Bought a fairly original C2 several months ago that had overheating problems (I thought), rough idle and poor low end response . Posted a few messages and got some great advice. Some of the suggestions were so esoteric they couldn't be found in a shop manual. (Like aligning the dimple on the distributor drive gear with the rotor ). Everything seemed to help a little until I got to the dimple...that helped a lot. Now it runs almost like new. Thanks again and especially to Duke Williams, Jack Humphrey and Joe Lucia. Your direct help and archive postings were invaluable. Les
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The infamous distributor drive gear dimple
The dimple deal is very interesting. There is NOTHING about it in the distributor section of my '63 Corvette Shop Manual, and I have never seen a word about it in ANY GM service manual.
It's one of those "system knowledge" issues that you learn by experience. I figured it out in 1965 when I first diassembled my distributor, put it together, installed it, and I could neither achieve the correct initial timing nor get the engine to run anywhere near right. After much consternation - reindexing the dist. a tooth ahead and behind and God knows what else, I finally noted the dimple and the odd number tooth count and figured maybe the dimple should point the other way - in the same direction as the rotor tip.
Voila! I was able to achieve the correct initial timing and the engine ran normallly. The dimple is there for a reason, but outside of the manufacturing documentation that must have explained how to properly index the drive gear, GM didn't place the information in service publications.
Go figure!!!
I sometimes wonder how many equivalent "man-lifes" have been wasted by a countless number of people trying to figure out why engines wouldn't run properly after the distributor was reassembled in the field - not to mention the number of engine hours when the engine ran like squat. GM really screwed everyone by never mentioning proper distributor drive gear indexing in the service publications.
Duke -
Re: The infamous distributor drive gear dimple *TL*
When I first observed the dimple, I thought it was an aid to correct distributor installation in the engine plant. There the cap was already on the distributor, and the dimple would indicate the way the rotor was pointing so the installer could correctly index the distributor. I never dreamed there was an odd number of teeth (count?? me?? not!) on the gear until a story on that very subject appeared in The Restorer - if memory is right it was by Gary Hodges.
TerryComment
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Re: The infamous distributor drive gear dimple
I wonder why they used the odd tooth count in the first place...seems like an even count along with appropriate cam gear would have created a simpler more foolproof system in the first place....CraigComment
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(Message Deleted by Poster)
Message Deleted by PosterComment
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how i found out about the dimple and the odd
number of teeth. after replacing a gear on a vertex mag for a race engine back in the late 50s. i wondered why when i put the mag back in the engine i could not get the timing set using a "buzz box". the mag had to be turned too far and the plug wires would not reach like they did before. it took me a while to learn what was going on with the gear teeth as i thought that the new gear had the pin hole in the wrong place. after checking the gear that came off the mag for where the pin hole was located i saw that it was different on each side in alignment with the teeth. i turned the gead 180 and it solved the problem. i still was not sure what i had done but it workedComment
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Way Back When, In The Old Days..........
here I was, a'sittin in me barn, with Sadie the Heiffer, udder all afull and a'readdy for a milkin'. Gosha'mighty she look'd about aready ta burst. An so I git ta thinkin, wha happens when the tin lizzie gets ta feelin tha indergestion. I kin rember wot Tom Jode done in Tha Grayps 'O Rath. Why, he done use' his ole waist belt ter fix da mixer in der Model T. We is goin now yon Arkansas ter Californee', ther land of milk an' honee.
Wen we got ter Bakersfeel we lern'd that this land wus not wut dey sed it reely wus. Dey made us work fer 3 cent an our, an so dat weren't enuf fer us to live on so we wet back home........but da bankers busted are land an we wuz orfens. God help us, 'cus we caint see da futchur!
Carl Sandberg
Salinas, Ca. 1938Comment
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Re: The infamous distributor drive gear dimple
OK, realize that I post this with a LOT of trepidation, as many of these guys know a LOT more than I do about vette's and have helped me out in the past on more than one occasion. I DO appreciate the help and have the utmost respect for folks that contribute to this forum.
from a previous post:
"...you find that it eventually contacts every single tooth on the large gear after some number of revolutions. In effect that one tooth, and all the others, "walks" around the entire mating gear"
This can't be correct. It sounds useful and beneficial, but if it was really true, then the timing would also "walk around the crank". The shaft ratios from the cam to the distributor must be 1:1 and must stay that way. If the cam gear and dist gear were not to mate 1:1, then timing would not last more than one rev.
Sincerely,
KevinComment
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Re: Way Back When, In The Old Days..........
joe if you want to go that far back my job back then was to set on the fence with my single shot sears and roebuck 22 and shot the pigs at slaughter time in the fall. did you ever eat brain puddin or ponhoss ?Comment
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Was that on the menu in Calrisle? *NM* *TL*
TerryComment
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Re: Was that on the menu in Calrisle?
terry i have not eaten any of that since we quit raising livestock after WW 2. when everyone got rich. the filets and the mahi mahi at carlisle were great,sure beats brain puddin and ponhoss.Comment
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Re: Was that on the menu in Calrisle?
I saw the filets and mahi mahi, but I wasn't sure if the brain puddin and ponhoss was before or after that.TerryComment
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Re: Was that on the menu in Calrisle?
You missed the Florida supplied CRABCAKES
jerComment
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sorry about that jerry ,i will give
myself 40 lashes.Comment
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Re: The infamous distributor drive gear dimple
Kevin,
You are not the only one lost. Either I have been extremely lucky in 30 years of playing with engines, or there is more to it that all this.
Timing is set by when the points open in relationship to the position of the crank.
The rotor just has to be near the contact for the correct wire. As such, you can point that rotor anywhere you want and still timing the car correctly. You may have the #1 wire at the front, back, left, or right, as long as the rotor points there, too, which means that the distributor gear can be in any position relative to the cam.
The distributor may not want to sit inside Corvette shielding, or vacuum pod may butt against other objects, but as long as the distributor housing is adjusted to where the points (Hall Effect, optical sensor, magnetic pickup, etc) open when the crankshaft is at your choice of 6, 8, 10, or 12 degrees before TDC, nothing in between matters.
Otherwise, it would be impossible to advance cams, use offset timing gears, etc.
While you probably never thought of it, I also find it hard to image that every single cam for a Chevy has had the drive gear start at exactly the same position since 1955. I imagine that cutting the gear on the stick is a separate operation on a different piece of cutting equipment than grinding the lobes, so that would require indexing every cam for the second operation to ensure that the position of the gear and the lobes are exactly the same.
That would have to also be true of every aftermarket cam, too.
The odd number of teeth are not to make it rotate, but to stop it from rotating. I believe a worm drive needs the driven gear to be an odd number relative to it, unlike spur gears which would then rotate relative to each other.Comment
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