Tue 19 Aug 2008
Summary: when resurfacing the manifold, leave the exhaust and intake manifolds bolted together.
- So they will be the same thickness when you’re done
- Because the bolts that hold them together are often rusted and will disintegrate and not go back together again later. You may have to drill and re-tap the hole, and use bigger bolts.
Every maintenance saga starts off the same way: someone says something like, “Oh yeah, that should be an easy fix.” This time at least it wasn’t me who said it.
When I first got the engine running on my 1930 Model A Ford Sport Coupe I noticed that there was an imperfect seal between the engine block and the exhaust manifold. I could see little puffs of smoke coming out. If you’re not a car person, the exhaust manifold is a cast-iron branching tube that funnels the exhaust out of the engine and into the exhaust pipe. I mentioned the leak to my friend Devin, and he was the one who said the famous last words this time, “It’s easy to replace that gasket. You don’t even have to take the manifold all the way off to do it.”
So I bought a new gasket, loosened the nuts on the manifold, slid out the old gasket, and slid in the new one. Easy. Except that it didn’t fix the problem.
I mentioned it to the guys at one of the meetings of the 3 Rivers Region Model A Ford Restorer’s Club and was told that I might have to have my manifold resurfaced. Apparently this is a common problem with Model A Ford manifolds. After a while the flat surfaces that are supposed to be perfectly flush with the side of the engine block get warped and no longer make a good seal. Fortunately Keith Waltower is in our club, and he is a very experienced mechanic of old cars. He told me of a NAPA shop down in Belle Vernon PA that had a giant belt sander that could do the resurfacing more quickly, easily, and cheaper than taking it to a machine shop. Apparently a lot of the cost of getting a part machined is in the set-up, and with a giant belt sander there would be no set-up.
I was trying to get the car ready to drive for a 4th of July parade in Cannonsburg with the Model A club in a couple of days, so I was in a bit of a hurry to get the job done. The place that Keith mentioned was about a 45 minute drive from my house, so I made a few calls to see if I could get the resurfacing done somewhere a little closer to home. Most places couldn’t do it soon enough, and they wanted about $80. So off I went to Belle Vernon with my exhaust manifold. In hind-sight I now know that this is where I made a critical mistake. You may even know what it is if you’re a Model A person, and we’ll get back to it later.
By the way, you do have to take the manifold off to replace the gasket. I discovered that you can’t really get the surfaces clean if you don’t. When I took my manifold off there were big gobs of the old gasket still on there that would have messed up the seal even if the surfaces had been flat. Both surfaces really have to be clean and free of rust.
The drive to Belle Vernon was easy, and it literally took about two minutes for my exhaust manifold to be finished. I was shocked. But the surprises kept on coming. It only cost $27.83! That’s about a third of the cost of the machine shops. I was feeling pretty smug on my drive home.
I had already ordered a bunch of parts for putting my car back together. I needed new studs (basically a threaded rod) since the nuts on two of the four of them were permanently rusted on. And believe me, I put some serious effort into trying to get them off. I think the intense heat must make the rusting problem worse in this one spot, because most bolts are fine as long as you grease the threads before you put the nut on. Keith gave me a great tip to solve this problem in the future. If you get brass nuts for both the manifold studs and the clamp that connects the exhaust manifold to the exhaust pipe, they can’t rust together. Genius.
I got back to the garage, and started to put everything back together. I was feeling pretty good about it because I was fairly certain that I had all the parts I needed, and that I knew what I was doing. I was going to be able to make it to the parade. That was when I realized my mistake.
This is going to get a little technical, but stick with me; I’ll try to be as clear as possible. On the Model A, the exhaust manifold and the intake manifold are connected to each other by two bolts. The bolts are there to keep the two parts lined up because they share the same studs in order to attach to the engine block. Each part has a half-moon shape that makes up one half of each hole that goes over the stud. When the intake manifold and the exhaust manifold are mated together their respective half-moon shapes come together to make up the entire hole that goes over the stud and gets clamped down by one washer and nut and held in place on the engine block. Because the only place I had a bad seal on the manifold was on the exhaust manifold, I only took that part with me to get resurfaced. So now when I put the intake manifold back onto the exhaust manifold, the half-moons were different thicknesses (since the exhaust manifold had been ground down), and the flat surfaces were at different levels. Therefore, there was no way to get a good seal to the engine block. I should have left the two manifold parts connected so that they would be ground down to the same thickness, and would meet up properly with the engine block. Arg. Double Arg. When I realized what I had done there was much cussing. Also, I learned later that you are better off leaving the two pieces bolted together since if you take the bolts out, the bolt holes tend to strip, and then you have new problems.
I tried to figure out a solution involving stacking up more than one gasket, or grinding things down myself with hand tools. I mentioned these ideas to Keith and as he implored me to just do it the right way I could hear the pain in his voice from having dealt with half-baked repairs in the past. Of course he was right.
I had a gig in New Jersey in a couple of days, and Belle Vernon was sort of on the way, so I took the entire manifold with me. This time I got to go down into the basement machine shop and see the fabled giant belt sander, and let me tell you, it was GIANT. I handed the guy my manifold, which he actually recognized, and it seriously took him 30 seconds to grind everything flush and erase my anguish. Even better, since they had charged me the minimum labor rate of one hour last time, they didn’t charge me anything this time.
I had about three weeks on the road for gigs in the Midwest right after the NJ trip so I wasn’t able to work on the car again until yesterday. It’s just so much better when you do things right. I got the manifold back on the car, it started right up, and doesn’t seem to be leaking exhaust anymore.
Here’s another great tip from Keith Waltower: when attaching the clamp that holds the exhaust pipe to the manifold, put a jack under the muffler and jack it up so that it is held in place against the manifold while you get the clamp in place. I’m not sure that I would have thought of doing it this way, and it makes it really easy. Also, make sure that you have the taller half of the clamp facing down. I used a little high-temp sealant from the auto parts store inside the clamp too.
The last thing I did was put a heat shield on the top of the muffler. It should help keep the cabin a lot cooler. I got it from Snyder’s and it was pretty cheap. It would’ve been a little easier to put on if a) I had done it before reattaching the muffler, and b) I had not tired so hard to put it on backwards first.
I’m off to do a test drive.