Engine suddenly quits running ?????

[Sonex541]

Well my Sonex just hit 100 hours and ever since I bought it a few years ago it had a small seepage of oil around the LF cylinder base , well last week I decided to clean it and take it apart and reseal the cylinders to the case , I pull the cylinders out enuff to clean it up and reseal but did not pull the pistons completely out of the cylinders , put it all back together ,pull it outside and let it run for twenty min at different rpms, and it was fine no leaks , well last night I snugged everything up and pulled outside and let it run again at different rpms for 25 min or so and everything looks perfect , so roll it back in hangar , today I go to hangar look everything over ,looks perfect , so I put the cowl on and get it ready for the big fathers day fly in and pull it out side let it run with cowl on and 10 min later , it stalls out ,WTF just happened , so I start it again and let it run and ten min later it quits running again , and it starts right bqck up , pull the cowl back off and let it run and it runs fine , nice and smooth with no issues , check everything and looks good , no I am getting nervous do I really wanna fly this dam thing. 100 miles away tomrow , well throw the cowl on and let it run again ten min later it burps a few times , but doesn't stall a few min later bam it konks out again , no I'm pissed off roll it in the hangar , slam the door , cancel my fathers day fly in , and come home and go online to tell my only friends that fly and know about Sonex , WHAT THE HELL IS GOIN ON WITH THIS , 100 hours of running like a top , , a few weeks ago while waiting to be cleared for take off , it was idlin real low and quit , but started it back up and it's been fine , I have no clue , vapor lock , ignition gettin hot , something is getting hot and not working , btw I have 2100 revmaster , not a aerovee ! Thanks Adam Simmons ,

[mike.smith]

Fuel line or fuel filter clogged? Fuel vent clogged? Air filter clogged? What carb are you using?

Mike

[Brett]

Tappets too tight?

[MichaelFarley56]

I don't know as much about the Revmaster, but just to make sure we're all on the same page here....

You say it will idle fine without the cowling for well over 10 minutes without any issue. Yet, after you reinstall the cowling, it will only idle for 10 minutes then shut down? It will restart okay, but it won't idle for over 10 minutes with the cowling on?

Is the cowling the only variable being changed here? How hot was the engine getting after your ground idle checks?

What is your air intake setup like? Is the air intake all in the cowling? I can't help but wonder if the engine is running rich with the cowling on and after a while it cuts out due to a mixture issue. What RPM were you at when the engine quit? Did it start to run rough or just stop?

Certainly a strage situation. I also can't help but ask this, but why are you idling your engine for that long? I try to keep ground runs as short as possible so I don't overheat the engine or glaze the cylinder walls. Have you flown recently? Any issues in the air?

[Sonex541]

I had it running at various rpms , so it not running rich , only reason I was ground testing is I fixed a minor oil leak at the bottom of cylinders , no matter what rpm , it eventually dies out or burps with the cowl on , without the cowl I let it run for over 30 min at different rpms and did not even skip a beat once , I'm sooooo confused and don't trust it now ,

[fastj22]

Sounds to me like your fuel line/gascolator is overheating on a cowl on ground run. Are your fuel lines insulated? Can you measure internal cowl temp?

[Sonex541]

That's what I was thinking , I do have a laser temp gun that I could maybe figure out how to do it , , my fuel lines only wrapped in orange fire sleeve , that's all , another issue is I fly out of a towered airport so it's tuff to keep flying over the aiport for 30 min or so incase she quits running , I was thinking about using my friends big Industrial fan and place in front of cowling and see what happens , I search for hours hoping to find something , if I find something the I can fix or pin point the problem. , I checked fuel flow. That's fine, what should I wrap the fuel line in , I'm nervous even taking this up , and I probably won't till I nail down the issue , missed my fathers day fly in , my p5151 needs wings installed , my fisher celebrity is down for new brake hoses and other tlc, issues , so I had to go up in my good friends Cessna 170 at least Its a tail wheel and we landed on grass , my two favorite things in flying .
Adam Simmons
Sonex 541sx

[radfordc]

The good news is if it is a hot fuel problem you will know when you have it fixed. Wrap all the fuel lines with foam pipe wrap insulation and then wrap the insulation with aluminum tape. Also make a heat shield for the gascolator. I used a piece of flat foam and wrapped the foam with more aluminum tape and then tied wrapped the heat shield around the gascolator.

If you can now run the engine with the cowl on for more than 10 min's you know you have it.

[mike.smith]

The good news is if it is a hot fuel problem you will know when you have it fixed. Wrap all the fuel lines with foam pipe wrap insulation and then wrap the insulation with aluminum tape. Also make a heat shield for the gascolator. I used a piece of flat foam and wrapped the foam with more aluminum tape and then tied wrapped the heat shield around the gascolator.

If you can now run the engine with the cowl on for more than 10 min's you know you have it.

But why would that suddenly be an issue now, after 100 hours of flight time? I'm not sure I buy it.

Maintenance causes a high percentage of engine failures. The change here was taking the engine apart and putting it back together. So we have to ask ourselves what might have changed, and how would the cowl on/off affect it?

Sonex (and others) note that the engine mixture behaves differently with the cowl on or off, presumably due to the warm air and rich mixture from the cowl on. So I suspect the mixture. My 2 cents.

Mike Smith

[vigilant104]

It would be good to know more about the engine and setup. It's a Revmaster--is it equipped with a Revflow carb, with an Aerocarb, or with something else? The Revflow is similar, in operating principle, to the Aerocarb. Revmaster also sells a valve to go with it which allows induction of cool external air or warm undercowl air--is the engine using one of these?

About the jug that was re-sealed: I'm assuming you re-set the valve clearances after torquing everything back down, right? How do the EGTs and CHTs look when running with and without the cowl?