E: Engine Alternative Pushrods

nkt267

Well Known and Active Forum User
VOC Member
Thanks for the idea about arrows-for-pushrods, I will get some for inspection. You cannot get alu tube material in high tensile basically so am interested what arrows are. 9 mm o.d. look good to me but I suspect the wall thickness to be minimal so guess I will keep the 10mm type with 2mm wall thickness tubing , available easily. Does someone actually run rods made out of arrows, what sizes ?

Vic
The thing about arrow shafts,they are rolled and welded not extruded.
The sizing for alloy arrows when looking at the listings is simple. Take 1916's for example:- the first 2 numbers (19) refer to the diameter in 64th of an inch ie 19/64"'s, the second 2 numbers (16) refer to the wall thickness in thou ie:- 0.016". X7's will be the highest tensile strength and Jazz or beginners arrows will be the lowest.
Also the bigger the diameter the stiffer the arrow, the wall thickness when shooting only affects the weight and therefore the distance/balistic arc.
https://eastonhunting.com/making-sense-of-arrow-spine/
the link will explain about 'spine' which is the amount an arrow will bend under testing for stiffness.
 

oexing

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VOC Member
Thank you all for clarifications, as to arrows I guess I will stick to using common 10mm alu tubing, 2mm wall thickness - as used in Horex and many thousands of modern BMW flat twins. We do not need to discuss if alu or steel may be suitable. Alu types have proved to be perfectly allright for that purpose, even at TWICE the length of Vincent massive steel pushrods. I had a Vincent type and one Horex alu pushrod on my scales yesterday: The Horex type, in my picture no. 1 and 2 at the left, are just 8 grams more weight than the steel Vincent at HALF the length and no adjusters at these !! Ridgidity is super important with very long rods . Alu has only one third of stiffness to bending (english term ??) compared to steel with same dimension. Nevertheless the 10mm alu tubing has proved to be safe at 28 cm total length, Vincent rods are only 15 cm so I don´t see the faintest risk to going for alu here.
Main reason for change to alu -apart from weight saving- is thermal growth and steel is not a good idea in an all alu engine because when engine hot you see more valve clearance than is desirable. With excessive valve clearance you lose all of the minimal quieting ramps that is designed into the olde standard cam profiles. You cannot do much more than having nil play at cold state with steel rods and live with it. Negative clearance is not practical as no way to assess the amount. With alu rods you then have the chance to set some clearance when cold. But in this moment just thinking: Aahm, still no way to stick a feeler gauge anywhere for checking on a Vincent engine ??? So it is for setting nil at the adjuster screw and from this position backoff a fraction of a revolution - like 20 degrees - for working clearance with alu rods ?? Or else finger feel . . .
As to steel pushrods, in the R 69S sports type Earles BMW they picked ultra light thin wall steel tubing for pushrods, 10 mm o.d. at 0.50 mm wall thickness, brazed ball ends - super . BUT: These engines have cast iron cylinders and the rocker units sit on steel distance pillars deep down in the head, so only 20mm of aluminium up there plus the engine case containing the camshaft for temperature compensations in valve setting. When I skipped the cast iron barrels for alu types it was the same nil clearance game as with Vincents - no big deal, modern cam shapes with long quieting ramps there.
Looking at the photo samples of pushrods above, poor practice not to waist the ball ends. I do ball ends for adjuster screws or pushrods in times, no question , machining ball ends like here in my pictures, so never any troubles elswhere then.

Vic

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clevtrev

Well Known and Active Forum User
VOC Member
Thank you all for clarifications, as to arrows I guess I will stick to using common 10mm alu tubing, 2mm wall thickness - as used in Horex and many thousands of modern BMW flat twins. We do not need to discuss if alu or steel may be suitable. Alu types have proved to be perfectly allright for that purpose, even at TWICE the length of Vincent massive steel pushrods. I had a Vincent type and one Horex alu pushrod on my scales yesterday: The Horex type, in my picture no. 1 and 2 at the left, are just 8 grams more weight than the steel Vincent at HALF the length and no adjusters at these !! Ridgidity is super important with very long rods . Alu has only one third of stiffness to bending (english term ??) compared to steel with same dimension. Nevertheless the 10mm alu tubing has proved to be safe at 28 cm total length, Vincent rods are only 15 cm so I don´t see the faintest risk to going for alu here.
Main reason for change to alu -apart from weight saving- is thermal growth and steel is not a good idea in an all alu engine because when engine hot you see more valve clearance than is desirable. With excessive valve clearance you lose all of the minimal quieting ramps that is designed into the olde standard cam profiles. You cannot do much more than having nil play at cold state with steel rods and live with it. Negative clearance is not practical as no way to assess the amount. With alu rods you then have the chance to set some clearance when cold. But in this moment just thinking: Aahm, still no way to stick a feeler gauge anywhere for checking on a Vincent engine ??? So it is for setting nil at the adjuster screw and from this position backoff a fraction of a revolution - like 20 degrees - for working clearance with alu rods ?? Or else finger feel . . .
As to steel pushrods, in the R 69S sports type Earles BMW they picked ultra light thin wall steel tubing for pushrods, 10 mm o.d. at 0.50 mm wall thickness, brazed ball ends - super . BUT: These engines have cast iron cylinders and the rocker units sit on steel distance pillars deep down in the head, so only 20mm of aluminium up there plus the engine case containing the camshaft for temperature compensations in valve setting. When I skipped the cast iron barrels for alu types it was the same nil clearance game as with Vincents - no big deal, modern cam shapes with long quieting ramps there.
Looking at the photo samples of pushrods above, poor practice not to waist the ball ends. I do ball ends for adjuster screws or pushrods in times, no question , machining ball ends like here in my pictures, so never any troubles elswhere then.

Vic

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Using 10mm dia, you will most likely find the rod binding on the push rod tube.
 
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