Help with troubleshooting hot cylinder

[Hambone]

I am lookign at a 1968 M20F and the current owner sent this :

 

" # 3 Cylinder runs hotter than the rest during climb.  In the Arizona heat it goes into the yellow (376-499 degrees) and at times I need to level off or go into a very slow climb until it cools down and then I resume my climb.  Once I'm into cooler air say around 4,000ft I can climb normally.  I think it is the LoPresti cowl not allowing enough airflow."

 

and

 

"The Cowl flap and Ram Air controls are backwards.  The cowl flaps are almost impossible to operate so I leave them open."

 

Could these be related to the hot cylinder?  Any other thinfs come to mind to cause the #3 to run hotter?  I am just ryingto understand the scope of the issue before I take the next step.

 

 

Thanks

[Bob_Belville]

Examine the baffle seals for any gaps. It is critical that cooling air pass down around and between the cylinders and not escape out the top.

 

Jetdriven gave me a great tip some months ago when I was working on this problem. He suggested I wedge a piece of baffle seal behind the #3 cylinder to open the space for more air flow. Cut my 35 deg difference from #3 to the other 3 cyls to 15-20.

[Cruiser]

If there is an engine monitor that has data saved from past flights I would be looking at it to see how high and how long this cylinder has been above 400°F.  It seems that high temps will dramatically shorten the useful life of a cylinder. If this data cannot be confirmed with the owners comments on the lack of cowl flap control I would be pricing it for a new cylinder.

[mike_elliott]

A LoPresti Cowl should enhance cooling over a stock 67 cowl, or a stock J cowl for that matter. The cowl flaps should be fixed. They should not be "almost impossible to operate" nor should they be "backwards". 400 Deg. should be considered a max climb temp. As TomK suggests, take a look at the engine data, and if not available, I would be really suspect of the future life of the cylinders, personally. Aluminum doesn't like to live at temps much above 400 for very long, in spite of a company who makes the only new replacement cylinders for that engine saying a higher redline is ok. (for them it sure is!)

[Shadrach]

Examine the baffle seals for any gaps. It is critical that cooling air pass down around and between the cylinders and not escape out the top.

 

Jetdriven gave me a great tip some months ago when I was working on this problem. He suggested I wedge a piece of baffle seal behind the #3 cylinder to open the space for more air flow. Cut my 35 deg difference from #3 to the other 3 cyls to 15-20.

I wonder where Byron got such an unconventional idea! ;-)

http://mooneyspace.com/topic/2688-interesting-engine-baffle-observation/?hl=baffle

[Bob_Belville]

I wonder where Byron got such an unconventional idea! ;-)

http://mooneyspace.com/topic/2688-interesting-engine-baffle-observation/?hl=baffle

Interesting history. The tip was certainly helpful to me and I was not around MS when the original thread was active. 

[Shadrach]

Interesting history. The tip was certainly helpful to me and I was not around MS when the original thread was active.

I took a hiatus shortly after hanging my IRAN'd engine (around the time I posted that linked thread). I know it's hard to believe, but I'd had too much Mooney drama in my life and took a knee for a while. It's good to see this place is still active!

[Hambone]

Thanks for all the great info, I will check it out.

[Swingin]

If he's saying the #3 runs hotter than the rest then presumably there is some sort of analyzer installed.  The reading he's getting off of #3 could be due to having a gasket-style probe installed on that jug, with bayonet-style probes on the other three.  Mine used to have bayonet probes on all four, and at my last annual the mechanic swapped #3 to a gasket-style probe for the analyzer, with the bayonet probe still going to the stock 6-pack analog cluster.  My #3 consistently reads 75 degrees hotter now than it ever used to, and that's the only thing that changed.  The stock analog gauge still shows in line with the digital readings from the other three jugs though.  Had me concerned for a while but after reading up, I've not too worried about it.

 

I would be more concerned about the stuck cowl flaps and the reverse-rigged ram air control.  Makes you wonder what else is going on in there.

[Shadrach]

Swingen,

You bring up a good point. The plug gasket probes do read higher all things being equal. Still, #3 is typically the hottest cylinder on the E and F models. So the first step for the OP to make is to ensure he's comparing apple to apples.

