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Rough running engine (sticky exhaust valve, or blocked injector?)

Almost 3 years later, #2 cylinder has done something funny again.

The EGT dipped a long way down and the engine started running rough. I immediately cycled the mixture all the way down, then all the way up, then leaned back to norma and by the time I finished that, everything was fine. This is the EDM700 log. It is sampled around every 5 secs which is too slow.

It doesn’t look like a sticky valve this time. More like a bit of dirt blocking the #2 injector.

The only notable thing is that #2 cylinder has a lower CHT than the others and at the time this happened (a long descent) it was 280F. In normal cruise it is around 300-340F. However, a later flight also at 280F failed to produce any problem. This shows the CHT:

The #2 exhaust valve, borescoped today a few flights later, looks ok

Any views?

Administrator
Shoreham EGKA, United Kingdom

Bathman wrote:

But how about running on UL91 wouldn’t that make these problems go away?

I can say that before my club changed from 100LL to 91/96UL (another unleaded fuel, very common in Sweden) we experienced the common problem with rough running on one magneto during the engine runup. After changing to unleaded fuel the problem disappeared completely.

ESKC (Uppsala/Sundbro), Sweden

I have engine monitoring but have excessively high egt before I can get CHT to 380-400 on an average cruise. I’m generally around 330-350.
Some articles say to ignore egt but at values over 1520 I start to be concerned.

After reading that article, I will admit to having wrongly learned to try to keep CHT low, as prettymuch everything else points to low CHT being good.
It’s a mine field really. I think it’s good to have lots of knowledge but you could co insane trying ro achieve it all.

United Kingdom

I’ve got very few hours in aircraft with appropriate engine monitoring capability and I would say that is a fair reflection onfthe UK GA fleet in general. I also add I have had a fair few sticking valves over the years.

So my question is what the average spam cam owner do about it?

Run it hard, lean on the ground, change the oil regularly. But how about running on UL91 wouldn’t that make these problems go away? Perhaps the little extra premium might be cheaper in the long run.I’ve got very few hours in aircraft with appropriate engine monitoring capability and I would say that is a fair reflection on the UK GA fleet in general. I also add I have had a fair few sticking valves over the years.

So my question is what the average spam cam owner do about it?

Run it hard, lean on the ground, change the oil regularly. But how about running on UL91 wouldn’t that prevent the problem in the first place? Perhaps the little extra premium might be cheaper in the long run.

Yes; Mike Busch mentions Ed Kollin. Ed posted here too, as @ed2.

Mike Busch gets a much bigger audience than Camguard

That is a great bit of research which explains lots of things; notably why Conti engines are now starting to see valve sticking: more and more pilots think that operating “deep LOP” is a good idea.

Detailed article.

Administrator
Shoreham EGKA, United Kingdom

That article seems to be “inspired” by this technical paper by Ed Kollins of Camguard fame.

EGTF, LFTF

I’ve just read an article on sticking valves, by Mike Busch, in the US AOPA mag.

I wish I had known the content this time last year, but nobody else did so either so maybe it isn’t well known.

The main points are:

  • it isn’t carbon that makes them stick; it is lead related compounds
  • low CHTs (e.g. running ROP) makes them more likely to stick (complicated chemical reasons)
  • an engine running rough at low revs is nearly always due to a sticky valve, almost never due to a bad spark plug
  • low/zero EGT on a cylinder at idle indicates this (as indeed I found out)
  • Lycos stick more than Contis because sodium filled Lyco valve stems run cooler (they last longer though)
  • avoid flying for a long time with CHTs below 350F (tricky to do long continuous descents!)
  • lean aggressively during taxi, to keep CHTs up

It is well possible that my #2 exhaust valve did get stuck during one long low power descent. The CHTs easily fall to or below 300F then.

Administrator
Shoreham EGKA, United Kingdom

For the isolated task of acquiring oil samples for testing that does look like the very best way.
Neat effective and probably quite clean too.

United Kingdom

To sample oil without contaminating it, I have found these to be the best style of vacuum pumps. You thread the clean sample suction tube through the hole in the top of the pump device, screw on a bottle, and then stroke the handle to suck up the fluid. The suction is developed in the sample bottle via an orifice in the pump, this pulls the sample up the tubing and into the bottle. Unless you overfill the bottle the suction pump does not get dirty and is not contaminated between runs.

When you are done, you unscrew the pump from the bottle, cut the tube at a clean point and pull it through the vacuum pump. Repeat as necessary. Very efficient and clean too.

You of course need the correct bottles (rated for suction) and a length of tubing which is consumed as you use it and throw it away. The whole kit (in a case) is a bit more expensive, but I guess it depends on what you want. For work I use the big kit, but on my own, I would just purchase the pump to go with the bottles I intended to use and a length of tube.

Last Edited by Canuck at 06 Nov 10:05
Sans aircraft at the moment :-(, United Kingdom

For the really cheap among us, low cost solutions are available. I have one for just these occasions…

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