Suggestions about ybock 312 compression

bobioknight

bobioknight

Member
Hey guys, the Tbird has been running great, getting the correct ignition advance made a huge difference. No more vapor lock or running overly hot in traffic, or fuel boiling.... So far.

I adjusted my valves today just heard a little ticking in the passenger side valve cover and after using the 90 degree technique for adjusting valves, it's all is back to a nice sewing machine sound.

Trying to figure out what the slight 1in idle vacuum bounce is. I thought Probably valves but here are my compression numbers, let me know how these look. And what I might easily do to get my lower numbers up a bit.

Prior to test I ran a couple hours, but prior to test the engine did have time to cool down, after checking compression, I ran the motor 10 minutes or so prior to adjusting valves. I went back and retested cylinder #2 and it went from 149 to 150. Not a big difference. By the way the engine was rebuilt 8 years ago and rarely driven, until lately.

Cyl = pressure
1 = 160
2 = 150
3 = 150
4 = 170
5 = 180
6 = 155
7 = 190
8 = 180
 
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The general rule of thumb about differences in cylinder pressures is they should be within 10% of each other. With a high of 190 and low of 150 your difference is ≈20%.
Enough of a difference to work at correcting it, and may also be the cause of the vacuum bounce.

My first suggestion would be to re-adjust all the valve clearances using a different procedure to arrive at TDC firing stroke for each cylinder, no shortcuts. If it involves turning the crank around more, that's fine. It might rule out some 'close but no cigar' variables, or at the least confirm the valve clearances are what they should be.
What valve / rocker clearance are you using?

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This is the technique I am using to adjust the valves. In case of wear on the valve seats feeler gauges could give you inaccurate settings, so I do this procedure and double check it with the feeler gauge. My rockers are stamped b2, the .019 gauge slips in easily with some resistance but not a lot.

(Get into the engine, with the lifter all the down obtain some tappet clearance then carefully rotate the adjust screw clockwise to obtain .000 valve lash. Just touching but not depressing the valve. Now rotate the adjust screw counterclockwise 90 degrees. The resulting clearance should be very, very close to .019 regardless of rocker arm face wear.)

Since the last rebuild (8 years ago) the car was driven short trips under 5 - 10 miles at a time, then sit for a month, driven, sit, drive, ect... Over the last year I have driven it a couple times a week weather permitting, but at cruising speeds through town.

I expect there is a lot of carbon build up in those cylinders, having never run long enough to burn off the rings and valves.

Would anyone suggest that as an initial step, I run a bottle of sea foam into my vacuum hose, until it stalls, let it sit overnight, and then run the heck out of it on the freeway. WOT.
 
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90° on the adjusting screw. I had that confused with placing the crank at #1 TDC, adjusting some valves, turning the crank 90° and adjusting other specific valves... repeat until all are done. Which may or may not be a real thing.

Double checking with a feeler gauge after the initial 90° screw turn is the way to go.

Short drives are not a good idea. It's best to get the engine up to full operating temp for at least 15 to 20 minutes every month or two. It helps remove most of the things that can contaminate motor oil or corrode the insides of the engine.
SeaFoam is well regarded by lots of folks, I've not tried it so have no personal opinion.
If you put it into the vacuum hose on the intake manif. above cyl #8, it may not get to the front cylinders.

Since the passenger side readings are generally lower than the driver side and the engine doesn't have that many miles on it...
what does anyone else think about double checking the torque on the head bolts???

A long run down the highway is always a good idea, unless you meet someone with a radar gun & ticket book :rolleyes:
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What? Do you think an officer would give a classic carbeurated car a ticket for legitimately burning off carbon. My dad told me some stories about getting pulled over as amid burning off carbon, cops would allow it at the time, even follow for safety. Covina California.

is it the distance at WOT that burns off carbon, or just driving long distance at normal speeds.

I also watched a you tube videos where a guy would not go all the way to .019, I think he suggested .015 not sure this is a good idea or not, but is anyone else doing this?
 
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bobioknight said:
I also watched a you tube videos where a guy would not go all the way to .019, I think he suggested .015
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Lemme put it this way...decreasing the gap increases the amount of time that the valve is OPEN during a given cam revolution. Increasing the gap decreases the amount of time that the valve is open during a given cam revolution.
Be very aware that when using a feeler gage, the bottom of the rocker arm surface has a STEP in it that can easily throw you off by MANY thousands of an inch. It is best to use a wire type feeler gage (inserted right in the middle of the valve stem to miss that step).
Make sure you engine rotation is where it should be for that valve adjustment. The shop manual has some excellent information which is very useful here !
 
bobioknight said:
... I also watched a you tube videos where a guy would not go all the way to .019, I think he suggested .015 not sure this is a good idea or not, but is anyone else doing this?
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With the adjustment too tight the valve spends less time closed against the (cooler) head, which can overheat the valve.
Burning a gap into the valve's sealing surface and overheating the valve stem are the usual result. Unless an engine has a special cam or valve train the recommended setting should be used.
You can ask me about the road trip that three of us spent a weekend swapping out an engine, in an out of state motel parking lot... the result of a swallowed valve.
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dmsfrr said:
You can ask me about the road trip that three of us spent a weekend swapping out an engine, in an out of state motel parking lot... the result of a swallowed valve.
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Boy is that worse case scenario. Yea, I will leave it .019 as specified. I will get a wire style gauge to double check my work. Thanks.
 
