camshaft replacement

dynodave said:

Last time I asked....(some years ago) Les Emery still sold his norvil cams which are steel not iron.
I have his 2S on a domi core, 7S domi core, 4S and 7S for late commando They were all tested for hardness.
I guess it's been a while...they were only about $150 back then. :mrgreen:
.

Click to expand...

These cams are made of steel then nitride harden (see Norvil website) this process leaves only a very shallow outer surface of hardness which has been reported on many occasions to fail.
As with iron cams the type of oil used an manner of using the engine seem as important as the cam manufacturing methods.

toppy said:

As with iron cams the type of oil used an manner of using the engine seem as important as the cam manufacturing methods.

Click to expand...

I think I would expand that to include any cam.
It's likely the old case hardened steel cam is the most forgiving to poor care and the stock MK3 cam is the least forgiving -but any of the cams can give good service if they are set up, run in and lubricated correctly.

I would rate a well done hardweld cam right up there with a case hardened steel cam.
I have seen a few hardweld cams some years ago that were pretty poor. They can flake or be porous if the weld is not just right.

I have not used a nitride hardened cam in a Norton. I have used them in car motors with mixed results. Jim

The oil feed through the cam looks like a good solution to the problem but unlike other modifications (brakes Estart crankcase breathers etc) no one seems to have developed it to a kit or upgrade that can be bought by owners (even if it means sending cases away for mods like some breather mods) who cannot modify there own cam.

comnoz found even his tiny cam holes drop oil pressure so much he had to create a larger pump to get away with it. Can't consider any single feature in a Commando w/o considering a few more, often too late, like comnoz had to work around. Most wear occurs on 'dry' start ups and any time not at least 2000 rpm, so best way to wear em is slow idle worm ups, as if carefully burping a living infant ya just woke up. Keep them sumps dry as ya can too.

One could adapt an oil squirter on the front cam lump and have that force lube the cam, with a needle valve to give pressure regulated flow, could be done off a stacked banjo from the head feed.

Sad that the cab lubing situation (just like most of the valve train) on the commando is pretty pathetically engineered :| I wish someone made rockers with corrected geometry, and made decent pushrods (the two sets I got that are new aren't even concentrically pressed in!), and that the whole valvetrain lubing wasn't just from cam follower dribbles!

dobba99 said:

...and why is a slow idle not good for these cams?

Click to expand...

Keep in mind that the cam is only turning at half crank speed. Unlike the con rod big ends that enjoy full-circle oil entrapment, the poor cam/follower interface is a very narrow line that has the weight of the valve spring, multiplied by rocker arm ratio, constantly bearing down against it. As Jim and others (Steve) have pointed out, the surface speed has to be high enough to keep the followers hydroplaning on the oil film.
Like Jim mentioned, car engines run roller lifters. This is a "Rob Peter to Pay Paul" scenario, due to eliminating zinc for converter's/emission's sake. They had to go to roller lifters! Now, if we could only find roller lifters small enough to fit in the lifter bores...

Nathan

Surely the shape of the followers affects the cam lift rate ? I think you will always have the situation where the hardness potential of the cam is unknown unless you know the material composition. Some steel companies have a portable emission spectrometer for typing steels. If you do a ring around and fine someone who has got one, you could spark the breather end of the cam then talk to a metallurgist about an appropriate heat treatment. I wouldn't primarily blame the lubricant. If the cam is soft and starts to pick up, the conditions might be slightly better with a high pressure lubricant, however with a good strong steel cam, shouldn't make much difference.
I'm wondering about that comment above that said cast iron cams are the 'dog's bollocks' in cars, they also use nodular graphite cast iron cranks. How can you heat treat it successfully ?

If you are wanting a hardened steel cam the normal alloy would be a 4340 or similar steel. This can be hardened enough to use a roller lifter.

Flat tappet cams do not need to be this hard to live a long life although the old original cams were this hard.

It really doesn't matter what the cam is made of if the oil is not doing it's job. Hard cams or soft cams will fail pretty quickly.
If the cam is being used correctly there is no metal to metal contact except at cranking speed. [or an idle that is too slow] That is where a hard surface is an advantage.
I also prefer an engine that wet sumps a bit to supply lots of oil to the cam on start-up.

A roller or radiused flat lifter does need a specific grind to get the correct valve motion although you can grind a large radius on a flat lifter and use it on a can designed for a flat lifter to slow the lift off the seat and make a cam a little "softer" without reducing the lift.

That is what I have done in my engine to make the 12A grind cam a little less racy. I use a 4 inch radius on the lifter. Some of the CNW bikes use this same setup. Jim

As far as a reason for cam failure outside of the material considerations, two major things can cause problems.

1: Coil bind. The spring coils hit one another at full valve lift causing the valve train to basically lock up solid at maximum lift. This erodes the lifter and camshaft due to excessive pressure.

2: Valve float. The springs are too weak, allowing the follower to 'float' off the cam surface, hammering the cam against the follower.

Valve spring tension specs can vary according to cam profile, and must be measured at installation.

Also always check for spring clearance on assembly of the top end. A quick and dirty check is to turn the motor to maximum valve lift and then carefully press the end of the rocker arm to check that its not bound up. The proper way is to measure installed spring height and calculate maximum valve lift, and then compress the spring in a press and check for coil bind at that height.

Just have a look at the worn cam lobe, why is it not running central with the tappets?
You cannot adjust the tappets so can you adjust the camshaft.
Mine has a side to side lateral movement of 3mm, is this OK.
The other tappets look fine with no sign of uneven wear.
Thanks
chris r

blacklav said:

Just have a look at the worn cam lobe, why is it not running central with the tappets?
You cannot adjust the tappets so can you adjust the camshaft.
Mine has a side to side lateral movement of 3mm, is this OK.
The other tappets look fine with no sign of uneven wear.
Thanks
chris r

Click to expand...

That looks pretty normal for contact. 3mm end play in the cam is a lot. I doubt that it had anything to do with the failure however. I would look at the cam bushings closely.
I can supply a webcam exchange and resurface the lifters if you want to send them. Jim

Thanks for the reply Jim, but as I`m in the uk the postage back and forth may make the cost near a new one from here.
The manuals all say the lifter MUST be replaced whenever a new camshaft is fitted. So you think it would be ok to take 1.5 mm off? and they would run in ok with the new cam.

blacklav said:

Thanks for the reply Jim, but as I`m in the uk the postage back and forth may make the cost near a new one from here.
The manuals all say the lifter MUST be replaced whenever a new camshaft is fitted. So you think it would be ok to take 1.5 mm off? and they would run in ok with the new cam.

Click to expand...

You will be OK if the stellite is at least .080 thick after grinding. Thinner and it may crack. See PM. Jim

Great news Jim, you just saved me £180.
I think I know what happened to the cam as the rocker shaft had moved in the head blocking the oil feed to the rocker so no oil running down the pushrod. Maybe not the only problem but it wouldn't help..

blacklav said:

Great news Jim, you just saved me £180.
I think I know what happened to the cam as the rocker shaft had moved in the head blocking the oil feed to the rocker so no oil running down the pushrod. Maybe not the only problem but it wouldn't help..

Click to expand...

I doubt that the turned rocker shaft would have an affect on the cam. Most of the cam lube comes from oil from the crankshaft.
Check your PM. Jim

Years ago I found excessive cam and follower wear in a 500cc Triumph Speed twin. We welded up the followers with cobalite because they were so worn they were concave right down to the hole through the middle. We then re-shaped them to the normal standard radius. The bike went a lot slower.