All about cams

A lot of the race cars use pushrods made out of chrome-moly tube with hardened steel ends - probably as light as aluminium ones and more rigid. A lot of earlier Triumph pushrods were similar, however I always used alunimium ones in my short stroker which revved easily to 10,500 RPM, before I fitted the 2 into 1 pipe.

acotrel said:

A lot of the race cars use pushrods made out of chrome-moly tube with hardened steel ends - probably as light as aluminium ones and more rigid. A lot of earlier Triumph pushrods were similar, however I always used alunimium ones in my short stroker which revved easily to 10,500 RPM, before I fitted the 2 into 1 pipe.

Click to expand...

If you feel the need to step-up to a level of performance beyond chrome-moly, this option is always out there.

http://tinyurl.com/me6gev7

acotrel said:

A lot of the race cars use pushrods made out of chrome-moly tube with hardened steel ends - probably as light as aluminium ones and more rigid. A lot of earlier Triumph pushrods were similar, however I always used alunimium ones in my short stroker which revved easily to 10,500 RPM, before I fitted the 2 into 1 pipe.

Click to expand...

Half right, Alan. You can make a steel pushrod that is "more rigid" (meaning more resistant to flex under columnar loading in this case), than the same diameter aluminum rod, but it will also weigh more. The chrome-moly (4130) pushrods supplied for British bikes back in the day from people like Alloy-Tech and Smith Brothers weighed significantly more than stock pushrods or aftermarket aluminum pushrods. A stock Commando intake pushrod with steel ends is typically around 30 grams, same as most aftermarket aluminum rods, but a chrome-moly one from Alloy-Tech was 50 grams. If you choose a wall thickness for the chrome-moly tube to give the same rigidity as a stock aluminum rod, it will still weigh more. The bottom line is that if you need more stiffness than you can get with aluminum in a given diameter tube, go with steel, but expect to pay the weight penalty.

Ken

WZ507 said:

acotrel said:

A lot of the race cars use pushrods made out of chrome-moly tube with hardened steel ends - probably as light as aluminium ones and more rigid. A lot of earlier Triumph pushrods were similar, however I always used alunimium ones in my short stroker which revved easily to 10,500 RPM, before I fitted the 2 into 1 pipe.

Click to expand...

If you feel the need to step-up to a level of performance beyond chrome-moly, this option is always out there.

http://tinyurl.com/me6gev7

Click to expand...

Agreed, this looks like the perfect material, but as far as I know, no one is currently making pushrods from it. That 3M flyer is almost 15 years old, and no longer correct. I looked into making pushrods for Nortons from the material back in 2002. This is a summary of the situation then, from my post in an earlier thread. Smith Bros were the ones who made the Harley pushrods mentioned in the 3m flyer. 3M just supplied the tubes.

"I'm pretty sure the best choice would be the aluminum/ceramic MMC tubes that 3M has, but Smith Brothers tried and gave up on making them. I talked to them about it a while back, and they said the rods worked fine on the Harleys they built them for, but the cost of production was just too high for the limited market size. They have to be machined with diamond tooling, and they had problems with the small diamond reamers breaking, adding lots of expense. The material isn't real cheap either. When I talked to 3M they were only supplying it in pre-cut 12" lengths, so you would waste a lot of material making Commando length pushrods."

If that's changed, and someone is now making pushrods from the material, that would be great, but they would probably be pretty expensive. The problem is the Nextel ceramic fibers in the composite are too hard and abrasive to machine with metal or conventional carbide tools, requiring expensive and fragile diamond cutting tools. On the other hand, it's been 15 years since Smith Bros gave up, so maybe there is better machining technology available, but I doubt it.

Ken

Dances with Shrapnel said:

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

Click to expand...

I believe that's a tough one fiatfan .

Click to expand...

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.

Click to expand...

Thanks for the info, I see what you mean by "tedious".... I´ll think about this a while 8)
Tommy

Applying auto racing pushrod technology to Nortons does not work well because autos use much higher rocker arm rations than Nortons and that gives them much higher loads on their pushrods. Steel pushrods offer no real advantage that pencils out when you do the math. Steel offers disadvantages because the thermal expansion is different than alum and the tappet clearances get thrown off depending on if the motor is cold or hot. Pushrod weight is very important with the 1:1.13 (edited) Norton rocker ratio - not to be forgotten when making comparisons.

