Engine hot start

[Frank Wadle]

Hello,

how do you guys restart your engine when it is hot after a flight?

In the past I just refueled, hooked up the glow starter and flipped the prop. No priming, no fuel injection, just flip the prop. That gave me instant restarts even with the hottest engine.
This year, with a different model, this technique does not work anymore.
It's the same engine I used before, just a different model and (and I think that is the key factor) a different fuel.
In the past I used 80/20 FAI fuel with all castor oil.
Now I'm using Motul synthetic oil.
Oh, by the way, we are talking about a Retro Discovery 60 engine.
It will start very easy when it is cold. I inject about 0.5cc fuel into the Venturi using a syringe, flip the prop a few times, hook up the glow starter, and backflip the engine....BANG! Instant start all the time. But when it's hot after a flight it is always difficult to restart...
So how do you guys restart your engines?

Kind regards
Frank Wadle

[Lauri Malila]

Too much carbon buildup in piston/top of cylinder causes it with Retro. L

[Frank Wadle]

Usually I would agree. But this engine is very clean and runs very good. It just refuses to restart when it's hot. I cleaned the engine earlier this season and it has almost no carbon.
Oh, another thing I changed from last year is the plug. Now I use a ENYA3. Could that be it?

[Lauri Malila]

I know what you mean. Just in case, remove the head and see if there is a rim of carbon in top of cylinder. Or under sealing ring of piston on exhaust side. If so, use paint polish compound to remove them.
Or, go back to KC2-plug. Enya is shorter reach and  it may affect the ignition sensitivity.
Is it one of my engines? L

[Frank Wadle]

I checked for carbon... None what so ever.
I cleaned the engine carefully maybe 30 flights ago. The seal-ring on the piston looks good.

It is a engine I bought used, but not from you Lauri 😊
As far as I remember I never bought a Retro60 from you... But I'm getting old and tend to forget things 😊

I'll try a KC2 plug this weekend.

[Lauri Malila]

Is something causing extra heat..? You said earlier that front bearing may have moved, I'd check the bottom end too. L

[Frank Wadle]

That was a different one. This one runs fine. It just refuses to restart when hot.

[John Leidle]

  Hey Frank,  my engines are medium warm after a flight because I run my stuff rich  but it they get hot I let it cool a bit choke 1 flip  then run it through several times & then put on the battery & they usually go.
  John

[Dan McEntee]

   I would say the answer is in the oil. That is the main thing that has changed.The castor oil probably made it run a bit cooler. Castor helps carry heat out of the engine in addition to lubricating. The synthetic is probably not doing the same job. The engine may seem to be running OK, but there may be a fine line where if it gets to a bit higher temp, while nothing catastrophic may be happening, it's heating up enough to have enough clearances in the top end that it won't support combustion. probably not enough residual oil left behind either to help that out. That's my 2 cents worth.
  Type at you later,
   Dan McEntee

[Dennis Toth]

Frank,
Some engines just need to cool between flights (like the Fox 35) to restart by hand. The team racing guys get them to restart because they don't heat soak before they prime and flip. Most of the time what happens is the case/cylinder hold more heat then the piston and expands a little more thus has low compression and difficult starting by hand.

If you can't let it cool, use a couple of choke flips and a starter.

Best,          Dennis

[phil c]

If the engine has noticeable compression when hot it should restart.  Most likely thing is the oil/plug.  If carbon build up bothers you try adding percentages until the carbon stops building up- usually 10-50% of the oil works.

It usually works better to refill and restart as fast as possible.  Letting it sit 5 minutes or so tends to let the crankcase bottom end heat up, which makes starts harder.  Any kind of a prime can flood it then.  Stunt motors usually have pretty good fuel draw which can flood a hot engine even without choking.  Flipping it backwards can work.  It won't draw fuel that direction.

Phil C