Commando Pushrod Tech

Thanks, Jim. I was hoping you'd chime in.

I've talked to Steve in the past about the clearance issue vs thermal expansion rate. He was using a 4S cam at first, and later his own variation of a 4S. With .016" clearance spec on the 4S, it wasn't much of an issue, but I recall him mentioning that on some cams he had to set the clearance at pretty much zero cold to get them to work properly. Can you add anything about how you choose what cold clearance setting to use with steel rods? With stock aluminum rods, I've always used the cold clearance settings recommended by the cam supplier, whether I was using iron barrels or aluminum barrels. It occurs to me now in hindsight, that maybe I should have used a different clearance with the alloy barrels. Presumably I could have used a tighter cold clearance with the alloy barrels, since they will expand more than the iron ones. Any comments?

Interesting info about the bronze ends. I never considered that. All I've ever seen are case-hardened steel ends, and the not-too-successful hard anodized aluminum ends. Do you make the ends yourself, or buy them in from a supplier?

Ken

lcrken said:

Do you make the ends yourself, or buy them in from a supplier?

Ken

Click to expand...

Is there something Jim can't make?

lcrken said:

Thanks, Jim. I was hoping you'd chime in.

I've talked to Steve in the past about the clearance issue vs thermal expansion rate. He was using a 4S cam at first, and later his own variation of a 4S. With .016" clearance spec on the 4S, it wasn't much of an issue, but I recall him mentioning that on some cams he had to set the clearance at pretty much zero cold to get them to work properly. Can you add anything about how you choose what cold clearance setting to use with steel rods? With stock aluminum rods, I've always used the cold clearance settings recommended by the cam supplier, whether I was using iron barrels or aluminum barrels. It occurs to me now in hindsight, that maybe I should have used a different clearance with the alloy barrels. Presumably I could have used a tighter cold clearance with the alloy barrels, since they will expand more than the iron ones. Any comments?

Interesting info about the bronze ends. I never considered that. All I've ever seen are case-hardened steel ends, and the not-too-successful hard anodized aluminum ends. Do you make the ends yourself, or buy them in from a supplier?

Ken

Click to expand...

Any of the cam suppliers I talked to said they're lash specs were for an iron barrel with aluminum pushrods. With that combo the clearance decreases around .004 in when the engine gets hot -as best as I have been able to measure- maybe more when actually running. When I use steel pushrods with an iron barrel I usually set the valve lash around .004 tighter than spec and haven't had any issues.

Using an aluminum barrel with aluminum pushrods the cold clearance and the hot clearance stays about the same so I set them .004 tighter than the spec.

Using steel pushrods with aluminum barrels has caused me grief with tight clearance cams. If the cam calls for .006 and I reduced it to .002 then it would work fine for a day of racing but next time I checked them I usually found the clearance was zero. The valve seats seemed to wear more and I attributed it to loose clearance when running. I also saw more valve tip wear. The cams that gave me trouble with steel rods were the 2s, the webcam 12a and the webcam 86c.

I had no problems when using the 4s or the 7s with steel rods and aluminum barrels.

The 560n480 beat up the valvetrain no matter what I did. The webcam 197 with a 4 inch radius lifter is nearly identical to the 560n480 but it is much easier on the valvetrain. I only got benefit from the bigger cams on small high rpm motors. Jim

And yes, I made my own ends.

I only got benefit from the bigger cams on small high rpm motors. Jim

Click to expand...

Could you expand on this a bit, I thought a bigger engine would tend to tame an aggressive cam down low and tend to come on cam-pipe sooner than a smaller engine. This is partly why I choose a Norris D instead of milder like 2S even.

hobot said:

I only got benefit from the bigger cams on small high rpm motors. Jim

Click to expand...

Could you expand on this a bit, I thought a bigger engine would tend to tame an aggressive cam down low and tend to come on cam-pipe sooner than a smaller engine. This is partly why I choose a Norris D instead of milder like 2S even.

Click to expand...

I have heard that also, what I have seen is longer duration cams need to turn at a faster speed to make the timing events work in sync with the intake and exhaust tuning.

Big engines do not usually like to turn that fast.

