A4A vs A4M

[JOhnH]

Bear with me as I am a retired IT guy that converted to a small business owner. I am not a mechanic. But I did spend a few nights reading POA.

It appears that my multi year search for the cause of my high CHT problem might lie with the carburetor.

According to Pen Yan (the holder of the my upgrade STC)
I should have an O360 -A4M with a 10-5193 carb.
Instead, I have an O360 -A4A with a 10-3878 carb. This config is for a Piper and is too lean for my Cessna 172n.

When I tried to search for the differences between the A4A and A4M, all I could find was a Wikipedia article (yeah, I know), that says the main diff is that the A4A should have Bendix mags (which I have)
But the A4M should have Slick mags (which I SHOULD have).

If I change the carb on the A4A, would I need to change the mags or the timing, or anything else I am unaware of?"

Or can I just swap the carb. The guy at Pen Yan said the carb is approved for the A4A but I didn't ask him about the different mags.

I also sent an email to my A&P with the same question but he probably won't get it till tomorrow.

 

[Skylane81E]

Bear with me as I am a retired IT guy that converted to a small business owner. I am not a mechanic. But I did spend a few nights reading POA.

It appears that my multi year search for the cause of my high CHT problem might lie with the carburetor.

According to Pen Yan (the holder of the my upgrade STC)
I should have an O360 -A4M with a 10-5193 carb.
Instead, I have an O360 -A4A with a 10-3878 carb. This config is for a Piper and is too lean for my Cessna 172n.

When I tried to search for the differences between the A4A and A4M, all I could find was a Wikipedia article (yeah, I know), that says the main diff is that the A4A should have Bendix mags (which I have)
But the A4M should have Slick mags (which I SHOULD have).

If I change the carb on the A4A, would I need to change the mags or the timing, or anything else I am unaware of?"

Or can I just swap the carb. The guy at Pen Yan said the carb is approved for the A4A but I didn't ask him about the different mags.

I also sent an email to my A&P with the same question but he probably won't get it till tomorrow.

Check the TCDS, it will spell out the differences between models. I can take a look later today.

 

[Ted]

Keep the Bendix mags. Slicks are crap, I wouldn't put them on my lawnmower.

Swapping to the new carb might help. Just keep in mind it might not run great at full rich. Quality control on them is bad.

 

[Skylane81E]

Ok, I looked at the TCDS and the A4M is "Identical to O-360-A4A except is equipped with Slick 4051 and 4050 magnetos instead of with Bendix S4LN-21 and S4LN-204 magnetos"

 

[Skylane81E]

What bendix mags do you have?

 

[Silvaire]

Here's a link to the Type Certificate Datasheet E286 Rev 21

See Note 5, Page 9:

O-360-A4M - Identical to O-360-A4A except is equipped with Slick 4051 and 4050 magnetos instead of with Bendix S4LN-21 and S4LN-204 magnetos.

Both models use the same carburetor however if you have an STC of some sort these specifications may no longer apply.

 

[JOhnH]

What bendix mags do you have?

Part numbers 10-51360-37 and 10-51360-29 is all that is listed in my engine log. But I looked those numbers up and they are Bendix numbers.

 

[Henning]

Please explain to me why the same engine at same altitude in a Piper should run at a different mixture in a Cessna?

 

[JOhnH]

Here's a link to the Type Certificate Datasheet E286 Rev 21

See Note 5, Page 9:



Both models use the same carburetor however if you have an STC of some sort these specifications may no longer apply.

Thanks,
After you mentioned it I looked them up and printed them out.
I do have an STC from Pen Yan that is specifies that I should have an A4M engine (which is covered by the same STC).
The A4M uses carb 10-5193.

However I have a O360 A4A with a 10-3878 carb which is for a Piper configuration and is leaner than I need. Charlie, from Zephyr Engines mentioned this in another thread, and when i called Pen Yan they confirmed it.

My only question now is why I had the wrong engine/carb (as defined by the conversion STC) and how long it has been that way. I assume that was what was in it when I bought the plane and what was put BACK in it when the other engine blew (at 1,000 ft and we had to land on a busy 2 lane road). It had the same CHT issue before throwing a piston rod through the Cylinder head, which explains why I am so anal about getting this corrected.

 

[JOhnH]

Please explain to me why the same engine at same altitude in a Piper should run at a different mixture in a Cessna?

I have no idea. But I have heard a lot of Cessna owners with O360s with high CHT readings and not many Piper owners making that complaint. My mechanic says it is because stupid Cessna owners keep putting multi cylinder engine analyzers in training airplanes. (he says that sort of jokingly, but only "sort of".

By the way, where are you now and when are you going to be back in Florida?

 

[Henning]

I have no idea. But I have heard a lot of Cessna owners with O360s with high CHT readings and not many Piper owners making that complaint. My mechanic says it is because stupid Cessna owners keep putting multi cylinder engine analyzers in training airplanes. (he says that sort of jokingly, but only "sort of".

By the way, where are you now and when are you going to be back in Florida?

Kake Alaska this morning, will be in FL beginning Oct.

