Ignition shutdown problem

[ndutton]

There are differences in shaft diameters on distributors

Are you referring to different distributors like Prestolite vs. Delco or are you saying within a particular brand there are different shaft diameters?

Hadn't heard this before and if true I'd like to see some further evidence. I just measured a Delco I have on the bench. Shaft diameter right below the slot for the rotor = 0.559"

[romantic comedy]

By the sounds of it, Art may be referring to tolerance differences, rather then the nominal shaft diameter. The old quality control issue.

[ndutton]

I hoped by providing a measurement I would encourage others. Let's see.

[romantic comedy]

Neil, I measured a distributor that I have hanging around. Delco also.
Shaft diameter is .561 inches.

I have not even seen the EI. I had thought that the ring was placed over the cam. Is that not the case? Where does it fit?

[ndutton]

Y'know, you're right. It's the cam measurement that matters when it comes to EI magnet collar fit. That's what Art is talking about, right? The question remains, do the measurements of the same component on the same model distributors vary and if so, by how much? We expect variation due to wear on the cam peaks.

[ArtJ]

There is indeed shaft tolerance differences in Delco distributors.
I am not about to take the distributor apart to measure again.
Don Moyer is aware of this and several other posts on this site
talk about this. Several people have cracked the Sensors trying to
get them on the shaft of Delco distributors. I don't know about
the Prestolite shafts.

I have two engines. One has the issue, the other doesn't. Interestingly,
the one with the issue is from the latest version of engine with the
sheet metal front and other cost reductions.

[ndutton]

I'm sorry Art, I'm really struggling with this and trying to grasp how Delco could could have such a wide tolerance range. Are there different Delco model distributors used over the production run of late model A-4s? I certainly don't know but it could explain the differences you're describing.

Of course not everyone digs into such things, peel the onion back as it were but one of the great things of this forum is the willingness of many members to get involved and provide information of their particular engine. That's why the polls are so interesting. So yeah, I'm interested in learning how wide the tolerance range actually is. It's not that I think anything can be done about it but still this has raised my curiosity. Maybe I'm the only one (been there once or twice) but as before, here is the dimension of the 4 lobe cam on one of my Delco distributors across the opposing flats: 0.624". The Delco distributor model number is 1112 446 4F 7.

I hope others chime in for comparison. Don't make a special project out of it but maybe the next time the cap is off a simple measurement can be taken. I'd like to find out what we really have.

[ArtJ]

Neil

Why not discuss it with Don Moyer. I know that Shawn who is on this
site very often broke a Mag Sensor due to this issue.

[ndutton]

I don't bother Don with my obsessions. He has enough on his plate already. If I had an engine problem that had me and the forum membership stumped then a call to Don would be in order but for something like this? Nope.

[sastanley]

I just had the cover off my distributor a few weeks ago. It would not be a problem to measure cam diameter, I just have to remember to take the relevant measuring items with me and take 5 minutes to do it.

Since we are discussing it, my particular issue was that when I used the supplied 1146A magnetic sensor, my rotor would not seat far enough down on the distributor shaft to lock its key to the shaft groove. I had to break the collar on the sensor to allow me to push the sensor farther down and allow the rotor to seat into the groove properly. Since the fit of the sensor is tight enough, this has not been an issue, except for the part where I knew I had to break a brand new part it to get it to work.

Since we are getting into details, and this is way more fun than real work, I see a couple of variables that could contribute to my issue:
-my Pertronix unit did not come from MMI
-cross referencing of different parts does not always mean they are identical. Maybe if I had a different rotor from the extensive list, (and/or purchased all my ignition parts from MMI ) its key would seat correctly and still fit on top of the mag. collar in its intended location. For the purposes of discussion, I am pretty sure my cap/rotor pair are Echlin brand from my local NAPA, and are probably cross referenced from Delco part numbers.
-"the P.O. factor"..I have no idea if any/some/all of the parts are original or not. I see this as a factor for most of us..very few of us have owned our boats/motor since new from Universal.

Just as an aside to comment further on the P.O./isolation factor related to our wonderful little engines...when Spencer got his C-30 & A-4 last summer, I was amazed how quiet his motor seems compared to mine at idle. I have a very apparent sound that sounds like valve spring slap that I thought was perfectly normal, as I'd not heard many other A-4's run in person until meeting some folks from this forum. Spencer and I spend lots of time with our heads in each other's boats, and even though I checked valves & adjusted them a couple years ago and noticed no visual anomalies, mine makes a noise his does not that sounds like a broken valve spring. - I do know that the P.O. of my boat, liked to leave saltwater in the cylinders and had to ream out at least the #4 exhaust valve to .316", as I found the tools on the boat to perform this work. And just maybe, Spencer's engine is not normal and mine is. My point is, if you only know your engine and how it behaves, you may not know what you don't know, until you've worked on a few others.

[romantic comedy]

I wonder where the specs for the aftermarket EI came from. I am thinking that the sensor may be made too small. Were the specs determined by measuring distributor shaft? Was it worn?

Distributors wear down. some have even said that they wear so bad as to make them useless.

[ndutton]

RC,
I'd expect normal cam wear would make for a looser fit on the EI collar and as stated earlier I'd also expect measurements at the peaks of the cam to vary widely due to wear. The flats should not be subject to any wear at their centers assuming a history of properly adjusted points dwell.

Shawn,
Was your tight collar experience with a single collar or more than one? Looking forward to your measurement to compare, thanks. Also thanks for raising the rotor variance possibility. It's as likely as anything else I suppose.

What about the Hot Spark guys (are there any?)? Any collar fitment problems?

[ArtJ]

Neil

The reason I don't want take my mag module off to measure shaft
is that I broke one intially without the benefit of knowing that the
module sometimes needed to be heated. I paid for a second one.
Don't want to risk a third one.

Regards

[sastanley]

Ha...more questions than answers

Neil, I'd have to pull out my spare EI and see if I purposely broke that collar too. A couple years ago when I was chasing down the ignition/running/no start troubles, I didn't know many of the intricacies of the things we are discussing now, like the rotor keying to the shaft, collar height, etc., and I simply can't remember what I did & probably the collar being out of alignment and/or the rotor not seating correctly could have been part of my issues until I figured them out. I think I decided since the EI unit itself may fail, but the mechanical collar should be reusable, I probably did not break the 'backup' magnetic collar. The fit is smooth enough that I can put it in place with two thumbs, but I have to use a screwdriver to pry it back up for fine-tune positioning (which is just off the plate to avoid rubbing).

Something else that may be a contributing factor..distributor shaft length above the EI/points plate? Isn't there a little retaining on the distributor shaft (under the timing springs?) that holds it in place? How does it work? Are they all in the same spot? Do we all have the same amount of shaft sticking out above the EI/points plate? - maybe another measurement point to consider.

[ndutton]

The reason I don't want take my mag module off to measure shaft is that I broke one initially without the benefit of knowing that the module sometimes needed to be heated. I paid for a second one. Don't want to risk a third one.

Roger that but as with much of this discussion it raises another question. May I assume you preheated the replacement collar before installation so we can't be certain if it fit your distributor cam fresh out of the box, right?

Look, I'm sure from the reports there's a variance somewhere. It could be the distributor cam, the plastic collars themselves or as Shawn suggested the rotors and/or distributor shaft height or maybe even a combination. It's my nature to want to find out for sure and with the forum members' help I think we can.

edit:
Here's another question. Can the EI mounting plate be removed for access to the advance mechanism with the EI collar in place? If not, how can you lubricate the mechanism if you're reluctant to remove the collar? I'll have to look at that the next time I'm at the boat.