Newbie to IC - running in different four-strokes?

[Jonathan M]

Justin, Denis - thanks for this! Especially good to know the idle will settle down after a few flights.

With the tank removed from the airframe, but before removing the bung or any of the neoprene tubes, I tried a pressure test by nipping off the filler and pressure tubes and blowing down the fuel tube. I couldn't detect any leak... but I did then get a serious blowback of residual fuel right down my gullet - yeuch!!

The likely culprit then emerged: the clunk tubing was actually too long, especially after it had slipped slightly off the copper pipe inside, and was sitting right against the back of the tank.  It also didn't help that my test was done on a slight downwards stope in the garden, thus with the nose slightly down - didn't think that one through!  So, I've cut 7mm off this and re-installed the tank (which is a Dubro rather than the Ripmax effort).  Will test/replace all the external tubing, lose the filter, and run the engine up again tomorrow... on the flat!

Edited By Jonathan M on 22/12/2016 20:56:45

Edited By Jonathan M on 22/12/2016 21:01:14

[Jonathan M]

Update: all issues now sorted and, after several more runs on the ground in the last week, finally maidened the Acro Wot today! (Lovely model, a real pleasure to fly! Did I mention losing it for a few tense moments in the low cloud!?)

The ASP 70 FS settling in nicely, still with the smaller 12x6 running-in prop and still lots of smoke and castor oil residue streaming over the wing, but with a fairly reliable tickover of 3500, slow enough to land into a light wind whilst avoiding the worst of the sheep-shit and the forest of mole hills pocking the patch!

Second flight we topped up the tank (say 50:50) with a mate's fuel containing 5% nitro. The idle seemed better as did the transition with the risk of cutout almost completely gone, but at full throttle the engine seemed to vary a bit in note and speed?

Should I stick with the Model Technics Special Four Stroke 0% nitro, or for my second gallon get the 5% nitro version?

Also, when would it be 'safe' to fit the 13x8 prop?

Jon

[cymaz]

Second gallon go to 5%. This will improve the idle reliability. Read Jon's posts from page one....all the info is there. Enjoy. Don't forget to get the regular prop on, this wheel act as more of a flywheel and improve the lower rpm on idle.

[Jonathan M]

Thanks for the steer cymaz... good job I got into this hobby just before my brain started its slow but inexorable mutation into a Swiss cheese!

Edjut Fact No 773: Turns out that the gallon of Model Technics Special FS fuel I've been using from the start already has 10% nitro in it... but at least its also lubricated with 9% caster and 9% EDL oil, so all this well within warranty instructions... I think!

Tried the bigger 13x8 prop for two flights today. Top end revs now down to 8,500 (but need to check I didn't muck up the TX full throttle settings by mistake... err... Edjut Fact No 774), mid-throttle at 6,500 and idles at 3,500 still, although I expect this will improve. Starts with a finger-flick when warm and only cut out once, luckily on a landing approach!

Is it worth checking the tappet clearances at this stage?

Just want to say this to all who've helped: THANK YOU ALL SO MUCH! I've got much yet to learn with this and future engines, but I'm finally airborne with an IC powered model and all the contributions have made all the difference to my understanding.

Happy 2017!

Jon

[Denis Watkins]

Now you are in the air Jonathan, it must be tricky to land at 3500 as the motor can still taxi at those revs, but as the motor runs in, this can be reduced, even 2500 will help on landing. All the Best

Edited By Denis Watkins on 31/12/2016 19:45:31

[Jonathan M]

Yes, coming in a bit fast now, especially with the big prop chewing forward, might revert back to the 12x6 for a while yet!

[Jon H]

12x6 is a little small for an ASP 70. I would use 13x6 or 7 if it were me.

As for your fuel, nothing really wrong with it but the castor will make a mess. A switch to 5% nitro will full synthetic oil at 15% will make it cleaner and make it run better. If (like many) you don't like the idea of oil that low then model technics sport 5 will be fine as well.

As I have said before though 15% oil is more than enough and guys at my club running ASP motors have no trouble with it at all.

The guys are right about the idle as well, 2500 is the top end you want to see for an engine that size

[Jonathan M]

Posted by Jon Harper - Laser Engines on 31/12/2016 19:58:31:

As for your fuel, nothing really wrong with it but the castor will make a mess. A switch to 5% nitro will full synthetic oil at 15% will make it cleaner and make it run better. If (like many) you don't like the idea of oil that low then model technics sport 5 will be fine as well.

Cheers Jon

MT's Irvine Sport 5 uses 18% Klotz Super Techniplate oil, which has a 1:5 ratio of caster in it (i.e 3.5%) - would be much less sticky than the current 9% of thick sludge down the wing!

Else, which 15% fully synthetic? Is the Laser 5 suitable?

I do find the layout of Model Technic's site information a bit confusing.

[Jon H]

Laser 5 and techpower 5 would both be perfectly ok and Laser 5 would be the cheapest option.

One of the reasons MT have so many fuels is they bring out new ones as things advance, unfortunately the old ones are tricky to discontinue as convincing people that less that 20% castor is safe can be a challenge!

