Re: Mk3 Cams

It's not just Mk3's that have had the problem with cams wearing out. My '72 750 wore out prematurely. There seems to be an element of pot luck involved. Your cam looks good so keep your fingers crossed that it stays that way.

The Mk3 was certainly the worst. Wasn't there a suggestion that the factory went 'belt & braces' but the two hardening processes weren't compatible ?

I don't think that periods were documented as they never admitted the problem but some Mk3s were assembled as late as 1977. When was yours built ?

The Mk3 also suffers, as far as I could see from having the least effective residual oil bath for the cam lobes. They progressively reduced through the Commando period as the castings were redesigned.

I would be inclined to speak to mick hemmings or Norman white for a definitive answer. There were some milky mouse replacement ones on the market but I would have thought they are long gone.

Mine was an April 1975 build and the first owner told me that it had a soft cam that was replaced under warranty, and a gearbox layshaft failure within the first year - this was also a Mk3 speciality.

The Andover Norton cams over at least the last 10 - 15 years don't seem to have had any problems.

The latest Andover Norton ones are chilled cast iron, they last well but need careful treatment, the torque on the sprocket retaining nut needs to be a lot lower than the workshop manual or the end of the cam will break off.

This also applies to the PW3 cam as they are both made by Newmans out of chilled cast iron.

My Mk3 Commando was built in June 75. The cam was shot at just under 25,000 miles. (1989) My understanding is that the metal used was the wrong spec and once the case hardening had worn off the end came quickly.

Someone suffered this fate on a European tour mentioned in a Roadholder report. (I think it was a silver Interstate that came back in a state! Over a year ago)

I have been involved with the MKIII cam issue since 1994 when I bought my first MKIII basket case. It was dead at under 9500 miles.

Since then I have helped diagnose many dead/dying MKIII and done plenty of cam swaps for friends and club members.

I own almost 3 dozen cams from various era of NHT. I bought an Ames hardness tester. And often test cams for club members.

Standard NHT had RC55+ hardness most of the time. 200000 era combats were in the RC40+ region. Finally the MKIII and reportedly some late 74 were not hard at all. I have NEVER tested a MKIII cam with any significant measure of other than RC19-25. That gentlemen is soft. A file or pocket knife will cut it.

I have a few theories of this gross defect developed by input from norton trade people and my own mechanical manufacturing training and degree. But I was not at the factory or offices of norton in the day so they remain theory and only fodder for arguments.

I will however state, I now own a 5 miles from new, never registered, MKIII that will get a new steel cam before I run it with a cam as soft as a candy bar.

http://atlanticgreen.com/hscam.htm

Just to add to my previous comment. A long conversation many years ago with a gentleman in the know told me that Norton knew of the cam problem. BUT by the time the case hardening had worn off, the warranty period would have expired!

The cases on my Mk3 had never been apart before just under 25,000 miles so why the difference in miles before failure?

Hard use? Soft use?

Lubricant quality?

Quality of cam difference?

I would say the main variables for cam life are lubricant quality, lubricant age and maybe how many cold starts the bike has. I would think riding briskly is probably better for the cam than slogging the engine.

I know this is a dangerous thing to say but I have had my MkIII from new, it is still on the first cam and it has 72000 on the clock. It will now die on the next run ...

Tony

Hope not Tony, do you know when it was built to try and establish a pattern. 72,000 seems a good mileage if you have not had major surgery, though I have heard of pistons and bores being still good at high mileage. The cam appears the weak link?

I think you are right Ian, all down to lubricant.

Quality of cam difference?

Well lets suppose the union guys were at the bar (excuse me... PUB) for an extra hour at lunch that payday friday, because the boss was sick that day...

norton factory or the hardening shop? I'll never know.

The cams sat in the casetite oven for an extra hour! Yum... extra thick hardness on YOUR cam/batch. Lucky you! LOL

Is it likely the actual low carbon alloy EN32B was bad...possible yes, but probably not.

Is it all related to an extra good oil diet? I'll never know.

But I DO know that 99% are soft...RC 19-21 mostly.

Cheers

Dave

Previously David Comeau wrote:

Quality of cam difference?

Well lets suppose the union guys were at the bar (excuse me... PUB) for an extra hour at lunch that payday friday, because the boss was sick that day...

norton factory or the hardening shop? I'll never know.

The cams sat in the casetite oven for an extra hour! Yum... extra thick hardness on YOUR cam/batch. Lucky you! LOL

Is it likely the actual low carbon alloy EN32B was bad...possible yes, but probably not.

Is it all related to an extra good oil diet? I'll never know.

But I DO know that 99% are soft...RC 19-21 mostly.

Cheers

Dave

OK Dave, good enough for me.

The orriginal chilled Iron cam on my 1960 dommy is still perfect but then it has the oil bath intact.

Something must have changed. I wonder what ? A change of supplier late in 1974 ? It is fairly evident that in addition to curing some long standing problems, the Mk3 introduced some new ones and there was never any further factory development. If there had been a 1976 Mk4, then perhaps it would have addressed some of the issues...

The main batch of full production Mk3s seems to have been made from October 1974 to the summer of 1975 with presumably few going to customers before January 1975 and the factory about to go bankrupt...perhaps this just wasn't long enough for alarm bells to ring and action to be taken.

The cams with tacho drive sold as spares during this period were presumably also affected...and once the factory ceased to supply, we entered the Wassell era of the late 1970s / early 1980s and added poorly brazed followers to the problems of monkey-metal cams.

The orriginal chilled Iron cam on my 1960 dommy is still perfect but then it has the oil bath intact.

I wouldn't expect a 60s Dommie to have a chilled iron cam from new as it is a relatively recent process.

I recently met a chap while on holiday who was involved in the Bridgend Ford engine plant. He told me that modern Ford cams are chilled iron and whilst they may be fragile when handled, they have good wear properties. Mick Hemmings' fitting instructions for PW3 cams gives advice for torque and loctite use on the cam sprocket.

For those of us waiting to experience cam wear, what are the symptoms? How much wear needs to occur before it noticeably affects running?

A wearing cam can progress almost unnoticed.

At the 2002 INOA rally, a guy drove his MKIII from Michigan to New Hampshire(1100km) . He did not notice much of a problem on the road. It did present a irregular idle. I had him pull the EX rocker covers off and one side went full up and down, the other(dead lobe) did a noticably smaller quiver.

FWIW The valve lash does NOT get bigger. The base circle is not what is wearing!

His bike went home in the back of a pick-up truck.

Since then I have diagnosed many dying MKIII cams. My never registered, 5 mile since new commando will get a cam change before I run it for the first time.

The only real sign of a cam lobe going is, if you're concientious with oil change intervals, an increasing 'christmas tree' on the magnetic drain plug but it's easy to go into denial about how bad it is.

In my early days with a Commando, I once took the top end off for a routine re-ringing and found one lobe almost half gone. With hindsight, the edge had gone off the performance but not so badly that it made much difference at legal speeds.

Sorry, chilled iron was used by Norton from the first Dommy but on the followers and other parts , the cam was Case hardened Ubas steel .Camshaft problems were very rare on all the pre Commando bikes in the day. None of my Nortons suffered any cam problem. Both my 60's bikes are still using orriginal cams. One Bracebridge and one Woolwich.