TheSamba.com :: View topic - Best way to flatten exhaust pipe flanges?

Wed Jul 15, 2015 4:22 pm

What's the best way to get all the exhaust pipe flanges nice and flat? I'm talking about the triangle flanges used all through the '75-78 exhaust system. I want to make darn sure these things will all seal up when re-assembled. None are so bad they need to be hammered on, but several have noticeable low and high spots so need to be trued up.

What I tried first was a long bastard file, but several hours worth of filing showed very little results. The file was brand new, yet it just didn't seem to remove much metal at all.

So today I tried mounting my angle grinder in a vice so the disc was horizontal. I locked the power switch so it would run continuously, and then tried grinding the flanges flat this way, by holding the part down against the spinning disc. This took off more material than the file, but was really pretty hard to control and seemed too easy to veer off from flatness.

Two questions:

1) How flat do these flanges really need to be to seal properly? (I do plan to use Hi-Temp red silicone sealer as insurance)

2) What have you done that worked well?

Wed Jul 15, 2015 4:33 pm

A belt sander is often effective, squishy gaskets and some bonus sealer doesn't hurt either.

Wed Jul 15, 2015 5:01 pm

Surprising the file is not cutting it?
As BD said a belt sander. If you don't have one. A local machine shop should have a belt sander used to do cylinder heads they could run them on.

http://www.thesamba.com/vw/forum/viewtopic.php?p=7271723#7271723

Good luck
Tcash

Do not know if these are the correct size.
http://www.amazon.com/Porsche-Exhaust-Gasket-Muffler-Exchanger/dp/B00EK8KUVC

Wed Jul 15, 2015 6:44 pm

Thanks BD & TCash -

I was real surprised the big file didn't cut well too, so tried using it on some of the NOS parts, figuring that the heat must have hardened the metal on the old parts. Didn't seem to make a great deal of difference, but then again the NOS parts were pretty much perfectly flat already.

I don't own a belt sander, but perhaps that'll be the way to go if I can't locate a machine shop tomorrow that will take this on right away. A lot of the small shops I knew of here have closed, but will try the engine builder that built our Mustang's engine as they're pretty close.

If it comes down to using a belt sander, any special abrasive? A recommended grit?

Also, still curious as to how flat these need to be. For instance, on one part I can see just a sliver (1/32"?) of a gap when I hold a file flat against the surface between the bolt holes. Good enough or keep trying?

Wed Jul 15, 2015 7:35 pm

I usually sand until there's at least a full ring of shiny, there may still be some pits or missed spots near the edge but I like to have enough to achieve a full seal all the way around. 50 grit Aluminum oxide cuts steel pretty good, but expect to go through a couple belts, especially when you tip the leading edge into the belt and it bites out a huge chunk of belt. Try a tool rental outfit, they'll have a sander and may even be able to recommend the correct abrasive.
Another option if you are at a real machine shop is the milling machine, clamp it in and face off the flange, quick and painless, the only problem may be they don't want to get thier machine all covered in rusty funk, if they are sandblasted first it'd make it much easier. They may also have a surface grinder that does the same thing.

Wed Jul 15, 2015 7:52 pm

The BEST way :!: Would be to take them to a machine shop that has a mill
and have them done.

Cylinder head resurfacing mill's can get them perfect.

Wed Jul 15, 2015 10:34 pm

^^^^ what they said

the flanges have been through thousands of heating and cooling cycles making them quite tempered. Even if you straighten them you will thin the metal where it has bent most and it will be back. A file isn't working because the metal is so hard. You can also heat them red hot and tap them back with a hammer until they are straighter. Another solution: http://www.germansupply.com/home/customer/product.php?productid=17102&cat=&page=1

Thu Jul 16, 2015 8:27 am

I did mine with a belt sander and it seemed to work fine...for the most part. The Victor Reinz gaskets that I bought from Bus Depot did not seal one or two of the joints, but the Elring gaskets worked like a charm. The Elrings seem to have a little more 'cushion' to them. I bought them from pelicanparts.com (SGK's recommendation) for $3.50 each, part# 443-253-115-B-M30. I sanded mine until they were nice and shiny. There was still little pock marks in the surface, but they appeared to be harmless. Some of the flanges needed to be straightened a little as well. I put them in a vice and gave them a whack or two with a hammer. Also, the copper nuts that Bus Depot sells for exhaust manifolds are kind lousy too. The ones from Pelican or Autohausaz are the nice flanged style.

Fri Jul 17, 2015 6:03 am

When I did ours, I had "adjust" the bolting tabs back with a large hammer. I made sure they were back just past flush (about 1/16") with the inner "ring" (pipe end), so that I could use a large flat file to smooth everything out until I had (at minimum) a full shiny ring like busdaddy mentioned. I used copper RTV and the bus depot gaskets, put everything together, THEN tightened the bolts, and have no leaks currently. I hammered the flanges back slightly past flush so that I was ensured pressure on the gasket, not the tab.

