Hello Mick,

If you buy the material (someone is sure to know the aluminium spec), then all you need is a drill with a couple of drill bits of the correct size, plus file and some emery cloth.

I have made con rods for quite a few engines, before I eventually got kitted out with machinery. I used an electric drill in a cheap Aldi drill stand for the drilling. Oh! you need a good rule and some patience too!

Before anyone tut-tuts at this. The relevant con rods have lasted to this day and some have had very hard use in combat planes. Making con rods that work well, is easy, with very simple tools. One gentleman who repaired engines had a swaging method to reduce the worn hole diameter and then simply redrilled the hole to size!

The bigger the engine, the easier it becomes as the measuring need not be so accurate. Now to dive into my bunker as the howls of the purists are heard

Andrew.

This spare on e-bay canada any good

Michael,

I believe I have an old style con rod from a Gemini Twin, they must be a weak point because my engine snapped one and I replaced it with two of the newer style ones. I am away from home until tomorrow but I will check and if it is still where I think it is I will let you have it F.O.C.

Bob

Hi Mick,

I've just finished a session in the workshop but took time out to find the con rod. It was a little battered here and there with a bruise on one of the faces of the little end so I ran an adjustable reamer through it to clean that up.

Three are a couple of marks on it but it looks to be OK. I would gently smooth out these marks to prevent them becoming stress raisers.

Contact me via the message board and let me have your address and I will try to get it in the post on Friday, hopefully you will get it by Saturday, unless of course you live in the South Manchester area and you could always drop by and pick it up.

Here is a picture of it before I ran the reamer through the little end.

On the other side of the big end there are two reference marks 180 degrees apart on the face of it in line with the centre line of the con rod.

Hi Mick,

the newer rods are dimensionally identical to the original and are made from tougher bronze than the original type so there is no problem with conversion. I have sent you the old one I had and it will be with you tomorrow. I would recommend fitting the newer type, however, if you can't get them then at least you will have a matching pair of older type rods which will be OK.

If I had to replace the rods I would make a new pair from Aluminium Bronze which is much tougher stuff than the old rods bronze that was originally used. A High Tensile Aluminium Alloy would be best but am not sure how it would affect balance/vibration

Dean,

it would be easiest if you were to copy the one I have sent to Mick if he wants to go down that route.

Mick/Dean,

I know that the big end is a nice fit on the polished shank of a 12mm Carbide cutter. Not sure about the rest though.

Introducing some pedantry, IDEALLY when the rods are fitted, the big ends should be tightened to the same torque as that used when they were machined. Taken as read that the caps will be assembled oriented as they were whilst being machined.

In this size, difficult to measure to measure the torque, without rather special torque spanners for low torques, or you could use a spring balance on an arm of known length.

In an ideal world, even after machining the bores, they could be measured with a bore set, or something of that nature and torqued in stages until as round as possible, and the figures noted. During assembly, the fixings are then tightened to the figures noted for each fixing. (That's what i did for an engine for a sports/racing car)

The reason for this procedure is that if the torque applied during assembly differs from that when the bore was machined, the resulting bore will be oval. The plane of the major axis of the oval will depend on whether the fixings have been under or over torqued compared to that applied before machining.

The devil is in the detail, but it does make a difference to output and life expectancy!

Howard