Wow! Rocker ratio of 1:13. What are you designing now?

More like 1:1.13.

As for steel pushrods and alloy barrels, one needs to factor that in when setting lash cold. With the 750 USS with Steve Maney alloy barrels, when running steel pushrods and a Megacycle N480 cam we set the lash to 0.002 cold for intake and exhaust.The motor was happy!

Dances with Shrapnel said:

Wow! Rocker ratio of 1:13. What are you designing now?

More like 1:1.13.

As for steel pushrods and alloy barrels, one needs to factor that in when setting lash cold. With the 750 USS with Steve Maney alloy barrels, when running steel pushrods and a Megacycle N480 cam we set the lash to 0.002 cold for intake and exhaust.The motor was happy!

Click to expand...

Yes you are correct - its 1:1.13 (I goofed but I'll be perfect starting tomorrow).

I think the alum matrix pushrod is very interesting.

Go to:
http://solutions.3m.com/3MContentRetrie ... on=current

But then just try to contact 3M about the aluminum matrix pushrod material.
THIS JUST IN (after some aging while being on hold) - The alumium matrix pushrod material is no longer available from 3M - another one bites the dust.

If the steel pushrods are heavier than aluminium ones, that is the end of it. I suggest that revving a commando engine above 7000 RPM is an expensive way to go. The bottom end would probably fail before you got regular valve float even with standard valve gear and cam. When I had the short stroke Triumph I polished all the valve gear and reduced it's weight. I used Wassell tappet adjusters which were hollow and cut the lock nuts in half. I haven't done any of that with my Commando engine. I've tuned it to pull, raised the gearing and I'm extremely careful not to over-rev it. I'm still thinking about fitting the Combat cam, however the downside is a worry.

Here's part of a quote from another thread at:
commando-pushrod-tech-t12779-15.html?hilit=pushrods

comnoz said:

.... Steel pushrods with aluminum barrels limit your camshaft selection to those built for large clearances. If you run steel pushrods and an aluminum barrel with a cam designed for .008 or less clearance you would set them at zero clearance cold but when the engine gets hot the clearances will increase so much that the quieting ramps will no longer be used. The valve train will then wear more rapidly. [particularly the seats] ....

Click to expand...

I was told that hot clearance would be up around .020" but I haven't verified that.

jseng1 said:

I was told that hot clearance would be up around .020" but I haven't verified that.

Click to expand...

Yes, it would be good to verify. Steve Maney uses aluminum barrels with steel pushrods and I doubt he is using big cams and has no problems.

I guess one would need to look at the hot clearances on a alloy pushrod/cast barrel and compare it to a steel pushrod/alloy barrel configuration.

Don't cams which have quietening ramps require bigger tappet clearances ? Which should we allow for that - or the barrel and pushrod expansion ? OR are ramp cams used so that larger tappet clearances can be used to allow for barrel and pushrod expansion ?

acotrel said:

Don't cams which have quietening ramps require bigger tappet clearances ?....

Click to expand...

My only experience of quietening ramps is on my ES2, in that case tappet clearances are unchanged (nil), but you do need to be careful setting the clearances. In the ES2 case at least the ramped cams seem to begin to lift a little earlier so if not careful you can do the tappets while on the ramp, which will give more effective clearance than intended.

A friend of mine tried carbon fibre pushrods in his BMW race bike. They were apparently very stiff, but they had zero ( effective) thermal expansion.

From memory a BMW pushrod is around 300mm long and there's significant expansion of the barrels so that carbon fibre pushrods were un-useable.

To get a decent hot clearance meant that cold clearance was negative. If you set them to , say 2 thou cold, they would be 15 thou when the engine heated up. The cam spec was 6 thou, so if you set them to 6 thou hot, you got 11thou LIFT instead of clearance when the engine cooled down.... made it difficult to start

pommie john said:

The cam spec was 6 thou, so if you set them to 6 thou hot, you got 11thou LIFT instead of clearance when the engine cooled down.... made it difficult to start

Click to expand...

Yep, that would be a little frustrating! :mrgreen:

pommie john said:

A friend of mine tried carbon fibre pushrods in his BMW race bike. They were apparently very stiff, but they had zero ( effective) thermal expansion.