Ok so back to the sea foam question, if I pour it into the vacuum line, I get that it might not run into each cylinder evenly. However, if I do this and see an increase in some of my cylinders that would be a good indication that carbon is the issue. Has anyone else here tried this. There is also a spray version which I could spray directly into each cylinder and let it sit overnight, I just don't have experience with rings to know if fluid even reaches them when applied in these ways? So has anyone ever experienced increased compression by either pouring sea foam or a long distance drive..... Or any other way?
 
Putting any liquid in should increase compression, it can't compress. A better way to check condition is with a leak down tester.
 
Two comments; pouring liquid to store or clean an engine is easy. If for long term storage, I use ATF. For cleaning valves, I use water. The use of Seafoam is better. Simply pour down the carb, slowley at first, when it comes out both exhaust pipes as white smoke, increase the pour rate so the bottle is empty as the motor dies.
Valve adjustments, most books call for .019. Some older books called for .018. For a stock engine, those are good numbers. My engine had a cam from Iskenderian. They said I could lower the lash to increase the lift and dwell. I had SS aftermarket valves, so they were OK with reduced lash. I ran my lash at .016 for years, and less while racing. I never did install hard seats. My valve seats were OK.
 
Ok tonight I ran sea foam into the carb, sputtering smoking, idle rough... Kept pouring until I used up about half a can. Tomorrow night I will run the heck out of it and recheck my compression on the number 2 cylinder which was the lowest and see if it increases after a night of sitting. If I don't see an increase I will do a leak down test.

Before my test run I will would it be a good or bad ideas to retorque the head bolts?
 
bobioknight said:
Before my test run I will would it be a good or bad ideas to retorque the head bolts?
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I've not had to do this myself so I looked thru other FordBarn posts.
The answer I found was... 'It couldn't hurt.' and in a few instances it did help.
 
No, he is not kidding, water works. usually used to de-carbon the valves. a mixture of atf, and brake fluid also works . I usually use water or straight atf. G.M. used to make a product called Top end eng. cleaner that worked very well. I also think you misunderstood about taking a compression test and then squirting oil in the cyl's. . it is called a wet and dry test . dry first then wet (oil squirted in ) the correct way to do a compression test is on a warm eng. throttle plate wide open and all plugs removed. do a check on each cyl. and record it. then go back and do the test again ,but squirt a little oil in the cyl.first. if the compression comes up your rings are weak If it does not, your problem lies elsewhere. letting the vehicle set over night to recheck compression will probably not show any difference
 
bobioknight said:
Are you being serious or pulling our leg.
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Serious. It's kind of a "touch" to do it right. I get a gallon jug of water, start opening the throttle as I trickle water in (warmed up engine). More water and more throttle until it's wide open and the amount of water going in is keeping the rpms about 2500. One jug is usually enough but I did an old ladys 460 Lincoln in my shop once that needed 2. The cloud of brown smoke was amazing.

I'm kind of a "if it's not broke don't fix it" guy and I don't really see a big issue although it is beyond the 10% differential. I would suggest you do the test with a different compression gauge. Decarboning it doesn't cost anything. If you don't drive it a lot, like every day to work, and it's running ok, not pinging then don't fret too much over it.
 
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willowbilly3 said:
I'm kind of a "if it's not broke don't fix it" guy and I don't really see a big issue although it is beyond the 10% differential. I would suggest you do the test with a different compression gauge. Decarboning it doesn't cost anything. If you don't drive it a lot, like every day to work, and it's running ok, not pinging then don't fret too much over it.
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Well guys, it was rebuilt 8 years ago with very little driving since, maybe once a week or month cruise the back road to the shooting range. Nothing that would burn off carbon, so now that I own her, I want to drive all the time and burning off carbon could be fun... My compression is 190 - 150 which is 20% difference so I expect I do have an issue, but the engine does not burn oil, the coolant looks brand new and it runs good, but my vacuum bounces 19-20 which indicates valves.

I adjusted the valves, but if there is carbon built up then I am not sure the adjustment would be correct, so I will burn off the seafoam today, run her a little hard today, do the water thing, readjust the valves and see what happens...

Does that sound like a good plan?
 
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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