All about cams

Usually when a certain bike such as the XR750 is mentioned in similar context to Jim's post, it is because it is a performance bench-mark.

I ran a megacycle 56-000 cam on my 850 for 20 or 30,000 miles. I had to take it out when an inner R/D valve spring broke and took it out. I think if I ran one again I'd plan on changing the springs every 10,000 miles. I had a second 56-000 that was in my bike when the crank broke and the swarf got in between one of the lobes and the follower. Megacycle said they couldn't repair it, but I wonder if web cam could?

With the 56-000 seemed to be slightly stronger than the stock. I wonder if further engine modifications would be necessary to really make use of it. Since I rebuilt my engine last winter and am not putting very many miles on it, it will probably be many years before I'm willing to split the cases to swap the cams out.

Eric,

like you have done, when I rebuilt my 850 three years ago I had a Megacyce 56-000 cam installed upon the advice of my engine builder

it is an improvement over the stock cam and I have been quite happy with it, we also put in new black diamond valves, springs and guides and cleaned up the flow

along with new amal premiers this work has resulted in a all around stronger motor with an even better top end, had Megacycle match my lifters to their cam also

The Megacyle 560-00 is a good performance cam and it uses stock lifters that have been re-ground to a 3" radius. This lightens the heavy stock lifters a little and allows the cam lobes to have a rounder (less pointy) nose - so wear is reduced a bit. It's ratio of lift to duration is a little steeper than some other Norton performance cams and this could be why ewgoforth's RD spring broke after 30,000 miles as he mentioned in his post above.

The BSA lifters have a 1-1/8" radius and this allows for an even rounder cam lobe nose - two roundish surfaces working together is better than when one of them is flat.

ewgoforth - no cam company is going to want to repair a damaged cam - especially if it wasn't their fault.

Not really surprised that their are 'different versions' of the PW3 cam, I bet cam grind shops all over the planet have tried to copy and 'improve it' over the long time it has been in existence.

Some steels are only superior to others in different criteria when it comes to cam manufacture, chilled cast, EN40 etc all have have very good properties which makes them useful for different situations, irrespective of the cam grind profile a coated racing cam of EN40 is more than adequate for the job, cheap to produce - ideal as it be will checked when in use and be replaced on regular basis. the coating can wear through sooner than than a chilled cast cam would wear out. The balance of cost/ease of manufacture/life/weight all have to balanced. What is surprising is that they all seem to cost the same when finished.

As for repairing any cam, why bother - they are so cheap when compared to crank, pistons, barrel etc all parts that could be destroyed by a failure. If it just welding up and checking for timing prior to batch manufacture, ideal - but as a performance cam in a race engine used for racing not parading, forget it, even in a road bike where a failure could end with the rider having a get off in traffic at speed, the cost of repair versus new is a no brainer in my opinion.

I have been continually puzzled by the posts on this forum about performance mods to road bikes which are mainly used for commuting and touring. I made a choice many years ago when I stopped riding on public roads and went racing. I'd love to own an immaculate road going commando, however in Australia the car licence is linked to the bike licence - lose one, you lose both. With my racer, I make it go as fast as I can afford and the 850 is a lovely engine to play with. The beauty of the situation is that on a race circuit, you can used the bike in anger as the designer intended.

Why would you be puzzled that people want to hop up their street bikes?

acotrel said:

I have been continually puzzled by the posts on this forum about performance mods to road bikes which are mainly used for commuting and touring. I made a choice many years ago when I stopped riding on public roads and went racing. I'd love to own an immaculate road going commando, however in Australia the car licence is linked to the bike licence - lose one, you lose both. With my racer, I make it go as fast as I can afford and the 850 is a lovely engine to play with. The beauty of the situation is that on a race circuit, you can used the bike in anger as the designer intended.

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What part of riding a higher performance Commando on the street puzzles you, Alan? Some of my biker friends also use their bikes for commuting and touring, but mostly we enjoy riding for pleasure, which usually means twisty roads at a brisk pace. A well set up Commando with some performance upgrades is a real joy for that kind of riding, particularly with a group of good friends. Riding a stock Commando is great fun, but even better with a bit more horsepower and some handling upgrades. Racing on a track if fine, and most of the group I ride with has been there and done that, and some still do, but it's not the same as riding on real roads. On the road we can ride as fast or as slow as we are comfortable with (and that can be fast enough for a good adrenaline rush), and can enjoy the experience of seeing different scenery, not just the same corners on a track over and over again. We are fortunate that we have lots of great canyon and mountain riding country around us. If all we had were flatland highways and freeways, I don't suppose we'd ride so much. I can see why you might decide to ride only on the track, as well as why you might prefer a stock bike for the roads, but you shouldn't be surprised that others make a different choice.

Ken

Oops! Just realized I'm guilty of a little thread hijacking in my response to Alan. Sorry about that, particularly on a thread as interesting as this one. Back to the topic of cams.

Ken

Rohan said:

acotrel said:

I know the Commando Combat 750 had a reputation for destroying itself, however that might have been due to over-revving - not enough gearing ?

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Close, but no cigar.
You really need to play catchup, and read up on the whole Combat saga.

