2 bolt dist. to 3 bolt cover

cuzncletus

cuzncletus

Senior Member
I need to adapt a 2 bolt distributor to a 3 bolt cover. Speedway has one advertised, don't know what else to do short of disassembling the engine. The engine is a 46 that was in a 39 with the old diving bell type dizzy that came on the 39's. The cam has a slot and had an off-set button for driving the distributor. Is this the button I need to put my two bolt to my three bolt cover?
 
You need to replace your timing cover with the later two bolt cover. These are readily available from the suppliers, and will require a new rope seal. Saturate the seal in hot oil, and do not trim it flush, but rather, to compress flush on assembly. The button used for the diving bell is not used with the two bolt distributor.
 
Two problems: The cam's drive slot is definitely offset. The drive on the two bolt distributor doesn't appear to be but has an eccentric machined into the drive, my guess is so it can't be installed backwards. Replacing the timing cover might let me bolt the distributor on but it doesn't appear it will line up. There will still need to be some kind of adapter.

I bought the two bolt from Bubba's. Not his fault, I just purchased the wrong thing. He didn't seem too high on diving bells and wanted no part of mine.

Would a three bolt crab work with my offset cam drive?
 
You can buy an adapter that will solve the problem quite easy and the distributo will work just fine. The slots will align with no problem. The only problem will be and extension bution for the cam, but I don't think that's necessary. You don't have to change covers. Now you must get one with a vacuum port.
 
I can't add anything, but will try and sum up what has been said. Earlier cars (like the 39) had a longer nose on the cam, a three bolt cover and a helmet distributor. Only the helmets are three bolt, crabs are two only. Later cars (46) had a newer, more compact design, probably because of fan clearance issues, the changes were: A shorter nose on the cam, a very compact new distributor (crab type) in which part of it extends into the space gained by shortening the cam, and a two bolt cover, which is dimensionally the same as far as the flat face goes, but it has two holes instead of three.

In your car, someone decided to 39-ify the 46 engine, and use the helmet dist. to do this they first fitted a three bolt cover, and then to compensate for the short cam nose, used a button to lengthen the cam to the same length of a long nose (39) cam.

If you want to convert the motor back to a crab type distributor, as said, the easiest way would be to refit a two bolt cover, discard the button and bolt up the crab distributor.
The next easiest way would be to buy a three bolt to two bolt adaptor from speedway and use that to mount your distributor, retaining the cam button. The adaptors are quite neat and do incorporate a vac port. I have used a couple before now.

That's it, all has been said above, but I thought it worth trying to spell it out in one place.
 
Mart said:
I can't add anything, but will try and sum up what has been said. Earlier cars (like the 39) had a longer nose on the cam, a three bolt cover and a helmet distributor. Only the helmets are three bolt, crabs are two only. Later cars (46) had a newer, more compact design, probably because of fan clearance issues, the changes were: A shorter nose on the cam, a very compact new distributor (crab type) in which part of it extends into the space gained by shortening the cam, and a two bolt cover, which is dimensionally the same as far as the flat face goes, but it has two holes instead of three.

In your car, someone decided to 39-ify the 46 engine, and use the helmet dist. to do this they first fitted a three bolt cover, and then to compensate for the short cam nose, used a button to lengthen the cam to the same length of a long nose (39) cam.

If you want to convert the motor back to a crab type distributor, as said, the easiest way would be to refit a two bolt cover, discard the button and bolt up the crab distributor.
The next easiest way would be to buy a three bolt to two bolt adaptor from speedway and use that to mount your distributor, retaining the cam button. The adaptors are quite neat and do incorporate a vac port. I have used a couple before now.

That's it, all has been said above, but I thought it worth trying to spell it out in one place.
Click to expand...


Mart,
Don't cut yourself short with your "I can't add anything".
Your summation and clarity is exactly what was needed here to bring it all together.
Bravo!
 
Thanks all for the info. One reason I went away from the diving bell distributor is I'm using a 46 type fan. With the two belts it was apparent that there would be interference between the belt and diving bell.

I don't think my two bolt distributor will just bolt up by replacing the cover. The drive slot in the cam is quite obviously offset. The Speedway adapter and button (theirs or mine) looks like it would work but again I'm worried about clearances between the dist. and belts. The adapter will create some forward offset; how much I don't know. Mart, have you ever run this set up?
 
cuzncletus said:
The drive slot in the cam is quite obviously offset.
Click to expand...

They are offset, that is what determines the proper orientation of the distributer. Are you saying it is offset more than normal? I'm not sure how that could be?

The distributer should end up in the same place with the adapter or with the two bolt front cover. Nether of these components determine the fore/aft location of the distributor, the cam length and the depth of the distributor housing do. Your distributor housing is going to be the same depth regardless of which method you use to mount it.
 
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OK. The button that drove the diving bell on my mishmash 39/46 motor has a key that's offset about .006. The key that drove the diving bell is .054 thick which appears thicker than the one available from Speedway. My two bolt centers up on this button fine with an offset of +/- .500 from the three bolt cover. Speedway's adapter measures ,420 thick. With gaskets this should work. Spadaro also lists one for $15 less that Speedway.

This has been a two day crash course in flathead distributors, covers, and cam lengths. Stand by for my next question which will be "How do you get this damn thing timed if you can't move the distributor and there's nothing to reference it to if you could?"

Thanks all. There's info available on this site that no book covers.
 
That's what the off-set it for!!! You set the distributor off of the car and the off-set assures that it is in the correct location. The only adjusting you can do on the car is a little fine tuning on the side adjustment marker. Here is one way to go about it.

Now are you ready for the next shocker? There are not timing marks in the first place, so just what would you time it to?? LOL ;)
 

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Sorry to be blunt, but you seem to be missing the point. The cam has a slot that drives the distributor. To make sure that you can only put the distributor in in the right position, they made the slot offset. This means you can only fit the distributor in the right way around.

The distributor is set up on a timing fixture. You set it up and gap the points to give the correct dwell. You then set the timing using the fixture. you then take the distributor to the vehicle and bolt it on. The offset slot drive ensures you fit it the right way around and do not fit it 180 degrees out. You connect the wires, turn the key and it runs.

If you do not have a timing fixture, you set the points to .015", align the marks on the adjuster plate and bolt it on. this time it will still run but may be a little off the ideal setting. You can always use a timing light to set the timing.

There are numerous methods described on this forum to help you time a crab distributor. One is called the two ruler method.

Hope this helps.

Mart.
 
My distributor is from Bubba's. I assume he set it right. I have a Chevy/Mallory conversion on an 8ba and it runs perfect.

I understood the reason for the offset to make sure the distributor could only be installed correctly. I've seen similar set ups on other types of engines. I've built quite a few engines including a lot of Brand X's part time at a machine shop when they got overloaded. Like a lot of us older guys here on the barn I'm retrogressing back to my youth, back when flatheads were to be feared. (By the way, I've had two engines, both Fords, built by a "professional" engine builder. One was a flathead. It really does make a world of difference versus my old garage built motors where basically someone machines it and you bolt it together.)
 
If Bubba has already set the distributor then all you need to do is bolt it on (with the adapter). The timing is already set and ready to go.
 
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