New 336° cam from BMW

[pommie john]

Originally Posted by Voltaire

Was thinking the same thing ... lighter stronger materials are now being used in Triumph valve trains, the Trident owner at the track was horrified when I told him BMW ones were nearly a foot long..... he gave me some places that make custom ones in the States that don't flex.....mind you how long is Triumph one...4"....?

I've looked at ways around the pushrod issue and haven't yet found a good solution. The chrome moly steel ones are stiff, but much heavier and with a foot long pushrod, there's significantly less thermal expansion in the rod so valve clearances vary as the engine heats up.

A friend of mine tried composite carbon pushrods. Very light and very stiff , but they don't expand at all with heat. It was so bad that if he set valve clearances hot, when the engine cooled down there was no compression when the engine was cold because the pushrods held the valves open! The only way he could make it work was either to set the valve clearances every time the engine was cold, and then reset them as it got hot, or never let the engine cool down!

[supershaft]

Originally Posted by motu

Valve train has always been the limiting factor with pushrod engines, that's why ohc is now the prefered option. But plenty of pushrod engines can be made to rev well, some even stock. I used to rev the unit 500cc Triumph twins to over 10,000rpm, completely stock. So if it's happy at 8,000rpm with no valve float issues, that's still safe on these engines - the bottom engine is up to the task ?

Not always. It depends on the stroke. Some pushrod engines run into piston speed problems before valve train problems. For instance, Triumph 650's are going to run into piston speed issues long before BMW 650's or 1000's.

[supershaft]

Originally Posted by Voltaire

Was thinking the same thing ... lighter stronger materials are now being used in Triumph valve trains, the Trident owner at the track was horrified when I told him BMW ones were nearly a foot long..... he gave me some places that make custom ones in the States that don't flex.....mind you how long is Triumph one...4"....?

I had some custom made at Manton here in Ca. Twice as heavy as BMW steel rods and three times as heavy as BMW aluminum rods which absolutely do flex a lot as evidenced by their rub marks. The big money pushroders (NASCAR and NHRA drag racers) have doubled and tripled their pushrod weights in the last ten or so years for more rigidity and power with relatively little effect on valve float rpm. I think my heavier pushrods did lower my valve float by a couple of hundred RPM BUT I am also running heavier intake valves (bigger) at the same time.

I forgot to add that I am running into the same issue as pj's friend with the carbon fiber rods with my 4130 pushrods. I am setting my exhaust at zero play and my intakes just slightly preloaded in order to get .004 and .008" when it is hot but it apparently isn't enough to effect starting at all so far.

[supershaft]

Originally Posted by pommie john

The main issue with high RPM in airhead engines has been cavitation at the oil pump. Essentially, the pump is trying to suck too much oil from the sump and it has so much suction that it causes bubbles to form in the pick up tube. The traditional way around this was to drill the pick up out bigger. ( I think it goes from 10mm to 13mm but one of the other guys will correct me if I'm wrong).

After doing this to my racer, it's happy running to 8500 with no problems. I have an oil pressure gauge just in case.

I believe some people have machined the pump thinner so it draws less oil.

I'm not familiar enough with the R65 engine to know if it's a problem with them too.

The later models come stock with that mod (and a lot of other mods as well). I don't know when they started doing it. My '92 has a 13mm oil pickup. I would guess my '83 R65 did too. I use to rev it well over its 7650 stock redline ALL the time. My stock electronic tachs top out at 8000rpm so I am guessing up above that. I am guessing my valves are now floating a little before 8500rpm. If it becomes an issue I can always preload my stock springs a bit. Right now they are bone stock.

[Voltaire]

The R65 has the larger oil pick up.
SS, I no longer beleive what the BMW rev counter says after seeing the ignition program on the lappy....its spot on...as it has to be...the rev counter less so....I gave up on the electronic one as it wet heywire over 7500.....the mechanical on is better but reads high.
No longer run one, just change up when the limiter hits

[RGregor]

Originally Posted by supershaft

Twice as heavy as BMW steel rods and three times as heavy as BMW aluminum rods which absolutely do flex a lot as evidenced by their rub marks. The big money pushroders (NASCAR and NHRA drag racers) have doubled and tripled their pushrod weights in the last ten or so years for more rigidity and power with relatively little effect on valve float rpm. I think my heavier pushrods did lower my valve float by a couple of hundred RPM BUT I am also running heavier intake valves (bigger) at the same time.

So your pushrods are ~150 grams?
And everything stock except your Ti-retainers? What are they? Probably around ~12 grams.

I believe your observations but I also believe in physics and mathematics.
Pure mathematics say that you'll need 26% more spring force than stock for the same rpm.
For 8500 rpm you'd need more than 1000N spring force.
The stock spring has around 800N max force.
Preloading 1mm brings an additional 45N only.

Somethings wrong in that calc.

Edit: these are the according data

Masses			Masses, reduced to valve side
Part	Stock	mod	Stock	mod
Lifter	60,0	60,0	43,2	43,2
Pushrod	54,0	150,0	38,8	107,9
Rocker	30,0	30,0	30,0	30,0
Screw	15,0	15,0	10,8	10,8
Valve(in)	86,0	86,0	86,0	86,0
Spring	54,0	54,0	18,0	18,0
Retainer	17,0	12,0	17,0	12,0
Keys	3,0	3,0	3,0	3,0
Sum			246,8	310,9
Rel. Change to stock			100	126,0

[RecycledRS]

RGreger what type of spring material are you using to get 18 grams?

