1967 L-79 Distributor Assembly Question

[Kenny H.]

I'll be re-assembling my L-79 distributor this weekend and have an assembly question. In some re-build articles I've read it says to fill the grease well with an absorbent material like gauze or similar, then pack with grease. Is that accurate to pack the cavity with an absorbent material, because I've never done that in the past. I was planning on just filling the grease well with EP grease.

Also, once I've filled the cavity with grease, do I install the plastic seal, then on top of the plastic seal I install the felt washer (impregnated with grease) for the points plate to sit on?

Thanks.

[Duke W.]

Re: 1967 L-79 Distributor Assembly Question

Use Delco 1960954 Distributor and Starter Motor Lubricant in the grease well below the plastic seal. I you don't have any, use a long life synthetic grease, like Mobil 1 synthetic.

Wet the felt washer with oil, but don't totally saturate it per the instructions in your COM, and place it on top of the seal. Then install the breaker plate.

Search my handle for a detailed thread on rebuilding a L-79 distributor in December, 2012. (I figured out how to make a Delco single point work perfectly to 7000 revs over 40 years ago.) It has several more helpful tips, including replacing the prone-to-failure breaker plate ground wire, setting end play, and optimizing the spark advance map. Sources and part numbers are included. I expect you will find that thread very helpful.

Be sure to reinstall the drive gear with the dimple pointing the same direction as the rotor tip.

Duke

[Ken A.]

Re: 1967 L-79 Distributor Assembly Question

Originally the well was filled with a mixture of sawdust & grease.

[Duke W.]

Re: 1967 L-79 Distributor Assembly Question

No, but I've heard sawdust and oil along with recommendations to use medical gauze and oil. Grease is an emulsion of oil and solids. Over time the oil will dry out and leave the solids, which are the flakes seen in the upper bushing grease wells on decades old distributors that have never been overhauled.

It's possible that some home brew mixture of solids and oil was used decades ago, but I believe it was replaced at least by the mid sixties by the 1960954 grease.

Why else would it be formally named GM Distributor and Starter Motor Lubricant?

Duke

[Duke W.]

Re: 1967 L-79 Distributor Assembly Question

I asked Joe L. if he could determine the time frame that 1960954 was released. He said probably the '73-'74 time frame, which is later than I figured. It's great stuff - "siliconized", but, unfortunately out of production. It's very slippery compared to wheel bearing grease, which gets gummy when you rub a dab between your thumb and forefinger. 1960954 is an excellent lubricant for low load high surface velocity applications.

Some is dark gray and some is red. I've used it for starter motor bushings, the distributor grease well, and tach drive gears, and I've also recommended it for FI pump drive cables. A one pint tub would probably keep a whole chapter supplied for the duration.

It's been discussed several times including photos, so it's easy to search.

I learned about it from a Corvette Restorer article back in the nineties.

Duke

[Richard M.]

Re: 1967 L-79 Distributor Assembly Question

Duke, Et Al.....For reference, here is Duke's L-79 rebuild thread. It took a while and a few unique Boolean expressions to find it.


https://www.forums.ncrs.org/showthre...554#post641554


This was my Advanced Search string which found it.....distributor AND ( *L79* OR *L-79* ) User: Duke Williams (22045)
Rich
p.s. great info Duke, thanks for writing that. I missed it back then.

[Duke W.]

Re: 1967 L-79 Distributor Assembly Question

All you had to do was search for threads started by me (there aren't that many) and go down the title list.

You should also search for a thread started by me on contact sets, so you can select the best one for your engine. It was also published in The Corvette Restorer.

Congratulations for deciding to overhaul your distributor. It's the most overlooked component on the engine. If you follow the advice including end play and spark advance map recommendations you will notice a definite improvement in your L-79's performance, especially low end torque and engilne smoothness. Just watch the tach because it will want to rev beyond the redline in the lower gears.

BTW, Joe L. got back to me and said 1960954 may date to circa 1964. It can't be nailed down because Delco used some part numbers "out of sequence", and it did not show up in Chevrolet parts catalogs until the '73-'74 time frame.

Duke

[Kenny H.]

Re: 1967 L-79 Distributor Assembly Question

Thanks everyone. I re-assembled the distributor last weekend and it went together well. I used EP Mobil 1 synthetic grease in the well, tach gears, shaft, etc. Very slippery stuff. Set the distributor gear end play at 0.004" , installed the gold springs from a Mr. Gasket 928 kit, and fabricated a new ground wire using electrical ends I already had and new stranded wire. I'm out of town this week on business, but will install it next weekend and see how it works.

[Duke W.]

Re: 1967 L-79 Distributor Assembly Question

If you haven't already done so, install a B26 VAC. The L-79 has a rather weird spark advance map - the lazy centrifugal curve of the 300 HP distirbutor and the very aggressive vacuum advance of the 365/375 HP engine, so my recommendation is to make the centrifugal more aggressive and the vacuum advance less aggressive. Assuming the OE cam or something close, the 12" B26 easily passes the Two-Inch-Rule with typical L-79 idle behavior of 750 @ 14-15".

