What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Exhaust blow-by

BigJohn

Well Known Member
I'm in the process of performing my second condition inspection. I found that there has been some significant leakage of exhaust gases from the right rear exhaust pipe muffler joint. See photo. I will have to remove the muffler and investigate of course, but wondering if anyone else has seen this?

15qdkz6.jpg
 
BigJohn,
I had this same issue on my first -12. I hired a Rotax Certified A&P and did a 100hr inspection with me "riding along". First thing is pull the muffler and clean the ball ends of the exhaust pipes and the sockets on the muffler. Next CAREFULLY bend the spring tabs so that the springs will have increased tension when installed. This will hold the ball and socket together with increased pressure. Before you reassemble the exhaust, put a healthy coating of Permatex Anti-seize(the grey/silver paste) on each of the muffler ends of each exhaust pipe. This will provide some sealing of the joint and make it easier to disassemble for later maintenance. Also, it looks like your springs might have some heat damage from the exhaust leak. My guy recommended replacing them since each spring is only about $3 a spring. I did all of the above with my mechanic and the exhaust leak went away. Please be careful bending the spring tabs as any muffler that has seen a few heat cycles could have brittle welds that can break if disturbed. Hope this helps.
-Bruce
 
Last edited:
Wow - that is "significant", John. How often do you pull the lower cowl?

Just wondering of the PITA part of the cowl installation process resulted in less surveillance than would be the case if more easily removable.

Bob Bogash
N737G

Finished my airplane today - 1 year and 2 days.
 
Thanks for the thoughts guys. Especially the part about the spring tension. That makes sense. I hope the tabs are still "bendable". Bob, you are right about pulling the lower cowl. The PITA factor definitely comes into play. I installed a quick drain on the oil tank just to avoid pulling the lower cowl on oil changes. I think it has been about 60 hours since I last pulled it. More info when I have pulled the muff.
 
Just wondering of the PITA part of the cowl installation process resulted in less surveillance than would be the case if more easily removable.

In all fairness to the 1000's of people reading your opinion Bob... what aircraft are you comparing the RV-12 too?

Have you ever removed the cowling from a Piper or Cessna or Beachcraft?
I have. Many times.
Some are easier than others. Some are more involved than the RV-12.

And then some... I think were designed just to give certain people something to complain about... ;)
 
In all fairness to the 1000's of people reading your opinion Bob... what aircraft are you comparing the RV-12 too?

Have you ever removed the cowling from a Piper or Cessna or Beachcraft?
I have. Many times.
Some are easier than others. Some are more involved than the RV-12.

And then some... I think were designed just to give certain people something to complain about... ;)

I can have my cowling completely off in 10 minutes. I believe that would place the 12 on upper end of the "easy/quick to remove" scale. That includes removing the air damper heat mod.
 
Getting it off is pretty quick and easy. Getting it back on is where the pain comes into play.
 
Last edited by a moderator:
Getting it off is pretty quick and easy. Getting it back on is where the difficulty comes into play.

This could be affected by a number of different factors...

- The adjustment of the oil hose clocking on the oil cooler (mentioned in the construction manual).

All the RV-12's I work on, will allow me to lift the cowl straight up into place and have the oil cooler drop on to the mounting lugs without me doing anything other having the cowl properly aligned while I raise it.


- Trimmed length of the exhaust pipe.

If I remember correctly, trimming so it extends about 7 inches beyond the bottom of the muffler is about right.


- Lastly, proper installation of the cowl.

If the cowl was pushed/forced into position when it was being drilled to the hinges to alleviate unwanted gaps, etc., you will have to apply the exact same force every time you install it. It also will contribute to puckers and distortion in the cowl shape, and reduced longevity of hinges and attachment rivets.
Another factor is whether the duct frame was installed with exactly the prescribed 1/4" gap around the entire perimeter of the radiator.

Any one of these will cause difficulty to varying degrees. A combination of all three could definetely cause it to be difficult.
 
Last edited by a moderator:
In all fairness to the 1000's of people reading your opinion Bob... what aircraft are you comparing the RV-12 too?

Have you ever removed the cowling from a Piper or Cessna or Beachcraft?
I have. Many times.
Some are easier than others. Some are more involved than the RV-12.

And then some... I think were designed just to give certain people something to complain about... ;)

C'mon Scott. Lots of airplanes have had easily openable cowls, not much different than the hood of a car (sorry - bonnet for the U.K. guys), that allow you to see the engine. Like the Cherokee - a quarter turn of two Dzus fasteners on each side and pretty much the whole firewall forward is open to see.

To me, this is not just a Maintainability issue, but also a Safety issue, in that you get to look at the engine during every pre-flight, instead of just an oil dipstick. If there are any leakage, rubbing, or other issues, they are front and center. Sort of like John Peck's leaking exhaust.

