Con rod material spec.

A few days ago I found a DC Spitfire (1cc) on a junk stall. Having extracted it from a liberal coating of what appeared to be a mixture of congealed castor oil and coal dust the general condition is not too bad except for the con rod which is badly worn.

My question to the experts on small engines is what variety of aluminium do I need to make a replacement, bearing in mind that it will only be run for demonstration purposes? It's flying days (and mine) are long gone.

I would use and recomend 2024 t3 or 7075 t6, it what I use in my engines

cheers

Dean

The good old HE15 which is now 2014 or the similar 2024 that Dean mentions are the usual choice.

If you use 7075, I would recommend a bronze bush in the big end and little end. If you use 2024 or 2014, it will be ok without a bronze bush in the big end and little end. Make sure you have a good surface finish in the little end to help stop it from flogging out. Small end wants to be about 0.01mm max diameter clearance, The big end or the crank pin end wants about 0.05mm to 0.07mm diameter clearance.

Edit, Make sure you have the grain of the material in the line of the rod, ie, running length wise. If you do not know the grain direction of the material, I do not recommend using it for a con rod.

Neil

Edited By Neil Lickfold on 29/09/2016 10:09:39

Thanks for the information gentlemen. I can now go shopping.

Neil, I agree bronze bushes would be good but given my somewhat agricultural skills may be a step too far. The original didn't use them (these engines were built down to a price) and given the limited running expected I think it would be simpler, while tooled up, to make a couple of spares. In the unlikely event that I ever get back on a flying field it will be my trusty ED Racer that comes out of hibernation.

Dean, Have followed your V12 build with great admiration. How about a world tour so we can see it in the flesh? I'm sure you would pull in the crowds.

Mike

LOL, yea sure no problem , umm you said it was your shout though right????, by the way I have used 7075 t6 in the v8 and v12 with no bushes and no sign of wear. I run needle roller pins for gudgeons and 4140 or p20 for the cranks. the v8 is good for over 10,000 rpm so far.

Thanks again Dean. I can assure you that as soon as it's my turn to win the lottery your ticket will be on it's way.