Posted by Jorgen on Sunday, April 19, 2009 @ 04:52 PM:
Hi Guys,
I have a couple of cracks in the exhaust system on the 4, one close to the nr 4 cylinder (where it´s a hot spot):
and the other one close to the clamp for the outer exhaust pipe on the left side:
Any suggestions on a fix, and if not- where do you find these parts? EIS aircraft?
Take 5(b) just 4 fun/ Jörgen
[Edit by Jorgen on Sunday, April 19, 2009 @ 05:09 PM]
Posted by Bob Grimstead on Sunday, April 19, 2009 @ 11:32 PM:
Hi Jörgen,
That crack by the flange is very common. I seem to get them every year. Or at least, I used to.
But I have not seen the crack further back by the clamp before.
I talked with Matthew (Skyhawk 3) about it some years ago, and he said they were always common on the Skyhawks' aeroplanes, despite their excellent maintenance.
For some reason, only the short, straight rear pipes seem to crack (on both sides), not the longer front pipes, although they are a longer unsupported length.
After many times welding the pipes on the outside of the flange (as they are in your photo) I eventually found the best solution was to clean out the hole in the flange, push the pipe into it, and then make the weld around the inside of the flange, around the face of the flange that presses against the cylinder head. After welding, you just have to grind the face straight on a planisher or sanding disc.
I did that on both my rear pipes a couple of years ago, and they have not cracked again for a long time now.
It may be that your pipes are just old and thin and brittle now, so you might have to start with new piping (very cheap from any exhaust repair centre if you buy mild steel pipe -- 28mm from memory, but do check) and new flanges. You can get these from VW specialists, or make up your own from quarter-inch (6mm) plate. Half a day's work with hacksaw, drills and files will do the job -- just like the old days in metalwork shop at school!
Good luck.
Yours, Bob
Posted by eugenio on Monday, April 20, 2009 @ 10:25 AM:
You do not need to get mad for that. The easier way to fix the problem is to use the old flange and a new piece of stainless steel pipe, or better, if you can find a new stainless flange, everything new.
The rear stack is quite easy to do since is only a straight pipe. Do not try to weld the old one you will find it very hard to weld, and in case you will succeed in the process it won't last because the material lost all his properties.
Use only stainless steel tig welded. The tailpipe is easy too to be done, is just a piece of pipe sliding onto the stack, drilled from one side and with the end straightened. I think you can easily find the stainless pipes in those shops selling parts for boats or specialized in stainless steel.
ciao
Eugenio
PS if you do it yourself and you're not a very-very skilled welder, it is easier to slide the pipe flush into the flange and weld it from the inside
Posted by Jorgen on Sunday, April 26, 2009 @ 09:18 AM:
Thanks a lot Bob and Mille Grazie Eugenio.
It´s reassuring to know it´s not as often the front pipe cracks, that looks quite a bit harder to copy. And again you´re correct Eugenio- I´m not a very skilled TIG welder but I have friends who are so I think I´ll be able to fix it.
It struck me that the reason for the cracks appearing in the shorter, straight pipes is probably a fatigue stress concentration- the longer front pipes have a greater distance to dissipate the stresses, which probably consists of the engine moving relative to the clamp/fuselage. Maybe a soft but heat resistant insert at the clamp could solve that problem?
It´s funny though, I haven´t noticed much higher noise. To me that´s another indication that if a lightweight muffler whith little or no power loss can be made (see "modifications- "RF3/RF4 mufflers"-thread) there is room for improvment of the noise reduction which could give better flying comfort for both the pilot and all spectators, with or without an interest for aviation.....
Take 5(b) just 4 fun/ Jörgen
[Edit by Jorgen on Monday, April 27, 2009 @ 03:56 AM]
