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Discussion Starter #1
Hi Guys I have a John Deere 50 NF tractor with a bad exhaust manifold on it. It is a very common defect on the old two cylinder two and 3 numbered series tractors. example 50 - 520 - 530
I would like ideas from someone who has replaced or repaired their two cylinder manifold. Ideas such as what replacement procedures are best - alternative repair ideas - pit falls of the job - what parts have to be removed in order to get old manifold out and new manifold back in - should I remove the gas tank? I have put this job off long enough and I am going to do it. Old tractors are a pain to repair, but it sure feels good to make a good and successful repair.
as always thanks for your help and advice. Klink
 

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Use plenty of penetrating oil and heat as needed to remove the old bolts. Make sure to have the needed gaskets and new bolts as the old ones will surely be roasted. Replacement is pretty straightforward. :good2:
 

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Depending on what is wrong with your manifold, you may be able to repair it in place. Cracks can be brazed or welded (with pre-heat and nickle-rod) quite easily. Not a very difficult job for even a novice welder.

If it is simply worn out or the head-to-manifold gasket is blown, then you will end up replacing it. While you are in there, you might as well replace the pipe leading from the manifold to the muffler. Lots of lube and heat are going to be your best bet for removing the manifold. As a heads up, you are probably going to end up snapping one or more of the bolts holding the manifold on. Don't worry, this is very common. I snapped two of the four manifold bolts when I did this same repair on my M last spring. If it happens, pull the head off and take it in to any reputable tractor or big truck shop... I guarantee they have seen this before and will know what to do. My local tractor shop charged me $45 to remove the broken bolts, check the face of the head, and magnaflux it. I hadn't planned to pull the cylinder head, but the silver lining is that now I know there is nothing wrong with it. I also used the head being off as an excuse to inspect the cylinders, clean and lap the valves, adjust the rockers, and replace the original head gasket.

I remember not having to pull the gas tank on my uncle's 60 when we did its head gasket, so I don't think you need to on a 50... But I could be wrong. If you would like to pull things off in order to make the job easier, there is certainly nothing wrong with that. Just make sure you take pictures and label things so you know how it all goes back together.

Make sure you have all the gaskets you need prior to getting started; including a head gasket. Spend a week or two (or longer if able) SOAKING the exhaust manifold bolts in PB Blaster, 50/50 ATF and diesel, or whatever your go-to penetrating oil is. Hose those bolts down as many times in a day as you can manage for as long as possible.

Good luck!
 

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Discussion Starter #4
Thanks to replies

To All
Thank You for your advices and tips. I'm no rookie, but not a A1 mechanic. If there are any other suggestions please reply. Its good to have other opinions, but usually diving in to a job with a little knowledge ahead of time is good. I check this website once each day.
Thanks
Klink
 

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klink-i changed my manifold on my 50 yrs ago. and for some reason i'm thinking i had to drain the antifreeze and take off the top water pipe. for the life of me i can't remember why i had to do that. i can remember changing out the rubber hoses on the bottom pipe at that time. i'm pretty sure the carb had to come off too. and in my mind i think the fan hub assemble had to come loose, so it could be elevated to slide something out of the way. sorry i just can't remember it all. that was over 25 yrs ago now. i will try to get out to the shed and look to see what i had done, if i can-ok. good luck and as others have stated-the worst part is the manifold bolts.
 

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The manifolds are usually installed with studs and nuts instead of bolts. That means when you remove the nuts. you have to lift the manifold straight up about 4 inches to get off the studs. That means you need to remove the fuel tank, fan shaft, and coolant manifold to have clearance to lift it. If you remove the cylinder head with manifold attached, There should be clearance to remove the head without removing fuel tank, fan shaft or coolant manifold. After the head is off, then manifold can be removed. If someone has had the manifold off in the past, they might have used bolts instead of studs to install manifold. That makes it easier to slide it out the side without removing so many parts.
 

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Discussion Starter #7
all good replies

Thanks again for the good info, I think I understand what needs done. I want to get job done before show season.
Klink
 

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Thanks again for the good info, I think I understand what needs done. I want to get job done before show season.
Klink
You gonna keep us up to date on your project?
 

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Discussion Starter #9 (Edited)
JD 50 Exhaust update

Update from klink I cut out the deteriorated carburetor heat exchanger intake bypass part of the exhaust manifold. there are no other exhaust leaks. The internal passages for the exhaust gases are plugged up with carbon - rendered useless - I installed a plate over the entrance end of exhaust gas intake heat exchanger. So I decided that I will not go farther on this repair at this time.
 

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Because modern gasoline vaporizes so much better than the old "tractor gas" ever could, you probably don't need the intake heater anymore. The tractor might even run better without it.
 

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Discussion Starter #11
thanks

Thanks to evergreen & everyone
For the time being, I will leave it as the picture shows. In the future, who knows! The carb heat exchange passages were full of carbon soot, so it was inoperative for many years. Most farmers left the exhaust valve in the cold position anyway.
Klink
 

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Thanks to evergreen & everyone
For the time being, I will leave it as the picture shows. In the future, who knows! The carb heat exchange passages were full of carbon soot, so it was inoperative for many years. Most farmers left the exhaust valve in the cold position anyway.
Klink
I am thinking about buying a 50 with the exact same problem. How did cutting this out work out for you?
 

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Discussion Starter #13 (Edited)
reply to question

Hi My JD 50 runs just fine with that recirculation piece cut out of the exhaust manifold. Yours will work if there are not any other holes or defects in the exhaust system. Also if the exchanger valve
was left in the cold position before it froze up. Its not kosher but it works for me at this time. To replace the exhaust manifold, it will take about an estimated $500 and a lot of mechanical tear down work on tractor.
Klink
 
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