Can you Help to Identify this Engine?

[Peter Jenkins]

I have bought an airframe with this engine in it. When I tried to start it the prop gets thrown off every time. The prop shaft is unusual (to me) in that it is threaded so that it screws into the crankshaft has a land and then a threaded end for the prop nut. The screw thread that goes into the hollow crankshaft is a right hand thread. Despite that, the prop will not stay attached.

Is anyone able to identify the engine, it is a 10 cc engine, from the photo below?

Secondly, how should I go about retaining the threaded shaft extension?

[Alan Gorham_]

It's an MVVS or Modela 61 I think. Looks like the carb may have been changed though.

Irvine Engines used to employ a threaded stud into a hollow crankshaft for prop retention and come to think of it so did the PAW 29 and 35 diesels at some point. I would just use a good quality stud retaining compound to secure the stud into the crank and when set, fit the prop as normal.

[Peter Jenkins]

Thanks Alan. I had thought it was an MVVS but the logo didn't look like their usual one.

What stud retaining compound would you recommend?

Thanks

Peter

[J D 8]

Loctite 242 blue, can be had in small tube's for about a fiver.

[Alan Gorham_]

It is the Modela logo cast into the case on your engine. Not sure why they have two names and two logos but there you go...

I have to say that I have several Irvines that use a stud fixing and have never needed to use retaining compound. I've got three SP40 engines which were used in Speed 40 pylon racing and can turn a 9 x 6 prop at 17000 rpm. Never had an issue with the stud coming loose.

Same with an old PAW 35 I had for years.

I've had great success with Loctite threadlock and bearing retainer products in other applications so I would say their 270 High Strength Studlock would be worth a go.

[Peter Jenkins]

Thanks guys. Much appreciated.

[Robin Colbourne]

In Communist times, Modela was the Czech export organisation for model aircraft equipment, whereas MVVS was one of the state organisations that manufactured model aircraft engines. After the fall of Communism, Modela disappeared, and MVVS sold directly. See FFKiwi's post here: Modela/MVVS relationship

[Shaunie]

Are you using a wooden or a plastic prop?
Are you using a fuel with too much nitro in it? I know nothing of this particular engine but didn’t many of the Eastern European engines expect to run on straight fuel?
you could put a disk of Emery cloth or wet and dry between the prop and the driver.

[Peter Jenkins]

Robin, thank you for that piece of info. It's always nice to know what the history is behind a name.

Shaunie, the problem here is not the grip between the prop and backplate but the lack of friction in the screw thread and the crankshaft. Improving the friction between the prop and driver is not the issue. The Loctite 270 recommended by Alan Gorham will, I hope, do the trick and keep the prop shaft and crankshaft to remain connected when the engine fires. I'm using 10% nitro but have some 5% as well so when the shaft/prop shaft remain together I will see if there is any difference in how well it runs with the different nitro mixes. I don't have any straight fuel and I won't get any as I have no other use for it.

[Peter Jenkins]

Hi Robin, just found this on the MVVS site under the About Us tab. It is exactly as you stated. It's also interesting to see the fortunes of MVVS rise and fall over the years. Interesting to see that one of the 2 current owners owns Krill Aircraft as well. At least they are still going strong after all these years. Funny how some of their diesels look very like PAWs!

[Former Member]

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[Peter Jenkins]

Barrie

The link in my post above would appear to bear out what you say.

Peter

[Peter Jenkins]

While I wait for my supply of Loctite 270 to arrive, the thought occurred to me that I had forgotten to ask how best to tighten the prop shaft stud into the crankshaft? Would a piece of hardwood inserted through the exhaust port to jam the piston in place be OK or NO NO! What would be a suitable alternative?

[Denis Watkins]

My own choice is that you have to pop a piece of timber in to the port Peter.

Get both the outer and inner threads absolutely clean. I used carbontet when we were allowed to get it.

But use your chosen degreaser before applying locktite.

Balance the prop of course.

A .60 can often benefit from a cooler plug too, and is worth a try when motors throw a prop.

