70 L46 distributor installed position

[Wayne M.]

Re: 70 L46 distributor installed position

Does this have anything to do with current discussion ? From Dec '67 issue of Chevrolet Service News.

[Edward J.]

Re: 70 L46 distributor installed position

Bill, note the position of the vaccum advance unit(1968) in Waynes pic. this is the position it should be in when the dist. is when installed correctly. The vaccum hose should be behind the vertical sheild.

[Terry M.]

Re: 70 L46 distributor installed position

Does this have anything to do with current discussion ? From Dec '67 issue of Chevrolet Service News.

Yes Wayne. It does. And that is the article I printed twice in The Corvette Restorer. I am going to suggest it for inclusion in the 1968-69 TIM&JG also. When the time comes I'll suggest it for the 1970-72 TIM&JG as well. Any other ideas, besides tattooing it on people’s foreheads?

[Duke W.]

Re: 70 L46 distributor installed position

It's amazing how this simple issue keeps rearing its ugly head, and I'm also amazed how many C2s I see that obviously have something wrong with the distributor installation. Few know about the dimple orientation issue, including a lot of "professional" mechanics.

One of the problems is that the proper dimple orientation - pointing the same direction as the rotor tip - is not mentioned in any service publication that I know of - so many just install the drive gear without checking, and there's a 50-50 chance of getting it wrong. If it's wrong the distributor housing will be skewed about 14 degrees at the same initial timing, which usually precludes achieving the correct initial timing before the VAC hits one of the two interference points.

The 1963 Corvette Shop Manual has a diagram of proper wire indexing on the cap, so in addition to having the dimple orientation correct the wire indexing also has to be correct. If either the dimple or wire indexing is wrong it's impossible to get the correct initial timing before the VAC hits one of the two interference points.

I expect that later CSMs also have a similar diagram, and everything changed in 1968 for C3s.

If you don't have a photographic memory that includes an image of the correct distirbutor wiring indexing and distributor orientation for your year, print out the scan above that was posted by Wayne and keep it with your other service documentation.

Duke

[Harmon C.]

Re: 70 L46 distributor installed position

I didn't have the tatoo but I had been their and done that.

[Dennis D.]

Re: 70 L46 distributor installed position

pretty straight forward, and as Terry stated, line up the stake marks and go from there

[Timothy B.]

Re: 70 L46 distributor installed position

If the camshaft has been changed to something other than GM the lower gear may need to be turned 180* to set the timing.

[Terry M.]

Re: 70 L46 distributor installed position

The two times that Chevrolet Service News article was published in The Corvette Restorer came about because I was frustrated with the number of C3s I judged with the distributor oriented as in C2s. In addition to the improper orientation of the vacuum port, this will put a kink in the tach drive cable and significantly shorten its life. Of course one could buy the right-angle tach drive adapter sold by the vendors, but that is a solution in search of a problem since Chevrolet never originally used such an item.

Since Wayne has been nice enough to provide an electronic version of the article probably no one will need to go back to The Restorer, but:
The first time was in 1993 or 1994 when John Amgwert was kind enough to print it. I did it again in 2001, just to drive home the point.

[Michael W.]

Re: 70 L46 distributor installed position

Is #1 position on the cap the same or are some Corvettes different? I think I read this somewhere.

Later models with HEI have the wires one position different than points type distributors.

[Bill L.]

Re: 70 L46 distributor installed position

Well I guess I am going to have to pull the distributor and see if the shop that did the distributor put the gear on correctly.

When I first started it up the distributor was positioned exactly as in AIM. However, I did not line up stake marks since I could not see the one on the manifold.

Just as an aside, were the stake marks unique to each motor and distributor combo?

Just curious how the location of the stake marks was determined at the factory.

Thanks,



Bill

[Terry M.]

Re: 70 L46 distributor installed position

Well I guess I am going to have to pull the distributor and see if the shop that did the distributor put the gear on correctly.
When I first started it up the distributor was positioned exactly as in AIM. However, I did not line up stake marks since I could not see the one on the manifold.
Just as an aside, were the stake marks unique to each motor and distributor combo?
Just curious how the location of the stake marks was determined at the factory.
Thanks,
Bill

[Duke W.]

Re: 70 L46 distributor installed position

My guess is that the dimple is 180 degs. out. If that proves to be the case you should go back and educate your "very reputabale shop". It's amazing how many of these guys are clueless about this issue. Let us know.

Set the crankshaft at the proper initial timing point (NOT TDC) on the #1 compression stroke and pull the dist. Verify dimple orientation and wire indexing, then proceed with reinstalling the dist.

Start with the rotor about 25 deg. CW from the clocking of the #1 wire in the cap tower as shown in Wayne's diagram. As the gears mesh the rotor will move CCW such that the rotor tip is clocked at about the same position as the #1 cap terminal in the diagram. Being off a tooth in either direction is 28 degrees, which should be very obvious.

Once the dist. is fully seated (you may have to tweak the oil pump drive shaft to get it to fully seat - a paint mixing stick works well for this) use an ohmeter (or just visually observe the points) and rotate the dist. housing until the points just begin to open. Snug the hold down bolt, hook up a timing light, start the engine, and make the fine adjustment.

If you follow the above procedure the timing should be within two degrees of spec, and assuming you are using the OE timing spec the stake marks should line up if the dist. and inlet manifold are original to the engine.

Duke

[Bill L.]

Re: 70 L46 distributor installed position

Thanks Duke.

Am I correct in setting the proper initial timing point by lining up the timing mark on the harmonic balancer at approximately the 8 degree mark once I find TDC?

That is what I did the first time.

Rest assured that I will let the shop know. Based on the other work they have done for me, I have to admit this is a little surprising if it turns out it is off 180 degrees.

Some day I may know what I am doing Thanks again! Bill

[Duke W.]

Re: 70 L46 distributor installed position

Thanks Duke.
Am I correct in setting the proper initial timing point by lining up the timing mark on the harmonic balancer at approximately the 8 degree mark once I find TDC?

Assuming that 8 deg. is the OE initial timing recommendation or the initial timing that you prefer, that is correct.

Duke

[John H.]

Re: 70 L46 distributor installed position

As the gears mesh the rotor will move CCW such that the rotor tip is clocked at about the same position as the #1 cap terminal in the diagram.

Duke -

I think you meant the rotor moves clockwise as the gears mesh..