Replacing 50 manifold... pull the head?

My 50 has had a cracked exhaust manifold (by the hot/cold valve) for a long time, but while sitting in the barn for several years the rust got much worse and chunks have come off. The left cylinder is putting more exhaust out the hole than to the muffler! Time to replace the manifold.

The fasteners appear to be bolts instead of studs/nuts so I'm hoping at some time in the last 60+ years someone changed it already... maybe they'll come out and not break off. Ya, sure.

After reading the service manual it appears that it may be easier to pull the head and THEN separate the manifolds from the head. I'm sure the guides are shot too (big puff of blue smoke when opening the throttle after coasting). Not interested in doing pistons & rings, but I'm willing to do a valve job if the head's going to be off anyway.

Thoughts?
thanks.
Charles

I replaced the Intake and Exhaust manifold on a JD 520. I removed the Fuel tank and several other components. Then I cut the heads off all BOLTS that attached manifold to engine block. Removed manifolds with bolts till threaded into Engine block. Drilled a hole in several pieces of scrap metal,dropped metal over each bolt sticking up from Engine block.
Welded scrap metal to each bolt. Following day I applied KROIL PENETRATING FLUID to each bolt. I had left a gap between the block and each piece of scrap metal.The bolts backed out of the engine block with no problem.

Bob

Without taking anything off I used a really sharp chisel and cut/broke the area around the outside manifold studs. As a matter of fact this is why they don't rotate...they are seized in the manifold. The intake bolts are no problem. Then slip the new manifold in place slide gasket under it and you're in business. These heads are sometimes thin under the gasket. Be sure it's not exhaust gas cut....be sure to wear some goggles when chipping away. I replaced the manifold on a 530 with a slick paint job...put some protection on the sheet metal.. Taking the sheet metal off is a lot of unessary work and you'll still have to chip away...

I pretty well used Bob's method on my 50, but I did have the head off for an overhaul. All of the bolts came out without too much drama, but one was really tight and looked like it wanted to break off, so I babied it for about a week, heating and cooling, candle wax, and every kind of juice you can imagine. It would move a barely discernable amount back and forth, but each time a little more, until finally came out. Cutting the heads off of the bolts, and then working the manifold off will leave you material to work with. That and lots of patience. Even with the bolt heads cut off, the manifold was a rassling match to get off - lots of tapping and prying/wiggling, but it's worth saving those bolts. You know where they'll twist off if you just sock a breaker bar on them and pull hard, ha.

After reading Machineryman's reply, I should add that my original intent was to save the manifold - it had a small crack on the side nearest the governor, and being a skinflint, I thought I should weld it and save the cost of a new one. That turned into a patience consuming project, and I was unhappy with the end result. I bought a new one. Breaking the old one off, but still saving the bolts, would have been smarter and quicker in my case.

I can assure you that you can't save these old manifolds. However I want you to know the procedure. Use a sharp and I mean sharp chisel and cut punch cut the outside of the manifold...you don't want to just burst it as pieces will fall down into the exhaust and intake. Take your governor roads and carburetor off...strip it down. Once you breakaway the cast you can then use heat and back off the studs. Placing the heat right at the head....be patience...you'll need an acetalene to do the work. After you get those out you can back the intakes out...use a good pair of channel locks...but it have good heads on the bolts you might jar them loose....they don't freeze in the manifold like the exhaust studs do...took me about an hour to get that one off the 530 but you just have to be patient and have the right tools and attitude....

Many of them are also leaking out the right side where they meet the cyl. head. I'd try getting the bolts out and if they break off then pulling the head is the best way. I mount them in a milling machine and drill out any broken bolts and then resurface the manifold gasket surfaces. I also do a valve job too. Really haven't seen one yet that did not benefit from a valve job.

Understand what Mike M is saying however this would be the most expensive way to go....one could always pull the head....It seemed that you were going on the cheap so I advised likewise. One could also overhaul the tractor since the head was off. This would enable better compression after the valve job....depends on your budget$$$$$$$$$$$$$$$

thanks... yes, the old manifold is complete trash already. It looks like I can attack it with a chisel, a 3" cutoff wheel air
tool, an angle grinder or a Sawzall! Either way I plan to remove the manifold from around the bolts, as you suggested. If any
debris falls in the exhaust ports I'll get it out with my big shop vac.

Yes, budget is an issue, since I never use this tractor - it's been sitting in the barn for years. I may just sell it, although
it'd be a lot easier with the manifold fixed $300 for parts not counting new bolts/studs.

