Exhaust Pipe Tie Bar

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Andy Young
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Exhaust Pipe Tie Bar

Post by Andy Young »

According to the factory drawings, all 540-equipped (and most others, I suspect) Maules are supposed to have a tie bar installed between the two exhaust pipes, back by the firewall. However, I see lots of Maules without the bar.

I’m looking for experience/opinions on how this bar helps eliminate or even contributes to cracking of the exhaust pipes.

Here’s why:
I have an M-6 with an IO-540. I have the tie bar installed. I have had to weld cracks in the exhaust pipes at almost every 100-hour inspection. I have replaced at least one of them with a new one from Atlee Dodge, and even had this one crack a year or so later. The cracks are usually right at or near the mount tab for the tie bar. I do have the clamps at the muffler just snug, so that the pipes have the requisite play at the ends, with the bar removed. There is much less play with the bar installed. It got me to wondering if they might be less prone to cracking if I left the bar off, allowing the pipes to move around more.

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onfinal
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Re: Exhaust Pipe Tie Bar

Post by onfinal »

Hi Andy
Please see the attached photo.

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Like you I have an IO540 M6. My exhaust tail pipes are secured to the silencer (muffler) with a standard Maule collar and at the firewall with a strap. The strap is the heavy duty baffle material, 'doubled over' lengthwise. Bolts, nuts and large penny washers secure both ends of the straps.
The tail pipe ends 'whobble' nicely, nothing is ridged. Silencers, tail pipes and fittings are the same since I have owned her. This is one of my pre-purchase photos.

Please note, since seeing the firewall in johnmo61's post on the gascolator shield, I have polished my firewall to a mirror finish. No more firewall envy here :D
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Mog
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Re: Exhaust Pipe Tie Bar

Post by Mog »

My M4 220C has the same straps. But mine are just two pieces of 1/8” reinforced silicone baffle material and are slack but supportive of the pipes. That said, my engine is mounted on rails rather than the rear engine mounts of some other setups. So that means my engine can’t rotate nearly as much as some other modern setups. So my setup allows the pipes to move up and down a little and the pipes are of course loose at the muffler. Certainly the setup I have does not impart any loads of consequence on the mufflers. I can see a use for the pivot mount setup of other models that use the Dynafocal mount setup but it’s pointless I believe on the older style with the supporting rails that go from back to front of the engine.

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maules.com
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Re: Exhaust Pipe Tie Bar

Post by maules.com »

Onfinal, your bit of tailpipe clamp that I can see doesn't look like a Maule U bolt clamp. What looks like a bolt head may be the locator dowel but may not be hard enough to resist wearing through. Losing a tailpipe is hot on the firewall or gascolater.

The Tie bar which you don't have on the picture is also to help to prevent the tailpipes moving loosely so as to contact the air egress tunnel.
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Re: Exhaust Pipe Tie Bar

Post by asa »

There's a guy on this forum selling a few of those tie rods and proper exhaust clamps, brand new, for you folks without who want them... 8)
viewtopic.php?p=56735

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norcal64d
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Re: Exhaust Pipe Tie Bar

Post by norcal64d »

I don't have an M6, but on my MX-7 I noticed after I bought it that the right exhaust tube was contacting the firewall. I ended up having to do some adjustments to the pipe to get clearance so my only thought would be, are you sure the exhaust tube won't make contact with the firewall without the spacer?
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andy
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Re: Exhaust Pipe Tie Bar

Post by andy »

The tie bar between the exhaust pipes keeps the pipes from moving sideways, which could loosen the upper or lower bolts in the hangar strap.
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Re: Exhaust Pipe Tie Bar

Post by onfinal »

Hi Jeremy
Thanks for the kind alert. The photo is from before she passed into my ownership.

As soon as I owned her, as part of my initial 'star service', we replaced the silencer (muffler) clamps in the photo with, as mentioned, standard Maule collar clamps (U-bolt clamps).
The tail pipe straps remain as in the photo, without the tie bar. The strap length is such that at their fullest extent of movement, 'wobble,' the tail pipes do not contact anything and there's no scarring. It has been this arrangement since 2015. Having never had the tie bar I can't comment on it.

