A couple weeks back, I posted about a new parts ad I read about in Hemmings Classic Car about close gap distributor rotors. The ad claimed that the rotors you buy now days pay little attention to the gap, and many of them are too large, resulting in hard starting.


I bought 3 of them for my 3 old cars, and installed one with a new distributor cap in the Cutlass today. From the pictures, you can see the difference in the rotor I replaced with about 8000 miles and the new one. Both are the heavy black plastic, the old one was the "good one" from NAPA.


My car started instantly when cold, idled perfectly, and warmed up and dropped to regular, smooth idle. After it was fully warmed up and had run for about 20 minutes, I shut it off and let it sit 20 minutes. Before, when hot, the car was hard to start, requiring a long crank and pedal halfway down. Today, the hot engine again fired immediately and idled perfectly!


I would highly recommend anyone that uses the rotor pictured to try one of these. I am amazed at the improvement. The 3 cost $33.00 with tax and delivery

 

Brand and part numbers?

 

Sorry. I had posted on the first thread. The company actually is a Corvette Parts site. I attached the ad that was in Classic Car, and wrote the part number, 1852722.


This rotor fits GM V8 distributors 1958-1974.

 

Nothing in the photos shows any gap difference- nor a gap at all. There is a tip to plastic wall difference, but no guarantee that the plastic walls are at identical locations. Some accurate measurements and maybe a sample on a cutaway dist'r cap would be more definitive. The trouble is you are trying to measure to a tip on the end of a radius and not a diameter, so it'll not be easy. Cutaway cap would be a great way to tell. Maybe that's what HMN did? Got a link to that article?

I am thinking maybe just putting a new rotor [with copper electrode] made the difference you experienced... or maybe you did other things also, like new plugs?

 

K&B Corvette Products.

He lists it as Part #1852722, as you said.

The interesting thing is that the '72 Parts Manual lists Part #1852722 [Delco Part #D-426R] as being only for engines '73 and up (interestingly Part #1870609 is listed for 455s '73 and up).
Part #1971247 [Delco Part #D-409R] is listed for '72 and earlier, and for '73 Marine and Irrigation.

Here is a picture of D-409R - It looks to me to be the same length the one you have:




Yours:




The NAPA ECH RR1670 ($8 each) looks to be about the same to me, too, but I can't be sure:




All of the major auto parts stores list the D-426R, and the pictures look to me like the other "emissions" version you showed, so I think that K&B is selling the right part under the wrong number (just to keep it "interesting").


My bottom line when buying car parts is:
If a Corvette specialty shop has them, they're probably available somewhere else cheaper.

- Eric

 

I replaced plugs, cap & rotor 8,000 miles ago. Today, I installed the rotor from K & B Special Products, and the cap with one from NAPA with the brass contacts. I only replaced the rotor and cap today, NOT the plugs. I see a huge difference in the 2 rotors in my pictures, assuming the black plastic cap is the same diameter. The old contact is much farther from the edge than is the new one. And the proof was in the pudding. It started up, both hot and cold, like it never has before. Instantly


There wasn't really an article in Classic Car, it was an info ad under their New Products section, which is in my above post.


I just used a micrometer to measure the two rotors and the contact. The rotor diameters are within 1/1000 of each other, so I's say they are the same. The old rotor contact is nearly 5/32 shorter. Meaning the gap is 5/32 farther away from the cap contacts than the new one. The picture may not be conclusive, but the micrometer doesn't lie. I will concede that the old rotor has 8000 miles wear on it, but I doubt it has worn 5/32 on an inch in 8000 miles.


I don't have any interest in these rotors, other than I tried them. I don't own the company and I don't sell them. Some rotors being sold are better than others. But the quality control of these parts is not what it was when these cars were new.

 

So measured from the center of the rotor (tab) to the tip of the rotor contact, the difference in length is 5/32 or .156? That's over an 1/8 which is .125.

 

That is correct, but I measured from the edge of the cap to the end of the contact. I first confirmed that the plastic part was the same diameter. Holding the 2 rotors in your hand, it is obvious that one tip is noticeably shorter. But that really doesn't' mean anything. The proof to me was the car started much, much faster. The starter touched the flexplate and the engine started immediately.

 

I wonder what the measurement is from the center of the rotor to the tip? I understand about it starting easier, I'm just interested in the difference between the 2. Your measure is a big gap.

 

Can you post a pic of both caps, oriented bottom to bottom, which will show how the caps match up in size (not that we don't belileve your measurements), and the difference in the reach of the tips. If it looks like you describe, I'm gonna get me one-o-dem...........

 

Eric, do you know if the Napa # ECH RR1670
is an Echlin part number?
IR like Randy, wont wone.

 

As far as I know, NAPA numbers that start with ECH are Echlin.

I plan to take a spin by NAPA tomorrow and see if I can compare a few caps, now that I've checked the numbers.

- Eric

 

Cool. I'll wait for the report, thanks.

