55.2-59 "Octane adjustment knob"

[BlouDon]

I'm referring to the round knob on the side of the dissy.

According to the manual this knob must be turned to adjust for octane, but the knob on my truck can turn many times.

I would appreciate knowing more about what this knob does and how it works please.

[sack54]

If you unscrew the cap, you will find grease inside. If low add some.
This is to add a little grease to dizzie to keep lubed, nothing else/
And only turn inward about 1/8 turn about every 6 months dizzie only needs a little lube

[BlouDon]

Originally Posted by sack54

If you unscrew the cap, you will find grease inside. If low add some.
This is to add a little grease to dizzie to keep lubed, nothing else/
And only turn inward about 1/8 turn about every 6 months dizzie only needs a little lube

Thank you!!!

That explains the grease I found on my fingers when I fastened the timing bolt.

[1project2many]

There is a manual available online that might be helpful.


This page shows the octane adjustment along with instructions for setting timing:
http://chevy.oldcarmanualproject.com...55ctsm0620.htm

Red arrow points to the octane adjustment in both photos. In order to adjust timing by the instructions you set the octane adjustment to 0, loosen the distributor clamp (yellow arrow in photo of your engine), and set distributor position using a timing light. Once the timing is set you can make changes for increased or decreased octane by loosening the bolt on the octane adjustment and turning the distributor.

[mr48chev]

"Octane adjustment" = resetting the timing to get along with some of the crappy gas that was around then. Not as bad as some you see these days but in the 50's and early 60's if you didn't go to a decent volume name brand station like Chevron, Texaco, Shell or Union 76 and stopped at some hole in the wall one pump station you stood a chance of getting gas that barely could be called gas and might be doctored with coal oil or some other cheap fuel to boost the owner's profit level. Or the guys who lived down on the border who drove over into Mexico to fill up at the time.

Now days it is more in the way of a way to fine tune the timing down to the N'th degree while on that distributor. If you have an adjustable timing light it is easy to have the ball on the flywheel line up with the pointer and then dial in the exact timing you want with that setup.

[whitedog76]

Wasn't it used for summer/winter tuning? Advance in the winter, retard in summer.

[BlouDon]

Originally Posted by whitedog76

Wasn't it used for summer/winter tuning? Advance in the winter, retard in summer.

Assuming fuel octane remains constant, the only way in which winter vs summer can play a role is when it comes to intake air temperatures. This engine has a rather low compression ratio, so it would really require very low octane fuel and rather high intake temps (30ºC or more) to make this engine detonate.

Having set the timing as per the book, timing would be very far away from detonation. I've advanced mine quite a bit which has added at least "1 horse" to the power output - but with so little, every bit helps. I also live at 1400m AMSL which calls for at least another 4 degrees of advance.

I'm running mine on 93 Octane (If that can be believed) and in our high summer temps (30ºC or more) there is no sign of detonation yet - even with timing rather aggressively advanced.