From memory a BMW pushrod is around 300mm long and there's significant expansion of the barrels so that carbon fibre pushrods were un-useable.

To get a decent hot clearance meant that cold clearance was negative. If you set them to , say 2 thou cold, they would be 15 thou when the engine heated up. The cam spec was 6 thou, so if you set them to 6 thou hot, you got 11thou LIFT instead of clearance when the engine cooled down.... made it difficult to start

Click to expand...

No doubt someone can paint themselves in a corner if they do not think it through a bit. Stock commando pushrods average about 8" (200mm). Aluminum has a coefficient of thermal expansion of 12.3, steel about 6.7 and carbon fiber around 1.0 so substituting CF for aluminum you have 1/10th the dimensional change per degree temperature change. That is a BIG difference.

For reference an example follows where we go from 0 degrees F to say hot oil in the pushrod tunnels at say maybe 300 degrees F.

Change in length = Length X Coefficient of thermal expansion X (change in temperature)
0.029" = 8" X 0.0000123 X (300-0)

That (0.029") is a lot. A cast iron barrel length will grow by something less than this as it has a coefficient of thermal expansion of around 1/2 that of Aluminum. Exactly how much is somewhat indeterminate without direct measurement since temperature throughout the barrel varies both radially and longitudinally.

An aluminum barrel will grow by something more than a cast iron barrel but its' heat profile will be different and it is complicated by steel through bolts.

In my mind the only way to understand the differences is to take direct measurements in valve lash from cold to hot for the various pushrod and barrel materials. With air cooled vintage engines, this measurement approach is not an easy task and there is a whole spectrum of how hot an engine is and how cool a pushrod is at any given point in time (hauling up a hill WOT in hot weather versus down hill at 1/8 throttle in the winter time).

The big difference I see from an applications standpoint are the relative stiffness of the different materials for pusrods. Steel has a Young's Modulus of 30 X 10^6 psi whereas aluminum is one third that at 10 and Titanium around 16. I believe Prof Gordon Blair's 4stHEAD software can model this and show the relative differences in valve motion using different pushrod materials. I can easily see where going from aluminum to steel pushrods could easily cause other problems in a highly stressed motor unless the valve train is designed for it. Most Commmando cams are designed for stock valve train components (other than the BSA cam follower upgrade)

Steel pushrods in tuned Nortons would seem to me to be fairly common! I have a set in mine.

Steve Maney supplies steel pushrods, with the advice that in an iron barrel half the clearance rcommended for the cam, and in his alloy barrels set the clearance so that you can just rotate the pushrod with your fingers.

Not heard of any issues.

If the pushrods are heavier and the cam is radical, the valve float problem could occur lower down the rev range, however are Commando engines usually revved that hard before something else fails ? I could believe that a commando motor with thicker crankcases and a billet crank, carillo rods and lighter pistons might stay together if it regularly reached the revs where valve float might occur. However it would be a very expensive exercise. The weight saving with Jim Schmidt's BSA type followers would probably be more than that which is added by using steel pushrods ?

Dances with Shrapnel said:

...In my mind the only way to understand the differences is to take direct measurements in valve lash from cold to hot for the various pushrod and barrel materials. With air cooled vintage engines, this measurement approach is not an easy task and there is a whole spectrum of how hot an engine is and how cool a pushrod is at any given point in time (hauling up a hill WOT in hot weather versus down hill at 1/8 throttle in the winter time).

The big difference I see from an applications standpoint are the relative stiffness of the different materials for pusrods...

Click to expand...

Yes. And from memory of what I heard you can have about .020" clearance with steel pushrods in alum cylinders when hot after setting them to 0 when cold. Confirmation is needed. So the question is - what are you loosing and gaining? If you are getting more clearance with steel pushrods then you are loosing lift. If alum pushrods are compressing then you are loosing lift (but clearances are tighter). So does it come out the same? No one seems to know for sure. Lots of bounce is happening at the valve at high RPMs but I'm not seeing any problem with the alum pushrods in Comstocks spintron (see page 4 of this thread). If I get a smooth ramp cam together for the spintron I will ask to have the pushrods filmed when its on the spintron at high RPM.