Revisiting Hot Start Recommendations

[Shadrach]

Jet,

I was just relaying my experience and understanding, not critiquing your technique... I was questioning the need for boost because in my application, the mechanical pump provides adequate pressure even at cranking speed to offer all of the flow my engine needs to start... I can appreciate that your experience is different...

-R

[Shadrach]

Skybyrd,

In my previous post I mentioned the heated fuel left in the injector lines "expanding" partially "vaporizing" and "puking" through the injector into the intake manifold... That is the fuel that is first fired by the engine... The rest comes on board as you feed the mixture in after the first few coughs and sputters... what do you mean by "increased friction of a hot engine"? What are you basing that on?

[jetdriven]

All the boost pump is supply positive presure to the fuel injection. We did a hot start today and it would not maintain green band fuel pressure from the engine driven fuel pump as soon as we gave it mixture.   Likely because all the fuel in the lines under the cowl were partially vapor.  The fuel pump delivers a constant steady 21 PSI to the injector. When you "1000 RPM touch nothing" start it, the only thing different is when you give it the mixture, steady fuel is there.

[Skybrd]

Shadrick: concerning your question  "what do you mean by "increased friction of a hot engine? What are you basing that on?"
 The increased friction is from heat expansion of the cylinders after its run.  The parts are tighter and the starter has to work harder to turn.  

[Skybrd]

Thanks Jetdriven for your test and post : "

All the boost pump is supply positive presure to the fuel injection. We did a hot start today and it would not maintain green band fuel pressure from the engine driven fuel pump as soon as we gave it mixture.   Likely because all the fuel in the lines under the cowl were partially vapor.  The fuel pump delivers a constant steady 21 PSI to the injector. When you "1000 RPM touch nothing" start it, the only thing different is when you give it the mixture, steady fuel is there."

I'll try your suggestion soon.

 

[Shadrach]

Skybrd,

All things, be equal, I believe that a hot engine is easier to turn over than a cold one... My skytech obviously feels the same way as it sometime struggles a bit then the engine is cold...coefficient of expansion notwithstanding... The same is true for my lawnmower, my motorcycle and every other engine I own...

[orangemtl]

I just had the original Iskra starter seize up on a 200 hour Continental 550 in my Acclaim. Thankfully, had two of the nicest A&P mechanics I've ever met at KDLO (delano CA) who troubleshot it, put a 'loaner' on my plane to get home, and wouldn't even take my money!  Amazing. Renews my faith in humanity.

The question: hot day; hot start a few hours prior. I'm low time like the plane, but it seems uniquely 'cranky' in hot starting, as suggested in serial posts here.   The starter should disengage when the engine catches, but can one burn it out after a series of three attempts to start a hot engine?  Seems hard to believe (didn't crank it more than 2 seconds after perceived start). I'm planning to replace the Iskra with a SkyTec:  as useful as some suggest here, or just placebo effect?  Also: there's an ST3 lightweight, and an ST5 nonlightweight.  Any advantage/dis to one or the other?  I welcome any and all input.

[Shadrach]

Sure it is... It's not the "cranking after perceived start". It's the repeated cranking before the start, without adequate time to cool.

[Skybrd]

Quote: jetdriven

All the boost pump is supply positive presure to the fuel injection. We did a hot start today and it would not maintain green band fuel pressure from the engine driven fuel pump as soon as we gave it mixture.   Likely because all the fuel in the lines under the cowl were partially vapor.  The fuel pump delivers a constant steady 21 PSI to the injector. When you "1000 RPM touch nothing" start it, the only thing different is when you give it the mixture, steady fuel is there.

[orangemtl]

I've tried the boost pump 'assist' in this setting subsequently (still 110 in the Western desert midday, so hot restarts are a common experience)----it helps. Thanks for the recommendations.

[tomn]

I have struggled with hot start problems on my 66 E that grew progressively worse over time - Skytek starter did not help.  Got so bad that it would only start once in a day and became harder to start cold.  Started have trouble leaning at altitude as well - took a lot of work to get EGT to settle.  Just replaced the fuel servo - all problems solved.  She starts hot or cold 1st or 2nd try and is running great.