As I get ready to make the first flight on my airplane, I note in the Flight Test Guide that it calls for pulling the cowling after the first flight. Ugh! That means I need another guy (I definitely cannot do it by myself!) And they're not just walking by my hangar door. When I installed the lower cowl a few weeks ago, I didn't have another guy - so I (tried) to do it with my wife. We almost made it, but in the end, we couldn't get the oil cooler holes and everything else to line up all at the same time, plus I scratched my paint pretty good. So I had to take it off again and wait until Tony T. came over a few days later on the ferry and we got it installed (with a lot of pushing and shoving and a few bad words.) Maybe, as you suggest, it wasn't made right and I'll have that problem for the rest of my RV-12 life.

Try not to be too defensive, Scott. Continuous Improvement is a mantra I preached for the last ten years of my working career. I believe in it. Meanwhile, many airplanes with problematic cowls have after-market mods to improve or rectify this very shortcoming - even Vans - as you can see by doing a search of VAF for things like camlocks etc. Some businesses - like Skybolt - even thrive on rectifying the situation.

Since you asked, here are an assortment of easy-opening cowls. Why even in my old favorite - the 737-200 - I could pop open the side cowls by myself in about two minutes, expose the whole engine, and latch them back up by myself in not much more time. And I've done it many, many times!

Bob Bogash
N737G

Super Cub, Cessna 140, Cessna Caravan, Beech Bonanza, Cherokee, Piper Arrow

i-Mkt78KV-L.jpg


i-LstsVMX-L.jpg


i-2ssGFwN-L.jpg


i-QxtgHZh-L.jpg


i-skqNXMq-L.jpg


i-XqP7nQ4-L.png


i-tsZL3hC-L.jpg
 
Just wondering of the difficult part of the cowl installation process resulted in less surveillance than would be the case if more easily removable.

Bob Bogash
N737G

Finished my airplane today - 1 year and 2 days.

C'mon Scott. Lots of airplanes have had easily openable cowls, not much different than the hood of a car (sorry - bonnet for the U.K. guys), that allow you to see the engine. Like the Cherokee - a quarter turn of two Dzus fasteners on each side and pretty much the whole firewall forward is open to see.

Bob,
I am not being at all defensive. I was just asking you to qualify your statement.

Your first post was talking about removal of the cowl. Now you are talking about looking inside. Two totally different things.

I guess all I can really say is that the RV-12 has the same cowl it has had since day one. So that is the cowl it had when you decided to build one.

BTW, other than the super cub cowl (which I think very few people would consider attractive for an RV), I think you are putting far to much value in how much (limited) inspectablility any of those engine comparments actually have when the cowl is opened.
 
Last edited by a moderator:
I voted with my wallet, Scott. You don't have to convince me on the merits of the RV-12. But, just like a car, a house, or even a spouse, nothing is perfect. I thought our mutual goal was to make a fine product even better. I don't need, or plan to get defensive about making comments on this Forum.

As to "removing" the cowl vs "opening" the cowl and looking inside, there is either no difference or a big difference when it comes to the RV-12, depending upon your perspective. The airplanes I pictured (what's so bad looking about a Bonanza cowl?), allow you to LOOK inside without removing the cowl. The RV-12 does not. If you want to look, you have to remove the cowl.

I find it comforting to look, and doing that during every single pre-flight is all the better.

As to there being "limited inspectability", I guess it depends on the individual airplane - but in general, I do not agree with that statement at all. It's very much like popping the hood of your car. You might not be able to see everything, but there's a lot to see. Have you popped a Cherokee cowl lately?

Bob Bogash
N737G
 
At work I'm responsible for the maintenance on over 40 GA aircraft of various types.

As Scott said, whilst you can open the cowlings on some of the PA28 variants (140, 151, 161) and other types, how much can you usefully see? Many of the PA28s (like the PA28-235 in the photos, Arrow, 180, 181, 236) have a one piece removeable top cowl and are rarely removed as part of a pre flight inspection.

The RV-12 top cowl is pretty easy to remove with practice and you can see enough with experience to satisfy yourself that all is well.

The easiest cowlings to remove completely are probably the C152 - pure joy! :)
 
I voted with my wallet, Scott. You don't have to convince me on the merits of the RV-12. But, just like a car, a house, or even a spouse, nothing is perfect. I thought our mutual goal was to make a fine product even better.

I understand your point Bob.

I will end with pointing out what gets discussed on this forum a on a regular basis, by the more design savvy members....

Every design is a compromise.

Designing the cowl on the RV-12 with hinge open panels that would have allow for pre-flight inspection of the entire engine compartment, would have directly gone against the goal of maximizing useful load and minimizing cost (possibly far more weight and $$$ than you might imagine).
I believe in the past you have said you felt both these were positive aspects of the RV-12.
 
This is one of the greatest examples of thread drift I have ever seen. The first three posts actually address the issue of exhaust system question. The next 15 posts are entertaining, but not very helpful to BigJohn. Check the thread before you post.
 
Last edited:
Nothing wrong with thread drift. It provides insight on what other owners are thinking about. I agree that Vans has a great product and sometimes seem to miss the opportunity to use forum input to improve it. I know it's not "official" feedback to Vans, but the forum is a market research gift to them.
 
