Bill Stewart

1936 320 cu in spark advance confusion

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The 1936 shop manual has a fairly lengthy description of distributor action, especially regarding the interaction of centrifugal and vacuum features, whether they advance or retard the spark, why they do "whatever" under certain conditions, etc.---------.  The explanations seem absolutely inconsistent to me. Do newer Buick shop manuals cover this topic in a different way? Is there some other resource that would help clarify this? 

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I'll see if I can:

 

1. Timing never goes less than base advance. So if you have it set to 6 degrees BTDC, that is the minimum you will see.

 

2. Centrifugal advance is solely tied to RPM. The springs are supposed to roughly follow the curve (solid lower line) in the shop manual but if they are original they probably do not. You can plot a curve with a timing light with the delay knob on it. Start with zero delay and make sure RPM is 450 or below and set it to the mark. Then advance by 100 or 200 RPM increments with the idle setting screw and see how many degrees of delay it takes to bring the mark back to the line. Compare to the shop manual and then send your unit out to be recurved!

 

3. Vacuum advance is additive to the centrifugal advance, so total timing advance is base + centrifugal + vacuum. The amount of vacuum applied to the advance depends on throttle position and RPM. Keep in mind the ports are above the throttle plates (relative to the manifold) so very little if any vac advance is applied at closed throttle and low RPM. If at high RPM though, taking your foot off the gas will result in the plates being cracked slightly so there will be some vac advance in play. The amount of vac advance as shown on the graph (upper dotted line) is kind of notional since the throttle position is not part of the graph, in fact the graph should say that the amount shown is max possible at the given RPM. My 1940 manual says at part throttle which agrees.

 

Hope this muddied things up nicely!

 

Cheers, Dave

Edited by Daves1940Buick56S
Clarity (see edit history)
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Thank you Dave. Your comments are helpful! I like to understand how things work even when they don't need fixing (yet). My newly rebuilt engine runs terribly rough over 20 mph. The distributor seemed to be the culprit but i couldn't figure out why. I had it all apart, cleaned, and could find nothing wrong. It just came back from Advanced Distributors where the advance was recurved (just as you suggested) so I do not need to do the calibrating with a timing light that you suggest. However, trying to time the engine drives me nuts. I literally cannot see the timing marks through the dinky opening down behind the starter and oil filter, even standing on my head, using a mirror. How do people time this engine?!

Thanks

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Dave has given an accurate picture of distributor functions, but, just wondering why you have focused on the distributor as the cause of rough running ?

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My experience is with 1937 and 1938 320 engines but I would expect the same to be true for your 1936 320 engine. Remove the bottom flywheel access cover. Paint the timing marks with yellow or white paint. Reinstall the flywheel access cover. Next, when you hook up your timing light, don't use the 6 volt battery in the car for power. Use a 12 volt battery for the timing light power source. You should find the timing marks easy to see with the paint, and your modern timing light that is designed for 12 volts will be brighter with the 12 volt power source. 

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Bill , what Matt said.  Going a little farther,  I rigged up a pointer and marker on the crank pulley/dampner.  I set the engine with the flywheel marks in the window with #1 ready to fire, then marked the dampner with a white mark.

 

  Another way, use a vacuum gauge.  Hook the gauge to manifold vacuum, start the engine, adjust the distributor to get the maximum vacuum on the gauge.

 

  Ben

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Thanks for all the helpful responses.

I have highlighted the timing marks with special emphasis at TDC and 10 deg. but I can't see them even when the engine is stopped with the marks in the window. The placement of the window allows me only a view of the ring gear. I used a 12v. light source with the timing light but simply can't get lined up for a view of the marks. Two of my friends who claim to be intelligent can't make this work either. (But they are Packard guys, so who knows). Is it possible that the view window is actually somewhat out of place? Just as I'm writing this it occurs to me that I can extend the marks out onto the ring gear where I can see them in the window. The idea of getting the marks and a pointer at the dampner may be the most straightforward solution.

Use of the vacuum gauge is a new idea to me. I'll sure do that too!

Many thanks! I can't try this till a fuel pump repair is completed.

Bill

PS 

To answer hchris, carburetor is rebuilt (also tried another carb), also has new points, spark plugs and wires, coil. No vacuum leaks. Good compression. I got to the distributor by default, I guess. Any other ideas would be welcome! 

