John-

Thanks for confirming the interference fit on the stud, so that I'm not going crazy.

And also thanks for the generous offer (this is typical of the spirit on this forum) to weld the nut on the stud, but I'm trying to engineer a solution here that 123 could offer to Corvair customers since many of us don't have a skill set that includes welding (to my regret).

I think some of the possibilities are:

(1) offer a cutoff version of the distributor stud that Clark's offers. I have to figure out how much would have to be cutoff and see if that leaves enough fine-pitch threads to attach the nut.

(2) offer a version of the Clark's stud with a welded nut.

(3) use a loose-fit 3/16-16 with a nut/washer on the bottom side to lock the loose-fit bolt. This seems like the easiest solution.


I'm open to any other suggestions that might be out there, hopefully which don't require the advanced skills of other Corvair owners. This is Corvair Distributor-for-Dummies...

1966 140 Monza PG convertible
Ventura County, CA

Unified threads come in different classes of fit. I bet the original GM stud you are dealing with is a clas 3A.

You probably could find the right bolt (technically a screw in this case) from a specialty fastener house. Or just modify the stud you have.

Below is a cut and paste from the innerweb.

Thread Fit
Thread fit is a combination of allowances and tolerances and a measure of tightness or looseness
between them. A clearance fit is one that provides a free running assembly and an interference fit
is one that has a positive interference thus requiring tools for the initial run-down of the nut.
For Unified inch screw threads there are six standard classes of fit: 1B, 2B, and 3B for internal
threads; and 1A, 2A, and 3A for external threads. All are considered clearance fits. That is, they
assemble without interference. The higher the class number, the tighter the fit. The ‘A’ designates
an external thread, and ‘B’ designates an internal thread.
• Classes 1A and 1B are considered an extremely loose tolerance thread fit. This class is
suited for quick and easy assembly and disassembly. Outside of low-carbon threaded rod or
machine screws, this thread fit is rarely specified.
• Classes 2A and 2B offer optimum thread fit that balances fastener performance,
manufacturing, economy, and convenience. Nearly 90% of all commercial and industrial
fasteners use this class of thread fit.
• Classes 3A and 3B are suited for close tolerance fasteners. These fasteners are intended for
service where safety is a critical design consideration. This class of fit has restrictive
tolerances and no allowance. Socket products generally have a 3A thread fit.

James
65 Corsa
SF Bay Area

Looking from the bottom there is no room for a nut

John Oostdyk
Thornhill, Ont
63 Rampy
65 Greenbrier
64 Convertible

measured with very near calipers the stud od is 0.377

John Oostdyk
Thornhill, Ont
63 Rampy
65 Greenbrier
64 Convertible

John-

Yes, there doesn't appear to be enough room to put a stabilizing nut on the bottom.



James-

I'm dubious that the original GM stud is 3A. A 3A should still thread into a 2B hole or nut and the Corvair stud would not thread into either nuts or thread gauges in the auto parts store. I think it is a custom oversize. It appears to be 0.010" larger in diameter than a conventional 3/8-16 screw.



I'm thinking I'll end up putting in a lock washer under a new bolt to try to stabilize it.

1966 140 Monza PG convertible
Ventura County, CA

Good point on the interference fit. A 3A is bigger on average but probably not .377".

You could helicoil the hole in the case (they do make a locking type if you wanted to go back to the stud). Not to sound pessimistic, but given the loose fit, you might damage the threads at some point. Preemptively doing a helicoil now might be better than getting stuck in the future.

James
65 Corsa
SF Bay Area

oh boy, starting to drift out into deeper waters now...

In looking at the stud, I think it might be tapered to lock into the mount at the correct depth.

I think it would be possible to make the existing stud fit (not interfere with the base of the distributor) if the fine-pitch portion were cut in half. I'm guessing it would be painful to try to cut the stud and not bugger up the threads.

So this might be boiling down to:

(1) use a 3/8-16 bolt with either Loctite or a lock washer

(2) use a 3/8/16 bolt and Helicoil the mount

(3) try to shorten the original stud

(4) get 123 to re-do the distributor shaft and clamp so that the body of the distributor is raised 10mm.


I'm leaning towards (4) as the hassles with mounting mount.

1966 140 Monza PG convertible
Ventura County, CA

vairTer Wrote:
-------------------------------------------------------
> oh boy, starting to drift out into deeper waters now...
>
> In looking at the stud, I think it might be tapered to lock into the mount at the correct depth.
>
> I think it would be possible to make the existing stud fit (not interfere with the base of the distributor) if the fine-pitch portion were cut in half. I'm guessing it would be painful to try to cut the stud and not bugger up the threads.
>
> So this might be boiling down to:
>
> (1) use a 3/8-16 bolt with either Loctite or a lock washer
>
> (2) use a 3/8/16 bolt and Helicoil the mount
>
> (3) try to shorten the original stud
>
> (4) get 123 to re-do the distributor shaft and clamp so that the body of the distributor is raised 10mm.
>
>
> I'm leaning towards (4) as the hassles with mounting mount.

