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Another Prestolite Dual Point Distributor Rebuild Question

AR67GTX

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The distributor guys should remember my thread last month where I sort of inherited a DP distributor from my friend with a 69 Hemi RR when he decided to keep his MSD distributor.

Without a long story the MDS just doesn't work and was shorting out the #1 plug wire to the underhood fresh air assembly and keeping the hood from closing all the way. It's 3 inch taller than a stock distributor and he was blowing a hole in the #1 Terminal boot about every time he drove it. So he went looking for another distributor and found one and I told him I could manage to rebuild this one too. He thinks it's a 67 Hemi distributor but who knows - tags can be swapped in a minute. The no. on the tag is 2642834.

Got it all apart and installed new bushings but got to looking at the cam stop and although the internals all look really nice - the cam just doesn't look right for the distributor. It's stamped LU and the slots are .475" long. The shaft is 39 LD, LAZ1039LD.

Does this sound right for a Hemi - that cam stop with the longer slots? The one I rebuilt earlier with an LB cam stop measured .400" in the slots for less mech advance.

He wants to plug the vacuum advance because that's what a Chevy racer/mechanic buddy he grew up with is telling him. But I'm afraid if the mech advance in this thing is 28 crank degrees or something like that and he can only time it initially at 8 degrees or so, it's going to run like a dog and heat up. It has a fairly mild hydraulic roller cam in it and a 4 speed/Dana 3.54. Does this sound like an incorrect cam stop? Is this tag even for a Hemi?

Thanks as always.
 
Yes the cam stop is correct and so is the shaft. It is a CAP distributor so it was based on initial timing of 0 Degrees. You get 32 degrees out of the cam.
 
Wow - 32 degrees mechanical - and CAP too - that sounds like a real performance unit - especially if he disconnects the vacuum advance. I hate to break this news to him.

I've welded up the slots on one before but I'm not that good of a detail welder - it was a lot of work. Have to keep the slot width just right too or the advance will fluctuate.

Has anyone done a chart correlating slot length to mechanical advance degrees?
 
Wow - 32 degrees mechanical - and CAP too - that sounds like a real performance unit - especially if he disconnects the vacuum advance. I hate to break this news to him.

I've welded up the slots on one before but I'm not that good of a detail welder - it was a lot of work. Have to keep the slot width just right too or the advance will fluctuate.

Has anyone done a chart correlating slot length to mechanical advance degrees?

I have been successful using the FBO curve limiting plate on these. With the only caution that the springs would have to be the same on each side to keep the plate centered as the whole thing spins. I have a Sun machine and noticed that the plate works better when balanced.
 
I'm not familiar with a FBO curve limiting plate. Could you post some details or a source?

I do have an old 59 Imperial dual point cam plate that measures a .390 slot. The cam lobes are a bit pitted but since he wants to run a Pertronix I don't guess that will cause any problem.
 
Correction 30 out of LU. By 69 all car had some form of emission control. CAP was Mopars. Earlier cars still had options. What Was IBS # on the tag?

Make sure if you use another cam stop it is dual point and L not R. For proper rotation. They are not symmetrical.

Not my chart so take with grain of salt.
 

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  • Total Mechanical Advance.pdf
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IBS # is 4006 WS 257

Yes, this other cam plate I have is a dual point. It looks like the slots in the DP are square with the plate ears. The single point cam plate I have, the slots are at a bit of an angle to the ears - but it's from a aluminum distributor so I'm not sure if that is a good check.

Thanks for the chart.
 
Is there a listing somewhere of distributor tag numbers. I used to have one of those little white book part number guides but seem to have misplaced it several years ago.
 
That book, and actual Service Manuals and Mopar Parts books have the data.
 
Is the IBS 4006 WS 257 number consistent with the shaft/cam stop?
 
IBS # is 4006 WS 257

Yes, this other cam plate I have is a dual point. It looks like the slots in the DP are square with the plate ears. The single point cam plate I have, the slots are at a bit of an angle to the ears - but it's from a aluminum distributor so I'm not sure if that is a good check.

Thanks for the chart.
4006 ws is a 1967 426 Hemi Auto or 4 speed with CAP
 
Yes, those part numbers are called out for that distributor in Prestolite SVM. 15deg mechanical advance at distributor (30 for motor). Should have vacuum advance with 9.75 dist degree max.

