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Ally push rods
Jesus-Ninja - 17/1/08 at 10:21 AM

anyone got any opinions on using internally threaded ally tube for push / pull rods with steel rose joints?

BenB - 17/1/08 at 10:33 AM

If you're worried re structural strength of ali then surely it depends on tube diameter and length, wall thickness, grade of ali used and what the push/pull rod is used for.

If you're worried about galvanic corrosion then that's a different matter

britishtrident - 17/1/08 at 10:35 AM

Bigest problem is likely to be that aluminium alloy and fine threads generall don't work well together but that shouldn't be a stopper.

However you could use alluminium alloy tube and head shrink threaded steel bosses in the ends, The valve push rods on late 50s/60s Rootes Sunbeam engines were made in a similar fashion. With a tubular push rod you can go up in diameter for the same weight.

Steel or light alloy the most likely mode of failure for a push rod is buckling --- so the stress calculation for the push rod would be the "Euler Buckling Formula - for columns with pinned ends).

[Edited on 17/1/08 by britishtrident]

02GF74 - 17/1/08 at 10:48 AM

if you are thinking of using as engine push rods, then most likely the diameter wil be bigger so you need to enlarged the passsges so the rods have clearance. I seem to recall you could by CF rods for B series engine.

iank - 17/1/08 at 10:51 AM

quote:
Originally posted by 02GF74
if you are thinking of using as engine push rods, then most likely the diameter wil be bigger so you need to enlarged the passsges so the rods have clearance. I seem to recall you could by CF rods for B series engine.


You could certainly buy CF rods for the A series. There are explicit warnings in Vizard about making sure they don't rub on the passages - they fail quite spectacularly if they do.
I'm not sure if they are still available, or anyone uses them these days. I suspect the kind of person trying for maximum output on an A series these days will be putting on one of the 16v heads, so won't need them.

Jesus-Ninja - 17/1/08 at 11:04 AM

quote:
Originally posted by 02GF74
if you are thinking of using as engine push rods, then most likely the diameter wil be bigger so you need to enlarged the passsges so the rods have clearance. I seem to recall you could by CF rods for B series engine.


Apologies - perhaps I should clarify - suspension pushrods for inboard springs / shocks

..hence the post in the "running gear" board...

Jesus-Ninja - 17/1/08 at 11:20 AM

quote:
Originally posted by britishtrident
Bigest problem is likely to be that aluminium alloy and fine threads generall don't work well together but that shouldn't be a stopper.


Yeah - I know how well steel strips ally threads. They don't call me the helicoil king for nothing. Actually they don't call me the helicoil king at all....

quote:
Originally posted by britishtrident
However you could use alluminium alloy tube and head shrink threaded steel bosses in the ends


is this as "simple" as it sounds? Is ti the sort of thing that can be done at home?

quote:
Originally posted by britishtridentthe stress calculation for the push rod would be the "Euler Buckling Formula - for columns with pinned ends).

[Edited on 17/1/08 by britishtrident]


Time to get my researching hat on then....


Thanks for the, as ever, comprehensive reply!

NS Dev - 17/1/08 at 12:50 PM

see no reason why not to do them in ally as long as you do thread insert the ends with steel helicoils, and use fairly thick wall tube.

The buckling equation may well be your friend on this one, as you will really need fairly thick tube to resist buckling, which then means that you can't use steel to best advantage as it will also have to be pretty thick, thus the benefit of using ally.

(I think, unless I have gone even more mad)

lsdweb - 17/1/08 at 01:56 PM

Many single seaters use aluminium tie rods with steel rose joints (different loads but the same principle) - photo