Small engines, particularly short stroke motors that turn a lot of revs can take advantage of the longer duration. Jim

Ok, I both do and do npt understand your findings so will start my Peel experiment with a flat lifter Norris D and see what happens with and w/o boost. Peel has factory small size valves with 6 mm stems, I've read smallish valve area also tends to tame a big cam down low but may stifle hi rpm, unless helped out.

The best results I have had for a blower cam has been short duration with wider lobe centers for less overlap.
If you are using high compression along with limited boost from a positive displacement blower you might want a little more cam. Jim

lcrken said:

Chris said:

I do remember a couple of years ago someone running carbon fibre pushrods.

Click to expand...

My friend, Martin Adams, tried carbon fiber pushrods in the engine in his Commonwealth Norton back in the '80s. As I recall, one of them shattered into tiny bits, so he went back to aluminum. I think I still have the other three pushrods.

Ken

Click to expand...

I bet carbon fiber technology has come a little ways since then. Might be worth looking at again. The drawback is that they won't expand like steel or aluminum.

the rule I used was if you add stroke = add duration and if you add bore = add lift if you don't want to rev the motor higher but this is a VERY simplified answer.

comnoz said:

I have heard that also, what I have seen is longer duration cams need to turn at a faster speed to make the timing events work in sync with the intake and exhaust tuning.

Big engines do not usually like to turn that fast.

Small engines, particularly short stroke motors that turn a lot of revs can take advantage of the longer duration. Jim

Click to expand...

swooshdave said:

I bet carbon fiber technology has come a little ways since then. Might be worth looking at again. The drawback is that they won't expand like steel or aluminum.

Click to expand...

A friend of mine ran Carbon fibre pushrods in his BMW racer. The lack of thermal expansion meant that with the alloy barrells he had to reset the valve clearances every time the engine got hot and again when it was cold!

If you set them cold, there was far too much clearance when hot, and if you then reset them while hot to a few thou, they would close up when the engine was cold and there was no compression so it wouldn't start.

bill said:

the rule I used was if you add stroke = add duration and if you add bore = add lift if you don't want to rev the motor higher but this is a VERY simplified answer.

comnoz said:

I have heard that also, what I have seen is longer duration cams need to turn at a faster speed to make the timing events work in sync with the intake and exhaust tuning.

Big engines do not usually like to turn that fast.

Small engines, particularly short stroke motors that turn a lot of revs can take advantage of the longer duration. Jim

Click to expand...

Click to expand...

My rule of thumb was if you increase the bore- increase the valve size, if you could add lift without adding duration that would work too.
Adding duration only tends to raise the RPM of the powerband and takes away that great midrange torque that is the best part of a Norton. Jim

pommie john said:

swooshdave said:

I bet carbon fiber technology has come a little ways since then. Might be worth looking at again. The drawback is that they won't expand like steel or aluminum.

Click to expand...

A friend of mine ran Carbon fibre pushrods in his BMW racer. The lack of thermal expansion meant that with the alloy barrells he had to reset the valve clearances every time the engine got hot and again when it was cold!

If you set them cold, there was far too much clearance when hot, and if you then reset them while hot to a few thou, they would close up when the engine was cold and there was no compression so it wouldn't start.

Click to expand...

I have seen that same problem with Ti pushrods. The cro-moly pushrods were a little better.
I think the better idea would be to increase the rocker arm ratio and then the pushrod-lifter weight wouldn't be so important.
Of course it doesn't matter anyway unless your running a very aggressive cam in a shortstroke type RPM range. Jim

Hi all! This is my first post on the forum so be gentle with me please. I'm not too sure if I should have started a new thread but my question seems to fit in pretty much with this topic. A while back I bought some Maney pushrods, and I've often wondered about the clearance setting, I run a 4S and cast iron barrels and have them set as Steve Maney recommended at "about 0.006'". When I ran the std rods I have had them set at 0.012' and but later set them to 0.016' which gives quite a difference performance wise. From a comparison I made on the "makeitfrom" web site it shows Thermal Expansion: 20 to 100°C (µm/m-K) as being 19-24.2 for alumunium and 12 for chromoly steel, this tells me the std rods will expand upto anything between 58 to 100% more than the Maney rods, so from this could I take it that an equivalent 0.016' gap using Maney rods would be between 0.008' and 0.12' ? I'm worried that at 0.006' I'm spending too long off the seat and lift is affected. (it goes well enough though!)
Comments and advice appreciated. Also many thanks to all, for all the info and guidance I've already stolen from this forum!

