[David Williams]

Has anyone else had any valve-sticking problems with recently installed Millenium cylinders?

G-BSEP is in for annual at the moment, and is scheduled to have her last two cylinders replaced, having had 3 replaced at the last annual and one replaced a couple of months before that. The engineer has found symptoms of valves sticking on all the new cylinders, which surprised me - I was aware of minor hesitancy in the first few seconds after a cold start in the last few months, but had assumed it was one of the old cylinders.

Reportedly, the manufacturer admits that it's a manufacturing problem with the clearances between the valve stem and the guide, and has agreed to re-ream the 3 that are still in warranty but is arguing over the one that is just out of warranty. We are asking that the two new cylinders should be reamed as well, but discussions are still on-going about this.

I was wondering how widespread the problem is. Anyone else had problems or heard anything? Previously I'd only ever heard good things about these cylinders.

[Colin G]

Point your engineer in the direction of http://www.dti.gov.uk/ccp/topics1/facts ... odsact.htm

[IanJudge]

Dave,

The overhaul man said the valves needed a little attention on our 250 hour old cylinders - but then the brand new ones didn't impress him either!

Good luck finding two cylinders. Neither Continental or Superior have a batch ready as far as I know - might have to get ECi Titans - those that one impressed our overhauler even less.

[Paul_Sengupta]

http://makeashorterlink.com/?V3C42258A
http://makeashorterlink.com/?O1E44358A
http://makeashorterlink.com/?X3051258A
http://makeashorterlink.com/?H5B42358A

[G-BLEW]

David

I think I'm right in thinking that you are a CPA member. If that is the case give them a call, they will have some experience and some advice. If not, then I would strongly advise any Cessna owner to join

Ian

[David Williams]

I think I'm right in thinking that you are a CPA member.

Well, I was - but I've stupidly allowed my membership to lapse. I think it's time to renew.

There is now more to this story than when I started this thread, and the situation is in fact completely different. A fellow group-member had misunderstood what he'd been told by our engineer, and passed the information onto me. Lesson learnt: Always speak to the engineer directly!

In fact, the supplier did not say that it was a manufacturing error, but actually that the exhaust valves were sticking due to overheating, resulting in carbon deposits building up in the guides. The rework that they did was not re-reaming, as I had been told, but cleaning out of these deposits. The 2 brand new cylinders fitted at this annual did not therefore require any work.

So the problem is actually rather more concerning. If the valves were indeed overheating, then one possible cause is the engine operating regime. And if that's the case, the suspicion naturally points to me because I do at least 50% of the aircraft's hours - and I'm pretty sure I'm the only group member who doesn't run the engine fully-rich.

When established in the cruise, I always run at 60% power at peak EGT. I've read in countless places (and been told by George Braley, Walter Atkinson et al on a thread I raised on the CPA forums) that this is a perfectly good place to run the engine - and is sufficiently low power that my lack of decent instrumentation shouldn't be a problem.

Another possibility is poor engine baffling. The baffle seals on G-BSEP were knackered, and I wanted to get them replaced at the last annual but was persuaded not to worry about it. The engineer has done it this time. But I'm not sure whether this on its own could account for excess valve temperature.

Yet another possibility is that the valves weren't properly ground in and seated, which reduces the metal contact area for cooling when the valve is closed. Should this have been done before the cylinders left the factory, or is it something our engineer should have done when he installed them?

For the next 10 hours or so, I'll be running fully rich at high power anyway - but I'm now uncertain what operating regime I'll go back to once the 2 new pots are broken in.

AIUI, there's no excuse for these cylinders failing to cope with peak EGT at 60%. But if there is some cooling problem, do I need to adjust my technique to compensate for this problem, even though I shouldn't have to?

And if I do decide to run a tad richer, will this actually be worse?

[2Donkeys]

EGT gauges as fitted to most light aircraft are as near to useless as any gauge can get.

You have no idea in reality what the "worst case" EGT is, nor do you have any idea of the spread of the peaks.

Engine monitors such as the EDM700 or the GEM range are not prohibitively expensive to install and could save you (or anybody else) a fortune on premature engine work.

I would look at the possibility of installing on in your aircraft - then you will at least know what is happening to your engine. The EDM range also records operating data for posterity, so if you do have an engine-basher in your group, he will be found out.

[Adam]

David what sort of engine monitoring equipment do you have?

[David Williams]

EGT gauges as fitted to most light aircraft are as near to useless as any gauge can get.

Absolutely true, which is why I run at what I feel is a very conservative power setting on the grounds that I can't know what the worst case is. In fact, I don't really use the single-point EGT gauge fitted to G-BSEP - I tend to lean to a 50rpm drop, which should correspond to a very approximate peak EGT for the "average" cylinder. I've been told and read repeatedly that at this power setting it really doesn't matter where I lean to.

As you say, I have no accurate idea of the spread (*). But if the hypothetical peak EGT is okay at 60%, the spread will mean that other cylinders have lower EGT by definition.

