Early Panhead Intake Manifold

[billpedalino]

I have my 1953 FLE motor on the bench and am setting up the intake manifold. The intake nipples are new and I'm fitting up a new V-Twin cast Iron manifold which, by the way looks very nice. In fact, I'm using one on my '47 FL and it works quite well and passes the pressure test nicely. Tedd sells this manifold as Harley did; only in the 3.625" length (Knuckle FL length) with responsibility of cutting it down left to the customer.

Using my trusty South Bend Model 9A, I cut the manifold down to 3.375" which is the correct length for the FL Panhead. However, I'm finding that when chucking the manifold up in the lathe, the clamped end does distort slightly (a couple of thousands) no matter how gingerly I apply the jaw pressure. If fact, for the second cut, I went so lightly with the jaw pressure that the manifold slipped out of the chuck. I now notice that even this slight distortion causes problems.

I assembled the machined unit onto the motor using peek seals and did a pressure test, and at only 10 psig, bubbles appear. My guess is that the OEM manifolds, when purchased new probably had a slightly greater wall thickness which enables them to be chucked up for cutting. OR...possibly they were held in a lathe collet (which I don't have) which would apply uniform pressure to the part.

In any event, it looks like I may have to buy another manifold from V-Twin but before I do I would like to know if anybody is selling a quality reproduction manifold in the correct length. Also, given the cost, at this point (unless there is no alternative) I have little interest in spending the $$ necessary in acquiring a worn out OEM manifold, having it built up and then machined down to the correct diameter.

Thanks....

[cdndewey]

I'll be needing one for my 53 FLE also. If you come up with anything, could you let me know please....thanks.

[larry]

There are a variety of ways to address your machining problem. If you can acquire a set of soft jaws for your chuck, they can be turned to the exact diameter of the part, thereby eliminating or greatly reducing distortion. Or, you can machine a plug to fit inside the manifold preventing distortion when clamped. Either way, the free end should be supported with a live center and cut with a thin parting tool. I would make the cut part way through and finish with a saw and file. I'm sure there are other methods; ask ten machinists and you'll get ten different answers, all of them correct. These oddball jobs require creativity. I bet your manifold can be saved.

[billpedalino]

Larry,
I'm not familiar with 'soft jaws', hence I stand to learn something! Can you tell me more? Where can I get them? How do they work? Looks like a visit to the Practical Machinist forum is in order!
Thank You...

[T. Cotten]

Bill!

I chuck on the inside of one spigot, and cut the other. '48-'49 steel manifolds, and Colony's, are very malleable, but my Cushman chuck holds them easily for turning off wear from brasses.

Were the PEEK seals a squeeze-on fit?

....Cotten
PS: It helps to balance the manifold to keep it from flying!

[billpedalino]

Cotton,

I was hoping that you would respond - You're the guy who's done this more than anyone.

So you insert the jaws inside the spigot and turn them out to grab the I.D. - You haven't found similar distortion in the outward direction? I like Colony parts, but their manifolds had that 'COLONY' name cast into the manifold in lieu of the Harley casting number. Is that still the case?

Also, I'm using a slow turning speed for the cast Iron and very slow pressure on the cutting tool, so I thought that minimal holding pressure would be ok....

[T. Cotten]

Bill!

My jaws are rounded on the outside, and distortion is no problem. Balancing is far more important, to avoid vibration and chatter. Most important is that the PEEK is a squeeze-on fit, and that its outside diameter is maximized within the nut. Plenty of mass-produced failures have crossed my benches, either from a poor fit, or the nuts coming loose. Plastic and metal are different animals, and require different dimensions.

And Colony stopped casting their name in their manifolds some time ago, replacing it with numbers that were not authentic, however they stopped offering them at all just a couple of years ago.

Tedd's are cast iron, not steel?

....Cotten

[larry]

Note that Mr. Cotten supports the free end with a live center, an important step in the process. Chucking from the inside would probably create less distortion and is certainly an option. Soft jaws are jaws that feature replaceable blocks of soft steel that can be machined to the exact diameter of the part. The part is held tightly with less pressure and essentially zero distortion. They can be cut many times for different jobs before needing replacement. Cost effective if you can get them cheap.

[T. Cotten]

Yes, Larry,

I use the bull-nosed center when I can, and it is a Colony in my picture.
But most often the bore of the manifold is not concentric with the spigot (particularly with cast bores, or if I had to swage distorted spigots that had been crushed inward), and I must let it hang in the air. The circa 1948 Cushman chuck lets me get away with it.

A puck and drawbar against a faceplate would work too.

That's still a lot simpler than cutting a "Y" design of manifold, believe me.
(I've made six different fixtures for those,... so far.)

....Cotten

[jim d]

I think you can purchase a expandable mandrel that can be machined to the size that you need. Maybe a exhaust pipe expander could be used with a little work on the lathe first to make it true. Even a Harbor Freight one may be good enough.
Jim D

[T. Cotten]

Sure Jim,

But you would have to hold it with a four-jaw chuck.
As I mentioned earlier, the bores of the spigots are quite often not concentric with the outside where the seal sits, so you would need to index it to keep to keep the ends parallel, and to avoid cutting the spigot dangerously thin.

....Cotten