Paul.

When I was racing with that same setup I took a guess and set them at .008 intake and .010 exhaust. I didn't have any problems.

The best way to really know would be to test the cam and then set the lash to give you the correct duration when the motor is hot. You want the valve to just leave the seat about 60 to 80 percent of the way up the quieting ramp with most cams.

If the lash is too loose then seat wear becomes a problem.

If the valve is too tight then the valve may overheat and cause preigntion or valve failure. Jim

I try very hard to never exceed 7,000 RPM with my 850 motor. Why do you need lighter pushrods Ken, - perhaps cams with longer duration and slower lift and closing rates might be better, if the exhaust system suits ?

Beng suggests increasing the column section in one direction....that is pointless as the column will always flex or fail in the direction with the least moment of inertia (least stiffness). Valves
float when the object with the most inertia ( consider lifter, pushrod, rocker, springs, retainer, and valve itself) floats. I have always had a "gut" feeling it was the valve or lifter that was the main culprit. The lifter has the added friction of its bore, which adds to its weight in effect. The valve train is not a monolithic structure, each component can "float" apart from its neighbors, although the spring, retainer and valve are joined, and may be considered a monolithic structure. The critical component in the latter structure is the valve.

I once tried shimming the valve springs to get more RPM....got it! ....for 300 miles....then wore the cam round. So beware.

slick

acotrel said:

I try very hard to never exceed 7,000 RPM with my 850 motor. Why do you need lighter pushrods Ken, - perhaps cams with longer duration and slower lift and closing rates might be better, if the exhaust system suits ?

Click to expand...

I'm not so much trying to get lighter pushrods as I am trying to get the most stiffness from a given weight. So far I've only sold them in a configuration that is the equivalent of stock pushrods, and to a very limited market. If I go any further with it, I want to be sure I'm offering the best designs I can for particular applications. Besides, I'm a gearhead, and I just like doing this sort of stuff.

Ken

The E3325 cams used in 1958 Triumph Thunderbirds had pronounced quietening ramps yet gave performance close to E3134 racing cams. I've used cams with over 360 deg. duration in my short stroke Triumph 500 which had fairly low lift, and the motor revved easily between 5000 RPM and 10,500 RPM giving good power. However the bang when the cam and pipe started working together made the bike simply nasty and difficult to ride. I agree with what Jim Comstock has said - the strength of the commando motor lies in its midrange power. I suggest the only trouble with that lies in the gearing. If the guys who are racing commandos today would give frank and truthful answers, it would be interesting to collect data about what works at Daytona, and a shorter circuit, and do some pattern recognition. Most of us fly blind to a certain extent, however I suggest port sizes, exhaust configuration, cam duration and timings, are critical to success. I suggest moving up the rev range to get more power, with a commando engine is a futile and expensive exercise. I don't believe the valve train is the limiting factor for revving the motor hard.

I read a comment somewhere that when the commando was being developed, the Norton factory sent one of it's erks to buy a Triumph race cam to copy. I've often wondered if the early race cams used by Norton for the commando were based on the E3134 ?

acotrel said:

I read a comment somewhere that when the commando was being developed, the Norton factory sent one of it's erks to buy a Triumph race cam to copy. I've often wondered if the early race cams used by Norton for the commando were based on the E3134 ?

Click to expand...

That should get PW apoplectic!! I had the good fortune to share an office with PW for a short time, and for the whole of the time he had an approx 10x cam lobe on his board, and he was up to his ears in calculations. So whilst its entirely likely that an E3134 cam was bought it would have been for comparison purposes I would suggest. Whilst I was there they certainly did buy the first Honda 750 four in the UK, if not Europe, and as soon as the first Yamaha "street scrambler" (DT1?) was introduced they had one of those as well.

cheers
wakeup