2 cylinders not firing on initial engine start

[EricJ]

Ouch.   Well you definitely have a smoking gun if you're having multiple spring failures on that cylinder.   Dry lifter lash needs to be checked.   See if you can find a part number on the spring to see if it's the right one, etc.

[GeeBee]

Multiple spring failures on that engine, not just that cylinder before the last spring broke?

[BrianL29]

36 minutes ago, GeeBee said:

Multiple spring failures on that engine, not just that cylinder.

Yes, 2 different cylinders have had broken intake valve springs.  First one was about 20 hrs after IRAN and the 2nd was about 35 hours.

[MikeOH]

2 hours ago, BrianL29 said:

Yes, 2 different cylinders have had broken intake valve springs.  First one was about 20 hrs after IRAN and the 2nd was about 35 hours.

This is really looking like wrong parts or bad assembly (as @EricJ said).

What does the shop say now that ANOTHER spring has broken??  I don't see how they can blame you.  This should be their problem.  Don't let them off with the "cam" BS.

[BrianL29]

Engine shop says-

1.  overrevving engine when cold-They quoted Lycoming to not apply power before oil is up to 160F.  

2.  springs are just coiled steel rod and have cycle limits...or might have been a bad batch.  You cant NDT them, so no way to know if they are good during an IRAN.

You'd think they'd at least pretend to review the IRAN documentation and look for possible issues.

Any opinions on the picture of cylinder with oil at the bottom? Normal or excessive? 

 

[MikeOH]

Number 1 sounds like more BS to me.  Unless you're starting up at 2000 rpm, or something.

I don't even understand 2?? I thought the springs were new?  No idea about aircraft valve springs but very common NDT of automotive valve springs is to compress to a known height and measure how much force is required; they make a simple arbor press type tester just for the purpose.

Oil looks a bit much for a new/OH cylinder unless it's not yet broken in.

[A64Pilot]

You Can NDI springs, but it’s not worth it, Crack growth in high strength steels which springs are is very rapid, so you could eddy current or mag particle springs, they pass and break soon after.

Valve springs rarely break in aircraft, in truth I can only come up with either a bad batch which is unlikely or excessive hours, also unlikely but possible I guess because maybe they have been put into more than one cylinder over the years?

I think I’d get another mechanic to collapse the lifter and check for proper pushrod length, too long shouldn’t break springs but would I believe cause burnt valves.

Sometimes rarely unusual events happen, like two bad springs in one aircraft that fail at about the same time. I don’t normally believe in coincidences, but maybe?

Over revving as in floating the valves can fatigue springs, but that shouldn’t even be possible in an airplane, and while revving it up when cold is bad as in usually causes cylinder and other things I can’t see how it hurts valve springs.

Oil looks excessive to me, and could well be coming from a valve guide, but oil unless consumption is stupid excessive or visable smoking isn’t really usually an airworthiness driver

Edited yesterday at 06:34 PM by A64Pilot

[GeeBee]

Have you done a compression check on each cylinder?

[dzeleski]

12 hours ago, BrianL29 said:

 

2.  springs are just coiled steel rod and have cycle limits...or might have been a bad batch.  You cant NDT them, so no way to know if they are good during an IRAN.

 

Nonsense. We have valve spring testers for this exact reason. Springs that are not healthy will absolutely show their signs. Bad springs will show up as an out of family curve.

https://www.performancetrends.com/Valve_Spring_Tester.htm

One common cause of broken valves in engines that run methanol and collect water in the oil. If the engine isn’t flushed or ran up to temp with pump gas rust can start to form on the springs and that little bit of rust can cause a fracture point for a crack to form. This is really common in drag racing applications.

For an engine shop to say there is no way to NDT a valve is insane. So they are just slapping used or even new valves into an engine and hoping the seat pressures and heights are correct? That’s a great way to get valve float, piston to valve contact, valve seat recession, valve failure, or valve spring failure.

Edited 19 hours ago by dzeleski

[A64Pilot]

I’ve always given cylinders to a shop that specializes in that, but I don’t think we shim aircraft springs like we do cars, if not I don’t even know why not, basing this only on I have never noticed a shim under a spring in an aircraft like I did cars back when I was building car engines.

Aircraft engines normally just can’t rev past TO RPM because of the prop governor and even if it fails one can’t rev real high unless it’s in flight at high speed, then maybe.

Anyway 2700 is valve float wise pretty much Diesel engine type of RPM, I mean really slow which while I assume we have big heavy valves that contributes to float unless our valve springs are stupid weak I just don’t see valve float happening?

Its largely why Lycoming cam disease confuses me, I’d expect it on highly loaded valve trains like hot cams on older generation cars turning over 6,000 RPM, but a 2700 RPM airplane engine ought to be very easy on the valve train.

[MikeOH]

@BrianL29

There was a cylinder replacement video posted today.  In it they had a parts error: wrong intake valve; too long!  I wonder if that is maybe what's up with yours.  They had NO valve lash!  It was obvious when compared to another cylinder; just need to remove the rocker cover and take a look.

[BrianL29]

Thanks for all the ammunition. During the IRAN they replaced the lifters and the camshaft. Valves and springs were reused. I will make sure lifter clearance is checked and we are replacing all the springs. Compression check would be interesting as well. I upgraded my savvy membership for additional support.

Lousy problem but I’m learning a ton about engines!


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