Posts: 3472
Joined: 3/31/2003 From: Tokoroa, NEW ZEALAND Status: online
Well my MDS had a bit of a catastrophic failure today.
The crankshaft broke (in the usual place).
It's partly my own fault -- I was told that the cranks in these engines were a bit fragile and I (stupidly) ran a heavy glass-filled composite prop -- a Bolly). It looks as if the crankshaft failed as a result of the torsional loads applied to it as tried to turn a relatively large mass with relatively short and powerful impulses.
Based on my experiences therefore, I'd really recommend that you use a light wooden prop on your MDS61 -- it'll put a *lot* less load on the crankshaft and probably avoid this kind of failure.
I sure got a lot more than $39 worth of fun out of it while it lasted though and I may well buy another -- I've got plenty of spares for a second engine :-)
Posts: 7119
Joined: 4/9/2003 From: Rosh-Ha'Ayin, ISRAEL Status: offline
Bruce,
Don't blame yourself (unless you tried to use your starter with the engine flooded... You don't seem likely to do that ...).
The fact that this engine is made in Russia, does not mean the crankshaft's steel, or its machining, is of the same quality as those of the AK-47...
Fatigue would have taken much longer to set in...
This crankshaft was flawed from the beginning; a crack, or a stress-point... I don't believe they offer actual warranty for these engines, but do check this out.
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Dar Zeelon - ISRAEL - ddzeelon@gmail.com MVVS - Jett - Nelson - Bolly - Mejzlik
Sounds like the rear bearing going out may have caused more problems than you was aware of Xjet. We can hope this was a one time faulty crank from the manufacture but something tells me its not. If its a stress point (design error)or a hardness issue they all may do the same thing. I personally am not looking forward to having a crank break, this could be a very dangerous to anyone close to the engine.
Kmot your RPM's are not to impressive, I would expect a rear exhaust engine of high perf nature to develope quite a few more especially useing a prop for a 46-50 sized engine. Oh well sounds like the old saying still holds true, If its to good to be true it prolly isn't.
I did finally got a email stating my engine has been sent.
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I've learned that you cannot compare yourself to others -they are more screwed up than you think.
Actually a 12x6 is a 60 size prop as per say a standard place to start with todays engines, but the engine make and type determines alot when considering the correct size prop. The older engines used say a 11x7.5 11x8 to get a few more turns , granted todays engines are far better in the RPM's than the engines of the 80's. Its not uncommon to see a modern day 46-50 outperform a 60-61 of yesterday useing the same prop. My 61 FX with a 11x7.5 semitar was getting 14,500 running a jtec muff. I have another 61 FX on a pipe running a 12x6 APC I'll fire it up today and get a reading and report back.
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I've learned that you cannot compare yourself to others -they are more screwed up than you think.
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RE: Hi Perf Russian 10cc at a bargain price! - 
