1970-Bronze

Ok, I took LARS's advice and ordered the MR Gasket 928G kit. It has a brass bushing which I believe I am to install underneath the mechanical advance mechanism. There is a pin and the bushing fits on it, but what holds it on? It looks like there's suppose to be a C-clip. There wasn't one in the kit or on the pin. Ideas? :nonod:

Once it's installed, do I just go with the amount of advance I get or do I need to modify the bushing to get the correct amount of advance?

:skep:

lars

The bushing should be a press fit - you install it by tapping it onto the pin with a hammer (pull the mainshaft out of the distributor to do this). If the bushing fits loosly, lay it on its side on an anvil and tap it with a hammer to make it oval-shaped. This will cause an interference fit and you can then tap it onto the pin with a hammer.

The advance curve length is determined by the length of the slot that the bushing rides in: the longer the slot, the longer the advance curve. The slot, measured from end-to-end, should not be any longer than .420". I like them a little shorter than that.

Once you have the bushing installed, slap everything back together regardless of the slot length and test the distributor in the engine: Set the total timing (at elevated rpm) to 36 degrees. Then, let the rpm drop down to idle and see how much initial advance you end up with. If you're in the 12-20 degree range, you're in good shape (I presonally prefer about 18 degrees initial). If you're outside this range, or if the initial timing is not where you need/want it to be, change the length of the advance slot to tailor it as you like.

To shorten the slot, I TIG weld the end of the slot and then file it to the right length. You can also use some good epoxy to fill in the slot a little and then shape it to length. If the slot needs to be longer, you can just use a Swiss file.


[Modified by lars, 5:22 PM 4/3/2004]

1970-Bronze

Lars,

I actually found an E clip that fit so I used it.

As the car sits, I'm getting 32º with about 10º inital. So, I just need to advance it to about 36º and that would give me about 14º inital - Correct?

Hook up the Vac Adv and I should have some where around 50º - correct?

Then just re-adjust the idle circuit - Correct?

Thanks again for your hep.

lars

Actually, if the bushing pressed on tight, you really don't need the e-clip.

Your timing sounds like you're right in the ballpark. Yes, you need to bump that total up to 36, and this will give you 14 initial. This should run very well, with a good idle and crisp off-idle throttle response.

If you run your vacuum advance off of manifold vacuum, you'll pull in another 16-20 degrees at idle, depending on the specs on your vacuum advance control unit. Some engine setups run well with this - others don't like that much timing at idle. If you get some roughness in the idle quality by running your vacuum advance off of a manifold vacuum source, try running off the carb's ported vacuum source. Use whichever vacuum source gives you the best quality idle and the best off-idle throttle feel.

At elevated rpm, with the centrifugal advance fully deployed (36 degrees), the vacuum advance will pull your combined total timing up into the 52-56 degree range. This is correct. I like to run about 54 as a target for the total combined maximum advance.

Good job on the tuning!