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Vetterman Crossover Exhaust Rubbing

tgmillso

Well Known Member
Sponsor
Hi All,

When performing my annual I discovered some rubbing occurring between the bottom of the crossover exhaust pipe from #4 and the top of the Y pipe that combines cylinders #1 and #2. My RV-7 setup is a stock standard IO-360M1B Vetterman Exhaust supplied by Van's, with 168hrs airtime. There is only about a 1/8" gap between the two pipes.
The questions I have are as follows:
1. Am I the only person who has observed this issue?
2. What is the standard clearance between these pipes?
3. What is the standard procedure for ensuring the minimum distance is obtained (shims, re-bending tubes etc).

Not keen on a 1400°F gas blast within the confines of my engine bay, I am looking at purchasing and fitting new tubes at this stage.

Cheers.

Tom.
RV-7 IO360-M1B
 
See below for the photos I failed to upload in the original post.
 

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From the looks of the pictures I’m guessing that is a superior cold air sump.
If that is the case and Vans supplied you with the exhaust, you bought the wrong exhaust.
Vetterman makes a specific exhaust for that sump.
 
The sump is just the standard sump on the horizontal induction M1B, purchased from Van's. The exhaust was also purchased through Van's at the same time. The clearance form the sump is fine, it's just that the crossover pipes are rubbing (the number 4 pipe is rubbing on the Y joint that connects 1 and 2).

Tom.
 
If that was mine, I would provide a detent (pound with a hammer) in each pipe at that area to create an additional 1/4" (1/8 on each pipe) clearance.

The bottom pipe wear area should be built back up with stainless rod and a heliarc before re-shaped.
 
I had Clint B from Vetterman build a similar exhaust for me....its for a vertical induction so not exact. When installed I was concerned also about the tight fit between those tubes you have shown us.

You probably are using a thick exhaust flange gaskets on all four cylinders. Spruce calls these the "Blow Poof" gasket and says its 7/64" thick. Clint had me remove this from I think just one of the cylinders and replace it with two standard gaskets that were stacked on top of each other. These are much thinner gaskets...even two stacked on top of each other lifted the upper tube giving more clearance.
 
Happened to Me Too

Hi Tom,

I had the same problem around 75-100 hours on my engine with exactly your setup: an RV-7 with a stock Vans IO-360-M1B and Vetterman exhaust purchased from Vans as part of a FireWall Forward kit. There is about 3/8 to 1/2 inch of clearance on my setup.

I tried different sized exhaust flange gaskets as Bcone1381 mentions, but it didn't help. I also did some grinding on the bolt flanges that hold the pipe sections together which gave a little bit more clearance (it allowed the bottom exhaust section to swing down just slightly). Ultimately what I think has worked (at least for the past 100 hours or so) has been to move my exhaust supports forward about an inch or so as shown in the photo with the white arrow. I realize none of this makes sense - the pipes where the contacting occurs are all attached directly to the exhaust flanges and should all be moving together, so clearly there are some dynamics in play. For whatever reason, moving my exhaust supports forward has either provided enough additional clearance between the pipes or has changed the dynamics enough to stop the wear and contact.

I had considered building back up the worn area by welding each area like Warren mentions above, but after thinking about it and talking to a couple of A&P's nearby, I decided against it because it might induce residual stress in the exhaust in the area and could crack. What I have done instead is wrapped a couple of layers of fiberglass tape around the contact area and safety wired it into place to provide a witness mark if there is any additional contact. It has been about a year and 100 hours and so far no additional contact, but I check it every time I have the cowl off. I continue to monitor the exhaust and if there is additional wear or a hole that forms, I'll weld it at that time since I'll have nothing to lose regarding the risk of inducing residual heat stress from welding it then - if it cracks after welding it then I'll replace it at that time.

- Alex -
 

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Many (including me at first) don't appreciate how much each cylinder, and everything attached to them, move around during normal ops.

I don't have any specifics, but the important takeaway is to keep that fact in mind when installing parts ... hangers, cables, cowls, baffles ... whatever joins or comes close to the moving exhaust/cylinders and the fixed airframe parts.

These photos are clear evidence that there's a lot going on up there!

Cheers
 
Hi Alex. Thanks for your detailed response. I suspected I wasn't the only one to see this, given the fleet size is so large, it's just that it hadn't yet been documented and along the lines of what wcalvert has said, there are probably many cases out there of this that just aren't yet known about.
I'm thinking the ultimate solution may be a combination of getting those tube sections replaced, adjusting the two clamp locations, changing the gasket thicknesses and potentially adding sacrificial stainless clamps in the area so that they wear through each other if they do contact rather than the pipes themselves.

Cheers,

Tom.
 
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