[supershaft]

Originally Posted by RGregor

So your pushrods are ~150 grams?
And everything stock except your Ti-retainers? What are they? Probably around ~12 grams.

I believe your observations but I also believe in physics and mathematics.
Pure mathematics say that you'll need 26% more spring force than stock for the same rpm.
For 8500 rpm you'd need more than 1000N spring force.
The stock spring has around 800N max force.
Preloading 1mm brings an additional 45N only.

Somethings wrong in that calc.

Edit: these are the according data

Pure mathematics? Mathematics is pure until we associate values to the numbers. Therein lies possible imperfection! I couldn't care less about the physics of it since all kinds of tuners have noticed since the early sixties that I am aware of that weight on the pushrod side of the rocker for some reason effects valve float rpm very little just as the tiniest differences in weight on the valve side of the rocker arm effects valve float rpm a great deal. Try to work that out on paper if you can but I still won't care much sense I am mostly interested in what works, not math. Especially bad math since, if some math predicts something won't work and it does work, it's not good math. There is no need to 'believe' in good physics! It's the bad physics that takes a leap of faith. You don't have to believe just me. Do some reading on the subject. My experience was just what the experts predicted. That's the kind of experts I listen to! I am sure some would have predicted that it wouldn't work at all but here I am and it works. It's great when things work out! Now I am not completely sold on the idea as of yet with only 2000 miles experience but so far so good.

I don't remember the exact weights. They are real close to three times the weight of the aluminum rods and twice as heavy as the steel ones. The retainers are only grams lighter but they really do increase any setup's float rpm by around 500rpm just as some experts predict. Predictions that can be duplicated. Now THAT'S good science!

[RGregor]

Originally Posted by RecycledRS

RGreger what type of spring material are you using to get 18 grams?

The spring has a weight of 54 grams. But as only parts of it are moving you don't count the whole weight.
Usual numbers are 50% or 30% of the spring weight.
54/3=18.

[RGregor]

Originally Posted by supershaft

Pure mathematics? ....

I did some reading on the subject and the way to calculate masses is the result of it.
Still it's a very primitive model as it does not take into account any flexibility.

Now, obviously your practical results and my theory differ. At this point asking questions way reveal some information not mentioned yet. Not the case here.
Good practical results beat bad theory. Any hints where to find the information you refer to in literature?

Happy New Year to all Adventurers here!

[supershaft]

Originally Posted by RGregor

I did some reading on the subject and the way to calculate masses is the result of it.
Still it's a very primitive model as it does not take into account any flexibility.

Now, obviously your practical results and my theory differ. At this point asking questions way reveal some information not mentioned yet. Not the case here.
Good practical results beat bad theory. Any hints where to find the information you refer to in literature?

Happy New Year to all Adventurers here!

I think I googled pushrods? I think Manton has links to sites? Tons of tuners are just recently running way heavier rods for rigidity. Circle Track magazine might be a source? Sprint car racers are the other cutting edge pushrod sport!

[RGregor]

Originally Posted by supershaft

I think I googled pushrods? I think Manton has links to sites? Tons of tuners are just recently running way heavier rods for rigidity. Circle Track magazine might be a source? Sprint car racers are the other cutting edge pushrod sport!

Thanks, I'll try that.

[Stan_R80/7]

Something worth considering about pushrod rigidity is the diameter and material modulus of elasticity. In the sport of archery (which is completely unrelated) aluminum arrows have been merged with carbon fiber to form a composite shaft. This allows smaller diameter, lighter arrows, that have the same stiffness as arrows made from aluminum of larger diameters due to the increase in material modulus.

As such, a (slightly) larger diameter pushrod made from aluminum-carbon composite will be stiffer than a standard aluminum tube without much of a weight penalty. I am not sure about the thermal expansion because of the carbon layer, but the length change will be closer to aluminum than pure carbon. I have to expect the 'state of the art' pushrod engine racers have looked into this material and it's just a matter of searching for the right keywords.

[supershaft]

Originally Posted by Stan_R80/7

Something worth considering about pushrod rigidity is the diameter and material modulus of elasticity. In the sport of archery (which is completely unrelated) aluminum arrows have been merged with carbon fiber to form a composite shaft. This allows smaller diameter, lighter arrows, that have the same stiffness as arrows made from aluminum of larger diameters due to the increase in material modulus.

As such, a (slightly) larger diameter pushrod made from aluminum-carbon composite will be stiffer than a standard aluminum tube without much of a weight penalty. I am not sure about the thermal expansion because of the carbon layer, but the length change will be closer to aluminum than pure carbon. I have to expect the 'state of the art' pushrod engine racers have looked into this material and it's just a matter of searching for the right keywords.

From what I have read, the state of the art pushrod guys (NASCAR, NHRA, and Sprint car) are for the most part using 4130 with a small minority using 4140 if I remember right.

[supershaft]

I was just thinking about one of my aviation bosses. He liked 1025 a lot for maybe something like this but I don't know if its available right now. There is a California pushrod maker (can't remember the brand name right now) that use to make them for the guys at B+S and whatnot with 1018. They make a lot of them out of 1018. I would prefer 1020. Personally, I like the way it machines much better than 1018! I had mine made out of 4130. It takes compression quite a bit better than 1018.