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

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Michael Black 118/07/2017 16:09:51
13 forum posts

hi all

I have an OS Gemini twin glow engine it's a fairly old engine and the parts are no longer made. I need a connecting rod made I wonderd if any one on the forum could do that for me. Sorry if that's a bit cheeky butI am willing to pay.


Andrew Tinsley18/07/2017 16:31:54
1046 forum posts

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


JasonB18/07/2017 16:50:40
17806 forum posts
1948 photos
1 articles

You won't get a simple conrod like you describe onto the crank shaft, needs a split big end to fit over the double throw crankshaft. probably better to also use bronze rather than Ali so the weights of the old and new rods have a chance of being balanced


Edited By JasonB on 18/07/2017 16:56:31

JasonB18/07/2017 17:19:06
17806 forum posts
1948 photos
1 articles

This spare on e-bay canada any good

Andrew Tinsley18/07/2017 17:33:23
1046 forum posts

Whoops I should have realised that a con rod for a twin is a different animal and will mean a split big end. So much more complicated than I realised.



P.S. A guy in the US who goes by the Ebay name of Shatterman. Does lots of spares for Enya and OS engines. He has lots more stock than appears on the Bay and is well worth contacting, he is a good guy and helpful with it!


Michael Black 118/07/2017 17:40:47
13 forum posts

Wow thanks for the replies guys Jason that's the later mk2 con rod mine is different, but your right it needs to be split to go over the crank. It's such a shame it's a lovely sounding twin engine perfect for the cub it was in. I have tried the RC forums to see if anyone has a damaged engine. Mods thanks for changing the title.

Thanks again Mick

Andrew Tinsley18/07/2017 17:40:51
1046 forum posts

Just thought that Tower hobbies in the US may have one. Just looked and the part seems to be 46105000. It is $61 and by the time you have added customs and PO charges, it would probably be around $100 They say limited qty available, so don't hang about.

Also try the Ripmax website in the UK. It is amazing what they have! You will need to order thro' a hobby shop, but worth looking.


Bob Rodgerson18/07/2017 17:45:24
591 forum posts
174 photos


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.


Michael Black 118/07/2017 17:50:21
13 forum posts

Thanks Bob that would be appreciated. Andrew that one is for the Mk 2 engine and unfortunately won't fit mine.


Michael Black 120/07/2017 20:46:39
13 forum posts

mickHi Bob

Wondered if you had chance to look for the con rod?

Clive Farrar20/07/2017 21:40:14
89 forum posts
35 photos

If you are willing to invest £37.50 then you can do no worse than to go to Just Engines.

They specialise in R/C model aero engines of the ASP and OS brands.

They do not list the Gemini but may have info but maore importantly they DO stock spares for the ASP 160,

see this link

From my previous experience ( i am an engine R/C flyer ) ASP engines are clones of OS and the parts are interchangable.

For the sake of sending them some measurements from the remaining good conrod you could have the solution to your problem.

I hope that helps

Regards Clive

Bob Rodgerson20/07/2017 23:05:28
591 forum posts
174 photos

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.


Michael Black 121/07/2017 08:13:51
13 forum posts

Thanks Bob

i have sent a pm

just as a matter of interest did it take much doing converting your engine to later spec rods? Clive thanks for the suggestion if I still have problems I will investigate just engines.


Bob Rodgerson21/07/2017 14:26:32
591 forum posts
174 photos

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 clarke 221/07/2017 15:26:49
155 forum posts
330 photos

Hi mick, I would recommend building an matched pair of rods from 7075 t6 aluminium if you want to use the engine much. This is what I use in all my engines that require a split big engine. Balance isn't an issue as the weight is the same for both sides. If you get stuck send me a pm and a sample I'll build you a pair.



Bob Rodgerson21/07/2017 17:55:04
591 forum posts
174 photos


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

Michael Black 121/07/2017 18:08:40
13 forum posts

Hi dean

Thanks for the offer it would be nice to upgrade the motor PM sent


Bob Rodgerson21/07/2017 21:58:53
591 forum posts
174 photos


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.

dean clarke 207/01/2018 03:13:33
155 forum posts
330 photos

Well I've finally found some spare time to get on with this help out project, here's some photos to show progress etc.

conrod blanks square up

conrod blanks square up2

conrod blanks square up3

conrod blanks ready to drill

Now for drill the big end caps etc

conrod blanks drilling big end


conrod blanks drilling big end2

conrod blanks ready to drill bearing holes

Drilling and reaming the big and little ends

drilling big and little ends

Now we're already to profile the outside

conrods ready to profile

Now I better get back to the shed to finish these off for Mick

cheers for now


Michael Black 107/01/2018 08:42:04
13 forum posts

Thanks Dean looking good


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