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Re: C2 Distributor Position
Pull the distributor, rotate the lower gear 180 degrees and all will be well. I don't know why, but occasionally it is necessary.Bill Clupper #618 -
Re: C2 Distributor Position
Pull the distributor, rotate the lower gear 180 degrees and all will be well. I don't know why, but occasionally it is necessary.Bill Clupper #618Comment
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Re: C2 Distributor Position
The most common cause of this problem (assuming the wires are indexed correctly in the cap) is the distributor drive gear installed 180 degrees from the correct clocking position.
The drive gear has an indexing "dimple" and it should be installed to point the same direction as the rotor tip.
The drive gear has 13 teeth and on close inspection you will see that the roll pin hole axis intersects the center of a tooth on one side and between two teeth on the other. Thus, the two indexing choices will alter clocking by one-half tooth.
So for the same initial timing, depending on the two gear indexing options, the final distributor postion will differ by 13.8 degrees, and on Corvette installations, incorrect gear indexing can result in not being able to achieve proper initial timing before the vacuum advance control interferes with the coil bracket or manifold.
If the distributor gear is correctly installed, the wires properly indexed on the cap IAW the applicable service manual, and the distributor is installed in the correct position, typical initial timing valves for all C1 and C2 engines should place the VAC approximately midway between the interference points, and the cap window should be close to normal to engine centerline.
C3 distributors have different installation clocking.
I know of NO service or overhaul manual that mentions proper drive gear indexing. Proper indexing of the gear is noted on distributor assembly drawings, however, if you don't have access to these, it's a matter of "system knowledge" that you learn by experience.
My particular introduction to this issue occured about 40 years ago, and after a lot of head scratching and tries, I discovered the dimple and figured it out.
There are still a lot of Corvettes out there that have the drive gear on backwards and/or incorrect wire indexing. It's pretty obvious anytime you see a car with the VAC butted up against the manifold or coil bracket.
DukeComment
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Re: C2 Distributor Position
The most common cause of this problem (assuming the wires are indexed correctly in the cap) is the distributor drive gear installed 180 degrees from the correct clocking position.
The drive gear has an indexing "dimple" and it should be installed to point the same direction as the rotor tip.
The drive gear has 13 teeth and on close inspection you will see that the roll pin hole axis intersects the center of a tooth on one side and between two teeth on the other. Thus, the two indexing choices will alter clocking by one-half tooth.
So for the same initial timing, depending on the two gear indexing options, the final distributor postion will differ by 13.8 degrees, and on Corvette installations, incorrect gear indexing can result in not being able to achieve proper initial timing before the vacuum advance control interferes with the coil bracket or manifold.
If the distributor gear is correctly installed, the wires properly indexed on the cap IAW the applicable service manual, and the distributor is installed in the correct position, typical initial timing valves for all C1 and C2 engines should place the VAC approximately midway between the interference points, and the cap window should be close to normal to engine centerline.
C3 distributors have different installation clocking.
I know of NO service or overhaul manual that mentions proper drive gear indexing. Proper indexing of the gear is noted on distributor assembly drawings, however, if you don't have access to these, it's a matter of "system knowledge" that you learn by experience.
My particular introduction to this issue occured about 40 years ago, and after a lot of head scratching and tries, I discovered the dimple and figured it out.
There are still a lot of Corvettes out there that have the drive gear on backwards and/or incorrect wire indexing. It's pretty obvious anytime you see a car with the VAC butted up against the manifold or coil bracket.
DukeComment
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Re: C2 Distributor Position
When I was having the same problem I pulled the dist. and the dimple was indexed to the rotor tip. I repositioned it 180 degrees anyway and now the vac. adv. can is directly between the coil bracket and the manifold as it should be.Comment
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Re: C2 Distributor Position
When I was having the same problem I pulled the dist. and the dimple was indexed to the rotor tip. I repositioned it 180 degrees anyway and now the vac. adv. can is directly between the coil bracket and the manifold as it should be.Comment
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Take a look at this thread
Dave,
If it is a replacement distributor, I'm sure the problem is the reversed dimple in the distributor.
