I’ve purchased a new camshaft from Norvil and it comes with a set of instructions, some of which seem a bit odd to me so I’d like to get a few opinions:
Query 1: The instructions say that if you fit a new camshaft, you MUST also fit new cam followers. (Similarly, the instructions say that if you fit new cam followers you MUST fit a new camshaft as well). Both of those statements just seem like a way of Norvil making more money. Surely, if the cam follower faces aren’t worn through or damaged, they will be fine - why would new ones be needed?
Query 2: The instructions say that once the new camshaft has been fitted, the engine must started and immediately run at 2500 rpm, it must not be allowed to idle or drop below 2500 rpm in the first half hour of running with the new camshaft. I can understand that a good supply of oil is needed on the cam lobes, but surely starting the bike after a complete engine rebuild and then running it at 2500rpm for half an hour is way over the top and possibly inviting trouble from other newly installed components? Surely the oil pump will be delivering sufficient oil volume to get the crankshaft to splash the cam lobes at a lower rpm - for example, just above tickover (and the cam followers will be similarly getting lubricated by oil returning from the rockers).
I’d be interested in hearing other people’s opinions regarding ‘running in’ a new camshaft.
Did Norvil say anything about assembly lube?
Hi Mikael. Yes - in a way. They recommend (and sell) a ‘special’ lube. I always use engine build lube when putting engines together so I was going to use that.
All new parts have to bed in. This generally involves taking care with the engine during its first few hours of running. You can buy special running-in paste to help lube the new parts. I used to use Slick 50 brushed over all the lobes in my engines.
To answer the first question about fitting all new parts. This is good engineering practice but not always necessary on a used motor. The reason being that the respective camshaft and follower faces may have worn at a slight angle and mixing new with old could lead to these faces not being in full contact with each other. This creates uneven loading, then heat then excessive wear. You will get a similar problem if you mix old clutch plates with new ones.
When dismantling an engine it helps to keep the old parts labeled so that everything gets replaced correctly in its previous position.
With regard to the Norvil instructions. If I ran my engine at 2500 rpm for half an hour while stationary, I can almost guarantee the neighbours would be phoning the Council and / or Police. There is also a good chance that the engine would seize after just 10 minutes of such running anyway.
It is good practice to change cam and followers together but not essential. Some people will immerse the cam in hot oil in the mistaken belief that this forms a protective ZDDP based film. This only happens in the presence of sliding contact between cam and follower.
Top fill with about 1/4 pints of hot oil before start up to ensure adequate lubrication. We did some work with Ford on the cause of catastrophic failure on lateral camshaft engines on dyno testing prior to installation. It took 9 minutes before splash and drainage from the top end provided lubrication.
Don't run in with cold oil and/ or low speed. These conditions are the most severe possible. Start with warm oil and run at light load and medium revs. That is to say, ride it but don't thrash it.
I replaced my worn cam over the winter. I used an Andover Norton one which comes with some assembly lube. I also replaced the cam followers because my old ones were very marked by the old worn cam. I have re-used followers in the past but only if they are in good enough condition to be refaced. They wear to match the cam so using old ones without having them refaced is risking your new cam as there may be point to point contact.
As for the running in procedure. If you read peoples experience on the Access Norton site, people who have rebuilt a lot of Commando engines, the Norvil advice is correct. What I did was to manually set the ignition timing. Get timing light ready to set ignition accurately (I had Lucas RITA ignition). Start the engine and run it around 3k revs to set ignition. Once ignition was set I ran the engine at 3k revs for about ten minutes (neighbours were out at work). I then put my bike gear on and rode round the block for about twenty minutes in lower gears to keep revs up.
Of course it will, hopefully, be years before I find out if what I did was effective or smoke & mirrors.
Was such a procedure followed in the Norton factory (or any other?)
Also my cam followers showed slight witness marks from the cam lobes but these could not be measured in any way. Not even felt by my finger tip. Had they worn to the shape of the cam, there must have been sharp edges depressions at each end of each wear mark.
