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Exhaust Manifold (F-Pipe) wont fit onto the head
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aerosurfer
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PostPosted: Tue Oct 30, 2012 6:41 am    Post subject: Exhaust Manifold (F-Pipe) wont fit onto the head Reply with quote

Doing a 77 2.0L rebuild

My old exhaust system was totally rusted out.

Sourced a full exhaust setup here in the Samba about 2 months ago. Im now trying to fit the manifolds onto new AMC heads. it seems as though the pipe has warped so the the head flanges are to close to each other.

I even removed the studs on the Cylinder and tried to fit to find the flanges wont even slide onto the cylinder.

Left manifold flange measured at the inside of the flanges is 140.89mm.

while the distance between the openings in the cylinders was 142.14

Image may have been reduced in size. Click image to view fullscreen.

Image may have been reduced in size. Click image to view fullscreen.


The right side was similar measurements. Even the old rusty manifolds slide onto the cylinder studs easily

Is there a simple way to salvage these and stretch them true? I dont have the equipment to move them that precise. or should I look for a new set?
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PostPosted: Tue Oct 30, 2012 7:19 am    Post subject: Reply with quote

A scissor jack between the pipes usually does the trick, you'll want to check the flanges for flatness afterwards too.
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PostPosted: Tue Oct 30, 2012 7:32 am    Post subject: Reply with quote

You can also drill out the flange holes a little, that helped mine fit.
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aerosurfer
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PostPosted: Tue Oct 30, 2012 7:45 am    Post subject: Reply with quote

Already have the holes drilled out.... thats not the problem, The inner part of the flanges are rubbing against the cylinder head and preventing them from even seating.

I need to stretch them out. I just tried the scissor jack, and with the pressure on i can get them spaced out, but cant keep them there when I remove it. Not sure if a torch would even be hot enough to flex the steel?
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Wildthings
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PostPosted: Tue Oct 30, 2012 7:46 am    Post subject: Reply with quote

bajafreaks wrote:
You can also drill out the flange holes a little, that helped mine fit.


You want to avoid doing this unless absolutely necessary as it will lead to leaking gaskets. Just spread the flanges with a jack as suggested. Just go carefully.
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PostPosted: Tue Oct 30, 2012 7:56 am    Post subject: Reply with quote

Did AMC make a replacement head for the pre 79 exhaust flanges?
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PostPosted: Tue Oct 30, 2012 8:09 am    Post subject: Reply with quote

Chris_914 wrote:
Did AMC make a replacement head for the pre 79 exhaust flanges?


I have heads with oval ports, and my old rusty ones slide right down on them
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PostPosted: Tue Oct 30, 2012 8:33 am    Post subject: Reply with quote

I had a 1600 single port motor where the intake manifold did not fit, (too Long). So I ask my neighbor if he could do some welding for me and he accepted. I cut on the carb side of the intake with a pipe cutter, marked the amount I needed to take in, and my neighbor welded it all the way around. Manifold fit beautifully and there were no intake leaks what so ever. On the exhaust, I would heat one side of the tubing, and use the scissor jack to expand it, or if you do have material to work with, use a pipe cutter, mount you two pieces and then weld.
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PostPosted: Tue Oct 30, 2012 9:31 am    Post subject: Reply with quote

Wildthings wrote:
bajafreaks wrote:
You can also drill out the flange holes a little, that helped mine fit.


You want to avoid doing this unless absolutely necessary as it will lead to leaking gaskets. Just spread the flanges with a jack as suggested. Just go carefully.


Mine hasnt leaked at all, sometimes all they need is just a little reaming out, but it sounds like his problem is a little more involved.
Could you grind the sides of the flanges "a little" where theyre making contact with the heads ? I had the same problem but with a little this and a little that they finally fit with out any leaks dont forget to heat up the copper gaskets also.
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aerosurfer
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PostPosted: Tue Oct 30, 2012 10:27 am    Post subject: Reply with quote

Thanks for all the input! I was able to get them spread apart with the scissor jack and the MAPP torch. Grinding wouldn't have worked as the flanges needed to be spread to also align with the exhaust ports. Everything is looking good now

Have 1 filed down now evenly, and about to start working on the other side. Appreciate all the help.

I know I can look it up, but what torque setting do I tighten down the Exhaust nuts to?
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PostPosted: Tue Oct 30, 2012 11:59 am    Post subject: Type IV exhaust Reply with quote

Hi don't forget to Anneal your Exh. gaskets. Retorque the Exh nuts a couple of times after the engine goes threw a heat cycle. Heat up to operating temp., let engine cool over night and retorque nuts in the morning. This way the nuts will not back off after the header has settled.
Good Luck
http://en.wikipedia.org/wiki/Annealing_(metallurgy)


Last edited by Tcash on Wed Jun 21, 2017 10:04 am; edited 3 times in total
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PostPosted: Tue Oct 30, 2012 12:54 pm    Post subject: Reply with quote

16 ft. pounds
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PostPosted: Wed Jun 21, 2017 9:40 am    Post subject: How Do I Avoid Damaging F-Pipe W/ Scissor Jack. Reply with quote

aerosurfer wrote:
Thanks for all the input! I was able to get them spread apart with the scissor jack and the MAPP torch. Grinding wouldn't have worked as the flanges needed to be spread to also align with the exhaust ports. Everything is looking good now

Have 1 filed down now evenly, and about to start working on the other side. Appreciate all the help.


