1955 Frog 2.49cc BB

With the Contra Piston stuck like it was, how were you able to get it to run? Maybe it was stuck in the right place?

Neat little engine, looks like the Hoppes worked well. Fettle away!

Cribbs74 wrote:With the Contra Piston stuck like it was, how were you able to get it to run? Maybe it was stuck in the right place?

Neat little engine, looks like the Hoppes worked well. Fettle away!

Not quite stuck in the right place but enough to fire up. It ran rough but once the contra piston had freed it was easy to tune up. Very noisy though!

This will be another engine to add to the ones I like to ogle and fondle!

Slight hijack warning

Ian I bet you have an exploded view of a diesel engine.... I have no idea what a contra piston is or what it does and much too lazy to look it up as I am sure wiki or some other source is out there

Your many posts of diesel engines intrigues me and here among friends I am loosing my fear of seeming ignorant or stupid

Nice engine, glad to hear you got the contra piston freed up and er running! I had a PAW .15 single bearing where the contra piston froze in the bore in the running position. It took me forever to get it freed, I eventually ended up tearing the engine down and carefully pressed the contra piston out from the inside of the cylinder (contra piston is integrated into sleeve) ran fine after I got it back together. Are you planning on flying it?

fredvon4 wrote:Slight hijack warning

Ian I bet you have an exploded view of a diesel engine.... I have no idea what a contra piston is or what it does and much too lazy to look it up as I am sure wiki or some other source is out there

Your many posts of diesel engines intrigues me and here among friends I am loosing my fear of seeming ignorant or stupid

Fred.
The best way to describe a contra-piston is that it's like a second piston in the same bore pointing downwards towards the piston, and acts as the head. It is adjusted up & down (it can slide in the bore) with the top adjusting screw to increase or decrease the compression. Screw it down, compression increases, advancing the timing. Screw it out and the compression pushes the contra-piston up, decreasing the compression and retarding the timing. Obviously the cylinder has to be taller than that of a glow engine to accommodate the contra-piston. Really, adjusting the compression is a bit like adding & removing head shims to a Cox to get the best performance.

Rod.

I sort of figured that but from the discussions I assumed it is designed to move as the engine cycles. From your description it sounds like once set to a particular compression ratio it is adjusted only with changes to conditions or needle setting to arrive at a properly timed and feed setting. Sounds easy...but from various web sites I know it is not really that easy.


Now if they could just make fuel that was not foul smelling.....grin

The only one I know of that moves is the OK Cub diesels. They have a "shock pad" between the contra-piston and adjusting screw which allows the contra-piston to spring up slightly at each ignition to reduce the shock load on the bottom end. Some other OK engines used spring loaded clamps to hold the cylinder down. At ignition, the whole cylinder would spring up slightly to reduce shock.

Rod.

Here are some pics of the paperwork that came with one of mine:

George





 

 

 

The box and documentation look to be in perfect condition. I like the recommended fuel mix but it does seem to have a high proportion of ether. When I ran up mine it was 33% paraffin, 33% castor and 33% ether with a dash of isopropyl nitrate. We can't get amyl nitrate any more.

Your 1/3 of each mix plus 2% is ideal to run any model diesel, and very good for running them in.

But many diesels once run in will give their best on various mixes.

Oliver Tiger 2.5cc mix is 50% kero, 30% ether, 20% castor plus 2% of IPN Oliver mix.

Webra Rekord 1.5cc mix is 30% kero, 40% ether, 30% castor plus 2% IPN Webra mix.

gossie wrote:Your 1/3 of each mix plus 2% is ideal to run any model diesel, and very good for running them in.

But many diesels once run in will give their best on various mixes.

Oliver Tiger 2.5cc mix is 50% kero, 30% ether, 20% castor plus 2% of IPN Oliver mix.

Webra Rekord 1.5cc mix is 30% kero, 40% ether, 30% castor plus 2% IPN Webra mix.

I agree but it is my personal opinion that higher proportions of ether makes the fuel more expensive. Certainly, increasing the proportion of paraffin makes for a more powerful fuel. These are the PAW recommendations.

Running in - 30% Castor, 35% Paraffin, 33% Ether, 2% Iso Propyl Nitrate

Fully run in - 25% Castor, 40% Paraffin, 33% Ether, 2% Iso Propyl Nitrate

Fully run in
- BR Models - 20% Castor, 48% Paraffin, 30% Ether, 2% Isopropyl Nitrate

Fully run in
- TBR only
(Racing and Speed) - 15% Castor, 50% Paraffin, 32-33% Ether, 2-3% Iso Propyl Nitrate

I am not sure about dropping the castor content to 15% though. Diesels get very hot - I certainly wouldn't use synthetic oil in a diesel! But I do find ether proportions over 33% strange.

[quote="ian1954"]

gossie wrote:I am not sure about dropping the castor content to 15% though. Diesels get very hot - I certainly wouldn't use synthetic oil in a diesel! But I do find ether proportions over 33% strange.

My guess would be that the oil (and ether) are replaced with kerosene for more power during competition. Also, some use non-standard lubricants that would be extremely expensive for general use. Then again, for top competition many do not care what they need to replace as long as the engine lasts through competition. Again, this is just a guess.

When I posted the FROG 2.49 instructions, I forgot to post pictures of my FROGs.
The one in the lower left was bought new in the fifties but has a WEBRA general replacement needle assembly that was available at the time (yup! broke the original). One of the others was bought at a swap meet, the final one from the bay. Apparently all were made different years and have small differences. Also, only the upper one has an unaltered tommy bar, the others were brittle and the "T" had to be repaired.
Someone posted years ago that these engines are prone to splitting the crankcase...possibly due to the huge front BB. So far, so good.

George

 

I have used down to 15% oil (all castor) in the Irvine .20 diesel (a twin ballbearing, true ABC engine).
To me there is very little difference in the power, it is mainly the fuel consumption that is affected.

One can think of this as a certain available volume of air (at full throttle), and you cannot have more kerosene than what is need for an ideal mixture during each compression. So the net effect is that you get a longer run for a certain tank volume by using less oil in the fuel. In competitions with a limited tank volume you will want as much of that volume to be combustible fuel rather than lubricants, in order to extend the run (in time).

For sports application I use 25% all castor, it never hurts to have enough lubrication, and I can use the same fuel for all engines, ballbearing or plain bearing ones.

I'm running the Queen Bee dieselconversion on this fuel too and it feels very smooth and well lubricated.