There are plenty of other manufacturers that don't fit heat insulation washers. (1/16" is 0.0625" by the way) Roy Bacons book says........

Thank you David, for correcting me, regarding 1/16â = 0.0625â. Although the Norton twin cylinder heads were one of the better designs of their era for cooling, the highest temperatures will be in the region of the exhaust valves (the exhaust lobes have less lift than the inlets, so there would be more room available there for insulating washers). Perhaps the thinner spring cups listed at the time were specifically for fitting under the exhaust springs to allow room for the insulators. As to whether not using the insulators may compromise the structure of the springs, there is a paragraph in the Service Notes where someone had experience of that happening when he left out the washers. Perhaps he was racing.

Where are all the Norton experts? Surely some of the old-school have internet access and are still NOC members!

One aspect of the Norton cylinder head, which would be worth discussing on another thread, is that there is a lot of potential lost from âthroughflowâ, where the incoming charge is scavenged or assisted by the closing exhaust valve. Itâs fundamentally a good thing; but as much as 40% of the incoming fuel & air can be wasted and burnt in the exhaust, especially if there are valve cutaways, or a dome on the top of the piston. Norton twins are prone to blueing of the exhaust pipes, so you can see the effect some of that wasted heat is having.

On the subject of the excessive wear on the left (inlet) lobe, Alan: If the camshaft was a good one, then there is another scenario which would lead to rapid wear. With the lobes getting most of their direct lubrication from oil draining past the cam followers, each followers (after 1970) should have one bevelled edge which must be fitted towards the front of the engine, so that the cam lobe gets the benefit where it needs it most. It might be worth having a look if you have access to your engine, to check the followers are fitted correctly. I think all the lobes would have worn in that case, however.

Paul

hi paul, appologies for taking so long to get back. rgm and andover have been dicking me along since april and still no definitive response to the problem. andover are suggesting it is coil binding, but my mechanic preloaded and checked the coils before assembly and then, as you described in an earlier post, hand turned the engine to test for any problems. the cam and cam followers were purchased new from rgm, the cam is an andover supplied item. there is no galling on the cam followers or camshaft, the coils have not bound and yet they still persist in denying any responsibility. as you can appreciate it does become a bit problematical when trying to resolve a warranty issue like this from 10000 miles away, however i did think that after spending more than 1400 pounds with rgm and hundreds more with andover that i would get better service than the buck passing and denial that has occurred since i returned the items to rgm last may. you mentioned a pw3 camshaft made by david newman. does he have an internet site ? regards alan

hi again, a post to some earlier comments. while the engine was originally supplied with a 2s cam and has the cankcase breather exiting the rear of the crankcase, the head not a combat head. the compression ratio is approx 9.2. regards alan