Rough Running

[GraemeSmith]

Aha.... here is why the engine started running rough as I taxied in the other day. And that horrible rich blackness bears no reality to the engine monitoring - so I'm going to assume it happened during the rough running taxi in. No 3 cylinder. EMPI head. 450 hours on head. Interesting carbon beginning to intrude under the copper cylinder head gasket - bottom left. Compression was good and heads had been retorqued 8 hours prior. Thinking it was an "almost" but not quite leak.

Glad I didn't have to go around!

[bvolcko38]

Any history of high CHTs? Number 3 is in back. My rear CHTs tend to run warmer.

[GraemeSmith]

Bill,

That number 3 is my "hotter" cylinder but I work REAL hard to keep it <194C (<380F) on climb out and cooler the rest of the time. Instrumentation suggested nothing "wrong". In fact I nearly taxied back to fly another pattern. But it was getting long in the day so I turned towards the fuel pump and taxied in. As soon as I throttled up to get rolling again - it was clear there was a rough run.

So to inspect this further - looks like there was a small amount of blowby at the gasket seal. But given how little there is here - perhaps just from the "jolt" in the head when the valve let go? Or it had not been happening long?

The attachment BlowBy.jpg is no longer available

To get the valve out to inspect it - I did more damage than was actually there in the first place - I was able to get the valve seat to re-seat - so I could then compress the spring and drop the valve out the guide. There is no discernable play in the valve guide - and it was not "stuck".

The valve contact area shows a nice gray uniform line and with the valve and seat removed - they marry nicely with no gaps or misfit. So I'm pretty sure it was sealing well up to the point of failure. It's hard to get a focus on the sealing edge but the "gray line" is good all round.



The valve seat - once back in place was essentially undamaged and rotated freely in the head. To get it out past the burr caused by it unseating I did a bit of damage to the far side of the seat and to the head where it had been sitting. Long and the short - seat was not really damaged as such. Just loose in the head.

There is no "granulation" on the inside face of the head that I have seen on heads that got too hot and so slightly "plastic".

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At least I did not put it in a field with an "unexplained power loss". !!

[Curry Matherne]

If you decide to get new heads from Sonex please take pictures and give your opinion on the quality. I’m trying to decide if I should get some heads from Sonex or have some of the Panchito heads from cb performance machined for a second spark plug.

[GraemeSmith]

I fitted a spare head I keep - an EMPI with dual plugs originally supplied from Sonex. Sonex lead time is currently 60 days. So I am not grounded.

I've just reluctantly charged back my CC after MOFOCO accepted an order in July for two week turn delivery, in October promised they would catch up by end of Oct and now are not answering emails and deflect phone calls.

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I'll probably go with Sonex again for a spare.