The caveat is usage, I am sure Andy does a lot more flight hours than I.
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Andy Young
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Re: Exhaust Pipe Tie Bar

Post by Andy Young »

Thanks for the replies, folks. I’m finding this to be a useful discussion. Though I don’t feel I have learned all I’d like to about this subject, the input thus far has been illuminating.

So far, the trend I’m seeing is that people who have the cross bar feel there are good reasons for it, while people who do not have it have seen few problems, with some indication of reduced incidence of pipe cracking.

Sample size is still very small, so too early to draw conclusions. Please keep the comments coming.

A few thoughts of my own:
I work on several Maules, and I have also seen the problem of exhaust pipes hitting the egress tunnel. My interpretation has always been that this is due to the shape of the exhaust pipe itself, allowing it to sit too far aft, or too high at the rear. I’ve solved it on some by shortening the first straight section of the pipe (the section that attaches to the muffler) by about an inch. This also gives more clearance between the pipe and the lower engine mount tube. This engine mount tube often exhibits signs of the excess heat, such as the paint being burned off. On one that I worked on, the pipe had actually been rubbing on the mount tube, and worn at least half way through it. Making this pipe mod solves those issues, along with creating enough space between the pipe and the mount to install a heat shield on the mount tube, which I have done on some. For what it’s worth, F. Atlee Dodge, when making new exhaust pipes for the Maules, prefers to have your original to copy, as they say that if they make it from the drawing, it will likely not fit the airplane correctly. I usually give them the old one, and tell them how I’d like the replacement to be modified from that.

Regarding the thought that not having the cross bar might allow the hanger strap bolts to work loose: that’s a valid concern, though I haven’t seen evidence of that on the ones I’ve looked at that lack the cross bar. I suspect that the lock nut stays in place on the bolt even if the strap is pivoting slightly. In any case, this could be mitigated by using a castle nut and cotter pin, though I’d still want to crank it down tight to reduce the chance for excessive wear on the strap itself.

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Re: Exhaust Pipe Tie Bar

Post by maules.com »

Often I find the locator hole is drilled into the tailpipe or the muffler stub pipe in the wrong radial position.
The tailpipe comes undrilled and either muffler or tailpipe is replaced on the other at a later time perhaps.
If this is so when fitting the tailpipe it can be rotated so as not to hit the egress tunnel (and/or shortened as Andy indicates).. The hangar tab is then welded on or an L shaped hanger can be held in position with a U clamp (not pretty but it works) so as not to place a sideways tearing movement at the juncture of hanger tab and tailpipe.
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Re: Exhaust Pipe Tie Bar

Post by onfinal »

Andy and Jeremy,
With reference to sample sizes.
Mine is the only M6 in the UK and she is the only Maule I have owned.
The breadth of knowledge and experience you both have is just not present here. So I will follow this with interest.
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Re: Exhaust Pipe Tie Bar

Post by andy »

About 5 years ago I was shocked to find that the upper bolts through the tops of both exhaust hangar straps that anchor them to the firewall were quite loose while the bottom bolts though the crossbar and exhaust pipe tabs were tight. I can't think of how this could happen, especially since I thought that the crossbar would limit the sideways movement that might eventually loosen the hangar strap bolts. They are a little harder to reach but now I check all four bolts for tension during every preflight. Since then I've never found them to be loose. It made me wonder if an A&P who did previous work on the exhaust forgot to tighten them. This is a heads-up for pilots who don't check the top bolts periodically.
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Re: Exhaust Pipe Tie Bar

Post by bobguhr »

I have an M6 235 and I was weld repairing cracked tabs at the tailpipe to cross bar attach point more often than not. I removed the cross bar and haven’t developed any cracks 150hrs to date.

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Re: Exhaust Pipe Tie Bar

Post by Andy Young »

Thanks Bob,

That’s another useful data point.

Andy

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