2 cylinders not firing on initial engine start

[BrianL29]

Hey all,

Strange problems started late November on my Bravo.  Latest in a series of them on my IRAN engine with about 40 hours on since then.  

When i start the engine, cylinders 4 and 5 do not fire up.  I let it idle for a while and typically no luck. I have to stop and start the engine 5-10 time and eventually they all fire.  During my re-starts I am doing a flooded engine start and trying to keep mixture as lean as possible and throttle close to idle and that seems to help.  

The first time this happened I remember accidentally trying to start with the mixture at idle. I stopped and tried again and had the throttle a bit too far forward and it roared to life a little harder than I would have liked. 

 The engine used to start on the first blade turn.  When it does catch quickly, then it does seem to start ok.  Lately it seems to crank for 4-5 seconds before it start and that is when those 2 cylinders don't light.  My engine has been buggy. I had broken intake valve springs at hour 20.  The crankcase seal pushed out around hour 27.  When it does start it runs smooth and EGT and CHT's look good.   

Any thoughts? Do you think the plugs are getting wet? I installed fine wire plugs mid October. I am tempted to put the old plugs back in to see what happens.     

[MikeOH]

When 4 and 5 "come on line" do they do so at the same time, or one then the other?  And, when they do, is the idle immediately smooth, or initially rough?  I'm wondering if you have sticking valves.  Which cylinders had broken springs?

[BrianL29]

Normally 4 comes on line first and then 5.  But I may have to restart a couple more times to get 5 going.  Its runs smooth as soon as they are all running.  Cylinder 3 had the broken spring.  

[MikeOH]

What were the symptoms when #3 had the broken spring?  Just speculating that might be the case here, though I wouldn't think it would ever run smooth!  Curious if you had an explanation for why the spring broke on a new engine?

[BrianL29]

When springs broke I landed fine pulled off the runway and the engine started shaking violently. I saw no EGT on #3. Obviously didn’t come back to life. We found both intake valve springs broken. Shop said that the new camshaft installed probably over compressed original springs and broke them.

My current problem seems to correct itself with time. I haven’t pulled valve covers but doesn’t feel like the issue.


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[GeeBee]

42 minutes ago, BrianL29 said:

Shop said that the new camshaft installed probably over compressed original springs and broke them.

I call BS! Sounds like a cam out of time with the crank

[EricJ]

1 hour ago, BrianL29 said:

Normally 4 comes on line first and then 5.  But I may have to restart a couple more times to get 5 going.  Its runs smooth as soon as they are all running.  Cylinder 3 had the broken spring.  

If you just leave it running while the two cylinders miss do they eventually come online?   If so, that sounds like sticking valves that just unstick as the engine warms up.   That's pretty common.   

[BrianL29]

I haven’t had both come on line by just leaving it running. I’ve had to stop and restart the engine. I’m guessing the longest I’ve let it run is maybe 10 minutes.

My savvy analysis indicated a potential valve failure on #3. I borescoped last month and everything looked good on that cylinder. I’ll have to check others.

Is it possible I’m getting too much fuel on initial start and soaking those plugs?

[Andy95W]

52 minutes ago, BrianL29 said:

Is it possible I’m getting too much fuel on initial start and soaking those plugs?

One plug? Maybe. Both plugs? Not likely.

What happens when you advance the throttle to 1500-1800 rpm?  What happens when you lean the mixture?

[BrianL29]

Engine shakes pretty good if I increase power that much. Leaning doesn’t change much. I keep it as lean as possible while I’m trying to revive it. 

[cferr59]

I had an issue like this after a cylinder replacement and after some troubleshooting found that there was no dry tappet clearance at all on the exhaust side.

[EricJ]

It's unlikely to be ignition related if the cylinders don't fire at all, since the ignition is redundant and it's unlikely that both sides would fail exactly the same.   So single-point-failure items like valves or fuel injection seem more likely.  

 

[Andy95W]

I’m with Eric.  It seems like it’s gotta be either no compression or no fuel to those 2 cylinders.

[MikeOH]

I'm completely speculating here, but it bugs me that you had that valve spring break on #3.  No way that was the 'new camshaft'; as @GeeBee said, that is BS.  I am beginning to wonder if the wrong valve springs were installed in some locations such that they bind.  That could explain #3 failing as well as your issues with #4 and #5.  Yeah, it's a long shot, but maybe the next time you start and have the problem, shut down and then pull the rocker covers on #4 and #5 and see if the valves are 'hanging up' (not closing)

[BrianL29]

Good idea on inspecting the valve springs. I need to narrow the problem down somehow.

