Brumbach

Take a look at the pictures. Is that a bushing on the limit pin? If so, what's the best way to remove it? Thanks

http://s220.photobucket.com/albums/d...h/Limit%20Pin/

63 340HP

Yes, it's the limit bushing. It reduces the number of degrees the pin travels in the rotor plate slot of the "autocam" assembly, and limits the centrifugal advance. You need the bushing, and usually, if the resulting advance is close to what you want it's best to leave the stock bushing stuck hard to the pin.

If you want to remove the bushing, make sure you have a quality replacement bushing (just in case the existing bushing gets wadded-up).

To remove and reuse the bushing, pliers or diagonal cutters can remove the bushing (sometimes, without damage to the bushing).

To install the bushing press it onto the pin with pliers, and if it does not hold tight squeeze it to oval the hole and to create an interference fit before pressing it onto the pin.

If you want less centrifugal advance, they used to offer larger bushings and even oval bushings that would further limit the travel in the advance slot.

A distributor tuner could also braze the end of the advance slot closed to limit the advance travel, and file the now shorter slot clean and smooth. This would allow the distributor to keep the stock bushing intact (a better & more permanent solution).

A few links may help (and a good tech collection link):

http://www.lbfun.com/Corvette/Tech/vettetech.html

The more specific timing links (you may want to look at both the ignition/distributor and timing tech sections).

http://www.lbfun.com/warehouse/tech_...101Article.pdf

http://www.lbfun.com/warehouse/tech_...%20ADVANCE.pdf

http://www.lbfun.com/warehouse/tech_...t%20Timing.pdf

The photos look like you have a very nice & clean distributor to start your tuning.

Good Luck!

Brumbach

I'm actually trying to increase my mechancal advance. I'm limited to 14 degrees and attempting to achieve 24+. Not sure how much I'll gain w/o the bushing but surely will be closer to the target.

63 340HP

14 degrees of angle travel at the distributor equals 28 degrees of travel on the crankshaft. Make sure you are working the conversion between distributor (camshaft rotation) degrees compared to crankshaft timing degrees of rotation.

Pulling the bushing will leave the smaller diameter pin exposed, and increase the degrees of advance travel. This is seldom desired for proper tuning.

Read up on the tuning recommendations and keep in mind that an engine can usually idle smoother and run with a few degrees extra static advance and less centrifugal advance, better than it will run with less static advance and more centrifugal advance.

Plasticman

It appears to me that the bushing shown is not a "stock" bushing, and is larger than "stock". But using "no" bushing (just the pin) will give you way too much advance.

63 340 HP's advice is right on, but if you are only seeing 14 degrees at the crank, then think you have found the cause with that bushing.

I have a Sun Machine, and have a variety of bushings (various diameters) that I use to set the total mech. advance.

Plasticman

62Jeff

To get you up to speed on what he's done so far
http://forums.corvetteforum.com/c1-a...-question.html

Brumbach

Any chance that this is not a bushing but rather a pin with a large bottom? The distributor is a repro for CC. I'm wondering if they have used a specially designed pin that is installed from the bottom up thru the football and the large base functions to limit the travel in the slot of the autocam as would normally be accomplished by the bushing. Treating as a bushing, I can't get it to move, turn or anything. I've even applied heat.

wmf62

it doesn't look to me to be a bushing. i would call CC and ask them what it's purpose is.
Bill

midyearvette

you already know what to do next!....remember, start with 15 deg.initial..

Plasticman

It "could be" a cap type bushing (enclosed bottom), or a solid larger diameter pin, but until you either remove it or call CC, you will not know.

Plasticman

63 340HP

The "bushing" could be a soldered bushing on the pin, or a larger pin soldered to the football (with reproduction pieces they may have tried to eliminate the more common mistake of loosing the bushing).

I would recommend adding a timing tape to the crankshaft balancer and document with photos and graph paper the timing at 5000 rpm and idle (with the vacuum advance plugged, run it up and test it). If you can, mapping the degrees of crankshaft advance at 500 rpm steps on graph paper will probably prove helpful.

I would do nothing more until you have a quality map of the existing curve of crankshaft ignition timing vs. rpm.

If the resulting curve reinforces your concern that you are not achieving enough centrifugal advance then return the distributor, or find someone who can grind the slot for the autocam assembly longer to achieve the advance you desire without damaging the football or shaft. The slot can be easily ground with a dremmel and the right bit, but it's wise to be sure of what you need before cutting material.

If you have any hotrod or racing performance shops in your area, a few calls to find out where they take their vintage V8 distributors for tuning may prove to provide the most benefit. You may end up in a residential garage where some old Guy has a Sun machine located for retirement hobby income (not in a clean room style boutique), but the end result is likely to give you a distributor tuned to the specifications you want with a timing advance curve graph to prove what you ended up with.

Good Luck!

Brumbach

CC says it's a solid pen. Sure glad I didn't bubba it out.

Plasticman

Did they say what the total mech. advance was suppose to be?

Plasticman

Brumbach

No but they acknowleged what I was getting was insufficient.

JohnZ

That's the biggest "bushing" I've ever seen - typically the production limit bushings look like the photo below.

Brumbach

Well I've reinstalled old faithful Mallory. Dual point, mechanical advance. It's getting 36 degree advance at or before 3000 rpm with an initial setting at 18 degree advance. On the repro, I had to set an initial advance of 22 degrees to achieve the same (with vac @ 25). Hopefully, I'm better off. Drives like a vette w/o pings but then again I didn't get pings out of 22 degree advance either.. Anyway, this'll keep me up and running while I send off the repro distributor. I think TI Specialty was recommended. Any others? I'd really like to keep the repairs to a minimum. Possibly only correcting the mechanical advance restriction. Thanks,

PS. The repro distributor has stamped on the autocam CCW 514. Wonder if the "14" is indicative of 14 degree mechanical advance.

Brumbach

I sent the distributor off to a reliable source. He changed the weight base and weights. I've reinstalled and had no trouble achieving 37 degrees @ 3000 rpm with an initial advance of 11 degrees. It's raining so I'll have to wait for trial run but feel confident it'll run good. Thanks for the help. Bill

Powershift

Glad to hear this.

Larry

midyearvette

please post your results as to which you like better, the stock dist. with vac advance set at 11 deg initial or the all mechanical mallory set at 18 deg initial with no vac advance, thanks......

wmf62

FWIW; as a practical matter, the vacuum distributor will ALWAYS be better for everyday driving.
Bill