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Compression Test Results for BJ8

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pkmh

pkmh

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Finally, I performed a compression test, but only as a cold test or letting the engine idle for a couple of minutes first.

At some point, I will want to do a compression test after the car has idled for about a half hour. I assume the results will differ but hopefully, with similar close proximity, yes?

But for now, I have recorded the results and would like to know if the results are good so far. I have seen from other threads how numbers can go as high as 180 or maybe more. Because my numbers appear relativily close to each other, that seems promising to me. True?


Starting with the #1 piston and then recording the rest, next in line, the results are as follows:

#1 piston = 145 lbs.
#2 piston = 151 lbs.
#3 piston = 153 lbs.
#4 piston = 149 lbs.
#5 piston = 145 lbs.
#6 piston = 144 lbs.

Anything else to know, add or advise, please feel free to do so and thanks!

Paul
 
Percentage wise, the numbers are within the range of worn, but satisfactory. What you really need to do, to determine the condition of your engine, is do a leak down test. And, why would you let an engine idle for half an hour? You only need to have the cylinders oiled to give you good compression readings.
 
Maybe I didn't do the compression test properly?

What I did for each cylinder was hook up the compression tester at one spark plug opening at a time and simply did a number of cranks for each or until a maximum read out was made on the gauge. The engine was not idling at any point of this test. Was that the way to go?

That being the case and if I did it incorrectly, what is the correct procedure or is there a link out there that would make it clear the proper way?

Thanks again.

Paul
 
All plugs out, too, or it won't crank well or long.
Numbers within 10% are good.
Finding a compression gauge with a recent laboratory calibration sticker is what is normally referred to as "impossible". No one knows if they're right (on the numbers) or not, hence the 10% variance between readings.
I do 5 hits......doesn't matter, as long as the same number are done on each hole.
If you get 150 on one hit on one cylinder, and it takes 15 hits to get 145 on the next, that's a problem.
 
Okay TOC, I will try it again with all plugs out.

When you say to do five hits, I am not sure you mean five crank rotations or five equal attempts on each hole (or both)?

Thanks for that.

BTW, I finally found the one link which explains compression testing simple enough and covers all that has been mentioned above, including how to tell if you have a bad gasket, bad valve, worn pistons and rings, so thanks for all the good advice.

Paul
 
10 crank rotations give 5 compression strokes. With all plugs out, you'll know........whirrr.....whirrr...whirrr....POOF!....whirrr...whirrrr...whirrrr.....POOF!

You are even enough that oiling of the cylinders probably is not needed (that would show poor ring sealing). You do oil after you do a baseline and record the readings. One squirt from a pump oil can in each hole, run the engine with starter a couple of seconds to distribute, and do it all again. Any noticeable increase is rings.
 
Some folks use two hits, some 4, some 10. All really a matter of preference, methinks. The shops I ran we settled out on 5.....that way we all had comparable readings. Just make the all the same. If you goof up, do 4 or 6, and the rest are 5, release the pressure valve and do it over on that one cylinder.
 
Sorry TOC. Progress is always on the slow side. And besides, I just finished syphoning the gas out for a new gas tank is on it's way now. Really need to revamp the fuel system.

But when I get back to doing the compression, I will refer here and try again and let you know.

Thanks for the info.

Paul
 
No Keoke, not yet anyway.

My car died in another town due to what I believe to be from lack of fuel reaching the carbs. I am positive the fuel pump is full of crud and the tank has got a lot of rust in it. Not soon after placing a new fuel filter before the carbs months before did it start accumulating with rust deposits.

So with a new fuel pump and tank plus another fuel filter (to be placed before the fuel pump), I hope I will not have any more stalling problems. I may have to go back and do a partial overall of the carbs again. If anyone can advise what I should use as a sealant(?) when I install my sending unit and whatever else is in store for me with the tank, etc., let please do me the honor of letting me know. Thanks in advance!!

I did do some other testing related with electrical, such as installing another new condenser, ignition coil, distributor tension wire plus checking the timing. Problem still persists. I already had installed a new cap, rotor, plugs, points and wires so that's out. I'm pretty sure it's the fuel system that's giving me grief.

So for me, no more driving the car this year. I also have to pull out the Brake Master and send it back to Moss. I am a victim of that recall they had over the summer although I probably fixed that bushing piece by doing a further crimping of the metal clip found behind it, but maybe later on I will know for sure.

Have a nice Thanksgiving all.

Paul
 
pkmh said:
No Keoke, not yet anyway.

My car died in another town due to what I believe to be from lack of fuel reaching the carbs. I am positive the fuel pump is full of crud and the tank has got a lot of rust in it. Not soon after placing a new fuel filter before the carbs months before did it start accumulating with rust deposits.

So with a new fuel pump and tank plus another fuel filter (to be placed before the fuel pump), I hope I will not have any more stalling problems. I may have to go back and do a partial overall of the carbs again. If anyone can advise what I should use as a sealant(?) when I install my sending unit and whatever else is in store for me with the tank, etc., let please do me the honor of letting me know. Thanks in advance!!

I did do some other testing related with electrical, such as installing another new condenser, ignition coil, distributor tension wire plus checking the timing. Problem still persists. I already had installed a new cap, rotor, plugs, points and wires so that's out. I'm pretty sure it's the fuel system that's giving me grief.

So for me, no more driving the car this year. I also have to pull out the Brake Master and send it back to Moss. I am a victim of that recall they had over the summer although I probably fixed that bushing piece by doing a further crimping of the metal clip found behind it, but maybe later on I will know for sure.

Have a nice Thanksgiving all.

Paul
Click to expand...
Be sure to blow out all fuel lines before installing new pump, tank, etc. I'm speaking from personal experience!
 
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