Fri Jul 17, 2015 6:44 am

poor man's option:
I did this job not long ago and acheived pretty good results with a large (like 1 foot by 2 feet) pane of thick glass (got scrap from a glass shop). The glass is as flat as you're gonna get. Then I bought some round sand paper disks with adhesive one one side, in different grits (80, 150, 300), slapped them on the glass and used elbow grease to get all the flanges into reasonably better shape. I did the u pipes and exhaust manifolds like this, my "pacesetter" muffler already had good flanges. It took a while but I did it in winter while hibernating, one flange at a time, maybe 1 hour at a time.
They are not 100% perfect, still some small pits here and there, but I figure the copper gasket sealer and proper gaskets will seal it pretty well. They look a hundred times better than before, and you can really control how much material you are taking off. I feel like you don't want to take too much off or else things might not line up/seal as well. A machine shop might just plane 'em down with no regard for that.
Someone who knows better than me might chime in with how much material is acceptable to remove, or it might be on Ratwell's site, but I'd look into it before dropping the pieces off somewhere, then finding out later you need to double/triple up on the gaskets or something.

Hope this is useful...

Fri Jul 17, 2015 6:49 am

In addition to making my flanges flat I now use copper gasket sealant on my exhaust connections and has worked really well to keep them Sealed long term

Fri Jul 17, 2015 8:22 am

I have one sort of like this....

http://www.harborfreight.com/17-inch-auto-body-hand-sander-1727.html

Fri Jul 17, 2015 10:15 pm

Thanks to all for the good suggestions and comments.

I brought my exhaust parts over to the engine rebuilder and as a test, he made fairly short work of grinding one of the U-pipe's flanges nearly flat, using a real big vertical belt grinder. After looking over the other the parts, he said he could do most of them, but not the heat exchanger flanges as the surrounding body tin is in the way. It would also be about a week before he could finish the parts. He also suggesting hammering the flanges (as others here have done) with a small sledge and a flat block of steel.

So, I brought the parts back home and picked up a cheap belt sander and a bunch of belts at Menard's (Home Improvement store like Home Depot) and plan to see how it goes this weekend doing it myself. I'm thinking of strapping/clamping it upside down on my bench so I can work the flanges horizontally and have a better sense of things. Will let you all know how it goes.

Fri Jul 17, 2015 11:18 pm

As others have mentioned, I've had good results with the copper RTV (with gasket) after filing. You're just never going to get it off once it bakes on... But it will for sure seal.

Sat Jul 18, 2015 12:08 am

Malokin Martin wrote: As others have mentioned, I've had good results with the copper RTV (with gasket) after filing. You're just never going to get it off once it bakes on... But it will for sure seal.

on my 1977 stock exhaust, copper RTV turned gummy while the red, which is lower temperature hardened.

Sat Jul 18, 2015 5:41 am

When I did mine (6 years?) ago, I hammered them flat with a regular old hammer. No heat. Then went to town on them with the big bastard file. You need an aggressive file to bite into the metal. They weren't "perfectly" flat but they were a lot flatter than before. Then I cut my own exhuast gaskets out of a large sheet of exhaust gasket material I got from the local FLAPS. The kind that has a core of perforated metal and covered both sides with a fibrous material. about 3/32" inch thick, it'll compress and cover up all kinds of sins.

Just took my exhaust apart and my gaskets pretty much disintegrated upon dis-assembly. But they never leaked.

Sat Jul 18, 2015 12:48 pm

I am about to replace a heat exchanger on my 77 thats cracked with a used one. Got new seals from autozone. They are the type that has a metal ring in the center. Is this filing/hammering process needed for flanges that are used? Or is this only for flanges that are new? Copper sealant is the agreed best sealer?

Thanks.

Sat Jul 18, 2015 1:57 pm

WhirledTraveller wrote: When I did mine (6 years?) ago, I hammered them flat with a regular old hammer. No heat. Then went to town on them with the big bastard file. You need an aggressive file to bite into the metal. They weren't "perfectly" flat but they were a lot flatter than before.

Did mime recently. Same process.

I see I wrote "mime", well I didn't talk while I did them, just a bunch of hand gestures.

Sat Jul 18, 2015 1:59 pm

BusPriest wrote: Is this filing/hammering process needed for flanges that are used?

Yes. I should hope if you bought new ones they would not need it.

Wed Dec 16, 2015 8:30 am

BusPriest wrote: I am about to replace a heat exchanger on my 77 thats cracked with a used one. Got new seals from autozone. They are the type that has a metal ring in the center. Is this filing/hammering process needed for flanges that are used? Or is this only for flanges that are new? Copper sealant is the agreed best sealer?

Thanks.

I used the German Victor Reinz flat gasket and have a bunch of leaks with my Pacesetter. I found these Beck Arnley gaskets with the inner lip (P/N 039-6099). They are shipping 2 to my local O'Reilly store.
http://www.oreillyauto.com/site/c/detail/BA00/0396...;ppt=C0022
That coupled with some copper sealant and I'll hopefully be ok. I just wanted to get this part number out there in case anyone else wants to try these.