OS Gemini FT 300 Making a con rod
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- เผยแพร่เมื่อ 11 ก.พ. 2025
- This is a detailed video showing the machining of replacement connecting rods for my OS FT-300.
I would like to thank Bruno Engert from Switzerland for sharing his time and talent making me this set of discontinued rods. Otherwise my engine would be a parts engine. Bruno and his brother Karl (Charles) make 4 stroke engines of their own design. I wish I had more of that kind of talent.
I would also like to thank David McIntire for sending my request to Bruno and the effort he makes showing his subscribers the history of glow engines, how to tune them, and how to service them.
Future videos will show this engine running on glow fuel and a comparison to my other FT-300 converted to gasoline.
This just blows my mind seeing all of the intricate steps involved here!!
Bruno has amazing skills and knowledge. I have since watched videos of making automotive connecting rods and they are made in the same way.
this was a delight to watch, there is something magical when a machinist is manually machining vs a CNC
Nice work a good part.
Bruno does great work.
I am also impressed by your videos!
@@mikeeiben3430 Thank you !
Glad to hear the con Rods are still doing well, dit not expect anything else since they were not my first ones I made. Nevertheless please keep me updated. Greest from Switzerland - Bruno
I plan to do a tear down and replace the rings shortly. I will let you know how it all looks inside.
Great video to see,, Thank´s for letting us in to your shop..
This video made me think about the Pratt & Whitney Wasp that was developed in 1930´s.. How did they do it ??? Magic :-)
Great job Bruno, amazing machine work.
Great stuff. Very interesting .
Thank you for watching.
Hi, thanks for the video nice job! I have one that just broke in flight, can't find one maybe I'll manage to copy your video
Sorry to hear about the failure. Were you running glow fuel or gasoline?
@@mikeeiben3430 only with methanol with the 4-stroke mixture, do you know if your friend is still motivated to make two more?
@@Padawan- the last time I asked, he was not interested.
I always run 20% oil content.
Totday I scraped my FT 300 - converted to petrol and front bronze(!!!) con rod blew to pieces. Crankshaft bearing was overhating and is now dark blue. On idle only onw cylinder fired both at full speed. For lubricant used MOTUL 800 1:20 (5%). OK I still habe the jig and will make myself a new set of ALU 7075, can't be worse....
Oh no! I run mine on the stand at 10:1
15:1 didn't seem to have enough oil coming out of the breather.
I should tear it down and check it.
I think solid bronze was used by OS mainly to get around the complexity of a split bearing on the big end. Did OS really ship aluminium conrods with no bearing inserts(?), I know this was a practice in the 1970s for very small 2 strokes but I didn't think they would do that on the big expensive engine lol.
I think some may have been aluminum with a plating of bronze on the earliest of them.
I just got a second hand FT-240 and after a quick pick inside I saw that it has the infamous aluminum (bronze colored) con rods. I wonder if I should be worried about running it, try to get some better con rods (somehow) or just live with it until it either survive or blows?
I would run it on 5% nitro fuel with 20% oil to insure good lubrication. They should be ok, especially with the smaller displacement.
My bent rod seems to be solid bronze, I tried to file through any coating and I couldn't. They're just a weaker design than the replacements. My engine has a very low serial number (0141). The other rod was replaced with the upgraded OS rod.
The person that I got the engine from ran it hard on 20% nitro fuel.
@@mikeeiben3430 Thanks for replying, I forgot to mention that the idea is to convert it to gas (or petrol depending on which side of the pond you are). I know nothing about this engine history apart that it needs new bearings all around (already on order) so after I take it completely apart and do a deep clean up I check on the conrods a bit more in detail but they definitely the ones with the OS logo on them (not the roundy ones,) but the ones with the recess along the center but casted not the machined ones. I think they are like the ones at the end of this video (although the ones at the end look different from each other to me) and they have the OS in the center (may be the ones in the video are facing the other way).
@@ferincr A gentleman from Canada contacted me, he destroyed his rods on the third flight after converting to gasoline. He premixed at a 20:1 ratio. I have a new in box ft300 that I converted to gas. I only ran a few times but at a 10:1 oil ratio. I think the older engine on glow fuel runs but I can't say the newer one is broken in yet.
@@mikeeiben3430 I wonder if the issue has to be with tight tolerances since the engine is designed to run on glow (methanol cools it down significantly) once running on gas with less cooling effect (therefore running hotter) the increased dilation causes seizing blowing the conrods🤔If that's the case a well used engine might survive longer but I'm not an engineer (not even close). I'll see if I can get some 7075 Al and play a bit on the mini mill, may be I just come out with some sort of usable conrods...II don't have all the high quality tooling shown in the video nor the skills shown by Bruno but as they say "the worst attempt is the one never made"...
@@ferincr In most gas conversion engines, 20:1 oil mix is adequate because the con rod runs close to the crankcase wall where oil collects, keeping the journal lubricated. On the FT engines they rely on the oil vapor in the air inside the crankcase, therefore they need more oil.
In my experience, the exhaust residue from 10:1 oil to gas is very black and hard to clean up. Glow fuel slime cleans up easily.
Do you make these available for purchase?
If you need some, I could send Bruno your contact information. He may be willing to make more.