Lasar Cowl Closure

[Buckeyechuck]

Anyone out there have a Lasar Cowl Closure for a C model they’d like to sell?  Looking for anything I can to reduce back cylinder temps. 100 hours on Penn Yann rebuild and still hot on 3 and 4. Mostly #4. Lasar is out of stock and doesn’t seem to be close to restocking. 

[AJ88V]

What is hot?  Can't say the cooling is that much better with the cowl closure.

[N201MKTurbo]

My old M20F always ran cold. When I added the cowl closure, my CHTs went up and my oil temps went down. And the plane went a couple of knots faster.

[MooneyMitch]

I was told by Paul Loewen several years ago, the cowl enclosure did nothing to enhance speed or cooling.  It was purely for asthetics.  

[Ragsf15e]

2 hours ago, Buckeyechuck said:

Anyone out there have a Lasar Cowl Closure for a C model they’d like to sell?  Looking for anything I can to reduce back cylinder temps. 100 hours on Penn Yann rebuild and still hot on 3 and 4. Mostly #4. Lasar is out of stock and doesn’t seem to be close to restocking. 

Your likely going to find that reworking your baffling is going to help a lot more than a cowl closure.

[Robert Hicks]

I’ve got a brand new one in the box I never got around to installing. Send me a pm if interested.

[Buckeyechuck]

9 hours ago, AJ88V said:

What is hot?  Can't say the cooling is that much better with the cowl closure.

I bump up to 450-460 on no 4 for a few minutes on 4.  That’s with climb speed at 130 and 26”mp/2500 rpm. #3 is about 15 degrees cooler. Cruise is 405-410 on no.4 and 385 on 3. 1 and 2 are 340 climb and 320 cruise. We reworked the doghouse in detail when installing the engine. Replaced all the grommets where plug wires penetrate the doghouse. Sealed joints with high temp RTV. used metal tape on all of the seams. Don’t know what more I could do without modifications. 

[AJ88V]

1 hour ago, Buckeyechuck said:

I bump up to 450-460 on no 4 for a few minutes on 4.  That’s with climb speed at 130 and 26”mp/2500 rpm. #3 is about 15 degrees cooler. Cruise is 405-410 on no.4 and 385 on 3. 1 and 2 are 340 climb and 320 cruise. We reworked the doghouse in detail when installing the engine. Replaced all the grommets where plug wires penetrate the doghouse. Sealed joints with high temp RTV. used metal tape on all of the seams. Don’t know what more I could do without modifications. 

I would say those numbers are high, but not atypical for a C model.

Which carb do you have?

[Andy95W]

3 hours ago, Buckeyechuck said:

I bump up to 450-460 on no 4 for a few minutes on 4.  That’s with climb speed at 130 and 26”mp/2500 rpm. #3 is about 15 degrees cooler. Cruise is 405-410 on no.4 and 385 on 3. 1 and 2 are 340 climb and 320 cruise. We reworked the doghouse in detail when installing the engine. Replaced all the grommets where plug wires penetrate the doghouse. Sealed joints with high temp RTV. used metal tape on all of the seams. Don’t know what more I could do without modifications. 

Those numbers are extremely high compared to my 64 M20C.

Most air leaks, I’ve found, are either to the front of the engine or underneath.  I added metal and rubber material to close significant holes around the starter and alternator, and also under and behind the oil pressure adjustment, behind and under #3.

Another factor could be your carburetor.  Some have approved modifications to flow more fuel.  Check your carburetor part number on the data plate.  If it is 10-3878, it is the lower fuel flow.  It should be either 10-4164-1 or 10-3878-M.  This would explain your climb CHTs but not cruise.

Since yours is a 1962, are your oil cooler lines still routed above the cylinders?  That adds a significant amount of heat to the whole system.  Later versions of the M20C those lines are routed below the engine to the oil cooler.

[Buckeyechuck]

8 hours ago, Andy95W said:

Those numbers are extremely high compared to my 64 M20C.

Most air leaks, I’ve found, are either to the front of the engine or underneath.  I added metal and rubber material to close significant holes around the starter and alternator, and also under and behind the oil pressure adjustment, behind and under #3.

Another factor could be your carburetor.  Some have approved modifications to flow more fuel.  Check your carburetor part number on the data plate.  If it is 10-3878, it is the lower fuel flow.  It should be either 10-4164-1 or 10-3878-M.  This would explain your climb CHTs but not cruise.

Since yours is a 1962, are your oil cooler lines still routed above the cylinders?  That adds a significant amount of heat to the whole system.  Later versions of the M20C those lines are routed below the engine to the oil cooler.

I’ve been away for most of three months rehabbing a relative from broken hip. Hope to head home this week - finally. Will check my carb number. Heading into my annual soon after I get home.  I will share some photos of my dog house then. My oil cooler lines have been re-routed along the cowl and up the firewall in back.  

