Rumely Oil Pull engine

[John RutzenParticipant @johnrutzen76569]

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.

[John RutzenParticipant @johnrutzen76569]

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

[Roger BParticipant @rogerb61624]

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**

[John RutzenParticipant @johnrutzen76569]

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.

[not done it yetParticipant @notdoneityet]

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.

[Andy_GParticipant @andy_g]

Posted by not done it yet on 17/02/2021 14:36:02:

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.

[not done it yetParticipant @notdoneityet]

Posted by Andy_G on 17/02/2021 15:37:

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.

[Andy_GParticipant @andy_g]

Posted by not done it yet on 17/02/2021 16:59:15:

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

[Former MemberParticipant @formermember12892]

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[Former MemberParticipant @formermember12892]

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[John RutzenParticipant @johnrutzen76569]

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.

[John RutzenParticipant @johnrutzen76569]

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.

[JasonBModerator @jasonb]

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.

[not done it yetParticipant @notdoneityet]

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

[John RutzenParticipant @johnrutzen76569]

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.

[Roger BParticipant @rogerb61624]

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.

[John RutzenParticipant @johnrutzen76569]

Hi, I've got myself an action camera now and done a descriptive walk round of the Rumely engine. Here it is on Youtube. The editing isn't very good, I don't know if anyone has tried to edit a video, I used Hitfilm Express but it's not easy to do.

[John RutzenParticipant @johnrutzen76569]

Hi, I've got it running and more or less completed. The engine still doesn't control very well, it's not flexible and does not seem to have a lot of power but it has good compression.

(1) First Run of Rumely Oil Pull Tractor Model – YouTube

[Roger BParticipant @rogerb61624]

Looks and sounds great to me It is interesting that it seems to run better under load. Maybe the compression ratio is a bit to high for the weight of the flywheel?

[John RutzenParticipant @johnrutzen76569]

Thanks Roger. The compression has got better the longer I have run it. I suppose the valves are bedding in? This is the first IC engine I've made so I have no prior experience. Now it's quite difficult to flick it over by hand. I got it to run better by following ETW's advice to make the inlet tract very small. I sleeved the carb bore round the jet so the annulus left is only about 0.7mm. The carb is an 1831 ETW with a float chamber.

[John RutzenParticipant @johnrutzen76569]

Here are some photos of the tractor.

[John PurdyParticipant @johnpurdy78347]

I wonder how many drivers in real life got a shock by accidentally leaning on the spark plug !!

[JasonBModerator @jasonb]

That's all looking and sounding rather good, I'm sure it's just a small tweak or two to get it running how you want.

[John RutzenParticipant @johnrutzen76569]

Thanks Jason, John, I don't know how many of them got a shock but I got one today! Gave me a jolt, I'll have to put some insulation on the nut. The other day the top of the spark plug blew out. The plug is one I made, the insulator is Corian and is just superglued in.

[John RutzenParticipant @johnrutzen76569]

Hello again, I'd left my Rumely over winter with petrol in it. When I tried to start it this spring it wouldn't go. Eventually after a lot of fiddling around I stripped down the float chamber and found a sticky gungy mess in the bottom that had blocked up all the passages. I was using normal unleaded 95 petrol. Does anyone know if this stuff can turn into a sticky mess or did some other substance get in there to cause this?

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