I'm in the process of performing my second condition inspection. I found that there has been some significant leakage of exhaust gases from the right rear exhaust pipe muffler joint. See photo. I will have to remove the muffler and investigate of course, but wondering if anyone else has seen this?

15qdkz6.jpg

Aloha John, replace the springs PN 938-795 (66MM )$3.28 ea and add some high temp anti-seize to the joint area when you install in. you can add a bead of high temp RTV top to bottom on one side of the spring to dampen it also

Lee
IRMT & A/P
 
Thank you for the good advice, and getting this thread back on track. I will be pulling the muffler off this coming week and will report on what I find.

Lee, do you think I should replace those original springs after only 140 hours? What about earlier suggestion to bend the tabs for more tension?
 
Testing extension spirngs

Connect one end of an old spring and a new spring together, then pull the opposite ends apart. The weakest spring will expand the most.
A scale can measure the force required to stretch a spring a certain distance. The spring could apply upward force on a weight sitting on a bathroom scale. Or a fish scale could stretch the spring. Each spring should be stretched an equal amount to get an accurate comparison.
Joe Gores
 
[Lee, do you think I should replace those original springs after only 140 hours? What about earlier suggestion to bend the tabs for more tension?[/QUOTE]

Aloha-those springs look heat soaked they are cheap to replace..on the tabs be easy they can crack if you torque them to much(done it:eek:)
Lee
 
IF heat softened the springs and this was the only problem, you would see gaps between the coils, which does not seem to be the case. Is it possible that the tabs were softened and released the tension? Of course we don't know how they looked when installed either.
 
When I connected the oil return line I moved the muffler against spring pressure and created the Sam problem. Reseating the joint fixed it.
 
My new S/S springs came today and since my airplane is still torn down for the inspection I dove right in. Removed the muffler and all four pipes. Cleaned all the joints and used the anti-seize paste liberally. Reassembled with nuts just snugged. Moved the muffler around to get it properly centered and torqued down the nuts.

Now for the interesting part. Most of the springs appeared to have very little tension on them, and it didn't take much force to pull the muff outward to loosen the joints. Didn't look right to me. Checked all the springs, and there was not even enough tension on most of them to create a gap between the coils big enough to insert a piece of paper into. VERY CAREFULLY (envisioning ordering new pipes:eek:) bent most of the tabs using a big screwdriver as a lever. Adjusted until all springs had enough tension to pass the paper test.

Musing about why my springs were so loose. Did I get a muffler that was welded up wrong? Couldn't be bad springs because new ones were the same as old. At any rate, I think my problem is solved. Time will tell.

I suggest all builders check spring tension when they first assemble their exhaust systems. If you can't pass a slip of paper between the coils investigate further. Call Van's Support before taking any action.
 
exhaust

hi i had the same leak. a local exhaust shop tried to expand the pipe a little because he said there was too much clearance, but, it was too small to fit in his expander so I just cleaned the joints and bent the spring mounts to apply more tension. I also replaced a spring that had nearly worn through the leak is still there but not as bad

and with the cowlings the more you remove and replace them the easier it becomes and it helps to adjust the clocking of the oil pipes to make the oil filter just slide into place also after 285 hours the hinge pins slide in and out very easily
 
My new S/S springs came today and since my airplane is still torn down for the inspection I dove right in. Removed the muffler and all four pipes. Cleaned all the joints and used the anti-seize paste liberally. Reassembled with nuts just snugged. Moved the muffler around to get it properly centered and torqued down the nuts.

Now for the interesting part. Most of the springs appeared to have very little tension on them, and it didn't take much force to pull the muff outward to loosen the joints. Didn't look right to me. Checked all the springs, and there was not even enough tension on most of them to create a gap between the coils big enough to insert a piece of paper into. VERY CAREFULLY (envisioning ordering new pipes:eek:) bent most of the tabs using a big screwdriver as a lever. Adjusted until all springs had enough tension to pass the paper test.

Musing about why my springs were so loose. Did I get a muffler that was welded up wrong? Couldn't be bad springs because new ones were the same as old. At any rate, I think my problem is solved. Time will tell.

I suggest all builders check spring tension when they first assemble their exhaust systems. If you can't pass a slip of paper between the coils investigate further. Call Van's Support before taking any action.

Hey John,

As I remember it, you replaced your muffler springs with stainless steel. I assume that you got them from Spruce. How satisfied are you with them? Any more leaks, or broken springs, and did you add the high temp RTV?

I'm noticing some blow-by evidence and I need to re-seal with that copper paste. I don't have any broken springs, but they do appear to have lost some tension. Tom
 
I'll jump in here... I installed SS exhaust springs from Spruce 100 hours ago. They were loose during the install so I re-bent the welded attachment bales to stretch the springs and add preload. Added benefit is springs are now spaced further away from exhaust tubing. I used high-temp RTV to pack the inside of each spring. Good fix...
 
Thanks Jim, I was hoping for a bit more tension, without the need to reshape the attachments.............Tom
 
Back
Top