[Andy95W]

14 hours ago, Buckeyechuck said:

I’ve been away for most of three months rehabbing a relative from broken hip. Hope to head home this week - finally. Will check my carb number. Heading into my annual soon after I get home.  I will share some photos of my dog house then. My oil cooler lines have been re-routed along the cowl and up the firewall in back.  

Sorry to hear about the relative’s broken hip.  Difficult process especially as folks age.

Your doghouse is probably in good shape.  The difficulty is that there are often big holes that are hard to see and work on.  When you get back home and you take off your cowling’s side panels, put a drop light inside the doghouse and turn off the lights in your hangar.  Look under all four cylinders for light leakage that isn’t through the cylinder fins.  Also look behind the doghouse, particularly where the upper engine mounts are located.  There should be large felt pieces that seal up that area, but are often missing or messed up.  Finally, put the light just under the prop and look forward under the engine to where the generator and starter are.

Additionally- there is supposed to be rubber baffle material attached to the forward part of the doghouse, top and bottom, all the way around the front.  It goes inside a small aluminum u-channel on the cowling.  All of that rubber material should be present and nice and flexible.

Also additionally- are the inter-cylinder baffles still in place below the cylinders?  These are sheet metal that extend between the barrels of cylinder 2&4 and 1&3.

Engine cooling isn’t really about airflow, it’s about the air pressure differential between the top of the engine (doghouse) and the area under the engine (leading to the cowl flaps).  Since it’s a fluid, the air in the doghouse will follow the path of least resistance- which is often big holes around the starter, generator, oil pressure adjustment, and engine mounts.  That lowers the pressure differential so less air is being drawn through the cylinder fins.

To summarize the problem areas:

- upper engine mounts

- around and under the oil pressure adjustment 

- around forward parts of the generator and starter

- baffling in the u-channel at the front of the doghouse

- inter-cylinder sheet metal baffles below the cylinder barrels

- other areas of the doghouse where it fits around the cylinders and case

[Utah20Gflyer]

On 11/3/2024 at 6:20 PM, Buckeyechuck said:

I bump up to 450-460 on no 4 for a few minutes on 4.  That’s with climb speed at 130 and 26”mp/2500 rpm. #3 is about 15 degrees cooler. Cruise is 405-410 on no.4 and 385 on 3. 1 and 2 are 340 climb and 320 cruise. We reworked the doghouse in detail when installing the engine. Replaced all the grommets where plug wires penetrate the doghouse. Sealed joints with high temp RTV. used metal tape on all of the seams. Don’t know what more I could do without modifications. 

All of those temperatures sound really high.  Are you climbing full rich?   If your doghouse really is well sealed I would also suspect your mixture is too lean. 
 

I have a G model which is the same firewall forward as a C model and I make sure to never exceed 430 in the summer while climbing but most of the time I can keep it under 400.   In cruise I am around 320-330.  Oil temps are normally 190-200 in climb.  
 

450-460 on a regular basis will likely shorten your cylinder life substantially as metals lose their strength in an exponential fashion as they heat up rather than linearly.  So, I would definitely figure out why your engine is running so hot.  

[65MooneyPilot]

I don’t know if your C has adjustable cowl flaps or not but if it does make sure they are opening the proper amount to get that good differential pressure. 

[Buckeyechuck]

On 11/3/2024 at 11:36 PM, Andy95W said:

Those numbers are extremely high compared to my 64 M20C.

Most air leaks, I’ve found, are either to the front of the engine or underneath.  I added metal and rubber material to close significant holes around the starter and alternator, and also under and behind the oil pressure adjustment, behind and under #3.

Another factor could be your carburetor.  Some have approved modifications to flow more fuel.  Check your carburetor part number on the data plate.  If it is 10-3878, it is the lower fuel flow.  It should be either 10-4164-1 or 10-3878-M.  This would explain your climb CHTs but not cruise.

Since yours is a 1962, are your oil cooler lines still routed above the cylinders?  That adds a significant amount of heat to the whole system.  Later versions of the M20C those lines are routed below the engine to the oil cooler.

Carb is a 10-3878-R  S/N G-50-8582. Was overhauled as part of the engine rebuild. 

[Buckeyechuck]

On 11/4/2024 at 11:31 PM, Andy95W said:

Sorry to hear about the relative’s broken hip.  Difficult process especially as folks age.

Your doghouse is probably in good shape.  The difficulty is that there are often big holes that are hard to see and work on.  When you get back home and you take off your cowling’s side panels, put a drop light inside the doghouse and turn off the lights in your hangar.  Look under all four cylinders for light leakage that isn’t through the cylinder fins.  Also look behind the doghouse, particularly where the upper engine mounts are located.  There should be large felt pieces that seal up that area, but are often missing or messed up.  Finally, put the light just under the prop and look forward under the engine to where the generator and starter are.

Additionally- there is supposed to be rubber baffle material attached to the forward part of the doghouse, top and bottom, all the way around the front.  It goes inside a small aluminum u-channel on the cowling.  All of that rubber material should be present and nice and flexible.