You wouldn't possibly consider that the cowling differences have more to do with CHT difference than carburetor would you? Or that the Piper cowl was designed for 180hp and the 172 was designed for 145? Besides, you are already LEANING the carb to EGT by the time you are complaining about CHT, so what difference does it make how much fractionally richer the carb can get?

I still don't think you have a problem lol, that's just the way it is when you put more horsepower in the plane than it was designed for, HP=heat. Rods in airplanes don't blow because of CHT, rods blow because of defects, damage, or old bolts. The damage is going to be caused by lack of oil and/or driving the engine by the prop; hard. In terms of heat, the cylinder head will weaken and break off the threads before the CHT induced temps will affect the rod to a critical point.

The ONLY way you will fix the problem you perceive to have is to sell the plane.

 

[Henning]

Here's a quick experiment, create a 1" lip extension at the bottom of the cowl opening and see what that does to your CHT.

 

[Silvaire]

T...I do have an STC from Pen Yan that specifies that I should have an A4M engine ...However I have a O360 A4A ...

What is Penn Yan telling you? Does the STC allow for the installation of an A4A? I ask because I don't know of any way for an STC to be valid if you are not in compliance with the specifications of it. You may need to get a special issuance from Penn Yan to cover your situation.

 

[JOhnH]

What is Penn Yan telling you? Does the STC allow for the installation of an A4A? I ask because I don't know of any way for an STC to be valid if you are not in compliance with the specifications of it. You may need to get a special issuance from Penn Yan to cover your situation.

That thought occurred to me. I am looking into that. Although they did tell me it is the same engine.

 

[charlie]

That thought occurred to me. I am looking into that. Although they did tell me it is the same engine.

The A4A and the A4M are the same engine. The A4A used to come with Bendix mags but later came from the factory with Slick. This may sound strange but all O-360's don't run the same nor do the carburetors. Back when I was running Penn Yan I would test fly a 172 with an O-360-A4M with a 10-3878 carburetor and find it unsatisfactory. Grab another 3878, install it and it would be fine. Put the first 3878 on the next engine and it would be OK. Same thing when I was doing much of the test flying of overhauls at Mattituck. One O-360 would be too rich with the 5193 carb and fine with the 3878. The next one might well be opposite. The carbs are the same except for the jets. Before there was a 5193 there was a 3878M with the 5193 jets that worked well in Archers that were too lean. The 3878M became the 5193. BTW 180 Comanches suffer from the same syndrome. The 10-4164-1 seems to work best in that application. As for the CHT remember none of these airplanes came out of the box with CHT gauges. Good thing because they all tend to run hot. I remember 1 cessna 170 I was test flying way back when that ran great but it had a big old CHT gauge that was showing in the high 400's. The owner called to see how the job was coming so I had to relate to him that all was well except for high cht. After I told him he asked if I has ever flown a 170 with a CHT gauge to which I answered no. He said that's the way it always was. Digital gauges are wonderful but sometimes provide too much information. Charlie Melot Zephyr Engines

 

[DanielH]

Keep the Bendix mags. Slicks are crap, I wouldn't put them on my lawnmower.

Swapping to the new carb might help. Just keep in mind it might not run great at full rich. Quality control on them is bad.

About the only thing I can confirm is Slick mags are crap and built very inconsistent. Have had a left mag that's been sent out for repairs multiple times, right one never.

 

[JOhnH]

Interesting. Thanks for the post.
That explains why I have the Bendix mags.

I also found in my specific STC that the engine can be either the A4A or the A4M or the A4N.

My mechanic says he might have a 10-5193 carb that he can borrow. If it helps I will buy one (and hope THAT one works the same)
If not I will learn to accept the higher CHT. I hope to know more by Monday.

That thought occurred to me. I am looking into that. Although they did tell me it is the same engine.

The A4A and the A4M are the same engine. The A4A used to come with Bendix mags but later came from the factory with Slick. This may sound strange but all O-360's don't run the same nor do the carburetors. Back when I was running Penn Yan I would test fly a 172 with an O-360-A4M with a 10-3878 carburetor and find it unsatisfactory. Grab another 3878, install it and it would be fine. Put the first 3878 on the next engine and it would be OK. Same thing when I was doing much of the test flying of overhauls at Mattituck. One O-360 would be too rich with the 5193 carb and fine with the 3878. The next one might well be opposite. The carbs are the same except for the jets. Before there was a 5193 there was a 3878M with the 5193 jets that worked well in Archers that were too lean. The 3878M became the 5193. BTW 180 Comanches suffer from the same syndrome. The 10-4164-1 seems to work best in that application. As for the CHT remember none of these airplanes came out of the box with CHT gauges. Good thing because they all tend to run hot. I remember 1 cessna 170 I was test flying way back when that ran great but it had a big old CHT gauge that was showing in the high 400's. The owner called to see how the job was coming so I had to relate to him that all was well except for high cht. After I told him he asked if I has ever flown a 170 with a CHT gauge to which I answered no. He said that's the way it always was. Digital gauges are wonderful but sometimes provide too much information. Charlie Melot Zephyr Engines