High revs after start

[digits]

Let's say you flooded your engine, and you use the mixture cut off, full throttle method of trying to start your fuel injected continental IO470.

If this happens after the plane has been shut down for half an hour after your last flight, let's say during a fuel stop, what damage would you do if you let your engine rev up too much because you are too slow in retarding the throttle?

I would think that there would still be oil everywhere so you don't suffer the same metal-on-metal damage you would do if you fired up with high revs on the first start of the week.

Any thoughts?

[Colonel]

Oil probably isn’t your problem.

Clearances are the problem.

Look for metal in your filter. If there is none, you got away with it.

FWIW I use absolute minimum RPM for the first minute after start for a cold engine - never over 1000 RPM

Mixture lean for max RPM then 1100-1200 RPM to minimize fouling of spark plugs and valves.

Wait for CHT 200F then runup to 1700 RPM, check the mags, leaning and prop.

Back down to 1100-1200 RPM and lean for max RPM until takeoff.

If straight grade oil, wait for 100F oil temp - it’s gotta circulate through the hot cylinder heads. Multi-grade oil, you’re good to go.

I knew a guy, had a T-28. Didn't get all this mechanical stuff. Jumped in and went. His engine made metal.

[digits]

Oil probably isn’t your problem.

Clearances are the problem.

Is that still an issue if your engine is warm?

[Colonel]

Well, as Larry King replied when asked about what brand of underwear he used:

"Depends"

shut down for half an hour

If it's cold and the wind is down the snout, it will be dead cold after half an hour.

If the OAT is 100F and there's no wind, it will still be warm but not operating temperature.

Put your hand on the cylinder head fins through the cowl opening right after shutdown,
and after a half an hour. See the difference? The CHT might be "warm" (best case 90F)
but it's sure as hell not 200F.

[digits]

Allrightie, fair enough. I was asking because I'm trouble shooting an issue that seems like a textbook example of vapor lock, but it happens after fueling in -20 degree celcius weather...

Engine fires with some trouble, runs for a second, then dies. Another flooded start procedure, engine fires, and dies again. After 5 such attempts, it finally keeps going. It happend with my AME on board as well, and he didn't have any clear cut answer. So wanted to try some things out before throwing random parts at it.

This is the right engine on a C310N. Left engine behaves normally. Right engine issue has happened 3 times now in more or less the same circumstances. Engine runs great once it's running.

Vapor lock at -20 seems unlikely to me. I have the feeling that more throttle makes it easier to start, but didn't want to overdo it either.

Any follow up thoughts?

[Colonel]

When someone is having trouble starting/running an engine, I go back to first principles.

1) mechanical. Are all of the metal moving parts inside the engine doing the right thing
at the right time? This isn't as stupid as it sounds - exhaust valves love to stick open when
cold. I don't think this is your problem.

2) air going in and out of the engine. No one ever thinks of this, but an engine is an air
pump and any restriction on the intake or exhaust (eg rusty baffling failing internally to
the muffler and plugging it up) is no bueno. I don't think this is your problem.

3) spark. Is it strong? At the right time? This might be related to your problem (long shot).
The TCM IO-470 probably has two impulse coupled magnetos, I'm guessing.

4) fuel. Here we go. Either you have too much fuel, or too little. Remember that liquid
fuel DOES NOT BURN - you have to prime, and give it time to evaporate. This doesn't
happen much at -20C with 100LL. Probably the best thing I can suggest is having someone
outside watch your troublesome engine start, and compare it with the good engine with respect
to priming (same amount of fuel pour out the bottom of the cowl) and - are there clouds
of black smoke that you can't see from the cockpit? Black smoke is excess fuel and it
means very rich - over-priming.

When your engine starts, and then dies, what is the fuel pressure indication? Too low
to read? It's almost certainly not enough fuel - what is your mixture position? I might
be tempted to turn on the boost pump after it fires. The Continental electric boost pumps
are tremendously powerful. Again, have someone outside look for clouds of black smoke.

[Colonel]

Back to temp ranges ...

CHT below 100F is bad news. Expect damage with RPM. Also, you have to
be thinking about your crankshaft bearing clearance, which go to zero as the
temp drops and the aluminum crankcase shrinks faster than the steel crankshaft.

CHT above 200F - give it the beans. Clearances should be good.

CHT above 100F but below 200F ... this is the expensive temperature. If
you open the throttle and get RPM and BMEP, you might or might not hurt
the engine, depending upon it's design and current clearances.

[digits]

Both engines need fuel priming after they fire to keep going, but the right engine usually needs it a bit more/longer.

Normally, I prime for a second. Press the starter, while starting, I press the primer button. When it fires, I release the starter button and have to press the primer a few more times to keep it going at 800 rpm with mixture just under full right and throttle open very little. That works in all temperatures for the first start.

Usually after fuelling or after it ran, I skip the initial prime and repeat the normal starting procedure, and that usually works (with some prime required after it fires to keep going).

If that doesn't work after 2 attempts, I start getting a bit worried. Even though I didn't prime much, or at all after some attempts, I tried the mixture cut off, fuell throttle start, and then the engine fires, but as I quickly pull the throttle back, it dies again. Which is tempting me to see what would happen if I left the throttle mid way during the troublesome start. But that doesn't seem too smart after reading the info.

I don't have a fuel pressure gauge, but I have a fuel flow gauge, which shows normal flow when priming. I did not look at it in detail when it was acting up, but I'll keep an eye out for that.

I'm just really confused that it fires and then dies, even when using the primer pump.

A colleague at work suggested taking a look at the E-gap timing. I'm not sure how that would help if the engine is firing though.

[Colonel]

Again, have someone outside looking for black smoke out of the exhaust.

That's a sign of over-priming. Also, fuel piddling on the ground underneath
the cowling, before start.

I suspect you are not getting enough fuel, for some reason. But you need
to validate this theory by watching the exhaust. If you have a HUGE cloud
of black smoke after start, you are putting too much fuel in the engine.

Without black smoke after start, you know that you need more fuel if it's
cranking and won't start - assuming you have spark.

Once you know for sure if you have too little or too much fuel, then you can
go looking as to why that is the case. But first you need to know which you
are suffering from.

[Colonel]

If it helps (Lycoming not TCM) the Pitts S-2B AFM recommends
half throttle for a normal hot start, with the mixture ICO.

Crank, and when it fires, mixture forward then throttle back.