Rumely Oil Pull engine

I don't think mine are anything special about the £10mark sounds right, 3 stone at that size.

For 30mm I would say you could go with a BS120, 3.12mm wide groove and 2.5mm deep

Thanks Jason, I'll get one ordered.

I have a query regarding the fitting of the ball bearings on my crankshaft. I was going to fit the outers in the housings using loctite bearing retainer but i want to ensure that the inners don't creep on the crankshaft. Or am I being a bit pernickety? I would have liked them a bit tighter than the fit I achieved but perfection is rarely attained in model engineering so I wondered if there is anything I could put on the shaft that would prevent rotation but still allow me to dismantle it easily. The ball bearings are doubled each side and are 17x 35x10.

Thinking about "Pull Rods" for the valves, how about a lever follower, under the cam. with a refined form of clevis on the pull rod?

Was that how the real engine did it?

Otherwise, the spring arrangement shown provides the opening force for the valve by keeping the follower in contact with the cam. and then if the linkage is secured to the valve, as a valve spring to hold it on the seat..

Or was the cam internal, with the pull rod external to the follower?

Howard

Hi Howard, yes the original cams were internal. What I have decided on is as you suggest, a lever follower under the cam with a bell crank action to pull the valve rod.

Hi everyone,

i am getting on well with my Rumely engine and pretty near testing it. However there doesn't seem to be much compression. I worked it out by calculating the volume of the head space and having read that it shouldn't be too high I worked it out for 6 to 1 but I don't think it's anywhere near that. I got me to wondering why we need compression? There is nothing about it in ET Westbury's book as to the reasons for it. Does anyone know why we need compression in petrol engines?

John

Compression allows for higher output and efficiency. The higher the cylinder pressure before ignition the greater it will be afterwards increasing the force on the piston and hence the output. The efficiency of an engine depends on the temperature difference between the maximum temperature at combustion and the exhaust temperature. The greater the diference the higher the efficiency. The maximun temperature and pressure are related which is why diesel engines with a high compression are mor eefficient then petrol engines which need to run lower compression to avoid pre-ignition.

For model engines the actual compression is not so important what is critical is that there should be minimal leakage. You say that you don't feel much compression. Does it feel 'springy'? Can you bounce the piston off the compression? This engine is a little smaller than yours but will hopefully give you an idea of what I mean.

**LINK**

thank you Roger, there isn't any bounce on the compression so I am having another go at seating the valves. Leaking valves is the problem. I think I may have to add a bit onto the piston as well to reduce the combustion chamber space.

The compression ratio for some engines of that era were not high. I have come across engines with a CR ratio of 4.1:1.

That may not be appropriate to a small scale model, mind.

My little horizontal engine is designed with 4:1 compression ratio, and runs quite happily with noticeable compression/bounce when flipped over (~21mm bore).

Leaky valves seem a likely suspect.

One, that I was thinking of, was about 117mm piston diameter and 5.2 litres capacity.🙂. Even if the valves/piston rings leaked slightly, they would still start quite easily.

Yeah, I suspected something as such.

I was seeking to address the "may not be appropriate to a small scale model" concern

John

Good to see something a little different being tackled

Looking forward to progress reports / photos

Bill

John

Good to see something a little different being tackled

Looking forward to progress reports / photos

Bill

I've added a some metal to the piston and it definitely bounces off compression now. I'm using Jan Ridders design blokker ignition and have made my own spark plug as well so I should be set for a test in the next week or two. I've used E T Westbury's road roller carb so hope it all works.

Hi, please could someone tell me if I should add oil to the petrol for a model four stroke? I've seen references to adding castor oil but I would appreciate some advice. Thank you.

I only add oil if it's an open crank engine with no drip oiler to lubricate the cylinder/piston. Even then it's just a couple of drops of 2-stroke oil to 50mls fuel.

Why not? Upper cylinder lubricants were quite common 40-50 years ago. Redex comes to mind from years gone by.

Hi Everyone. success today! I got the Rumely engine running. I had a leaking exhaust valve so I remade it in a cage and left a sharp edge for the valve. I then lapped it in very lightly with Solvol Autosol and got it to seal. I got it to start by injecting neat petrol into the inlet. Once started it picked up and now the problem is it goes too fast! I can't get it to tick over so any help appreciated please. The carburettor is to ETW design for his road roller and the fuel tank is about 3 inches below the carb. I just scaled it up by 1.5.

Another question- how can i measure the speed? It just looks frighteningly fast to me.

Congratulations

I would suggest that you raise the fuel tank so that the fuel level is maybe 1/2" below the carb. There may not be enough suction at low speeds.