Hi Guys - this is great thread and very helpful. I face the same issue. My old manifold sprung a leak w/ a crack at the top of the pipe. Just ordered a replacement.

Question:

1. To avoid cracking it again - may I ask how you heated it e.g. what parts you used the MAPP touch on, when you used the scissor jack?

2. I tested with my old pipe and promptly cracked it at the cast ears (the braze gave way) - it seemed too much pressure there. May I ask where you placed the jacking points and how you did it - so as to cause minimal damage to new unit?

If the above failed I would be tempted just to cut it, bolt it up and re-weld the middle for a perfect fit (even if it is a bit crooked). This would work for both scenarios (too long cut trim and re-weld) (too short cut add some pipe as a sleeve and re-weld).

Q.3 Is normal stainless MIG wire good for this part of the pipe - what would you recommend?

Thank you.

D/O
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PostPosted: Wed Jun 21, 2017 12:15 pm    Post subject: Re: Exhaust Manifold (F-Pipe) wont fit onto the head Reply with quote

An appropriate sized pry bar and some heat applied to the pipes and tweak them a bit. Once tweaked you need to take a straight edge to the tops and be absolutely certain they are square to each other. If they need altering use an 18in bastard file and elbow grease to square them up to one another.

Opening the flanges 1 size is a good idea as to give a bit of wiggle room.

Also use some Permatex equiv of Loctite 518 on the copper gaskets. This will help to hold them in place while installing the heater boxes and seal them up when heat hits it it will carbonize. Use the Permatex on the head side to hole the rings in place. Then when making final install of the heater boxes put a bead around the end of the pipes prior to final placement.

Be sure the pipes fit the way you want before final install of the copper rings.
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PostPosted: Wed Jun 21, 2017 12:55 pm    Post subject: Re: Exhaust Manifold (F-Pipe) wont fit onto the head Reply with quote

Image may have been reduced in size. Click image to view fullscreen.


I would guess that heating the bottom of the pipe a nice cherry red near the bottom of the bend would spread the pipe flanges quite nicely as the pipe cooled. No jack necessary.

The judicious use of heat in the rights spots would also bring the flanges back into alignment pretty well so minimal filing would be needed. With luck this whole job could be done in 10 minutes or so.
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PostPosted: Wed Jun 21, 2017 3:28 pm    Post subject: Re: Exhaust Manifold (F-Pipe) wont fit onto the head Reply with quote

Thanks for the tips guys - I will add my progress to this thread to contribute to the knowledge on this topic. Cheers D/O.
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PostPosted: Sat Aug 12, 2017 5:49 pm    Post subject: Re: Exhaust Manifold (F-Pipe) wont fit onto the head Reply with quote

I just put the scissor jack against the flanges and cranked it apart, then it was pretty snug I applied the torch to it. Once heat soaked I cranked the jack a little more. And I repeated the process until the measurement was what I needed. Then let it cool with the jack in place. It was a bit of trial and error and took me a few times. I don't remember where I focused the heat most, but I never got anything red hot. I know I had no inclination I could crack or break the pipe when I was doing it, as they seemed pretty robust.

Good luck
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PostPosted: Sat Aug 12, 2017 9:12 pm    Post subject: Re: Exhaust Manifold (F-Pipe) wont fit onto the head Reply with quote

Having a VW repair shop that knows of these problems will come in handy. Shocked
Since this has been an ongoing problem for years with this exhaust manifolds.

Here in Calif.. Shops will install the manifold on a "known good cylinder head"
before fixing the crack so that it will fit properly Before giving it Back to the
consumer.

As you know,this has been a major problem with all exhaust manifolds for
well over 30 years........... Think 1975-1979

Easy to weld the crack when installed on a head on the Bench...Really Speak to the hand Speak to the hand
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PostPosted: Sat Aug 12, 2017 9:54 pm    Post subject: Re: Exhaust Manifold (F-Pipe) wont fit onto the head Reply with quote

Which VW repair shops are you talking of? I would very much like to know about them.
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PostPosted: Sat Aug 12, 2017 10:39 pm    Post subject: Re: Exhaust Manifold (F-Pipe) wont fit onto the head Reply with quote

I live in the bay area. San Jose area.

Any air-cooled VW repair shop here or down south worth going to will know
this is the way to fix the F-Pipes.

it is really not possible to just take the pipe into a welding shop and expect
them to weld a crack without mocking it up on a cylinder head for a good fit.
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