272" y-block cam timing

[40cpe]

I have a 272" that was professionally rebuilt, don't know the rebuilder's credentials. Chasing low vacuum for power brakes, I found it at 13" vacuum at 10 degrees advance and carburetor adjusted to max vacuum. 28 degree dwell. It has a Edelbrock 600 carb. I adjusted valves and raised static time to 22 and got it to 17". I made a 30 mile drive Saturday in 85 degree weather with the AC on and it ran at about 200 degrees. I haven't tried to verify TDC with the bottom pulley timing marks. The radiator core appears new, can't verify that, but all the fins, etc, are as new. What effect would the timing chain marks being off have on vacuum and operating temperature? What more could I check? It has been a long time since I've driven a y-block, but it seems to run, rev, and idle good. Thanks in advance, Gene

[dmsfrr]

Originally Posted by 40cpe

....I haven't tried to verify TDC with the bottom pulley timing marks..... What effect would the timing chain marks being off have on vacuum and operating temperature? What more could I check? It has been a long time since I've driven a y-block, but it seems to run, rev, and idle good. Thanks in advance, Gene

Timing chain... depending on how far off it is, it wouldn't run well and the vacuum and compression would be low.
It won't hurt to do a compression test, and you'll have baseline readings for the future.

It's possible the damper pulley ring with the timing marks on it could have slipped if the rubber is getting too old.
If you don't mind taking the passenger side valve cover off and spark plugs out it's not too hard to check. You may need a helper to turn the engine while you're watching things up top.

Looking at the engine from the front, turn the crankshaft clockwise until the cyl #1 intake valve opens and closes. (it's the 2nd valve back from the front of the engine) Then with your left little finger down in the #1 spark plug hole, about a 1/4 turn more. You should feel air coming out & the piston stop moving upward. With the #1 piston in this TDC position the "0" marks on the pulley and timing pointer should line up.
If you're really curious and remove the crank damper pulley bolt & washer, the crank keyway should be at 7 o'clock.

Except for 'approx 1/4 turn more to #1 TDC' this unfortunately won't tell you if the cam is slightly out of position in an assembled engine. Maybe someone else knows how to do that.
.
The parts in these example photos won't look identical to the ones in your car, they're on a 292 T-bird, but the procedure and misc. positions are the same.

[40 Deluxe]

Originally Posted by dmsfrr

Timing chain... depending on how far off it is, it wouldn't run well and the vacuum and compression would be low.
It won't hurt to do a compression test, and you'll have baseline readings for the future.

It's possible the damper pulley ring with the timing marks on it could have slipped if the rubber is getting too old.
If you don't mind taking the passenger side valve cover off and spark plugs out it's not too hard to check. You may need a helper to turn the engine while you're watching things up top.

Except for 'approx 1/4 turn more to #1 TDC' this unfortunately won't tell you if the cam is slightly out of position in an assembled engine. Maybe someone else knows how to do that.
.
The parts in these example photos won't look identical to the ones in your car, they're on a 292 T-bird, but the procedure and misc. positions are the same.

Try this: With the passenger side valve cover off as noted, roll the engine over and watch the front rocker arm (#1 exhaust) open and begin to close. When it is almost closed, the intake valve will begin to open. What you want to do is "equalize" the opening and closing of each valve. That is, both valves need to be open an equal amount (exhaust about to close; intake just starting to open). You can lay a straightedge across the valve retainers and rotate the crankshaft (with a socket and breaker bar on the pulley bolt) until the straightedge touches both retainers equally. When this is done, the timing mark on the pulley should be at top dead center or within a couple of degrees. If not, either the timing chain was installed wrong or the dampener ring has slipped.
To do a rough check of the ring, put a temporary top dead center ('0' degrees) mark on the pulley in line with the pointer and ,using the original marks as a guide, put another mark at 10 degrees advance. Start the engine and set timing at 10 degrees using the temporary mark. If it now runs normally, the ring has slipped. For a more precise check, buy/make a piston stop that goes in the spark plug hole and use the degree wheel method.

[40cpe]

40 Deluxe, I think I understand the valve overlap check, at that position the #6 cylinder would be at TDC, right?

I don't quite understand the timing mark check. I think I would put a temporary TDC mark at the pointer at the position above. Then 10 degrees advance to this temporary TDC mark? Where can a Y-block piston stop be bought? I know an object can be placed in a flathead spark plug hole and fed down above the piston to use as a stop. I'll work on aligning the valve overlap later today. If the ring hasn't slipped AND the timing chain is installed correctly the pointer should align (approximately) with TDC on the ring?

Thanks to both of you for the advice. I know it took a good bit of typing.

[Ole Don]

When you are happy with you cam timing, try a smaller carb. I found that a 500 CFM Edelbrock on a four hole two inch high spacer gives the best low speed and mid range throttle response. If you normally drive at 5000 RPM and above the 600 would be perfect.

[dmsfrr]

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Originally Posted by Ole Don

When you are happy with you cam timing, try a smaller carb. I found that a 500 CFM Edelbrock on a four hole two inch high spacer gives the best low speed and mid range throttle response. If you normally drive at 5000 RPM and above the 600 would be perfect.