Also, it's tough to tell if the gold or silver spings are the lightest. They both have the same OD and number of coils, but IIRC measurements showed that the silver springs have a slightly smaller wire diameter like about 1.5 thou.

Can you try both and measure the point of maximum advance for each? It may be tough to tell.

In any event, I think you will be very satisfied with my recommended setup assuming you used a set of high breaker arm tension points, but don't hesistate to tell us what you really think!

Duke

[Kenny H.]

Re: 1967 L-79 Distributor Assembly Question

Duke:

I failed to mention that one of the reasons I elected to blueprint this distributor in the first place was some unacceptable advance readings when I was checking the total idle timing. Further investigation revealed the distributor had a B1 VAC which I suspect was contributing to poor performance, so at that point I elected to take everything back to stock specs, including installing a B26 VAC which I did.

I intend to start with the gold springs and develop the advance map then try the silver springs and compare. I was planning on ultimately using the ones that gave me all centrifugal advance between 2,700 - 3,000 rpm. I have a dial-back timing light so getting a good comparison shouldn't be a problem. I also have an old Sun 45 timing light that I've been using on my M-38 military jeep for decades, and honestly by fabricating an accurate timing tape I get identical readings with the Sun 45 as with my dial-back, even if it's not quite as convenient.

I doubt that I'll put it on a chassis dyno since I didn't have a baseline to compare to, but once I get the distributor back in the vehicle I'll report back on my anecdotal opinion on performance. Thanks again for the input.

[Stuart F.]

Re: 1967 L-79 Distributor Assembly Question

Ken;

Perhaps you described your rebuild plans in another thread, but I was wondering if not can you mention what components you replaced, if any, i.e. main shaft and bushings, cross shaft (and end thrust button), etc.. If any, could you describe the work you did or had done?

I recently did my 63 L-76 distributor and went through a major decision process as to what I should replace based on condition and costs, etc. The main concern was with the cross shaft which was boring a hole in the housing as it does not have any end thrust button (nylon or brass), modifying for either would have required additional housing machining. I was prepared to replace the main shaft and cross shaft, but decided against it due to the shaft grooves and scratches were only above the lower bushing location and the side play was minimal. I also decided to retain a matched gear set between the main shaft and cross shaft, and used a steel set screw to provide control over the end thrust of the cross shaft.

I am, therefore, interested in hearing about your decision process on your rebuild.

Stu Fox

[Duke W.]

Re: 1967 L-79 Distributor Assembly Question

Duke:

I intend to start with the gold springs and develop the advance map then try the silver springs and compare. I was planning on ultimately using the ones that gave me all centrifugal advance between 2,700 - 3,000 rpm.

Keep in mind that the L-79 distributor curve is nonlinear. On Jim's car the gold springs brought almost all the advance in by 3000. It took another 500 revs to get that last couple of degrees, but that's certainly better than the OE setup where all the advance is not in until 5000, and the more aggressive centrifugal could be felt SOTP as better low end torque and a nice linear pull from midrange to top end.

Most early distributors and the '65 365/375 HP distributors have only 24 degrees centrifugal and the "curves" are linear.

Feel free to run as much as 40 degrees total WOT advance as long as it doesn't detonate. I usually shoot for 39. Idle quality should be better and total idle advance should be in the mid-twenties. There might be some slight variation if the centrifugal curve starts below your chosen idle speed (750 is a good choice), but with the tight end play there should be no visible scatter at any engine speed.

Stu - check out the link in post #6. In that case the main shaft bushings were fine as were the tachometer drive gears. The upper bushing grease well just had a few greasy flakes left, but the tach drive gears still had plenty of grease. IIRC when Jim bought the car it had been in storage for about 20 years and only had about 80K miles.

Duke

[Stuart F.]

Re: 1967 L-79 Distributor Assembly Question

Thanks Duke for setting me straight. Been traveling to Chicago this past week and finding hot spots to keep in touch. Believe post #6 and Kens PM will answer my questions well.

Thanks again.

Stu Fox

[William F.]

Re: 1967 L-79 Distributor Assembly Question

Have read that timing mark on 8" balancers are about 2degrees more than actual advance. Will applying a timing tape make degrees read from tape be the actual degrees advance?

[Stuart F.]

Re: 1967 L-79 Distributor Assembly Question

I have a timing tape on my 63 L-76 that I got from Jegs. I originally got it and applied it (from under the car) for use with setting the valves, but have found it useful in place of a dial back timing light. The letters are yellow on black and stand out well with my old Monkey Ward white light timing light. You will need an assistant to operate the throttle and read (hold) the engine speeds where you want to take your readings, I.e. Every 1000 rpm or 500 rpm to log in your readings.

Stu Fox