Technical -54 engine, -56 (or later) head

I just realised (after checking the cast numbers) that my -54 Chevy has a -56 or later head (cast 3836848).
How is it different to earlier head?

 

More compression.

 

Yes, that I found out searching the net. Hopefully better mileage and a bit more torque.
Shall I do something different doing a tune up. Different gaps on plugs etc?

 

No, it should work with the same specs.

 

Ok, thanks.
Maybe you can help me with this other problem too.
Why does the dizzy move clockwise while revving?

Oh, I may just have found the answer.
115hp 235 distributor is meant to move clockwise!!!
Who knew... ...not me.

 

Vacuum advance. Actually, that's retard, as vacuum drops when you open the throttle.

 

Should revving advance the spark time not retard it? Let´s say constant 1500rpm and the advance should be there with vacuum (not weight/springs)?

 

There are two advance devices. Revving it will advance the timing (this happens inside the distributor), while opening the throttle more will retard timing (the whole distributor rotates).

 

Actually there is three on these engines. Normal vacuum, mechanical + octane selector.
Still, that doesn´t explain the turning on my dizzy.
Here´s a little u-tub video showing how it should move.

 

"Octane selector" is really just setting the initial advance, it is not something that changes on it's own.

Look carefully at the vacuum advance mechanism. The distributor housing is clamped to one part of it, the other part (with the vacuum diaphragm) is bolted to the engine block.

 

You might want to use a timing light, and see what the timing is actually doing under different conditions. It's not easy on these engines, though, since the timing pointer is so hard to see (the hole in the bellhousing, and the steel ball in the flywheel)

 

I agree about the octane selector, it´s there just to ease minor adjustments By the owner/mechanic. Still I can´t seem to figure out why there is different movement between my dizzy and the ones I´ve seen on many videos (like the one I just posted).

 

Agreed, the placement of the bb and pointer are plain stupid. Anyway, I do have a timing light and I´ve used it on many cars and occasions with great results.
Now I´m just baffled.
Maybe I should just quit and buy more bicycles .

 

If it is a true 54 it has shimed mains an or tough to stop a rear main seal leak. 55-62 were better; if you find this, clocking the rope seal will help. Good luck

 

Look at where the vacuum advance tube is connected to the carburetor. If it is connected to the ported vacuum connection, then it will not get vacuum until you open the throttle. If it is connected to the manifold vacuum, then it will get vacuum at idle.

 

What does "clocking the rope seal" mean?
Sorry, english isn´t my strong point.

 

It´s up there on the original carb, where it´s supposed to be on these Blueflames.
Also, when I unplugged it from the carb and sucked it, it moves ccw.

Wait a minute.
I just (maybe) realised something.
maybe the problem is too high idle speed.
I work alone so I, ve no way to see the dist when I start the car, so I dont see the initial movement of the dist. I can visualize it only when it´s running, so maybe there´s vacuum pull already and when I rev it a bit it makes the vacuum drop.
Dough! I don´t know.

 

So, does the action of the vacuum advance make sense to you? or are you still confused?

 

Don't put the split on the centerline where the cap meets the block. With a neoprene seal split seals on a SBC they tell you do it in the instructions. With a rope it's harder. First you drill 1or two holes for a 6-23 set screw on the cap. You then put the seal together on the split. Then you remove the cap and crankshaft, remove the crushed upper rope seal carefully, place it back in with one side up about 3/8-1/2" up, replace the crankshaft, put in the cap rope seal in to match the block seal. When torqued correctly screw in the 1-2 6-32 set screws, sometimes the set screws need to be part way in so you can get between the crank flange and the cap. On a street engine you probably don't need the set screws. Also cram as much as you can of the rope seal in the slot. It should be hard to turn over the crank until it frees up.
This not easy but it's part of my blueprinting. Good luck .

 

It´s starting to sink in
Vacuum takes care of needed advance on low rpm when engine still is able to create vacuum and when
rpm increases and vacuum becomes less/none then the mechanical advance takes controlWhere is the change point? How do you find/alter it?
So, back to the problem I have. Idle is pretty good, little vibration (mayde due to the Isky Cam + valves)
but constant mild rpm driving (normal street driving) is bumby, stuttering. So,what to do?

 

The vacuum advance is used to retard timing when the engine is under load. When there is little load on the engine, the air/fuel mixture is not very dense (high vacuum), so it takes longer to burn, so it needs to be ignited sooner. When there is load on the engine, the mixture is more dense, and burns faster. So it needs to have the ignition happen later.

The mechanical advance is used to advance timing as RPM increases. The mixture takes a certain amount of time to burn, so the faster the engine is running, the earlier it needs to be ignited, so it will finish burning when the piston just starts to go back down in the bore (the beginning of the power stroke).

As to your problem: if you change the initial timing, does the running get better? or does it get worse or not change? It could be a mixture problem, (too rich or too lean), not a timing problem.

 

I have to take my time tomorrow and just keep trying different combinations of timing and mixtures. I did go to a autoshop earlier and they checked the exhaust levels and said it was ok.

 

Under what conditions was it OK? Did it run on a chassis dyno when they checked it? or just idle?

 

Unluckily just idle.