[Hambone]

Ok, flew in th eplane today and noticed something.  The EDM 930 is presumably set up for the make and model ot is instaled in.  I noticed that the yellow warning range is set to 475 degrees.  THe #3 did run a bit hotter than the others by about 30 degrees orso, maybe sometimes as high as 50.  But in level cruise the temps seemed to be about 375-380 on the low end and the #3 was from 405 to 415.  So , my new question is , Is it possibl that he temps I am seeing are "normal" for this setup?  Who sets the ranges in the 930?  Because if the near 400 taboo is gospel then theis plane runs hot all over.  Can someone help me understand this?

 

 

Thanks

[Shadrach]

I think you have a baffle issue...

[kellym]

Interesting history. The tip was certainly helpful to me and I was not around MS when the original thread was active. 

I have the document that the Cardinal Flyers Online developed to document the benefit of gap in front of #2 and behinde #3 on Cardinals. It helps on both the fixed gear with parallel valve O-360 and RG with IO--360 angle valve, because Lycoming did not cast any fins on the intake side of their cylinder heads, but there is heat there that needs cooling air. I do not recall if George Braly had anything to do with it, as they developed this at least 15 yrs ago. Also the Grumman Tiger group found that they had valve problems because #3 ran hot and #1 and # 3 get 50% less oil than the pilot side cylinders in the valve rocker box. Exhaust valve life is greatly extended if you keep the heads below 400. The TLS engine had the same problem before Lycoming and Mooney developed the Bravo mod that installed oil cooling of the valve guides on its parallel valve heads.

[jetdriven]

A LoPresti Cowl should enhance cooling over a stock 67 cowl, or a stock J cowl for that matter. The cowl flaps should be fixed. They should not be "almost impossible to operate" nor should they be "backwards". 400 Deg. should be considered a max climb temp. As TomK suggests, take a look at the engine data, and if not available, I would be really suspect of the future life of the cylinders, personally. Aluminum doesn't like to live at temps much above 400 for very long, in spite of a company who makes the only new replacement cylinders for that engine saying a higher redline is ok. (for them it sure is!)

The F cowling is very efficient at cooling, A friend of mine's 1975 M20F (with lower closure) wont get above 330 CHT even when ragging on it.  Mine runs 360-370 under the same circumstances.  I wonder if this is typical, but according to Shadrach's posts, I think it is.

 

The LoPresti cowled 1977 J I flew cooled great in cruise, at least as good as the stock cowl. However, when practicing power-on stalls at 65%-75% power and <80 knots, the CHT climbed alarmingly fast. It went from 350 to 420 in less than one minute.  The owner says you need at least 100-120 knots to cool it properly.  He wasn't kidding.

[jetdriven]

I wonder where Byron got such an unconventional idea! ;-)

http://mooneyspace.com/topic/2688-interesting-engine-baffle-observation/?hl=baffle

Yeah that was one of the posts that got me really thinking, and convinced me to try it. There is also a Harmon Rocket builder who did the same thing, and I did read about a Cardinal RG pilot as well.  It sure can't hurt, and I think it helps. Its also cheap.

 

http://www.vincesrocket.com/Engine%20and%20Prop.htm

[pinerunner]

The F cowling is very efficient at cooling, A friend of mine's 1975 M20F (with lower closure) wont get above 330 CHT even when ragging on it.  Mine runs 360-370 under the same circumstances.  I wonder if this is typical, but according to Shadrach's posts, I think it is.

 

The LoPresti cowled 1977 J I flew cooled great in cruise, at least as good as the stock cowl. However, when practicing power-on stalls at 65%-75% power and <80 knots, the CHT climbed alarmingly fast. It went from 350 to 420 in less than one minute.  The owner says you need at least 100-120 knots to cool it properly.  He wasn't kidding.

This is a telling piece of information. I was drooling over the LoPresti cowling but decided to stick with my original and the easy access one gets to the back of the instrument panel. Now I'm doubly glad to have the original.

 

Dave