 

In effect what you've done is reduced the amount of voltage needed to jump that gap. That made it easier for the coil to saturate and reduced that saturation time. That would explain the easier starting and smoother running.

You could go a step further and trim that rotor contact to a point which would reduce the area the spark would jump from. Electricity builds up on the tip of the rotor in the milliseconds before it jumps the gap. The less area the easier it is for the spark to jump, just like a spark plug. Electricity also likes sharp edges to jump from which also makes it easier for the spark to happen. Sharp edges combined with smaller gaps makes everything work easier.

I'd be willing to bet that if you took any old rotor and cut it into a point at the end like an arrowhead you'd see the same easier starting and smoother running. Of course the drawback to this is the rotor won't last as long or stay sharp forever. Every spark erodes a little off each time. In fact that new rotor has a much smaller tip on it illustrating what I'm talking about. It's not sharp like a point but it is narrower allowing things to work easier.
So who wants to solder a fine wire to their rotor and tell us how it works?

 

the cap on the left loks better

 

As far as measuring from the center of the cap to the tip, the center isn't easy to find. Do I put the end of the caliper on what I think is the middle of the contact? There is no definite middle, and it is springy and moves quite a bit. That is why I measured the cap diameter and found they were for all intents and purposes, identical. Then I measured from the outside edge to the end of the tip on both caps and compared the 2 measurements. The new cap tip measurement is between 5/32 and 1/8 longer. That means it is closer to the contact edge.


I don't think I have found anything other than a rotor that is closer what the engineers originally designed for our cars. The aftermarket, for the most part, have done a less than stellar job reproducing parts that are dimensionally identical to original, or made from the same quality of materials.


The rotor I replaced was a NAPA RR169R and a RR165 cap. I used an RR165 cap again this time. I will see if there are any other measurements I can make and post them. So far, I am very pleased with the results, but it has only been one day. I will update a bit down the road.

 

Is that old rotor still available, or tossed out?

This measuring stuff "with a micrometer" to the 1/32 of an inch is driving me nuts. Mix and match precise instruments with fractional eyeball guessing approximations?? A good micrometer, well used, can read to 0.0001 or a tenth [of a thousandth of an inch]. More accuracy than needed here. A Caliper well used can read to +/- 0.001 or a thou[sandth of an inch] easily. Perfect. A ruler, graduated in fractions [hold up sign of cross to ward off the evil of FRACTIONAL INCHES].... with eyeballing and parallax and whatnot, you would be lucky to get accuracy of 1/32" aka 0.031 or thirty one thou. Darn near adequate for this task.


At least we got the OD's of the two rotors verified the same to within 0.001", a good start. So, if we use THAT surface for a reference [with the assumption that they are perfectly round and centered], then the tip location can be pegged and compared. I agree that 0.150" or so more gap and a fatter tip will degrade the spark production and transfer. We'd like to have a 0.001" gap, but since the cap can move about that much on the distributor... that's not practical. The rotor and cap would crash. We won't even start in on how much the cap can move if you bought a restamped distributor from Capt. Clever who machines the OD down a few thou in order to remove the original numbers...

I suggest sticking with digital or dial CALIPERS for measuring, unless of course you have a CMM at your disposal. A nice straightedge and a proper machinist's square and we should be all set. For the ultimate- take your 4" grinder and make a cutaway cap so we can see the gap and the difference under actual installed conditions. I assume everyone has a spare distributor lying around for such purposes.

To summarize, ME WANT ONE TOO- one of them slim-tip, small-gap rotors.
Wondering how the red UHV Rotor compares to these black GM and aftermarket offerings.

 

Interesting you mentioned this. I had a problem with my car starting right after I finished my restoration. Every part is new and I know how to set up an engine. Damn if I could get it to start properly, Went through all the new ignition parts. Tested wire resistance, plug s coil, very thing. I then notice on careful inspection that the burn pattern on the inside dist.cap electrodes was very poor and not what it should be. After lots of measuring with my micrometer, I determined the position of the rotor tip and cap electrodes was off compared to my older one. Changed it out and bingo started right up. First thought was crappy made in China junk. Looked at the inside of the cap "Made in Canada" ,Damn!! Are all these parts we buy becoming so poorly made they don't even function as designed. I was going to return it for refund but thought how Am I going to explain that to a 20 year old parts kid. Probably never heard of a distributor before!! Still looking for a new cap that will work.

 

We spend time making sure our plug gap is dead on, as well as the dwell angle if equipped with points, and then just "assume" that the rotor and cap contacts have the correct gap.

 

I just re-measured using an old school square with slide ruler and measured from the outside edge of the rotor to the end of the rotor tip. Look at the square, not the rotor. Depending on if the camera looks straight down or a little left or a little left can make the rotor tip distance from the edge seem to move.

 

I did not find the elusive ECH RR1670 at either of the two NAPAs that I went to, and if I want to order it into the store, they'll charge me "between five and ten dollars" for UPS (which is a load of &%$), so I'm going to look for it on line.

Meanwhile, I can tell you that the CarQuest 51-5579 and the NAPA RR169R both have the "short" electrode.