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You said the engine was rebuilt. With this in mind are you shure the flywheel was installed in the correct position? The flywheel CAN be bolted on in the wrong rotational place. Buick engineers kinda goofed by not making the bolt holes line up in only one position.  Just a thought.

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Robin,

Now that would be kind of a nightmare.....! And it sure would explain why I had not been able to see the timing marks in the window! .....And that it runs so rough over 20mph. I had thought of the flywheel position earlier to explain the rough running but convinced myself that I used old marks that were on it to replace it properly. I Can't really imagine not positioning it right. To me, the engine seems to suffer from irregular spark, not physical out of balance. It just doesn't have the rhythmic feel I would expect from an out of position flywheel.

I will have to wait till my fuel pump is returned before starting the car. Some parts in rebuild kits for the fuel pump were incorrect (very annoying and seems to happen often) so I gave in and sent it away.

I can hardly imagine having to take the engine out again, but your thought may turn out to be very perceptive.

Bill

 

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Ok, so if the distributor is suspect try a vac guage as Ben suggested; you are aiming for a steady 18 - 20 inches at idle to start with, move the distributor back or forth to achieve this. If you can get a steady idle reading then take the revs up and down and watch for steady vac changes, hesitation or erratic readings will need investigating, plenty of good info for deciphering faults on the net.

 

I find the vac guage a far more useful tool in tuning than religious adherance  to timing marks etc. with changes in fuel and so on, the original settings aren't necessarily the best for our engines anymore.

Edited by hchris
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As to finding the timing marks, can you access the front of the flywheel via a splash cover at the bottom of the bell housing ? or perhaps remove the starter motor for a better view, this would at least allow you to mark them for better visibility.

 

Of course this wouldnt solve the problem if the flywheel has been fitted incorrectly.

 

Which means you are left with how to verify the timing, painful as it may seem I would be removing the valve cover/s and slowly turning the engine by hand (two pairs of hands might be better) to get #1 at tdc, verifiable by watching #6 valves as they begin to rock, ie at the point where #6 inlet just begins to open and #6 exhaust is closing you would be at tdc #1 within a degre or two.

 

At this point you should hopefully see the distributor rotor pointing to #1 ignition lead and the points just opening, you might also chalk a mark on the  crank pulley to help bettter with tuning or further fault finding.

 

In all of this if it sounds like I'm telling you how to suck eggs, then ignore the above.?

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hchris

I've brightened the timing marks and can actually see if I try hard enough. I will need to do as you suggest to see if the timing marks are in the right position. Do I ever hope the flywheel is where it should be! Thanks much!

Bill

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My 36 Pontiac has a setup about like that, the timing mark is inside a hole where you cant really get your head to look, and even if you could there would be inaccuracy due to parralax.

 

I made a pointer for the balancer, and attached it to a bolt on front of the engine. It is round stiff wire, coathanger or similar. It is a good idea to bend it in such a way that it lays on something (in my case the top of the timing cover), so that if it gets loosened you have some hope of getting it back exactly like it was.

 

You find true TDC by putting a stop of some kind in cylinder #1 (disconnect the battery and remove all the spark plugs!). Since my engine is flathead I used a huge ziptie against the far side of the cylinder for the stop, on the OHV Buick I think the sort of a stop that screws into a spark plug hole could work. These are readily available for small block Chevys if your spark plug thread happens to be the same. Otherwise you might need to weld or epoxy a piece of steel dowel into an old spark plug housing.

 

Screw the stop into cylinder 1. Rotate the engine by hand slowly and carefully with a wrench until it stops. Make a dot on the balancer. Now rotate the engine the other way (almost a full revolution) until it stops. Make another dot. Now make a more permanent line exactly between the two dots. This is your new TDC mark.

 

I would also recommend putting timing tape (marked in degrees) on the balancer. MSD makes a set of timing tapes that cover a bunch of common balancer sizes. If you can do this, you can read advance right off the balancer with an ordinary timing light. While I love "dialback" style timing lights, I haven't had a lot of luck getting them to work on prewar cars.

Edited by Bloo (see edit history)
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I have confirmed that the flywheel is in the correct position by using the method for manually timing in the 36 shop manual. ( starting with the position of the #3 exhaust valve, turning the flywheel slightly, the timing marks end up in the window, something that could only happen if the flywheel is in the right place) Now I just need to get my fuel pump.

Thanks for all the other ideas and methods. It all goes into useful general info.

 

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