Of course nobody does double blind trials, so all we are left with is the world wide web on which anyone can paste anything. Or do the same dark arts described above apply only to Nortons? I bet so few owners follow the Norvil instructions to the letter (not least owing to noise) that they are totally safe from warranty claims...they've put me off changing my cam anyway.
Commando camshaft failures are not uncommon so why risk not following the procedure?
Ref the factory. When the bikes were built at Andover they were taken for a blast around the Thruxton track apparently. I've no idea what they did at Wolverhampton, but the earlier Andover built bikes seemed to have less cam failures, but there may be quality of supply differences too.
SRM can resurface a set of cam followers for a reasonable price - around £100. So is there any reason not to have this done rather than lay out over £300 for new followers? The followers I’ve got look in good condition.
When the bikes were built at Andover they were taken for a blast around the Thruxton track apparently.
I worked at Thruxton Airfield in 1971/72 and never saw a single Commando go round the track except on race days. The Norton Racing department was based in an old hut on the south side of the circuit and Peter Williams quite often waved to me as I rode passed his office on my Dommie towards the main hangar. I don't recall any of the race bikes they built ever being taken round the circuit either. When I asked if I could ride my bike on the circuit my request was refused. However, one of my co-workers once took his scooter onto the track and completed a full lap without falling off.
At that time the airfield was owned by one company but the perimeter circuit / race track by another. We weren't even allowed to used the perimeter to move aircraft from the parking area to the maintenance hangar.....which was owned by yet another company.
Norman White set up his first Norton repair business in one of huts just a few yards away from Peter Williams' office. I think that was probably in latter part of 1973.
Regarding run in - I have mused about this often - what about running in on the bench by belting to an external power source ? ( electric motor , etc. ). With the plugs out this should be relatively easy to achieve. Is this not a good idea because the temperatures are lower,the dynamics of the forces are different ( pistons are being pulled by rods rather than the Pistons pushing on the rods , etc ) This would certainly solve the noise & exhaust issues .
I would welcome knowledgable input on this .
Thanks - Richard
I have re-built a few Dommy motors 88/99/Atlas and never had any issues at all with cams or followers . Perhaps because the parts were all pukka Norton or AMC manufacture. I would lightly stone and re-use good followers that showed a base circle witness mark and have stoned off any sharp edges. Assembly lube is good ,and oil poured down the pushrod tunnels will fill the cam trough. Not allowing the motor to idle will ensure that oil gets around properly . This is common practise with car engines that suffer with cam wear and need oil splash to top up hydraulic lifters. There is the point that if the new cam fails and you cannot prove new lifters were fitted then some suppliers may baulk at honouring the guarantee , not that I have much faith in that , although RGM has not let me down up to now.
You need warm/hot oil and a ready supply at start-up. Most damage is initiated within a few minutes of a cold start. When the valve train scuffing test used by european engine manufacturers for lubricant approval was developed, we measured the rate of scuffing during the initial low temperature / low speed phase. With alll but the best oils , onset of scuffing occured in less than 5 minutes.
I seen to remember that Bugatti instructions told the owner to drain the sump into a pan and warm it on the stove before starting up in the morning.
But I'm not sure why starting cold and new is so much different from starting cold and old when looking at contact between two finely ground surfaces. And what do mass production factories (car and m/c) do with the millions they turn out every year?
In the days when Bugatti made racing cars, the reason for heating the oil was to lower the viscosity and improve flow. In one of the RAC TT races in the 1930's Alfa Romeo turned up with 3 of the leading drivers in the world and 2 extra cars for Tim Birkin and Earl Howe. The works mechanics were puzzled that the British drivers waited until just before the off before filling their engines with hot oil and hot coolant. When the flag dropped the British drivers took off at max speed and, irate at this, the wotks cars gave chase only to run their bearings on the first lap.
With regard to modern practise, on an atomic scale even the best engineered surfaces resemble an alpine landscape, think of turning Austria upside down and running it over Switzerland, running in removes, in a controlled manner, the highpoint of the asperities and allows slidding to occur without localised welding of the asperities with consequential damage.
It is true that many engine makers will dyno test each engine up to full power from first start, but they will use a special first fill oil for the purpose.