Also additionally- are the inter-cylinder baffles still in place below the cylinders?  These are sheet metal that extend between the barrels of cylinder 2&4 and 1&3.

Engine cooling isn’t really about airflow, it’s about the air pressure differential between the top of the engine (doghouse) and the area under the engine (leading to the cowl flaps).  Since it’s a fluid, the air in the doghouse will follow the path of least resistance- which is often big holes around the starter, generator, oil pressure adjustment, and engine mounts.  That lowers the pressure differential so less air is being drawn through the cylinder fins.

To summarize the problem areas:

- upper engine mounts

- around and under the oil pressure adjustment 

- around forward parts of the generator and starter

- baffling in the u-channel at the front of the doghouse

- inter-cylinder sheet metal baffles below the cylinder barrels

- other areas of the doghouse where it fits around the cylinders and case

Thank for a plan for trying to tighten up the doghouse. Originally when we reinstalled the engine we fabricated new seals for around the generator and starter and for the cowl opening from red rubber. After having the initial temperature issues I purchased a seal kit from GeeBee. We have installed a part of that kit. I will do the light leakage testing as soon as I get into the annual. I will also try to take some photos to share. 

[Buckeyechuck]

On 11/7/2024 at 12:05 PM, 65MooneyPilot said:

I don’t know if your C has adjustable cowl flaps or not but if it does make sure they are opening the proper amount to get that good differential pressure. 

Cowl flaps are set to open 1”, might be a bit more. I never close them. 

[Buckeyechuck]

On 11/6/2024 at 11:23 AM, Utah20Gflyer said:

All of those temperatures sound really high.  Are you climbing full rich?   If your doghouse really is well sealed I would also suspect your mixture is too lean. 

Climb at full rich and 26” mp/2500rpm. I think the carb is set slightly rich as I get a bit of engine roughness coming downhill and under 22” mp. 

[Buckeyechuck]

I started taking my airplane apart for annual today and took some photos of the doghouse. I used the lighting technique to look for openings and found some mostly at the front bottom in front of #2 & 4 cylinders. Will discuss with my A&P a plan to close up. Also may use some RTV at the top rear were I can’t tape as well and a bit of light is showing through. Not sure if this will fix my issue but can’t hurt any. 

[takair]

Seems like a few opportunities there with the light…  Also, left, forward, lower flex seal is out of the slot.  May not be an issue, unless it somehow flops the wrong way.

[McMooney]

Birdy is 2 to 3 kts faster with the cowl closure,  i already had shiny new baffles so can only tell you she doesn't seem to get as hot.  think she had the extra large version of the guppy mouth

[Buckeyechuck]

14 hours ago, takair said:

Seems like a few opportunities there with the light…  Also, left, forward, lower flex seal is out of the slot.  May not be an issue, unless it somehow flops the wrong way.

Out of slot as I was starting to remove the top of cowl.  Stopped to take photos. 
 

Thanks for all the ideas. There are some large gaps at the starter. Any closure ideas?  Would this have much effect on air to #4?  

[takair]

1 hour ago, Buckeyechuck said:

Out of slot as I was starting to remove the top of cowl.  Stopped to take photos. 
 

Thanks for all the ideas. There are some large gaps at the starter. Any closure ideas?  Would this have much effect on air to #4?  

They used to use felt, but well cut and placed baffle seal material will work (pop riveted).  It is not so much that you are not getting air to number 4, it is more the fact that the leaks apply pressure to the lower deck of the compartment, so basically it acts to equalize pressure between the top and bottom of the engine and thus reduces flow through the cylinders.  Can’t guarantee that it will be the fix, but I would hope you get measurable improvement.  The C models run hotter than E, so you won’t see low 300s, but would be good to stay under 400 as much as possible.

[Buckeyechuck]

I found the bottom seal to be a bit short of the groove so it seems to be pushed down out of the groove and could be allowing air to escape to the lower engine compartment as Takair has stated above.  I’m going have it repositioned it to tighten it up.   Will post results when the annual is complete.  

 

[DXB]

On 11/8/2024 at 9:36 PM, Buckeyechuck said:

Carb is a 10-3878-R  S/N G-50-8582. Was overhauled as part of the engine rebuild. 

What is your max fuel flow at takeoff?  As noted above, the approved carbs are 10-3878 and the 10-4164-1. A-3878-M is a 10-3878 that has been modified to be as rich as the 10-4164. I don’t know what -R means, but this could be part of your issue. It is unlikely the entire issue, but the cowl closure will not help. The baffle design here is garbage even in perfect condition- imperfections can make CHTs intractable.  Also double check your mag timing, consider retarding it to 23 or so from 25. 

[Andy95W]

Oftentimes the -R refers to a “rebuilt” part.  I definitely think the carburetor is part of @Buckeyechuck’s problem, particularly in the initial climb phase.  IMO, he should get his overhauled to the -M version, or better yet exchange for the 10-4164.