Nemett Bobcat

Have noticed a problem,

Have just finished the Bobcat Project and have been setting it up to start the engine. In 4448 page 153 is says to set to BDC and then rotate engine anti-clockwise (backwards) to 40 degrees. This engine by the description of the cam set up, rotates anti-clockwise viewed from front of engine (fly wheel end), so you would have to rotate engine clockwise for backwards to get to 40 degrees. I believe this to be contradictory.

The next problem is, if this engine rotates anti-clockwise, then the crankshaft thread should be a LH thread, so the prop or fly wheel does not inadvertently fly off. From this I would suggest that we change it to a clockwise rotation engine, which means if we set the cam shaft lobes the opposite as described i.e. anti-clockwise viewed from the chuck of the dividing head, then everything will fall into place, otherwise we make a LH thread crankshaft (unless I am missing something here).

As you can see from my pictures I have got another carburettor fitted this is a J.E Howel design (I have made the one as described as well), I will see which one runs best).

Engine must rotate anti clockwise view from the front (flywheel) end to tighten the nut, you use a spanner clockwise to tighten a normal thread nut, so the shaft has to rotate the opposite way, ie anticlockwise.

As KWIL says engine runs anti-clockwise when viewed from the prop end this is so you can use standard off the shelf propellors which are designed for that direction of rotation.

Also read the Note on page 152 of issue 4448 about fitting a locking device to stop the prob unscrewing in the event of a misfire. I think this is also mentioned on one of the drawings.

I suppose it all comes down to what Malcom called the front of the engine, as he was making the marine version then the flywheel would be at the back but if it were the aircooled then the prop would be at the front??

J

Edited By JasonB on 15/03/2013 10:28:13

I believe Malcolm once had a prop shed itself following a misfire. It is interesting as of all the glow engines I have seen or owned, none of them has been supplied with a locknut.

Neil

I will have to apologise to everybody I have had a senior moment got completely disorientated the description is right no problems ,will keep people informed when I get it started will be fitting a water pump running off the fly wheel

I happened to be standing behind Malcolm when the mis-fire occurred and the prop wound its way off. Luckily the plastic safety fence was far enough away so that gravity caused the prop to hit the fence at about knee height. I had a perfect view of the face of the man standing directly in line with its trajectory - talk about a paleface! I've made a mental note to check that all crankshafts have a flat on them and a matching washer to discourage rotation.

We miss Malcolm.

Geoff

Good point Geoff - the flat and washer with a d-shaped hole IS something most of my engines have.

And, yes a shame Malcolm passed on so soon - he was shaping up to be a worthy succesor to ETX making IC engines accessible to all. I imagine he would have gone on to tackle furher interesting subjects.

Neil

Edited By Stub Mandrel on 15/03/2013 21:36:25

Neil

Mine is not going anywhere near an aircraft nor have a prop fitted just for bench running, so it will be the marine version with some means of pumping water through it. Therefore I'm interested in this option so if you have any ideas you'd like to share please?

Pete

Pete,

I have made a water pump from this site http://www.model-engine-plans.com/engineplans/combustion/howellwaterpump.htm very clever design will mount it off the crank or flywheel depending on the ratio see photos

Neil

That looks very neat and thanks for pointing me over to Jerry's site. $21 doesn't seem to bad a deal when you consider some of the prices people charge these days

Pete

Well that started me on a journey when I realised that Jerry was the source of the ignition kit Hemingway are offering. A Google later led me back here to this thread

**LINK**

Plenty of info on the links quoted here for the beginner to get confused by but essential reading.

I also see that the double ended coil suggested for the Bobcat is no longer available. Any suggestions?

Pete

Novus 2 from Minimag should do the trick

**LINK**

Jason

Thanks, At risk of heading way off topic here so I'll move over to the old ignition system link and ask

Just worked it out so no need, thanks again for the info

Pete

Edited By Doubletop on 04/04/2013 10:00:25