There are whole threads here devoted to thrashing out this subject, not to mention reams and reams of info in books and magazines.
And post-mortems ad infinitum - it was possibly one of THE most famous tales of mechanical disasters in recent motorcycle engineering history.
Hint - the (many) threads on superblend bearings may be somewhat related.
But there were other factors involved, including rushing things to market that hadn't had enough testing...

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old news

https://www.google.ca/search?q=yamaha+r ... K9ebCpl5AL

http://www.r1-forum.com/forums/7801073-post1.html

"The transmission gears, both wheel and pinion of 2nd gear, may break due to extremely high stress and or improper transmission operation due to inadequate component strength and stress concentration to the tooth land. 3rd and 4th wheel gears, the gears may be deformed due to excessive stress by hard usage due to inadequate component strength. In the worst case, the gears may break."

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http://www.cycleworld.com/2015/12/15/re ... box-issue/

Cams it was.... Is there a way you can identify what cam you have without splitting the crankcase? I was not planning to do that, still hope it won´t be necessary. The cam lobes look great, so that potential reason to split the cases is not valid. It´s an 850 -73, the cylinder and pistons have been removed.
Tommy

The issues of an R1 Yamaha are hardly relevant to those of a commando. When the commando was built, most Japanese bikes already had reliable gearboxes. The biggest problem with the commando is it's gearbox - not enough speeds and not close ratio. Installing hotter cams when the gearbox is wide ratio does not help much. The power-band for hot cams is usually narrower. If you wind the heavy crank up in the commando then play at the top of the torque curve, it is a much better deal.
My car is a 6 speed manual Mazda 6 - it has extremely good acceleration, and is very driveable around twisty tight roads. Most Australians don't buy manual cars these days.

I think if I was trying to do what you guys are doing, I'd be looking at a 5 speed Triumph gearbox from the 70s. I think they are essentially a Quaife cluster. I think I saw a while back where Dave Nourish was making a Norton style case for them. Also Phil Pick of Triple Cycles was making two pairs of gears which raised both second and third up towards fourth gear. So the box becomes close ratio in the middle. You should be able to get out of the exercise for under $3000. And the box would be very resellable.

Jim - great thread.
Keep up the great work.
Someday, when my 750 needs freshening, I'll place a big order - rods, pistons, followers, cam . . . . .


Ken,
IIRC, it is a Berco, rocker, out of Canada as you say, war surplus, and yes, Mike cut the masters from scratch.
It's frustrating, he's leaving money on the ground . . . . if only we could get him to at least finish some grinds . . .
but, he's happy . . . .
And, your thread "hijack" was appropriate too.

oops, double posted

fiatfan said:

Cams it was.... Is there a way you can identify what cam you have without splitting the crankcase? I was not planning to do that, still hope it won´t be necessary. The cam lobes look great, so that potential reason to split the cases is not valid. It´s an 850 -73, the cylinder and pistons have been removed.
Tommy

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I believe that's a tough one fiatfan .

cjandme said:

fiatfan said:

Cams it was.... Is there a way you can identify what cam you have without splitting the crankcase? I was not planning to do that, still hope it won´t be necessary. The cam lobes look great, so that potential reason to split the cases is not valid. It´s an 850 -73, the cylinder and pistons have been removed.
Tommy

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I believe that's a tough one fiatfan .

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Maybe more like tedious.

First check to see if there are any obvious markings on the cam that compare to catalog listings or pass to the forum for input. If that fails, reinstall the barrel with lifters. Get a dial gauge and crank mounted degree wheel and profile the cam. Plot the data and compare to various cams available. See Megacycle catalog for cam listings as well as atlanticgreen website for other cam listings.

You always run the chance that someone combined flat lifters with a cam ground and designed for radiused lifters.

Can anyone identify this cam from a 500 domi motor. It has XI stamped on it. Below that is, embossed in casting T2219, below that embossed as well is (S)2. Thanks Dano

Rohan said:

.... didn't the JPN racers find the alloy pushrods flexed too much for use much above 7000 rpm ....

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Many times I've heard about alum pushrod flex but I've never seen any evidence of it and I've never seen an aluminum pushrod fail. This could be bogus info thats being passed out over and over. It looks like aluminum is just fine and higher quality stiffer pushrod material even more so. See Comstock's pushrod vid below at over 7000 RPM.

[video]https://youtu.be/U0vKfMZqQQk[/video]

jseng1 said:

Many times I've heard about alum pushrod flex but I've never seen any evidence of it and I've never seen an aluminum pushrod fail. This could be bogus info thats being passed out over and over. It looks like aluminum is just fine and higher quality stiffer pushrod material even more so.

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A question I've also pondered. We covered this subject at some length a while back in this thread

commando-pushrod-tech-t12779.html?hilit=pushrods

but I haven't managed to pursue it any further since. I tend to believe that aluminum is perfectly satisfactory for most Commando engines. Something else might be needed for the ultra short strokers running in the 9000+ rpm range, but I have no experience there. I've never had a problem attributable to aluminum pushrods in any of the engines I've run, and I put a lot of race miles on them, but none of my race engines got revved much above 7500 rpm.

On the other hand, high performance race cars that use pushrod engines almost all use steel pushrods with as large a diameter as they can fit. Of course, with well supported camshafts and larger diameter lobes, they can run way more extreme lift profiles than the Commando can handle, so that's not much of a comparison.

Ken