SU carb vacuum calcs for Alta engine

[cardiffrob]

Strange request.

I have a 1 1/8 SU carb on an engine with a ported vac take-off where the butterfly sweeps over the port. This will give little vac until just off idle throttle position, I assume, whereas manifold vac will be the same figures except for high vac at idle. Now, if I have a drilling between the butterfly and the dashpot on the straight 1-inch section, does that have zero at idle and low figures all through the rev range with the exception of high vac when the throttle pedal gets suddenly depressed and before the dashpot has had a chance to rise? It will certainly never get as high a vac figure as the manifold.

I'm after finding the ideal spot for this Upper Cylinder Lubricant device (Redex Lubrocharger) from the 1950s that came with no instructions. Ideally I would have thought it only wants short shots of UCL whereas manifold vac would keep it drawing oil all the time? Not much internet info on this, unless I'm googling the wrong phrases?
I have the original Redex fluid here as well as some Marvel Mystery Oil, as used on aircraft engines for the same purpose.

It would be nice to be able to help keep this engine alive for as long as possible since spares are almost non-existant, unless someone knows where there is another for sale????

 

[Chris Stevens]

Why not just add some 2T oil to the fuel? Something thats sucking oil into the inlet system under vacuum is going to make for very smoky running, and wont do much to help motor live longer. If you know where to look its possible to get just about anything made, and UCL isnt going to do anything to head off the effects of many years of wear.

 

[Cobbler]

Hi Rob, I've only known Redex added to the fuel, was one old penny a shot, one shot per gallon. With regards to the effectiveness of it, my mates father was a mechanic in one of the local garages & he said you could always tell if it was used in the cars when you stripped them as the ports & valves were clean & the valve stems lubricated.

The drilling that is to the edge of the butterfly sounds like the one for a advance & retard take off, except if I recall it wasn't used on the side valve engines. The drilling between the dash pot & butterfly should in theory have constant vacuum I would have said, but very low, hence it being called a constant depression carburettor. Even on tick over the dashpot rises slightly to maintain an even air/petrol ratio.

I don't suppose this info helps much, as its only my thoughts on it. I don't suppose the magic aircraft fluid is Kygas is it, don't know if the spelling is correct, but I think it was injected into the manifolds as a sort of Easystart. I've only seen it once & that was on a Bedford diesel van with a knob on the dash. When I asked about it he told me it was a system off an aircraft, or as fitted to aircraft. No doubt someone will be along in a minute that knows about it

EDIT, just tried on Google & I think the spelling is Kigas

 

[gordon stephenson]

I was a redex junkie in the 80s ( found a full 5gall drum in the back of the oil store) 1/2 a cup in with the engine oil keeps the internals sparkling, Also a drop in with the petrol on fill ups, And the odd squirt down the carb while giving it a good rev, It did catch me out once, going for a long trip down to Devon, Thought i would give it a treat and put a load extra in with the petrol. While blasting down the road,about 50 miles later engine lost power,running lumpy etc, one cylinder not firing, Quick check and found one of the plugs had whiskered same as a two stroke used to, quick clean and ok again,

 

[cardiffrob]

Oh yes, Kigas is a manufacturer of pumps for injecting neat fuel into intakes as a primer. I used one on an Auster I used to fly.

The Redex and MMO had good reputations in their day but that was a long time ago so I'm not sure if the same is still true. Ethanol doesn't lubricate but oil lasts longer so maybe there is a balance in there somewhere. I agree on the cleanliness issue, having run our other sidevalve on MMO in the fuel tank. This Alta was rebuilt just before we got it (hence the scary price!) MMO say theirs is the same formula but Redex say theirs now contains zero lubrication ability.

I'd forgotten that the SU was described as a CD carb so that makes sense that it would be constant, yet lower, in the middle area. I've already got the 2 drillings in the carb for the advance mechanism and between butterfly and dashpot so I'll connect it there and open the valve a bit further than would have been the case for higher manifold vac. Just a thought, the damper would still be slower to react than the butterfly so there would be a brief extra depression under acceleration. Fitting it certainly can't hurt.

 

[Cobbler]

The damper being slower to react is what gives you a slightly richer mixture on pickup, gives you a greater depression over the jet to pull more fuel through, hence the damper in the top to slow it down. I'm delving back in my little grey memory cells nearly 50 years now on the principles of SU carbs.

 

[500e]

Do you have the round 3inch Redex meter chrome bezel white card with a metering needle to adjust the drip feed if I remember correctly on the Singer 1500 we had the inlet was just inboard of the butterfly
50s tractors had Ky-gas, it was a pump to spray diesel over an element in the manifold this produced vapour that the motor ingested with the standard fuel charge
Had a look & found this

 

[cardiffrob]

Yes, that's the one I have, plus the original tin with fluid in.

Probably worth me getting the engine installation finished and running it to see what vac is pulled at the middle of the carb body. If it is anywhere near half the normal idle figure of circa 18 inches then I can run the system from there without having to drill and tap the new manifold. Real bu66er to get the carb off now that the rest of the engine bay has been fitted.

Thanks for the help, everyone!

 

[dannyp]

IMO i wouldnt bother

modern oils are amazing compared to the oils made when the enigne was. and dose the upper cylinder really need any extra lubrication th episton is fitted with an oil scraper ring to remove excess oil and just leave a film on the cylinder wall, the piston skirts on older engines the grudion pin tends to be quite low and the piston skirts are long and all thats working below the oil scraper ring where everything is been coninualy blasted with oil fog.

also if an enigne did need any help it wouldnt be on idel or overrun when there is loads of vaccume it'd be when it's flat out when there is no vaccume.

id go for a good fully synth low ash / smoke 2 stroke oil and put a sot of that in the petrol, at something like 100:1 mix

 

[Chris Stevens]

Interestingly enough castor base oils were developed to lubricate aero engines, and at the time were state of the art, and could cope with far more heat than the other oils around at the time. Today though very few people would choose to use castor over a modern oil, which is superior in almost every way.

If adding 2T oil to fuel to help provide some measure of upper cylinder lubrication, not a good idea to use any sort of low smoke type, as the additive used to reduce smoke tends to degrade lubrication performance (at least according to a technical paper produced by Yamaha!).

 

[cardiffrob]

It's more to do with the experiences of other owners where they are finding the valves seize up in the guides, possibly due to Ethanol not helping matters. Demand for exhaust valves is so bad that there are now plans to have a batch made. Pricey! The logic, as it was explained to me, is that a vac operated system will lube the valves at low throttle but will not oil things at WOT whereas oil in the tank will lower the octane rating and put extra oil into the cylinders all the time. When pulling away you get a squirt every 10 seconds or so at every gear change. 0-60 in 14 seconds with this engine conversion against 0-56 max in nearly 50 seconds for the standard engine. Since the kit is sitting here on the bench it seems a good idea to at least give it a try? Can't hurt, can it? So many of these things were sold that there must be some validity to the concept.

Googling led me to some discussions over ZDDP oils. Penrite Shelsley Light 10W-60?