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Alignment problem on MP distributor

H

HotRod777

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I have an odd problem with a new MP distributor. It’s in a fresh 383 and is actually running well, but I spotted a possible problem. Unfortunately the distributor is the current model that is built by Pro-from/ China/ whatever. After the initial break-in of the motor, I pulled and opened up the distributor up needing to weld the T-bar (it had like 25° mechanical coming in. However, looking at the cap and rotor, the rotor appears to be running too high, essentially topped out solid against the top center contact of the cap. The way I can tell, the tip of the rotor finger is not where the arc is jumping from, its jumping from the top of the rotor finger to the BOTTOM of the cap contacts... the rotor has actually scraped away some of plastic from the underside of the cap. The contacts on the cap so no arc marks in the proper, outer perimeter location on the contacts.
I tried trimming 1/8” from the bottom of the rotor to no avail, it bottoms out on the top of the shaft up inside the rotor. Is there any way to shim the body of the distributor up in relation to the shaft?
 
I would strongly suggest just getting another distributor. Something is really wrong with that one, maybe how it was shimmed. You don’t need to buy that unit...try Rehrenberg on e-bay or Bouchillon Performance might have some that they check out in advance for you. Rehrenberg will provide support to you if there are problems, he was great with a timing issue that I had a while back. His current e-bay listing is $96. Also, I highly recommend not welding the slots but use the FBO advance limiting disc instead, it works really well and you can change it repeatedly as you mess around with tuning.
 
over the years as part makers have sold junk that dosent fit like the old days. look at an old rotor compare height and depth of where the shaft goes in the rotor is the depth / height the same ? make sure the notch in the rotor seats down all the way . other than that so many junk replacement parts. i just want good stuff for my hard earned money and i think all of us think like that. good luck sir.
 
Good thing the op pulled that dizzy apart.

I like to run on the cheap but sometimes its not the best option. I’m still learning that lesson. :mad:
 
I bought a new Firecore from Mancini and am happy with it. It has an adjustable advance plate, so no welding is needed. It even came with the plastic adjustment keys for the advance settings, so adjustment of the mechanical advance is pretty straight forward.
:thumbsup:
 
I spoke to Summit and they are sending another distributor to try. Here is a pic of what I mean. This motor has at least 5 hours of run time and you can see where the arc is jumping to the terminal. I drew the black arrow and it shows the arc dust and how the rotor seems to have scraped the terminals.

A69BA215-856D-41EC-A789-D9FB30E81956.jpeg
 
I have a similar distributer. I had to remove approximately 1/8 inch from the bottom of the shaft tang. The dist was bottomed out on the oil pump drive. I noticed before I started the engine. Your distributor may have been damaged if it has the same issue.
 
Get rid of that pos. Save yourself the headache of being stuck on the side of the road someday and buck up for a billet msd. They are probably made in China too but way better quality. The pain of the initial cost is quickly forgotten with a few miles of trouble free driving. Your engine will run smoother and you have more adjustment and built in rev limiter.
 
Try to find where the conflict originates before you cut anything.
I think the distributor would noticeably wobble if it's bottoming between the shaft tang and distributor body bottom with the hold down loose. You might find you need to shorten the shaft tang or even take the top of the shaft up inside the rotor down a bit.
If you find you need just a few thousandths between the block and distributor maybe stack a couple of these...…

upload_2019-7-25_8-34-49.png
 
Good info so far. Once I get the new dizzy today I’ll compare everything closely and see if/where any difference is between each. I’ll be swapping in my welded Tbar but will measure closely with calipers overall length/height of each to see if any parts/shims are different.
I know there better choices out there, but I’m getting a new unit at no cost so for now, I’m going to try to get this one set up correctly. I did not notice the center contact being broken/ ground down but yes it clearly has too much pressure on it.
The housing seats solidly in the block but what I haven’t checked is if while “seating” is the shaft being pushed up in the body from it being too long/ bottom tang too long/ etc.
David, per your comment above, was it just the bottom of the flat blade that you trimmed? Meaning the shoulder part of the shaft was ok? (I guess could pull out the drive gear and check the engagement)
 
If the distributor is, as said, a new purchase, why even mess with it? I know it's fun to see if you can "fix" a part, but maybe that's why there is so much crap on the market. If the manufacturers and distributors had to refund or replace every bad repro part, sooner or later the parts guys would weed out the problem brands, because they are costing everybody time and money. JMO. Don't mean to point fingers at any individual...
 
Something is not right for sure. Thinking it was made with to many upper shims in it there should only be one around .020 or so. Can you take a picture of the rotor that came out also?
 
Well the plot thickens. The replacement came. The rotor on this one does not seem to be riding quite as high but it is still arcing up from the top of the rotor finger to the bottom of the terminals. Since I now have a second dizzy at no cost even if I send back the the other, I figured I’d experiment. I ground the top of the T bar shaft down 1/8” and got the rotor seated that much lower. Fired it up, still runs fine, but after 10mins of running still see NO arc witness on terminals in the correct spot. Then I stumble onto what I think might be the problem. Eyeballing the rotor center point (by the carbon dot mark on the top contact tang) if you align that with the carbon button of the cap the rotor finger is 3/8” short of reaching the terminals. I confirmed what I was seeing with calipers, the rotor is that short. In this arrangement the only possible point that it could fire across would be the top edge of the rotor finger up and outward to the inside bottom of the terminal. This is a head scratcher.
Just for S’nG’s I’m going to grab a parts store cap and rotor this morning and see if they are any different, if the rotor is longer.. if it is are not, I’m at a loss...
I know everyone is going to say “just throw it away, those are junk”.
I understand that, but this is what I have right now to work with and I’m want the car usable this weekend.

On a related note, If I decide to go with a different dizzy I think I would go with the one that Mancini sells. The Firecore that still has a tan, female cap. That one is a plug and play with an orange box, correct?
 
The rotor should be a CH 303. Do you have a picture of the rotor you have now?

is it like this?
smp-ch303_sn_ml.jpg
 
Last edited:
It’s not in front of me right now but the rotor isn’t that skinny, the back, plastic side is wider looking then that. I’ll post a pic later this morning.
 
I am thinking you have a dp rotor in it.
s-l300.jpg
 
Totally mind blown. I bought a cap and rotor kit, comes in the same box and it’s still WAY short. Pictured are:
Old rotor that came with MP dizzy is white, the Duralast gold part store one is grey. Shown is measurements with a mic. It’s rough measurements but show what I mean, it’s .1000 short each way. In this arrangement the only path to arc is up and out on an angle to the closest point, the bottom edge of the terminal.
In a slant6 thread on another site they are measuring between .015 and .030 rotor tip to terminal clearance which is what I would think would be correct.

Halifax, do you have parts on the shelf to check what I am seeing???

7AAA3767-FE5D-47E5-A4A5-A0193850C0F0.jpeg 08A22680-5C45-41A9-99F4-214946E4E0F0.jpeg 49701E07-6BD7-47D9-B8D9-E4EC5F74BEBD.jpeg 47CE813E-9626-41F2-B102-9CC984F1476A.jpeg
 
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