[Jonathan M]

Thanks Jon.

Well, the last third of my gallon of Special Four-Stroke 10% is now completely redundant. The engine is just too unreliable to fly on this - randomly cuts out at all but fastest throttle - and I've been using a mate's Irvine Sport 5 which gives complete confidence! I also love the fact that the whole starboard part of the aircraft (wind, u/c, fuse and tail parts) is now gum-free!

Prop is now a 13x6 which is completely comfortable for me, and - despite tickover still a bit high - low wind landings are absolutely fine (Acro Wot ARTF).  The mid-position of my 3-way cut-off switch reduces throttle a bit more on the ground to prevent unwanted taxiing, but sometimes cuts out.  I imagine this will improve with use.

Cheers

Jon

Edited By Jonathan M on 09/01/2017 08:59:43

[Jon H]

It still sounds as though your slow running needle is not quite right, most likely still rich. It might also be worth looking at the valve clearances to see if they are a bit on the wide side. They should be .1mm or 4 thou. If you arent sure how to check this i am sure someone at your club can help.

You should be able to idle at 2500rpm or so without any trouble. It might even be worth trying a new plug, the OS F being my choice

[Denis Watkins]

As Jon says Jonathan, a new plug is worth it, as you may think you started with a new plug, but the 1st plug in a new motor gets blathered. That is a technical term I use at the field and means "spoiled ". In a new motor the shiny element tends to grey over more quickly than its run in counterpart. My run in 70 ticks over reliably around 2200 but is 5 seasons old.

[Jonathan M]

Thanks guys - I've now dealt with a few factors and much happier with the engine!  (Almost no longer a complete IC Newbie!?)

I'd already swapped from the original ASP plug to a new OS F so that stayed the same, but now using Laser 5 fuel.

I re-set the tappets, which were in fact considerably out. The Just Engines instructions are clear, but this video by them was also very helpful: **LINK** My only uncertainty was which TDC to use from the complete cycle of strokes, but assume this makes no difference as valves are closed in both cases.

On my previous settings (i.e. the last time I flew) the RPM range with the 13x6 prop was from 9,900 down to 3,000. I then fiddled with the low-speed mixture - it turned out to be a bit too lean and when I richened it almost 1/8 of a turn the reliable idle reduced to 2,500 with no significant hesitation when the throttle is advanced, which I reckon is as good as it'll get until the engine has a couple of seasons under its belt.

Finally, how often should the engine be serviced, what does this involve, and do people do this themselves or send the engine off?

Edited By Jonathan M on 11/01/2017 15:35:55

[Martin Harris - Moderator]

It should be done at TDC on the compression stroke - watch for the inlet valve opening on the preceding down stroke. You need to be aware of valve overlap on most engines at TDC on the exhaust stroke where the inlet valve opens before the exhaust stroke is completed to take advantage of inertia in the gas flow - and the exhaust valve may not be fully closed at this point.

Edited By Martin Harris on 11/01/2017 15:50:47

[Jon H]

Martin is right, and in terms of maintenance its a simple case of if its working fine, leave well alone. Only if it starts behaving out of sorts do you go looking for the problem. Often, 'preventative' fiddling causes more problems than it prevents!

[Denis Watkins]

The most significant "servicing" for 4 strokes Jonathan are in the area you have been working. These motors can be starved of oil in the tappet covers due to no pressure and often work on fuel vapour from time to time, so a drop of oil along the moving faces a regular intervals based on use, and down the followers. Again, the tappets are barely audible when set, but just listen for a marked increase in noise, as this is usually due to loosening, but is not a common occurance. Otherwise, leave the motor alone and just provide a good plug and recommended fuel.

[Jonathan M]

Thanks for these tips Martyn, Jon, Denis.

Re plugs, is this black residue (around the current OS F plug) a sign of anything amiss?

Edited By Jonathan M on 28/01/2017 22:01:59

[Jon H]

its the castor in the fuel. I wouldn't be too concerned as the element looks ok. If the coil looks dull or is distorted its time for a new one

[..]

No Jonathan nothing is amiss, reading back over the thread you seem to be looking far to deeply into what is essentially a very simple internal combustion engine.

Also just a side note , four stroke engines have a soft aluminium plug thread as opposed to some two stroke units that have a harder steel bushed thread. Be careful & try to not repeatedly remove & refit the plug as wear & damage may occur.

If it's running ok then fly it & through use it will get better.

[Jonathan M]

Cheers. I probably do mither a bit too much, but do also like to really understand mechanical (and electrical) things and learn to keep them sweet.

As a kid in the 70s I learnt my aeromodelling entirely by trial and error - lots of them, especially with small glows and diesels! There was no local club I could join, and my old man had no mechanical interests. There was no internet, only the monthly mag and the salesmen at Henry J Nicholls in Holloway right the other end of London by bus!

Now, if the rain holds off for long enough tomorrow morning , I'll be up the patch for some more four-stroke Acro Wot action.

😀