Os Gemini twin glow engine - conrod req'd - no longer made

OK so on with the show................... outside profiling under way

next its onto radiusing the little end and the outside flanges of the big end, although as I have a few other conrods to get to this stage before taking the machine vise off it may be a few days before more swarf is made from these blanks.

Cheers

for now

Dean

Nearly missed this update looking good, strange how big they look I know they are small great work Dean 👍

Edited By Michael Black 1 on 21/01/2018 22:49:43

HaHa, well they are in fact fairly big compared to what I normally make, I'll post a photo showing your rods compared to some for the engines I'm currently building.

cheers

Dean

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

So here's a quick photo update to show the comparison of the OS Gemini rod to one from my latest Supercharged two stroke V8 project

So anyone know the torque settings for an m2 big end bolt or perhaps the torque setting for the 0/80 bolt used on my V8 rods, I generally just use the torque setting of T.E. but not the F.T or E.F.T. and I've found that using the tightening instructions of " tighten till it shears and back off half a turn " doesn't really go to well either. i'm fairly certain that foot pounds and inch pounds torque on either of these bolts would result in the sheared off torque setting and that would be a bit of a waste of time. so anyone got any bright idea's. LOL (i'm kidding of course, no-one torques small model engine bolts, you don't have the same distortion when machining as in full size practice, well nothing that's actually measurable anyway.)

cheers

Dean

Try this chart:

**LINK**

No doubt the ordinary torque wrench will not be sensitive enough, but there will be an optimum torque even for small screws.

"Do it up until it strips" is really meant for British motorcycles, where it is going to rattle undone anyway. (As is "If it moves, weld it, if it doesn't move, get a bigger hammer."

The distortion from under or over torqueing will depend largely on the flatness of the mating surfaces. If it is possible to get these surfaces lapped wonderfully flat before the final boring operation, there is much less chance of distortion on final assembly. There is a dowel or similar, isn't there?

Just a thought - Tim

Edited By Tim Stevens on 01/02/2018 12:43:09

There are plenty of torque screwdrivers that work down to 1Nm or less, some with interchangeable tips

**LINK**

**LINK**

O.k. here is the latest on these rods. below shows the progress

And.... all finished

You may want to polish the crankshaft mick to ensure a good running surface, also double check the diameter before I post them back to you and let me know, should be a nominal 10mm or 9.98ish. Oh and also don't forget to torque the big ends down to the correct setting, which is 0.35nm

cheers

Dean

Here is another, it's quite affordable and useful for my target rifles as well as fasteners on my model engines.

**LINK**

0.35 Nm is about 50 oz-in, so within it's range **LINK**

* Danny M *

Nearly missed this again thanks dean looking great. The crank is 10mm and I wil make sure I polish and torque down when installed. Really excited to see them in the flesh as they say.

Mick

Edited By Michael Black 1 on 07/02/2018 20:22:05

No Problem, will pop them in the post this weekend, sorry it took so long mate but we got there in the end.

Cheers

Dean

Hello,

And sorry for resuscitating an old thread.

As you can see this is my very first post here, I just bumped into this thanks to google so I decided to join and ask...

I just got a O.S.FT-240 Gemini that I'm thinking in converting it to petrol and it has the infamous aluminium (bronze coloured) old conrods.

I read about them failing but I'm not sure how serious the issue is. I do have a small milling machine and some (very little) machining experience so I wonder if I should get some 7075 Al and try to machine a pair or just run the original ones??? I'm afraid that if they fail the damage could involve other parts that are also extinct.

I saw a video from a guy in Switzerland (very professional looking job) also the pics here from Dean that looks like he took a slightly different approach to it so is nice when you see things made in different ways, at least makes me feel more encouraged to give it a try.

I'd appreciate any input from anyone with experience on either these engines or machining these. I don't know how precise my mill is (just blame it to the machine) coupled to my limited experience. The biggest brake I find is that I might be missing some very precise measuring tools, I do have the basic stuff (calipers, indicator, regular 0.01 micrometer, and that's about it)

Thanks,

Fernando