Synthetics

[Paul Jefferies]

I am getting back into the hobby after a long layoff and have been digging out some of my old engines. Having stripped and de-gummed them they seem to be ok but I would like to prevent the gumming up happening again. I understand that fuels that use synthetic oil are must better in this respect but could there be any problems in using synthetic oil in old engines which have previously been run on castor based fuel?

Paul

[Alan Gorham_]

Yes there might well be a problem.

Some older engines such as enyas used a cast iron piston and steel liner. The grain on the cast iron absorbed castor oil and formed a varnish which helped the running fit and explainedwhy engines ofthis type lasted such a long time before the fit "ran out".

Switching to a synthetic oil for engines of this type strips away the castor oil varnish and leaves a sloppy piston-liner fit and your engine is then clapped out.

More modern engines with ABC type piston and liners should be ok in most cases.

[Paul Jefferies]

Alan, many thanks for that. I had a feeling that there might be something like that but I couldn't remember what it was! So is it only engines with cast iron pistons that should not be run on synthetics? I have a venerable OS40FSR which was badly gummed up. That has an alloy piston with a ring and I have freed it and put new bearings in. It still runs well on castor fuel, would it be safe to use a synthetic based fuel in that?

[Alan Gorham_]

The ring will be made of cast iron so the issue will still occur.

Obviously the contact area of a ring is much narrower than a ringless piston so the wear rate should be less.

You could try fitting a brand new ring before running on synthetic oil.

You mention degumming the engines but have you deglazed the liner bores? This is where you use a plastic scouring pad as used for dishwashing to scrub out the castor varnish.

[Paul Jefferies]

No, I didn't deglaze it because I thought it is an old engine and the glazing must compensate for some of the wear. The ring appears to be free so I tried it and it runs well so on the basis of "If it ain't broke don't fix it" I decided to leave it. Should I deglaze it?

[Alan Gorham_]

Paul, it's a tricky one.

My understanding is that a well used engine with lots of varnishing will be prone to accelerated wear in the varnished areas plus localised overheating.

If your engine seems ok I would be tempted to leave as is and run on castor based fuel.

If you are keen to switch to synthetic then I would deglaze and fit a new ring and then run the engine in as the piston liner fit will have changed.

I don't think there's a definitive answer to your original question but I have seen a few engines over the years be switched straight from castor to synthetic and either start overheating on every run or losing compression soon after.

However, I bet there will be some people who have switched straight over and never had a problem.

Personally, I fly all my modern engines of ABC type on synthetic right from the word go and keep castor based fuels for my older engines. Since I still fly engines that were bought in the 1980s and are still on their original piston and liner then I'm happy with my approach. Your mileage may vary as they say on the tinternet.

[Paul Jefferies]

Alan thanks for taking the time to reply. Yes I think you are right that it will be safer to continue using only castor based fuel, probably in my more modern engines as well. I have no problem with castor based fuel other than the gumming up problem if the engine is not used and I am told that synthetics are somewhat cleaner........ ie. less goo to be cleaned off the model after flying.

Perhaps I need to find a good "afterrun" to squirt into the engine which will prevent it from gumming up...... any suggestions?

Paul

[Alan Gorham_]

Your reasons are my reasons!

I find a fuel that has a good quality modern synthetic oil in is less draggy so letting the engine provide more power.

I also like the way that many fuels with synthetic oil have anti foaming agents in that alleviate the need to pack the fuel tank with foam to prevent fuel foaming and vibration.

They are also cleaner as you mention but perhaps not as clean as you might think. You will still have to wipe oil off the model after a flight.

Yes, the gumming thing can be a problem with castor based fuels. Especially in four strokes and other engines with ball race bearings.

If you have to use castor then the technique of running the engine dry of fuel from its normal running temperature is a good way of cleaning it out ready to have after run oil put in.

Model technics do a convenient sized bottle after run oil which is normally easily availablein model shops.

I have used it in the past and am not convinced its especially designed as a specially blended oil. I never had any problems with it though.

You are trying to prevent internal corrosion as well as gumming. One thing I like doing is making sure the piston stays at BDC for a couple of days after flying to let any acidic burnt fuel residues escape the exhaust port. I also shove some after run down the carb intake after my last flight of the day before putting the model in the car and then flicking the prop over a few times to make sure the bottom end of the engine is protected.

The worst thing I find for gumming up is to store the engine with castor residue in it for extendedperiods. Either use the engine regularly or if it needs storing them a good dose of after run after flushing the engine out with parrafin or petrol, then plugging the carb intake and exhaust port and then popping in a plastic bag should stop gumming.

[Wilco Wingco]

Old ENYA s seem to be causing problems. Some say that if you run one on synthetic it will remove the "varnish" and cause a sloppy piston fit. Another thread says he has been running an Enya 50 on synthetic for ages with no problems re power loss or sloppy piston. I have just res-erected an old and very reliable SS 40 which I used to run on castor, all my fuel is now synthetic. Help???

[Jon H]

Posted by Wilco Wingco on 28/01/2020 12:59:09:

Old ENYA s seem to be causing problems. Some say that if you run one on synthetic it will remove the "varnish" and cause a sloppy piston fit. Another thread says he has been running an Enya 50 on synthetic for ages with no problems re power loss or sloppy piston. I have just res-erected an old and very reliable SS 40 which I used to run on castor, all my fuel is now synthetic. Help???

Its nonsense, use synthetic. it will be fine

[Peter Christy]

I switched all my engines from castor to synthetic decades ago. Never had a problem with any of them.

This subject was discussed at length recently: **LINK**

Worth a read, to save going over the same ground again!

--

Pete

[Wilco Wingco]

Thanks for the posts. I have just found a copy of the SS 40 instructions on the net and under fuel it say "20% castor or high quality synthetic oil". Problem solved.