Logically - if 123 plans to sell the distributor to Covair owners they should make it WORK without modifying the engine distributor mount. Just me.

They seem to be addressing the issues (most likely based on feedback from vairTer... this is posted on the web site when search for Corvair.

Quote

In R&D currently unavailable - Corvair 6 cylinder Naturally Aspirated Bluetooth Programmable 1962 and up

Here's another possibility:

I threaded a 1/4-inch screw completely through the mount hole and used a nut on the backside to tighten the clamp. I don't feel too bad about downsizing from a 3/8" bolt to a 1/4" bolt since I'll be using a Grade 8 bolt for added strength.

The only fly in the ointment is that the backside nut ends up being only 1/8" spaced away from the fan belt. I have fears that when the fan belt is moving and shaking that it could rub up against the nut.

Any thoughts on the wisdom of this approach?

Still waiting on 123 to comment on redesigning the distributor to use the original mount.

1966 140 Monza PG convertible
Ventura County, CA

Aside from the natural dancing around of the belt, the length of your specific belt will determine the clearance to the nut, because the idler, living just above it, moves forward and rearward to set the tension. Worse if a spring-loaded idler is used. It will be moving the belt back and forth during acceleration and deceleration of the motor, as it adjusts the slack.

Seth Emerson

Check my new Performance Corvair Web site: [www.perfvair.com]

Located in lovely San Jose, California

I think you may have addressed this early on in the discussion, but why exactly won't the original stud work with a nut on that new clamp?
Seems like it would be easier to do, even if it means figuring out how to shorten a too-long stud or use a lower profile nut. As mentioned, it's not that much torque on the nut, so a low-profile version would not be out of the question in that regard at least.

Sorry if it was spelled out in plain English already, but I think I missed the subtle details.

thanks

paul

Paul-

Original stud is the "too-long" stud; aside from the length, it would work fine.

I've never tried to shorten one (and preserve the threads), so I don't know how hard it would be to cut it off. Hacksaw?

1966 140 Monza PG convertible
Ventura County, CA

So, you complain about belt clearance…. (The least of your problems.)

Perspective in your picture above could be off.

But, the belt should not angle away from the groove in the harmonic balancer, so you have a belt alignment problem.

It has nothing to do with the distributor….

Well, after 4 pages of posts, it would appear that you bought a distributor that is not really compatible with a Corvair engine.

vairTer Wrote:
-------------------------------------------------------
> Paul-
Original stud is the "too-long" stud; aside from the length, it would work fine.
I've never tried to shorten one (and preserve the threads), so I don't know how hard it would be to cut it off. Hacksaw?

With the stud removed, take a 3/8" fine thread nut and install it on the stud at the height you want. Clamp the assy. in a vise by the nut with the part you want to cut off sticking out. Cut it off with a hack saw or cut off wheel. Remove the nut to restore the threads. LIGHTLY, sand, grind or file a chamfer on the top of the stud to give it some "lead in". Run the nut on and off a few times. Done Dun Duun

Been aircooled since 1973
Northwest Ohio 45840

RobertC Wrote:
-------------------------------------------------------
> Well, after 4 pages of posts, it would appear that you bought a distributor that is not really compatible with a Corvair engine.

We all knew that from the get-go.

I'm happy to see him experimenting with it and detailing the process along the way. This distributor has some some very cool options available to the user.

Dave W. / Gilbert Arizona
65 Corsa 140/4
66 Corsa 140/4
66 Corsa 140/4 w/factory A/C
66 Corsa 455 Toro V8
65 Monza Convertible 110/4
66 Monza Convertible 140/4 A/C
65 Monza 4DR 140/PG w/factory A/C
65 Monza 4DR EJ20T/5

Yes, I think Dave got my thread intent exactly right. This was meant to be more of a multi-episode soap opera detailing the challenges of installing a new piece of equipment. I knew going into it that there would be issues, but that everyone (myself included) would enjoy the drama and details.

I have confidence that this will eventually work. And I'm usually a pessimist in my day job (science R&D) and used to high probability of failure.

Stay tuned for more episodes....

1966 140 Monza PG convertible
Ventura County, CA

By switching the bolt to a 12-point 1/4-28 x 1.25", I was able to buy a bit of margin to collision with the fan belt. The gap increased from 1/8" to 5/32" (hey, every little bit helps...).

I'm still working on getting the tips of distributor to seat in the oil pump slot. That is a bit of a challenge.

1966 140 Monza PG convertible
Ventura County, CA

Thanks for going through all this trouble, it is interesting to watch! Check out low head or ultra low head socket cap screws, this would give you even more clearance.

_________________________________________
Ryan Counterman (Moderator)
1965 Corsa Kelmark V8 400 HP ///1965 Monza Sedan 110/PG /// Ultimate Corvair Hauler/// Don Eichstaedt's 1965 Corsa Racecar
West Michigan Corvair Club /// 1966 Corsa GTP Convertible Mid Engine 3.8L Supercharged

Ryan-

Excellent. Thanks. Let me dig deeper...or shallower.

1966 140 Monza PG convertible
Ventura County, CA