3 weeks ago
Thursday, 13 September 2012
That's the noise that the engine was making right after startup. Then the ticking went away as the engine warmed up. Dad quickly figured it out: he had a cracked exhaust manifold. Curb side manifold, large crack in the middle of it.
Last week Dad jacked the front of the motorhome, pulled the right wheel off, and got down to work. But what was supposed to be a relatively simple and straightforward job quickly turned into a nightmare...
Replacing an exhaust manifold on a 440 V8 is not very complicated. The manifold is held against the engine block by 6 studs and 6 nuts. Once the exhaust pipe and spark plugs are out of the way, the nuts are removed and the manifold can be pulled off. Then you put the new one in with a new gasket, and reassemble. Simple, isn't it?
First Dad noticed right away that someone, a previous owner maybe, had already messed with this manifold. The two center studs where way too long, protruding by about 1.5 inch over the manifold. The outer right stud wasn't even a stud... it was just a bolt, a plain, non-graded bolt. The other 3 studs looked normal.
(Sorry I don't have pictures, I'll try to have some later on).
Dad started with the bolt. Yes you guessed it, it snapped right off, with almost no effort, as soon as he put a wrench on it. It broke flush with the block... This one will have to be drilled out. Dad made himself a drilling guide to center his drill bit in the center of the stud, and managed to do an OK job at it, using his hand drill. Using a tap, he should be able to fix the threads worn by the drill bit.
Then the nuts on the 3 "normal" studs came off with no fuss.
Now the 2 center studs. It looked like the guy who put them on simply used regular threaded rod. Yep, plain 'ol threaded rod like you can buy at Home Depot. These are soft and break easily when new, can you imagine how brittle they get after years of heating/cooling/rusting ?
Now Dad had to be very careful, because cause this could have quickly turned into a big costly mess...
Instead of putting a wrench on them and risking breaking them off, he first cut the nuts off wih his small grinder and a cutting disk.
Now the manifold could be removed, so Dad was left with three good studs, one missing stud (the broken bolt one that he drilled out) and in the center those two pieces of threaded rod, sticking out by about 3 inches.
A new manifold for this engine looks like this:
Notice the holes for the outer studs (2 on each side), and 2 the recessed holes, near the center, for the 2 center studs. While standard nuts are used on all 4 outer studs, the 2 center ones require what Dodge calls "sleeve nuts", wich are long nuts that seat at the bottom of recessed recessed holes in the manifold. These "sleeve nuts" look like this:
With these special nuts, the manifold is held against the engine block but remains free to expand when hot. But it looks like the guy who once "fixed" this manifold had no clue about this. He simply used regular nuts (with washers to cover those "inconvenient" recessed holes) on his home-made, 4-inch long, threaded rod studs. This mistake in fact prevented the center part of the manifold from expanding outward as it got hot, and eventually caused the manifold to break.
For Dad, the easiest way to deal with the threaded rod studs was to let them in place and reuse them. But using regular nuts and washers on them was out of question: that would probably cause the new manifold to break again later. Using OEM "sleeve nuts", as it should be, was impossible with these home-made studs: normal studs have coarse threads into the block, and fine threads at the nut end. With their fine thread, sleeve nuts wouldn't work on the threaded rods' coarse thead.
Another option was for Dad to fabricate his own sleeve nuts, using coupling nuts. Coupling nuts are longer nuts, used to joint threaded rods and look like this:
Another risky option was taking the chance to try to remove the home-made studs. They were rusted and well seized into the block. Many times Dad put some heat on them, hit the end with a hammer, trying to break the bond with the block, sprayed some penetrating oil, prayed a little, swore a little, tried them with the wrench but nothing moved...
I left the operation room (Dad's backyard) that afternoon with the surgeon (Dad) in a grim mood, still thinking about what he was going to try next with those stupid threaded-rod studs. It was his 4th day working on this problem.
Me, I was now on a mission to search the web and try to find him a replacement manifold at a fair price.
But good news came later that night. I relieved Dad phoned me: "You now what? I got them! I got both of them out!"
I don't know how he did it, but with great care and patience, he managed to unscrew the damn threaded rods without breaking them off. It's a bit of a miracle I'm telling you!
Now he will be able to properly reinstall a replacement manifold, with the proper studs and nuts. He's still debating between having his old manifold welded by a specialized shop or using a new (used) one. I found one up for sale on the web, and as of tonight I'm waiting for the seller to set his final price.
I asked Dad if he checked the left side manifold for cracks. I could see what was going on in his mind when he heard my question, and he just looked at me and said: "No I did not, and one thing at a time, will you!!"