The thread was on a 67 327/300 HP when I put it's original distributor back on, after quite a few years with a replacement.
Jerry Fuccillo
#42179Jerry Fuccillo
1967 327/300 Convertible since 1968Comment
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Take a look at this thread
Dave,
If it is a replacement distributor, I'm sure the problem is the reversed dimple in the distributor.
The thread was on a 67 327/300 HP when I put it's original distributor back on, after quite a few years with a replacement.
Jerry Fuccillo
#42179Jerry Fuccillo
1967 327/300 Convertible since 1968Comment
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Re: C2 Distributor Position
Duke,
Thank for the explanation. I have run into this situation a number of times in non Corvette applications. I is nice to finally understand how to correct the problem.
RandyComment
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Re: C2 Distributor Position
Duke,
Thank for the explanation. I have run into this situation a number of times in non Corvette applications. I is nice to finally understand how to correct the problem.
RandyComment
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Re: Take a look at this thread
Jerry,
I'm a little confused with your discussion. Are you saying that the correct setting for a 327/300 hp distributor is right up against the coil? I believe that most of the other guys mention that I shoild be able to get 6 deg. BTDC with the distributor in the middle between the coil and intake. Right now I cannot get 6 BTDC but only 12 BTDC withthe vacuum can against the coil. I'm planning to pull the distributor and rotate the gear 180 deg. as sugggested in this thread.
Dave K.Comment
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Re: Take a look at this thread
Jerry,
I'm a little confused with your discussion. Are you saying that the correct setting for a 327/300 hp distributor is right up against the coil? I believe that most of the other guys mention that I shoild be able to get 6 deg. BTDC with the distributor in the middle between the coil and intake. Right now I cannot get 6 BTDC but only 12 BTDC withthe vacuum can against the coil. I'm planning to pull the distributor and rotate the gear 180 deg. as sugggested in this thread.
Dave K.Comment
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Re: Take a look at this thread
The point is that the dimple should be facing the same direction as the rotor tip. Don't just arbitrarily rotate it.
YOU MUST ALSO CHECK THAT THE WIRES ARE PROPERLY INDEXED ON THE CAP IAW THE SERVICE MANUAL!!! Do not overlook this step!
And then the dist. must be installed with the gear teeth indexed properly.
If you do everything "by the book" all should be well.
If all is correct by the book, the the initial timing should be achieved with the VAC about halfway between the interference points and the cap window near normal to the cranshaft axis.
300 HP distributors have 24-30 degrees centrifugal depending on model year, so you should set the timing to achieve a nominal of 36 total initial plus full centrifugal. If you have a 24 deg. dist. and it detonates at 12 initial you will have to either back off the initial or you can file the advance slot (or use a different limit bushing) to increase the centrifugal 2-6 degrees, then back off the initial to achieve about 36 total as above.
DukeComment
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Re: Take a look at this thread
The point is that the dimple should be facing the same direction as the rotor tip. Don't just arbitrarily rotate it.
YOU MUST ALSO CHECK THAT THE WIRES ARE PROPERLY INDEXED ON THE CAP IAW THE SERVICE MANUAL!!! Do not overlook this step!
And then the dist. must be installed with the gear teeth indexed properly.
If you do everything "by the book" all should be well.
If all is correct by the book, the the initial timing should be achieved with the VAC about halfway between the interference points and the cap window near normal to the cranshaft axis.
300 HP distributors have 24-30 degrees centrifugal depending on model year, so you should set the timing to achieve a nominal of 36 total initial plus full centrifugal. If you have a 24 deg. dist. and it detonates at 12 initial you will have to either back off the initial or you can file the advance slot (or use a different limit bushing) to increase the centrifugal 2-6 degrees, then back off the initial to achieve about 36 total as above.
DukeComment
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