Suggestions about ybock 312 compression

I agree. Since she's running good and not giving you any other problems don't jump into a big project of trying to 'fix' it.
A few easy-to-do things to help her out like the seafoam, maybe a head re-torque, a blast or two down the road.... and enjoy driving her around.

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willowbilly3 said:
Depends on how fast the vacuum needle bounces. Valve problem is almost like a vibration of the needle and float level is more of a drifting. Since few stock, healthy engines generally show more than 165 psi in my experience, I'd say the 150 is pretty normal and the 180-190 high from carbon deposits.
Did you say that you have adjusted the valves? Often wear in makes them tighter, not looser due to the seat wearing in. My 2 cents is the factory specs are on the safe side of sloppy and I usually set them on the tight side of the feeler gauge slide.
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It is a fast vibration, I ran down and purchased another larger vacuume gauge and it barely moves and when it does it just floats up and down very little.

150 being normal or close to it is good news I could not find anything that indicates what a good or bad amount would be. 190 being caused by carbon, wow that seems like it is backwards. I thought carbon would cause less pressure do to not sealing well. I ran the freeway this morning, it ran really well and strong, I bounced around from 2300 to 3800 rpm, it seemed to have plenty of power to have kept going but I did not want to push it too much. Temps stayed normal.

When I got home, I pulled the spark plug on the lowest cylinder, checked compression and it was lower than before, I did not pull all e plugs like I did before when I checked compression, I did open the throttle, but compression only went to about 130. I was surprised to see the drop, but thought maybe the drop was do to less carbon and needing to readjust the valves after "the cleaning".

They did seem a bit looser this time, I readjusted all of them again, this time, I adjusted a tad snug to the gauge. All running smooth still. But noticed going up a steep hill it stutters and idling when I sit at a light for over a couple minutes the idle starts fluctuating a bit and I get a bit nervous it is going to stall but it doesn't. I set idle at around 470rpm.
 
It's not unusual to have a different reading between hot and cold. Again, 130 isn't bad so the difference between high and low would have needed to be noted. Carbon can build up in the combustion chambers, especially on cars that get only granny type driving and that bumps the compression. In stock form I doubt if a brand new 312 off the showroom ever did 180-190. 470 is a bit low on the idle, I'd bump that to 550-600. We could start a whole new thread that would never end on the stutter on hills, could be a lot of things.
FWIW, back in about 83 I bought a 1959 Belair with a 283. It had 100 psi in every hole (tired). I ran the stink out of it for many years and it ran great, gave it to my sis and her son drove it to high school and it probably still runs but hasn't been started in about 8 years.
 
An update after running 1/2 of a bottle of seafoam through the carb and the other half in the fuel tank. I let the engine site overnight, in the morning I ran the engine just a few minutes until it smoked, shut it off and waited again the following morning to drive the heck out of it.
I readjusted the valves with Snug pressure on the gauges this time, Here are my current numbers
Cyl = pressure before and after...

1 = 160 after 170
2 = 150 after 150
3 = 150 after 152
4 = 170 after 160
5 = 180 after 170
6 = 155 after 155
7 = 190 after 150
8 = 180 after 160

After checking compression I readjusted my timing 12* advanced at 500rpm, 40* total advance at 2500 rpm, adjusted my idle mixture screws a bit richer and choke idle to 1000 rpm during cold start, 19in vacuum, 480rpm idle, Engine seems to be purring along nicely. I will drive it around town and highway, if all is well, I want to drive to escondido 30 mile trip on a Cruise Grand night.

One strange thing, after cleaning the carbon, my oil pressure at idle is running 50psi and higher but drops back down to normal when it warms up. I am not sure where this random pressure is coming from, maybe sea foam made its way down into my oil but I am going to do an oil change before I drive her again. The engine does not burn oil at all nor does it smoke. Any thought about the pressure would be appreciated?
 
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Your oil pressure seems normal enough to me.
If I asked before I've forgotten. What oil are you using?

The 20 psi difference between the lowest and highest compression reading makes me confused, but that's normal too, so don't be concerned.

If you were working on my '55 it would be running and driveable by now. :rolleyes:

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Yes it is totally drivable, I was surprised to see such a difference in those high numbers coming down to a "normal" range, I expect they will continue to balance as I get her out on the freeway on longer trips, instead of all backroad 35mph cruising on a Sunday afternoon trips. Well for oil, I would like your opinion, since I am about to do an oil change it would be good timing, not sure what's in there now and I have not needed to add any... So what's it gonna be?
 
bobioknight said:
..... I pulled the spark plug on the lowest cylinder, checked compression and it was lower than before, I did not pull all e plugs like I did before when I checked compression, I did open the throttle, but compression only went to about 130. I was surprised to see the drop, but thought maybe the drop was do to less carbon and needing to readjust the valves after "the cleaning".
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On a Chasing Classic Cars episode Wayne C. came across a 30k original miles Stutz Bearcat(?) from the late 20's/early 30's(?). There was nothing wrong with the engine, but the head was off.
Their explanation was... due to carbon buildup from the relatively poor quality of fuel back then the compression was raised to a point the engine would knock, and pulling the head to de-carbon the engine was a relatively normal service procedure.
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dmsfrr said:
If you were working on my '55 it would be running and driveable by now.
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I was complimenting your ability, compared to mine, at having your car on the road.

Higher oil pressure when cold is normal, esp if it has a straight weight oil in it like 30w or 40w.
The multi-weight oils like 10w-30 or 15w-40 flow better when cold, toughen up when heated and are often preferred for this reason. That being said... oil brand and weight is often a matter of personal preference, local climate, and engine condition.

What to change it to?
Personally I'm following the advice of this guy...
https://www.ctci.org/gilsgarage/EngineOil.php
Chances are you can use the same oil you're using in your diesel truck.
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dmsfrr said:
What to change it to?
Personally I'm following the advice of this guy...
https://www.ctci.org/gilsgarage/EngineOil.php
Chances are you can use the same oil you're using in your diesel truck.
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Thanks for the compliment, it has been a learning process, forums like this getting advice has been a huge help. Gil's Garage, is a great source so far his advice has not steered me wrong. Thanks for pointing me to the oil page, I missed that. I do tinker on her engine a lot, probably way more than I need to or should do. But it's a labor of love for all of us here I am sure.
 
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