Also... the parts catalog shows that the exhaust bolts are six 7/16" by 3-3/4" long, and the intake is four 3/8" by 3-1/4" long.
I assume those are standard (UNC) thread, not fine thread. Those lengths are not available locally but McMaster has them, so I need to pre-order.

you can buy the bolts at any hardware store and shorten to lengths needed....use grade 8. The most important is to get the heavy washers that fit the bolts and then once installed to retighten a couple of times after heating and cooling of the engine. Not rocket science.

Today I started the "smash and bash" removal of the old manifold. The parts book is a little misleading - there are six 7/16 bolts 3-3/4 long, two of which hold the intake and four for the exhaust. (The four 3/8" ones hold the intake and exhaust crossover together). The new manifold came in the mail too, complete with gasket set.

I got out a 3" cutoff wheel, the Sawzall, a 2# and a 4# hammer, and started cutting. Eventually I got the exhaust off in pieces without having had to remove anything other than the carburetor and air intake pipe. The two intake bolts, and even one of the exhaust bolts, came out with no trouble. But unfortunately the remaining three didn't go so simply (when does rusty 64 year old hardware ever?)... one more came out with two cycles of alternating acetylene torch and PB Blaster. The remaining two are broken off with about three threads showing

I tried several times to weld nuts to the stubs, but never got enough penetration (due to the 1/4" high stump conducting heat to the head? Or maybe just not enough amps, although I filled the nut each time with weld and the whole thing was glowing red). Anyway even with careful "rocking" the weld would break off before the threads would back out. Grrrr.

So I applied PB Blaster to both stubs and called it a day. Working in 90F heat + humidity is no fun even when things are going well, and it's hotter in the steel building even with both doors open.

Thinking of dragging out the buzz-box (Lincoln stick welder) and really putting some amps to it.

Anything else I should try short of dynamite? I really don't want to pull the head because then I will feel obligated to do the valve job too. Although at this point it's not much more work (valve cover, remove rocker arm assembly, ten nuts for the head studs!)

Dr. Charles: The way I got the studs out of using good pair of vise grips then getting hold of the stud and working it back and forth...I would try to jar it...but if you put a solid twist on them then they will possibly break off....now that you have broken off and have a short stub...take a nut the is slight larger...you might just jam it over the stub then weld directly down the center use a 6011 3/32. After you weld let it cool as the heat has expanded it in the hole. Then use your penetrating and work it back and forth...don't over force it trying to get it out...it's a finesse type work....

Another method that has worked well for me, that I learned here is heat the bolt pretty hot, then as it cools, touch a candle to the bolt. Too hot and the wax evaporates or burns off, too cool and it doesn't penetrate around the bolt. Be careful heating the head too much near the head gasket, it'll leak. Ask me how I know...

I got it done this afternoon. Just kept cycling between heating the bolt stub red-orange, PB Blaster, hammer taps. I finally
gave up on trying to get a good weld to a nut, and drilled a hole in a piece of 1" angle iron and welded that to the stump. The
left-side bolt finally yielded just a little, at which point I kept working it and applying more oil and eventually it came out.
Only seven threads engaged, too.

Now the remaining bolt was a real PITA. More of the above, plus welding it to the angle iron FIVE times before it finally
started to move without breaking the weld first!! I used 5/64" rod with my little Chinese inverter welder cranked up all the way
(allegedly 80 amps). The buzz box Lincoln was in the other garage and it was just too hot to lug that thing around

The head surfaces actually looked good, although scraping the ancient intake gasket off was another minor chore.

A few of the farm store bolts that I'd shortened needed cleanup with a 7/16-14 die before they'd go all the way in. I used a
thread chaser on those holes, too. Then it was just a matter of putting everything back together ("reverse of disassembly")
Unfortunately I didn't get to test it because the fuel bowl gasket is dried out and cracked, but those can be bought easily.

Thanks for all the helpful suggestions - I think I used every cutting and welding tool I own on this project!

now you know the meaning of fineese.....does anyone on here know how to post without deleting all the previous....

Great to hear you had success

Bob...

Have worked on tractors for 6 years...however this post is very interesting. I suppose it pointed out one's style. I learned to get the most out of machinery without doing brain surgery, however there can be a total tear down and assemble....I can tell you for a fact that when you go now for repairs at shops it comes down to a dismantlement and selling a bunch of new parts. Back in the day things could be brazed/welded/repaired/adjusted/restored without getting all new parts. I suppose it's the replacement economy in motion. Still doesn't fit old tractors.