40cpe, here's a link to a cfm calculator.
https://www.summitracing.com/experta...cfm-calculator

Yes the vacuum secondaries do compensate for the carb being oversize but a smaller one will potentially be more efficient for general use. Just FYI: the cfm rating of the oem '57 312 single 4bbl Holley carb is approx 410.

[40cpe]

I agree that carburetor is too large. I haven't had this car long and am trying to sort it out. I might eventually go to a two-barrel. Being what it is, it will never be a race car.

[40 Deluxe]

Originally Posted by 40cpe

40 Deluxe, I think I understand the valve overlap check, at that position the #6 cylinder would be at TDC, right?

I don't quite understand the timing mark check. I think I would put a temporary TDC mark at the pointer at the position above. Then 10 degrees advance to this temporary TDC mark? Where can a Y-block piston stop be bought? I know an object can be placed in a flathead spark plug hole and fed down above the piston to use as a stop. I'll work on aligning the valve overlap later today. If the ring hasn't slipped AND the timing chain is installed correctly the pointer should align (approximately) with TDC on the ring?

Thanks to both of you for the advice. I know it took a good bit of typing.

1. Right
2. Yes, 10 deg. from the temporary TDC mark.
3. Summit, etc. sell them but since you have 18 MM spark plugs you may have to make your own. Just knock the porcelain out of an old plug and thread it for a bolt.
4. Yes.

[40cpe]

I followed 40 Deluxe's instructions and the spring retainers were level when the factory TDC mark was on the pointer. It didn't take much movement of the pulley from TDC mark to make it obvious they were not level. I pretty confident now that TDC mark is correct. I don't know how much out-of-level to expect the retainers to be if the marks on the chain were off 1 link, but they were right on best I could tell. I held a light on the underside and there was no gap on either side.

[40 Deluxe]

Next check the ignition mechanical advance. If it doesn't advance the timing as RPM's increase, the engine will run hot and power will be down.

[40cpe]

40 Deluxe's last post prompted me to realize that with the .68 overdrive I'm only turning about 1600 at 60 mph. I was curious what my advance was at that rpm. The total mechanical is about 22 degrees and is about 15 degrees mechanical advance around 1600 rpm. Total vacuum is about 22 degrees. I need to drive the car with the vacuum gauge in the car to see how much vacuum I'm pulling under road conditions. I know my gearing isn't optimal (3.25 rear, 27" tires) and is probably loading the engine too much. The rpm is about 2500 in 4th gear, so I 'm confident that the timing is sufficient in 4th. I can vary the initial timing to obtain adequate timing. Is there an opinion about how much total advance and how much total plus vacuum is required?

[dmsfrr]

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[dmsfrr]

Originally Posted by 40cpe

..... Is there an opinion about how much total advance and how much total plus vacuum is required?

I'm guessing there are too many equipment, condition and fuel variables to come up with
a one-size-fits-all total timing advance number.
The answer is likely, 'a little more, but not too much'. If the mech and vac parts of the distributor are working correctly... advance the timing a bit at a time and note if you get ping/pre-ignition knock in the engine on hard acceleration, then back off the timing advance until that goes away. You might end up at about 10 degrees of initial timing advance.

.

[40cpe]

I took it down the road to check vacuum while driving. On level roads at about 60 in 5th gear (~1600 rpm) it should have 15 degrees initial, 15 mechanical, and around 10 vacuum. Same speeds in direct it should be 15 initial, 22 mechanical, and 15 vacuum. After it was full warm I drove about 5 miles in each gear and didn't see any temp difference.

[miker98038]

I'm assuming your right about the timing marks. If so, you're in the ballpark for total initial, total, and vacuum advance. If anything, maybe on the high side. If you've got a hand vacuum pump (they're cheap and also bleed brakes) you can check were the vacuum advance comes in. How are you arriving at the temp reading-original gauge, aftermarket, or infrared?

I think the 15 inches at 60 in direct is about right. Big car, 272, etc.

You're right about the gearing, 5th might be a bit too tall for 60 mph. More important, you might be right on the edge of tipping into the power enrichment circuit at 10 inches. The Edelbrock manual will give the springs rating by color if I recall correctly. You can check those by just pulling the air cleaner and the metering rod. Might also be worth a look somewhere down the road.

[40cpe]

I have a vacuum pump and checked the vacuum advance to start at 6" and all in at 15".

It was running about 17" in direct (4th) and 12-14" in OD on level ground.

I'm watching the original gauge and using the infrared to determine the temps at various gauge readings. I'm reading on the manifold side of the thermostat and at the temp sending unit. Dead on hot on the gauge shows about 205 on the infrared. I've let it sit after turning it off on about 200 degrees and checked it after the heat soak and read 210 on the infrared and the dash gauge was above the hot mark. No gurgling or bubbling at that temp.

I'm about to decide that the AC condenser blocking air and adding heat to the incoming air is a little too much for the radiator to handle.