Rivers 2.49cc and DC 1cc engines

[TerrydParticipant @terryd72465]

Thanks for the belly laugh Ian, it was really welcome.  It’s a good job I was using my right index finger at the time, I didn’t feel it too badly as the nerve endings have never grown back following the end being sewn back on after the bandsaw incident.    

 

But that’s another story.

 

Also thanks for the encouragement Ramon, I appreciate the contributions from both of you!!

 

With such support and advice, how can I fail 

 

Best regards

 

Terry

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Posted by Ramon Wilson on 19/04/2010 10:25:20:

 

Jens advice on establishing the starting position may prove problematic if the contra piston is very tight in the bore. Screwing right down over compresses the engine and it could (not will) lead to damage to the con rod. 

 

Regards – Ramon

 

Check first the contrapiston are not stuck in the sleeve before resetting the start point before starting the engine.

 

How to resetting the compression ratio before starting the engine:

 

To example the screw are 6mm with treads 1 mm or cylinder head gasket at 1 mm thick, and the cylinder volume are at 2.49ccm.

You want to set 16:1 compression ratio as start point.

How to find:

To calculate all volume i am using centimetre instead millimetre and it is easier…

Bore: 1.475 cm ,stroke: 1.457cm = 2.49 ccm

The contrapiston has diameter 1.475 cm and stroke are variable with compression screw or in case fixed compression adjusted by cylinder head gasket.

To example we set 1 turns with compression screw and the screw are moving up 0.1 cm cause treads are 0.1 cm (M6x1 metric screw) or use cylinder gasket in 0.1 cm thick  washer (gasket) instead compression screw to example in fixed compression diesel engines.

Now we calculating headvolume: 1.475 cm:2=0.7375 ,

then calculate volume 0.7375mm x 0.7375mm x 3.14 x 0.1cm = 0.17 ccm

2.49ccm + 0.17 ccm : 0.17 ccm = 15.64:1 Compression ratio

It is near to 16:1 in compression ratio , now you are ready to starting the engine..

 

Depent on fuel mix the compression ratio can be between 15:1 and 18:1 as start point before fine adjusting the compression setting while the engine are running.

 

Some model diesel engine has a stop pin mounted at cylinder head where the compression screw has a limited rotating until a turns, this is ready calculated to adjust compression ratio from lowest to highest level.

Edited By Jens Eirik Skogstad on 20/04/2010 22:00:15

[Ramon WilsonParticipant @ramonwilson3]

Thanks for your info Jens.

 

I do find this interesting that you do this as I have never ever given a thought to the mathmatics of compression. As I’m sure you are aware compression varies depending on load as well as fuel and of course ambient temperature too.

 

I confess my knowledge is purely practical having run them for many years and the technical side has never been a concern – all have their individual characteristics though – some start and run so readily whilst others can be so obstinate at times. I mainly used diesels with the odd glow – Mercos mainly – until I began to take an interest in control line aerobatics in the eighties when I began using glow motors in earnest. Apart from a very short period into some very low key team racing the diesels have always been used for sport flying.

 

I do not ‘collect’ engines but I do think they collect me! I’ve always had a passion for them since that first one at age thirteen but most of them have been very much ‘come and go’ over the years. It never fails to amaze my long suffering wife how they seem to accumulate so rapidly though the current ‘stock’ is well down on what it used to be. I had a good clear out at the last Watford ‘Swapmeet’ and sold all I took bar two. Funnily enough Ian they were OS 40s – I still have ’em.

 

Apologies – going off topic,

 

Thanks agin Jens regards for now – Ramon 

 

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