OS 72 alpha spares

[Glenn Philbrick]

I am trying to find a conrod for my os 72 which has split! I've tried most of the usual UK suppliers but no no so far. Any ideas where I might get it from ?

[Richard Wills 2]

https://www.rcjapan.net/index.php?main_page=product_info&cPath=80_413_432&products_id=10397

[Engine Doctor]

plus 1 for RC Japan

[Glenn Philbrick]

Thanks , will give rc Japan a go, I'm not in any hurry but still can't quite understand why it failed in such a catastrophic manner. There is no sign of any other problems but I will renew the bearing while the engine is in bits.

 

 

[Engine Doctor]

Best place and prices  for bearings is Simply Bearings. 

[Jon H]

do you have a photo of the busted rod? Just curious to see what happened to it

[Glenn Philbrick]

This is the offending con rod. I expected to find the piston seized which would put strain on the con rod, but the piston and liner are fine. It's in a puppeteer and was on its second flight when it stopped and threw off both nuts and the prop, I had to land son wind but all is well with the model

 

[Jon H]

thats incredible, never seen anything like that before. 

 

I can see the crack runs through the oil hole for the little end, and its understandable that a fatigue crack might propagate from that hole, but how did it jump the gudgeon pin and split so perfectly? 

 

Could you take a photo of the broken face of the straighter half? I am just curious to see if anything of note is visible in the material. 

[Paul De Tourtoulon]

Me neither, I have seen a few real and model ones, but never been split down the center.

[Engine Doctor]

Never seen that before. Might ge worth sending a pic to OS ?

[Glenn Philbrick]

Ok will see if I can get a better photo tomorrow

[Martin Harris - Moderator]

Is there a witness mark on the piston skirt? It looks to me that the bend is centred on the indentation on the broken edge so that would suggest the bend occurred after the rod split. 

[David Ovenden]

Its hard to imagine any way a vertical split like that could occur in normal circumstances without there being a manufacturing fault  or metallurgical flaw with the con rod.

[Glenn Philbrick]

Photo of the con rod in more detail. The engine is fully stripped now and there are now signs of any other damage. The bearings are ok. There is a mark on the bent half of the rod where the crank pin must have hit it. The big end bush was still on the crank pin. Luckily I think this must have stopped the engine immediately so no damage was caused by bits flying around.

Glenn

 

[Ace]

Incredible 🤔

All faces except the bottom big end look as though they have been cleanly cut, re-assembled and fractured under load. 

Just checked it wasn't stared on the 1st April - no. 

[Martin Harris - Moderator]

It might be worth approaching Ripmax.  It was quite a few years ago but they were very supportive when I reported a manufacturing fault on a second hand, several years old but unused engine for a club mate.  Their comment was that they would replace parts that had obvious manufacturing defects however old the engine was…

[Jon H]

Looks like the little end oil hole went first given its so much darker than the rest of it. I think i also spy a half moon shaped fatigue crack propagation on the other side of the little end as well. 

[david james 1]

I had an OS 81 alpha - gudgeon pin broke - a fairly unusual failure.

 

I think the alpha series were an unsuccessful experiment which OS soon terminated.

[Glenn Philbrick]

I hope not as I have three OS_56 alphas in small bipes that I fly regularly. They are just the right size being a bit smaller in size than other four strokes of a similar capacity.

[Richard Wills 2]

The 56 and 72 have been revised to 56II and 72II, other current model in the alpha range is the 155

[Jon H]

2 hours ago, david james 1 said:

I had an OS 81 alpha - gudgeon pin broke - a fairly unusual failure.

 

I think the alpha series were an unsuccessful experiment which OS soon terminated.

 

It was interesting to me that OS sung the praises of their internal crankcase vent system with the MkI's only to revert back to a nipple in the backplate on the MkII while the latter promotional material contradicted that of the first.  

 

The only experience i have of them is a 155 i was sent by a customer to test vs our own while it was being developed. I didnt fly it, but on the bench it seemed to run very well and was generally a nice engine. Beyond that i cant really comment on how well they go. 

 

All i can say is that i miss the surpass series as my 91SII is an excellent engine, the 52's were good too and were a decent price at the time. I also miss the FP series, the LA's were rubbish. 

[John Stainforth]

I have an OS 115 alpha - excellent engine. 

[Solly]

I have an 81 alpha, it was unused for the winter and when started up ran very erratically in the air. The carb was dismantled and looked OK.  On the advice of the late Brian Winch I fitted a breather nipple to the backplate and it runs perfectly. His explanation was that any oil present in the internal vent passage, which is very small, can dry and form an occlusion.

[J D 8]

                     

2 hours ago, Solly said:

I have an 81 alpha, it was unused for the winter and when started up ran very erratically in the air. The carb was dismantled and looked OK.  On the advice of the late Brian Winch I fitted a breather nipple to the backplate and it runs perfectly. His explanation was that any oil present in the internal vent passage, which is very small, can dry and form an occlusion.

    That is probably why OS themselves went back to the standard breather.

[Nigel R]

Does ml70 or other synthetic oil dry out and go gloopy?