- Eric

 

I was out earlier too and went to Napa,
Carquest and Orileys. All were junk chinesium
bullsh!t. I even asked for one for a 427 Vette, no.

The only one close was Carquest kit # 8120 by Accell
that looked close in the picture they had.
Both the cap and rotor, for $67 bucks!

His MSD rotor # 8442 was chinesium bs too.

 

The 1670 is listed on the NAPA website. I don't know what the length of the contact is on a new one. All I know is how short the one on my 8000 mile used one is.

 

NAPA lists an RR169R and an RR1670. If you compare the specs., they are identical and cost difference is $0.30. I hate it when they don't tell you the difference in the 2 items.

 

A bit more information:
It looks like some of the Corvette guys (Eewwwwww) have had the same discussion, and concur that the 1670 is the long-electrode model.

Here's a picture from one of them:




I just ordered one of these from NAPA on line. Interestingly, while the counter guy told me he'd have to charge me somewhere between five and ten dollars to order it in for me, the web site charged me sales tax, but no shipping. $8.43 total.
We'll see if it comes.

- Eric

 

I did a cut away for comparison of a rr1670 and a bwd select d138 rotor. I have to admit I would not have believed it had I not done this. The rotor gap on the bwd d138 was .097 and the gap on the rr1670 was .035. the pictures are not the best but you can see for yourself.

 

Still waiting for my order from NAPA. They sent me a message saying it would take a bit longer because it's not in the warehouse.

I took the liberty of rotating your picture and reposting:











- Eric

 

No surprise there for me, but it's nice you posted the pics for people to see. It's one of those long lost performance secrets.

 

That IS quite a difference.
Think I'll order two.

 

Nice cut-away view. Is it the part difference or could it be the specification? I compared a couple rotors I had laying around - an Accel and a GM flavor that were identical. So the spec. for some generation HEI rotors may differ from others? I'm thinking there was a reason the common part number (in any brand) has the shorter length? Something with the coil saturation as Trip mentions makes sense.

HEI has some strangeness indeed. My hard starting issue was the coil polarity. Chevy coils are yellow/red leads where Olds are white/red. These have a polarity difference with the coil windings. The distributor pickup sensor gets glitchy when the starter (dvr side) emits an RF field mixed in with reversed coil polarity when starting. Sounds insane but the documented problem proved to work simply swapping the coil to the Olds version. Crane has the proper reversed polarity coils. They list both styles. Chevy's have the starter on the passenger side and the rotor turns in the opposite direction. The RF emission field affect changes where the common yel/red polarity coil works best. Strange.

Now, throw in a genuine Delco module. Forget that aftermarket "performance" junk. Toss the mystery brand modules too. Use PC-CPU thermal paste that runs $6.00 a tube. Get it at Radio Shack something like - "Arctic Cool". Good wires, cap and A/C plugs gaped at .35-.40. Max your timing and swap the mechanical advance springs a touch lighter and you'll have a killer ignition system up to the module's rev limit.

Edit: Wait, is this rotor we're talking about for a points style cap? I assumed it was a newer HEI style.

 

I wonder if these would work out the same as the NAPA part?


http://www.ebay.com/itm/Accel-8124-D...a47537&vxp=mtr


I have these on my car with Crane XR 1 (I think it is), seems fine.

 

Okay, the rotor came UPS today, in a 1980s-'90s era NAPA Echlin box.

So here it is:

I've photographed it here compared with a Delco-Remy rotor from a 101-1 kit (rotor number is not listed, but the Uni-Set points are D1007) and a Standard Blue-Streak rotor (no number on the rotor).

You will notice that the Blue-Streak rotor is almost identical to the Delco rotor, with thin ribs and edges, while the NAPA RR1670 rotor is made of much thicker material, with a thicker electrode and heavier (and springier) central contact.
Objectively, the weights of the Delco, Blue Streak, and NAPA rotors, respectively, are 20, 35, and 75 grams, so the NAPA rotor doesn't just look heavier.

I tried to get solid measurements to locate the edge of the contact point with regard to center, but all of the surfaces are slightly slanted or curved, and it is impossible to get reliable measurements, so I won't waste your time with bad data.
Subjectively, the NAPA electrode does look as though it's farther out there, though.

Finally, you will note that, while the counter guy told me that it would cost me $5-10 extra to have him order the part to the store, the NAPA internet division did not charge me postage.












Hope this is helpful,

- Eric

 

Thanks for posting Eric.
Mine should be here in a few days.
Have you installed it yet?

 

Yup, but I haven't started the car, as it's rainy, cold and dark out.

Probably over the weekend.

- Eric

 

That is how the old Accel rotors looked that we used to buy in the late 60's, early 70's. The same color and heft. There was a matching cap. Notice where the contact tip is how there are 2 long, fat posts to stop the tip from moving at the outer end. Look at the other 2 rotors where they are lightly reinforced there, and the plastic is smeared over a bit. I've seen lots of rotors break there.