(*) Although I suspect the spread is comparatively good - leaning until the aircraft is falling out of the sky used to result in horrible roughness before the first batch of cylinders were replaced, but nowadays it stays pretty smooth. Don't really undestand why it's made a difference, but it definitely has.

It is my understanding that EGT has much less impact on valve temperature than one would expect - and that CHT is rather more important. Would you agree or disagree with that?

I would dearly love to fit a proper monitor, having used one in a friend's 182 - but I don't think the rest of the group could be persuaded of the benefits. What sort of approximate cost would we be talking about?

So out of interest, if you were flying a carburetted engine with just a single-point EGT and no CHT gauge, what would you do with the mixture and power setting?

[2Donkeys]

Lots of good questions there:

I agree with your general belief that at power settings of 60% or so, you are unlikely to damage the engine with any form of leaning. The risk is obviously at higher power settings. I only really lean to LOP in my aircraft when in an airways-level cruise. Although I understand the theory (I think), I am not brave enough to follow John Deakin all the way.

With a Carburetor engine, leaning is always going to result in some degree of premature roughness because of the unbalanced amounts of fuel making it into the final mix. There could be any number of factors behind the rough running you experienced prior to the new cylinders going on.

As far as the effects of CHT and EGT on valve temperatures are concerned, I have read articles that support your view that CHT ultimately matters far more. Clearly an excessive EGT won't help matters though. Knowing the actual values for he CHTs and EGTs really is indispensible in situations of this sort. Dodgy baffling, for examplem, could easily result in one cylinder running at a much higher CHT than the others despite your stewardship of the engine.

A device such as an EDM700 will cost between £3.5K and £4.5K to fit, depending on who you go to and how hard you push. You can spend a lot more and have extra data such as OAT and Oil temperature fed into the display - this isn't strictly necessary though.

My leaning technique would be the same as yours. Once in level flight lean back slightly to achieve some of the benefits of leaning, and then once the engine has settled (perhaps 3 or 4 minutes), lean back to the rough run, then add 1/4 inch or so to restore even running.

[Adam]

So out of interest, if you were flying a carburetted engine with just a single-point EGT and no CHT gauge, what would you do with the mixture and power setting?

The Mooney is fuel injected with a single-point EGT and a single CHT gauge. I lean to the Red line on the EGT which is what the POH says.

I would dearly love to have a proper JPI EDM 700 fitted and then GAMI Injectors but I need to persuade the group that this is a good idea - Figures of fuel savings would help!

To answer your question - what ypu are doing seems correct I would have thought that you will get more carbon build up running too rich as there is incomplete combustion taking place. After all the clouds of black smoke issueing from an overly rich petrol engine is carbon.

[David Williams]

I would have thought that you will get more carbon build up running too rich as there is incomplete combustion taking place.

That was always my understanding as well, but the cylinder supplier said that high valve temperature can cause oil to "cook" onto the stem or the guide.

I struggle to imagine that a fully-rich setting (which I'm 99% sure everyone else uses) would cause a deposit build-up within 100 hours' of usage since the pots were fitted last year, so I'm still blaming myself at the moment.

I also suspect that our fully-rich setting is not as grossly rich as it could (or should) be. When I hit FL110 last summer, I tried slowly twiddling the mixture to fully rich, expecting to get a rough-running engine. But even fully-rich at FL110 the engine was perfectly smooth with a barely-audible rpm drop. I reckon the fully-rich setting should probably be richer than that - but it's probably no bad thing since it spends at least 50% of its cruising time there.

Hmmmm... I've just thought of induction leakage as being another possibility....

[2Donkeys]

Hmmmm... I've just thought of induction leakage as being another possibility....

An induction leak is normally given away by two things:

1) Rough running on the ground

2) Premature loss of power as you climb - the extent determined by the severity of the leak.

You occasionally get a bit of a whistle from the engine at low power settings, often audible only from the outside of the aircraft.

[Flyin'Dutch']

Adam

Figures on fuel saving can be had from http://www.gami.com and on enginemanagment from the John Deankin articles (Pelican Perch) google his name and all will be revealed.

We are about to get and EDM for the Maule, unfortunately that is a carburetted engine but at least it will give us a better idea what is happening under the bonnet.

Brilliant pieces of kit and the 4 pot ones are a lot cheaper.

[Paul_Sengupta]

This is an O-300 isn't it? Contintental engines (with brand C cylinders?) are notorious for sticking valves, especially when running leaded fuel. A lot of people in the US with O-200s or O-300s only run on mogas...they report an end to sticking valves. They say if you have to run avgas then an additive such as TCP is useful and leaning essential. I would guess that running full rich doens't help.

Given that there may be a problem with Millennium cylinders anyway (see the threads in the links I posted) and that O-300s suffer from sticking valves as a matter of course, there may be more than one problem here.

Oh, and I don't think running lean at 60% could cause a problem per se.