C3: Distributor End Play Specs

[Tony H.]

Re: the best reason for the closest spec

Did drawings for all distributors change after the L-88/LS-6 introduction or just those for those engine options/distributors? What did the drawings call out for end play for 1970 distributors?

[Clem Z.]

joe you correct about the changes when you

cut the deck,heads and intake manifold. the relationship between the cam gear and the dist gear must be check or you will have wear problems. also you need to check the end play in the oil pump drive shaft to make sure it is not bound up.john is correct the FI dist were shimmed to .002/.007 endplay as stated in the ST-12 service manual and they used heavy black print to high light these specs.

[Duke W.]

Re: the best reason for the closest spec

We've had this discussion before. My source for the two to seven thou spec is a SPECIFIC NOTE in the 1963 Corvette Shop Manual. Previous discussions presented anecdotal evidence that only FI distributors were built to anything near this spec, with most others having on the order of thirty to ninety thou clearance. The note in the '63 shop manaul DOES NOT distinguish between FI and non-FI distributors.

I recall it was also stated by several that original GM blueprints did not show this tight clearance spec, so your report, John, is new to me. If the blueprint spec was two to ten thou, why did Chevrolet built millions with such indifference to the as built end play?!

My own experience, and that of many others, has proven over the years that using this two to seven thou end play spec will result in more reliable ignition, especially for high revving mechanical lifter engines.

Ovehauling the distributor including shimming the end play up to two to thou is part of the engine "blueprinting" process, and I highly recommend it, especially for engines with redlines over 5500.

Duke

[John H.]

Re: the best reason for the closest spec

I only have a few samples of the Delco drawings, but the first one that shows up with .080"-.086" clearance is the #1111240 ('67 L-88 T.I.); #1111927 ('68 and '69 L-88 and '69 ZL-1 T.I.) and #1112076 ('71 LS-6 T.I.) and #1112167 ('72 LT-1 , 28-32 oz. points) are also .080"-.086". The #1112979 ('75 L-82 HEI) shows .010"-.112", and the #1103368 ('80 305 California HEI) is metric, but converts to .026"-.102". Everything prior to '67 shows either .002"-.007" or .002"-.010" on the Delco drawings, and .002"-.007" in the Shop Manuals.

[Joe L.]

Re: C3: Distributor End Play Specs

Tony-----

The specification of .030" to .086" is the spec for the finished assembly WITH spacer washer(s) installed. The spacing washer is 1/32" (or .031") thick. This washer is a hardened steel piece and usually has the finish that you describe. Usually, only 1 washer is used between the gear and distributor housing. The NOS examples that I have all use only 1 washer.

[Clem Z.]

if my memory has not failed me

the aluminum housing distributors use a shim that has tangs on it to prevent it from turning with the gear and wearing the aluminum housing so if you make any changes make sure the one with the tang is installed.

[Joe L.]

Re: the best reason for the closest spec

John and Duke----

With a few possible exceptions, I think that the change to the .030"-.086" spec actually occured about 1962, or so, for cast iron housing distributors. This is the same time, of course, that the change was made to the use of tach drive distributors on all Corvettes. Prior to that, the spec was .002"-.010".

Another "clue" here is the SERVICE parts specification for the .005" shimming washers necessary to achieve the .002-.010 spec. The applicability for these shimming washers was as follows:

1956-57-----ALL

1957-59-----Fuel Injection with high lift cam

1960-65-----with Fuel Injection

1965--------passenger car with special high performance 396 (distributors GM #1111098 and 1111100 with ALUMINUM housing)

1966--------passenger car with high performance 427 (distributor GM #1111150 with ALUMINUM housing)

Otherwise, the only washers shown for 1955 through 1982 applications were the 1/32" thick washers. For the above-referenced applications, one of the 1/32" washers was used in conjunction with an "as required" number of the .005" shimming washers. The .005" washers would produce an installation within the .002-.010" spec. Of course, the .005" shimming washers could be used on other distributors but they were never specified as a SERVICE part for any other distributors. Likely, this is because they were never part of the PRODUCTION assemblies for these units.