I agree on the shop excuse being BS. I picked the wrong shop and regret doing an Iran vs overhaul. Live and learn.

Any opinions if I should continue to fly before solving the problem? I can’t decide if this is a nuisance start up problem or a time bomb.


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[PT20J]

Since it seems repeatable, I would remove a spark plug from each cylinder and remove the rocker covers and compare the valve motion in all cylinders when rotated by hand. 

 

[Jim F]

If you know that you have zero fuel in the cylinders, you know that the mags are grounded, the mixture is ICO, and the throttle is at idle you can pull the prop through by hand and see if you have compression.  I would also do a cold compression check.  I don't think I have ever heard of a valve sticking after a teardown, but they might not have pulled the valves during the IRAN.  The broken spring is interesting and if you have one, I would pull the rocker cover and inspect all valve springs.

good luck and let us know what you find

Jim

[A64Pilot]

22 hours ago, EricJ said:

If you just leave it running while the two cylinders miss do they eventually come online?   If so, that sounds like sticking valves that just unstick as the engine warms up.   That's pretty common.   

I agree, look up “Lycoming morning sickness” It needs to be rectified immediately, it can lead to damage if you don’t.

[A64Pilot]

4 hours ago, PT20J said:

Since it seems repeatable, I would remove a spark plug from each cylinder and remove the rocker covers and compare the valve motion in all cylinders when rotated by hand. 

 

While he’s doing that, pay attention to the rockers, see if any get real loose, if one does it means the valve is sticking partially open.

On edit, I would not even crank it again myself, I think it’s time to get a mechanic involved. I guess pulling valve covers is benign by itself, I would pull a plug from all cylinders, but rectifying a sticking valve is beyond what an owner should do unless they are have their P license.

Valve springs break from fatigue, there isn’t any way unless a push rod was way too long that a new cam could break them, I’m not sure a push rod that long even exists.

Edited Saturday at 10:25 PM by A64Pilot

[MikeOH]

Is it possible that an incorrect cam with too much lift was installed?  If the rocker covers are off, maybe measure valve lift?

[A64Pilot]

29 minutes ago, MikeOH said:

Is it possible that an incorrect cam with too much lift was installed?  If the rocker covers are off, maybe measure valve lift?

I don’t see how, but measuring valve lift can’t hurt. Too much lift or a too long push rod often has the rod being bent, never heard of valve springs being broke from too much lift myself, yes they stack up and then something has to give, the push rod does, but sticking valves can damage a cam and possibly lead to Lycoming cam disease, it’s thought that is a contributing factor to some cam failures.

I believe if a valve sticks fully open the engine could swallow it, and that is very often catastrophic and most always results in engine failure.

I really think a licensed mechanic is called for to eliminate sticking valves myself.

https://www.lycoming.com/content/prevent-sticking-valves

Edited yesterday at 12:21 AM by A64Pilot

[BrianL29]

Thanks for the input.  I agree, I need to have an A&P look at it.  My primary mechanic just retired and my back-up moved away, so I'd like to do as much of the diagnostics as I can before I let someone tear into it.  

If anyone has any recommendations in northeast Ohio, let me know.  

[GeeBee]

Lycoming "morning sickness" on an engine just IRAN'd is just plain wrong. Especially on an engine that gets as much valve lubrication as a TIO-540. Something is not correct.

Wrong timing or wrong parts.

 

[EricJ]

2 hours ago, BrianL29 said:

Thanks for the input.  I agree, I need to have an A&P look at it.  My primary mechanic just retired and my back-up moved away, so I'd like to do as much of the diagnostics as I can before I let someone tear into it.  

If anyone has any recommendations in northeast Ohio, let me know.  

Just a random shot in the dark, but has the flow divider had any attention lately?   They're very simple, but if something inside is obstructing those two lines I could see maybe some oddball failure doing that and resetting when the pressure goes away on a restart.   Just another random thing to think about.

Something you can easily do as an owner is remove the plugs for those cylinders and just check condition, gap, resistance, etc.   While the plugs are out, borescope the cylinders and examine the injector nozzles, valves, anything else that might look funny.   It's kind of tricky to do, but you can rotate the prop to open the valves and check the stems as well as you can...you need a cooperative borescope to do that well, but it's a good way to see if there's evidence of something obvious making the valves stick.