Can you tell me number stamped on the vacuum advance arm? Also would like to know spring length, and washer stack thickness if you can.

If you tell me your imperial dist #, and stamps on bottom of Cam stop and letter on top, maybe able to tell you what mechanical advance it has. Though you may also get that from Chrysler SVM.
 
Regarding the Mopar Advance limiting plate...Here it is. He sells on e-bay as well. http://4secondsflat.com/Mopar Mechanical timing limiter plate.htm

I have used about 5 of these, all very successfully, on different generations of Mopar distributors. I have noticed that the actual degrees may vary slightly versus what is stamped on the disc. Less so, as I said before, if the springs on the weights are matched.
 
Yes, those part numbers are called out for that distributor in Prestolite SVM. 15deg mechanical advance at distributor (30 for motor). Should have vacuum advance with 9.75 dist degree max.

Can you tell me number stamped on the vacuum advance arm? Also would like to know spring length, and washer stack thickness if you can.

If you tell me your imperial dist #, and stamps on bottom of Cam stop and letter on top, maybe able to tell you what mechanical advance it has. Though you may also get that from Chrysler SVM.

The 59 Imperial cam stop has a W on top and LC on the bottom.

The vacuum cannister has a "10" stamped on the arm. It has a small hole in the bottom that was patched with JB Weld for some reason. But he plans on having me install a repro one.

The shaft has two of the cupped sheet metal washers at the top and at the bottom it had a .031" shim washer. It had very little play so depending on how it goes back together I may have to go a bit smaller. I pressed the upper bearing down enough so the cupped washers can seat fully in the housing.
 
That looks pretty trick. Glad to know about those and looks like something to have on hand. My attempt to weld up a cam stop would have gotten me an F in welding class. Dabbed in bits of weld, wire brush, dab in more, wire brush, dab in more, etc. Looked like a piece of crap when I was done but after grinding and filing and filling in a few pits here and there and more grinding and filing it came out OK and works very well - bunch of work for amateur welders.

Thanks

Regarding the Mopar Advance limiting plate...Here it is. He sells on e-bay as well. http://4secondsflat.com/Mopar Mechanical timing limiter plate.htm

I have used about 5 of these, all very successfully, on different generations of Mopar distributors. I have noticed that the actual degrees may vary slightly versus what is stamped on the disc. Less so, as I said before, if the springs on the weights are matched.
 
Believe the 10 is for degrees and they are for hemis.
 
I need the Imperial Distributor IBS # to look it up in the manual. BUT... the one LC with W Cam Stop I have came from a IBP single point distributor for a 413. That camstop will not work in your IBS hemi distributor as the cam lobe diameter is smaller for single point versus dual point. You can check between the two you have. It should be obvious once you look at the dimensions.

To be clear, your talking about the vacuum parts on the Hemi distributor correct? Did you remove vacuum fitting and measure spring length and the internal washer stack thickness? That would be helpful to me. The arm number is the max vacuum advance in distributor degrees.

Lastly, the service manuals for Mopar have the rebuilding specs for dual point distributors. You do not want a lot of lateral or axial play. The double stack thrust washer at the top is normal. Depending on how the collar was drilled, I have found one position may give different clearance then another, and you certainly have to have it on correctly. Later Chrysler types with plastic collar are notorious for this. So I am surprised you would have to press bearing down because too tight. Normally you would have wear and it would be looser.
 
OK - I'll check the lobe dimensions on the two cam stops. Misunderstood what shim stack you were asking about so I'll have to remove the end of the vacuum can to measure that this evening.

On the upper bushing I just made sure to press it down enough so that the cupped washers would sit flat on the housing and not ride up on the bushing. That's the way it was originally when I took it apart.

Not sure you guys would do this as a standard practice but I'm starting the bushings lightly and inserting the shaft and setting it in my hydraulic press to seat the bushings with the shaft guiding the bushings so they start straight. The shaft is just riding in the bushings and going down with the bushing - I'm not pressing on the shaft in any way. Then I'm lubing everything up with the shaft in the bushings, chucking the lower end of the shaft in a drill and spinning it awhile in both directions which seems to take care of any stiffness and leaves me with a play-free shaft that spins smoothly. Read about this on an old Chrysler Imperial website. So far with these particular oil impregnated bushings I'm using this has worked OK and haven't had to resort to reaming.
 
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