Engine choice ?

[Braddock, VC]

Despite my earlier conservatism, I am interested in this method of running in as I've had several asp/sc/magnum 4 strokes and offloaded the lot as they ALL lost compression within a season, the two magnum 61 fs were easy as weston uk swapped the piston rings foc but the asp 52s (2 off) sc 30 wre acquired s/h. I put it down to cheap quality and only buy saitos and lasers now though I'm going off saitos and back on to OS for the same reason.

[Jon H]

I have had a total of 5 ASP 4 strokes over the years and having followed the standard run in procedure I found that after a year they lost compression. This has been my experience with everyone else who has owned them as well.

Given the properties of Iron and Steel (the ring and liner materials) they need some heat to run in correctly and go through all the work hardening processes. Also an engine needs to be at full operating temperature and expansion for all the parts to get to their correct size and run in at this point. But running the engine cold and wet the rings stay soft, the parts don't expand correctly and it will either have soggy compression from day one, or loose it later as the ring didn't go through the proper hot/cold cycles. This is made worse in cheap engines as it is likely the metal is not as good quality.

What I have done with the last 4 engines (3 61 asps and a 52 sc) is pre oil the rockers and crackcase and then hand start the engine. I run it very rich for about 2 or 3 minutes at about 5000rpm to make sure everything is oiled up, I then open to full power and lean the mixture very quickly until I hear a good rpm rise and quickly throttle back. I DO NOT PEAK THE ENGINE. As most ASP engines are shipped with the slow run needle a good 1.5 turns too rich it gets a good glob of oil when i reduce power. I keep running in the 5000 - 6000 rpm is range for another minute before another 5 second blast at full chat. Keep an eye on the temperature (it should be too hot to hold but not too hot to touch) and that there is some smoke from the exhaust. you can also wave your finger in the exhaust stream (don't burn yourself) to see if you get some oil on your finger. After repeating this for 6 or 7 minutes I hold it flat out to see if it holds rpm for 10seconds when leaned for max performance, if so I will leave that setting and set the slow run. By now the engine will have been running a good 10 mins. After another few minutes of just playing with the engine through the whole range (you should be able to tell if its happy) I stop it by cutting the fuel and let it cool down naturally. Compression should be good by now and the ground run in is essentially complete. For the first 10 flights I wouldn't use full power for long periods and leaving any cowls off is a good idea as well.

This method is a modification on the running in instructions recommended by Laser engines here in the UK. I have adjusted it slightly due to the different construction of the ASP liner vs the Laser. While I know its against modelling folklore to do it this way it really does work as long as the engine is not run on crap fuel, over heated, over leaned, over propped or left screaming flat out, there is some science to it. The 3 61's run in like this have been flying for about 10, 5 and 3 months respectively. All still have fantastic compression and have never stopped in flight. The 52 has not yet flown as its home is still on the building bench!

Soon another member will be running in another SC52. I will try and a get a video of our adventures.

[Steve Hargreaves - Moderator]

Interesting stuff Jon....your method pretty much mirrors what I do but I never really thought of it in this way. The key points are getting enough heat into the engine & ensuring it's adequately lubricated & not over loaded. I do wonder if the manufacturers are so worried by people running engines lean & siezing them they advise running them far too rich. I recall that the SC instructions suggest the needle valve should be open 5 turns (counts them!!!!) for the first start.......given that they run at about 1 1/4 turns out this seems excessive.

Given the amount of fuel going into a glow engine the cooling effect of all that methanol when running rich must be enormous. With the amount of oil in the fuel (20% or so) it seems very unlikely the engine will be starved of lubrication...unless its is run very lean.

[Jon H]

Steve, I agree totally. I have run model 4 strokes in test conditions on 2.5% oil and they did not have a problem in my 3 hours of testing. They were Lasers though and they have an oil ring forcing oil into the crankcase. Even so, I think your view of manufacturers trying to make instructions idiot proof is valid. this is true of the blatant contradiction that is the saito instruction sheet. The factory paperwork says '20% synth no castor' and yet the importer says '20% castor nothing else'.

It also dawned on me that this method is similar used in a model diesel which has....yup, iron and steel for piston and liner. the trick is to run the engine lightly loaded or the gasses hold the piston ring off the liner wall. For a 52 size I would use an 11x6. We used 12x6 on the 61's and that worked well.

Edited By Jon Harper on 21/05/2014 17:01:08

[Steve Hargreaves - Moderator]

With petrol motors running 50:1 oil mixes & using about 1/3rd as much fuel as a glow motor it shows how little oil an engine can survive on....granted most petrols have a roller bearing big end & I guess this is where the critical factor lies. How little oil can you run & still lubricate the plain bearing in the con rod adequately.

I recall people throwing their hands up in horror at MT Dynaglow which has 10% oil.....I recall it was a very powerful fuel!!!

I wonder how low you could go & still have long engine life...

[Simon Chaddock]

Steve

Petrol is itself a much better lubricant than methanol hence the 50:1 mixes.

Of course if you really want to use very little a positive feed and a dry sump will do it on a 4 stroke.

[Jon H]

The old nugget of 'petrol is a better lubricant than methanol' is accurate but totally meaningless in the case of a model 4 stroke as it never has fuel anywhere near the bottom end. The two engines I was testing were Laser 4 strokes with bronze bushed big ends and at 40:1 they have shown no signs of distress. I will be trying 50:1 in the near future.