Edited By Denis Watkins on 13/11/2020 10:28:15

[Engine Doctor]

NEVER ever put anything into the exhaust port to lock an engine ! you will damage the cylinder and the engine will be scrap .  the piston and liner are precision fit items and anything like a screw driver or piece of wood will damage them  have had many engine sent to me with this type of damage and its so un-necessary . Similarly never use "Piston Stops " sold by some model shops that screw into the glow plug thread  these can damage/crack the piston crown that then fails when engine is run and again wrecks the engine .If you really have to lock an engine then filling the cylinder with engine oil will do the trick but still risks damaging the piston ,conrod or crank if you don't know what your doing. The stud should not need anything to lock it in unless its very loose then a mild thread lock will be ok . It will stay locked once done up with the friction of the threads.

Edited By Engine Doctor on 13/11/2020 10:51:08

[Former Member]

[This posting has been removed]

[Peter Jenkins]

Engine Doctor - thank you for your warning. I have tried tightening the shaft using a pair of lock washers on the prop shaft end and normal cylinder compression to tighten against. It simply comes loose as soon as the engine fires as the friction on the threads is insufficient just using compression pressure to tighten against. I had not considered a hydraulic lock. That being the case, I propose to try Loctite 270 and not overtighten the shaft against the hydraulic lock and hope that does the trick.

Doc Martin - thanks for the warning. What would you suggest then?

[Former Member]

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[Peter Jenkins]

Double posted!

Edited By Peter Jenkins on 14/11/2020 01:36:21

[Peter Jenkins]

Doc, I think you may have misunderstood my problem. It's not the prop nut that's coming loose. The prop shaft screws into the crank shaft so there are two threaded ends with a land separating them. I can do up the prop nut nice and tight and I have a locknut as well. It is probably as tight as for a 4 stroke if not a tad more. The threaded stud that screws into the crankshaft is what comes unscrewed. Using the 2 locknuts to exert torque to the crankshaft thread is limited by the engines compression. ED's suggestion to use a hydraulic lock to generate the required friction on the threads may solve the problem or may not. Using strong threadlock plus the hydraulic lock seems a more likely solution. I know that torqing the prop nut should be sufficient but after the prop came loose every time the engine fired I thought I'd ask for ideas on this forum.

I am using a glow panel and the plug is what came with the engine. I used 10% nitro glow fuel.

Hope that answers your points.

[Denis Watkins]

Peter, just double check the depth of the hole in the crank, and the prop shaft stud thread length,

that this is long enough to tighten up.

but not so long that the prop shaft " bottoms out " unable to tighten.

Is a simple remedy if the stud is too long

[Engine Doctor]

I did have an old MVVS diesel some years ago that had the stud at the front of the crank. The thin shaft surrounding the stud was cracked and this caused the stud to keep coming loose. The only cure on this engine was to silver solder a high tensile stud into the shaft . No problem after that . I figured that most engine don't have replaceable threads on the crank shaft so why not ? Your engine was a good engine but not particularly collectable so won't affec it's value but will make it usable .If you go down this route make sure the stud is running true , a lathe will probably be needed to check and rectify if needs.

E.D.

Ps before considering above check that the collet that secures the prop driver is gripping the shaft properly. It should be very tight on the shaft and need a puller to break the joint . If it's loose or spins then that's your problem. A damaged prop driver or collet will spin allowing the shaft to loosen causing the problem.

Edited By Engine Doctor on 14/11/2020 09:35:50

[Former Member]

[This posting has been removed]

[Peter Jenkins]

Denis - thanks. Will check that point.

ED - there is no collet that secures the prop driver. The prop driver sits on top of the land that separates the two threads. If that means that there is a problem with this engine then I might swap it for one of my Irvine 53 Mk 2 engines. As the MVVS seems to be an old model would the Irvine have the same amount of power?

[Engine Doctor]

Hello Peter it does sound and looking closer looks wrong to me .

There should be a thin collar , part of the crankshaft that a collet can grip on.

Can you post a pic with the prop driver off and showing the front bearing area  and the rear of the prop driver ?

It sounds like someone may have fitted another prop driver hoping to fix the problem.

If the prop driver sits directly onto the stud and only presses against the bearing center then nothing will stop it coming undone and if started the prop could come off , very dangerous.

The MVVS 61 was a powerful engine with plenty of torque . The Irvine 53 is a nice engine ,possibly not as powerful as the MVVS but if it will fly the model with a little power to spare then it should be fine 

 

E.D.

 

Edited By Engine Doctor on 15/11/2020 11:45:06