The Stovebolt Site Forums The Shop Area Engine Shop how much advance do you run? '57 235

I know that TDC is the suggested advance on a 1957 235 (mine's a car), but most people I heard say they have better results with today's fuels (non-ethanol of course) by running more advance.

How much advance are you guys running with your 235s? Mine has a pertronix in the stock distributor. Other than that and an alternator, my car is stock.

I do not check advance any more.

If you have a vacuum gauge, attach it to the vacuum port on the intake manifold and rotate distributor to maximum vacuum (at idle speed). I think that some people then "back off" the distributor (turn counter-clockwise a few degrees).

"I know that TDC is the suggested advance on a 1957 235 (mine's a car), . . "

You probably mean the timing mark on the flywheel, rather than TDC?
Is that from the car Shop Manual?

Nothing runs at TDC.

Old Hudsons timed at 5 degrees AFTER top dead center.
Jerry

Why?

It had something to do with the offset of the wrist pins in the pistons. Those engines ran a very long stroke for torque purposes, and the angularity of the rod at the top of the stroke necessitated a late timing setting to prevent piston slap at idle when the piston was in a "float" position with neither side of the skirt loaded against the cylinder wall. They engineered the wrist pin offset to allow the piston to rock over against one side of the cylinder before the plug fired, and made up the timing difference with a very quick centrifugal advance curve. Making broad-brush statements about ignition timing settings reminds me of Forrest Gump's mama's comments.
Jerry

Yes. I am absolutely positive that quote was precisely the one Hotrod had in mind...

“Mama always had a way of explaining things so I could understand them.”

So, by "-5" you mean "-5 + the total of mechanical advance".
"Runs" and "timed at" are only the same in your rather feeble mind.
I repeat: nothing runs at TDC, and by "runs" I mean RUNS, LIKE WHEN YOU DRIVE IT.

At least it doesn't have a manual spatk advance on the left handgrip like some folks' favorite toys.
Jerry

Those were good for more than starting. As a kid I thought it was cool to retard it all the way riding thru town and get a nice blue flame out the exhaust.

I have a 235 in a 56' 4400 truck and I'm going to adjust the timing for the first time with a vacuum gauge. Mine also has a Pertronix in the stock distributor. The only vacuum port I have from the intake manifold runs to the vacuum wipers and the Hydravac. Before I screw this up, here are my questions:

Do I unhook the Hydravac and wiper connection and hook the vacuum gauge directly into the intake?

Do I disconnect the vacuum advance that runs from the distributor to the carburetor? If so, should I plug it at the carb until the adjustment is complete?

Yes, plug the gauge into the manifold port. I leave the vacuum advance line in place.

New to the forum, but not new to 235's.
I own two '51's, one has a stock '55 235, that one is set @ 4* advance.
The other 235 is not stock, is a 1961 235, and has Petronix. That one is set at 8*.

My first experience with the vacuum gauge timing wasn't a total success. I connected my vacuum gauge into the intake manifold where the wiper and Hydravac are normally connected. I did not disconnect the vacuum advance that connects to the carburetor. The Pertronix setup had already been completed and the truck cranked right up after it was installed. The vacuum reading on the gauge would never remain steady when the truck was running, idle or accelerated. It bounced like a ping pong ball from about 15-20 on the vacuum gauge but never stabilized at one point. I adjusted the distributor to try and get it to its maximum vacuum reading and then backed it back down a small amount. The truck ran well and seemed to have more power than its previously had. But re-cranking it while its hot was not happening. So I had to tinker with it to get it to restart.

What did I do wrong or what could cause the vacuum to be so erratic?

I would first eliminate a few "variables" when using idle vacuum to adjust the ignition timing (and the carburetor mixture):
- disconnect the wiper "vacuum motor" and use that port on the intake manifold to measure vacuum
- disconnect (and plug seal the line) to any other device that uses vacuum (like the brake system hydrovac unit/line)
- disconnect (and plug line) to any other device that uses vacuum (2-speed rear end and speedmeter selector, if you have these)
- there is no need to disconnect the distributor vacuum advance

This way you are eliminating other possible "sources" of vacuum leaks.

Take a piece of paper (a dollar bill works well if you have any of those left) and lean it against the end of the tailpipe. If it is being sucked inward from time to time, you either need to adjust your valve clearance, or you have a sticky or burnt valve. This will give you an erratic vacuum reading.
A vacuum leak at the carburetor or the intake manifold will as well.
Carl

That is almost exactly what I did. This picture shows the line that comes out of the manifold and runs to the HydraVac. It also splits at the firewall and a branch runs to the wiper motor. I disconnected that large line from the manifold and tied in my vacuum gauge at that point. I did not plug that line since it was disconnected and I didn't know where it could be tied into the system at that it would cause a problem. Should I have plugged the line that supplies vacuum to the HydraVac and the wipers?

http://i1259.photobucket.com/albums/ii549/Parksman/Intake%20Vacuum_zpsykhi34oj.jpg

I don't know if that is the correct setup to even supply vacuum to the the HydraVac and wipers? I've ordered the electric wipers from Newport so that will be eliminated from the system next week.

Thank You Carl. I just saw your reply too. I will try that in the morning.

You're using manifold (full) vacuum instead of ported vacuum.

I have used a small plastic valve made to regulate air flow from an aquarium air pump to damp out the erratic needle movements of a vacuum gauge. You can run it wide open or cut the flow as much as needed to get a fairly steady reading. This has worked well for me in many different applications.

I tried the 'dollar bill' test and it did occasionally pop the paper back to the exhaust pipe. I'm hoping for an exhaust leak instead of a burnt or sticky valve.

On my old tractors I use spray carb cleaner around the base of carburetor and the intake manifold gasket to try and isolate vacuum leaks.

Any other suggestions for isolating the problem?

Unlit propane torch works very nicely for finding vacuum leaks. Start by briefly holding it over the top of the carb so that you will know what to listen for when the propane creeps in through the leak.
Carl

Mid 1970's Porsches also have their idle timing set a few degrees ATDC...otherwise they will backfire and blow up their plastic 2 piece intake plenums.

Interesting thread.

The original poster has not checked this thread since he made the first post.