The specs for the 1975+ HEI distributor with aluminum housing was .010" to .112". Aluminum housing distributors used for points type ignition (pre-75)usually had an end play spec of .025" to .096". None of these, of course, were ever used on Corvettes and none were ever made with a tach drive gear.

Aluminum housing distributors, especially the pre-HEI type, usually used TWO washers between the gear and the distributor housing. One of these was the same 1/32" thick washer used for all other distributors. The other was a 1/32" thick tanged washer. In some applications, especially the HEI type, just the tanged washer was used by itself.

[Joe L.]

Re: if my memory has not failed me

clem-----

Your memory has not failed; the tanged washer is used on aluminum housing distributors. However, until the advent of the HEI systems in 1975, no Corvette ever used an aluminum housing distributor. Many other Chevrolet applications did, though.

[Tony H.]

[Tony H.]

Re: the best reason for the closest spec

Joe,

Do you have an NOS distributors [not for sale, of course] from pre-1962 Corvettes that would have met the tighter specs of 0.002" to 0.010"? What were their end-plays?

[Joe L.]

Re: the best reason for the closest spec

Tony-----

No, I don't have any of these old distributors. Except for FI, these distributors were usually of the cast iron "bowl" configuration.

[Jim T.]

Re: C3: Distributor End Play Specs

My original owner 70 350/300 engine would die back in 1983 from driving down a interstate when I would take a off ramp exit whenever I let off the gas. Could not figure out why. I would stop and it would start and idle with no problems on regular street driving. This happened repeatedly, but only leaving interstate. I removed the distributor and the end play was excessive in reference to using the specs in my 63 Corvette service manual. My 69-70-71 service manuals do not have this information. I used shims bought from GM for the task. After shimming to what the specs called for in my 63 Corvette service manual and driving the car on the interstate like before, the engine no longer quit. Since I did not do anything else to fix the abnormality, I have always believed the fix was shimming the distributor to the end play specified in the 63 Corvette service manual.

[Tony H.]

Re: C3: Distributor End Play Specs

Jim,

And the 63 CSM listed the specs at ???? 2-7 mil?

[Joe L.]

Re: C3: Distributor End Play Specs

Tony, Jim, et al-----

That's something else I should have mentioned. I DO agree that the distributor end clearance shown in the service manual is .002" to .007". It's even described this way in the later editions, including the manual for 1970 Chevrolet (including 1969 Corvette) (page 6Y-27 of that edition). The manual says to "add or remove shims" to achieve this spec. One would have a hard time removing any since the only one ever installed on these cars was the 1/32" thick washer. One could add them, of course, and it would take quite a few of the .005" shims to do the trick.

Actually, I think that this end clearance reference is some sort of an "anachronism" that found its way into the manuals. Certainly, it's at odds with the specifications shown on the blueprints and other more specific specification information for the distributors of this era. Beyond that, the service manual procedure is somewhat "generic" in nature; the blue prints for the actual distributors and other more specific specification information are decidely non-generic. So, I tend to go with the specs for the actual parts as being the most "authoritative".

[Jim T.]

Re: C3: Distributor End Play Specs

Joe and Tony- I stand corrected concerning my 1970 Chevrolet service manual which covers the 69 Corvette. Mine as well does have the information note between 5. and 6. about the mainshaft end clearance of 002"-007". Wondering why I had the thought that it did not when I posted about doing my distributor shimming adjustment back in 1983 on my 70 Corvette, I believe I found out why when I also checked my 1971 Chevrolet service manual. The note that is in my 63 and my 70 service manuals is not included in the 71 Chevrolet service manual concerning mainshaft end clearance being the above and adding or removing shims as necessary. I should of cross checked my manuals before posting.