SHOCKED With Compression Check
- Thread starter Cape Codder
- Start date
Patrick L.
Well-known member
Bill W, Don't worry about these other guys. Some folks are just plain nasty and take things far too seriously [ usually themselves]. The vast majority here are good helpful guys that really try and they like to kid around at times. So, just ignore the others, its not worth getting upset over. If they don't like what you want to say, they don't have to read it.
just plain bill
Senior Member
Sure would like to know if Cape Codder found his problem that caused his low compression !
Purdy Swoft
Well-known member
Its just the moon!!!!!!! Bill, don't leave!!!!!!! Just let it shed like water offen a ducks back. What would we do without a Mayor??????? Nobody is perfect all of the time, not even me.
FL&WVMIKE
Well-known member
Tom Wesenberg
Well-known member
With my luck it would be a mislabeled button, and is really an ejection seat!
Yes, I'm also wondering how the compression turned out?
I usually hit the starter (all plugs out of course) for 3 compression strokes on each cylinder. Like Mitch said, I really haven't found any difference by having the throttle open.
Patrick L.
Well-known member
He may have been chased away, hope not though.
BILL WILLIAMSON
Well-known member
"Maybe" his compression guage has a tire valve core in it??? They don't work well, takes a special core for a compression guage.
I always crank them 10 compression strokes, or until the guage doesn't go up any more, and make sure the battery is charged FULLY. Compression will be higher if you have a 12 volt system. Bill W.
marc hildebrant
Well-known member
Bill W.,
Why would the compression be higher with a 12V system ? Isn't the compression just the amount of increase in pressure due to the change in volume ?
The rate that the compression happens should not effect the amount of compression which is just a function of the amount of change in volume.
Marc
Why would the compression be higher with a 12V system ? Isn't the compression just the amount of increase in pressure due to the change in volume ?
The rate that the compression happens should not effect the amount of compression which is just a function of the amount of change in volume.
Marc
Kurt in NJ
Well-known member
There is a special valve core, it has a very light spring --I don't know the # but they got us 2 boxes at work as AC valve cores (no good for ac cores, the vacuum pulled them open when trying to charge the system)
The "highest" reading from spinning 10 compression strokes is only good if you are in a contest ---one has to remember that the engine only gets ONE compression stroke to run, no more than 5 compression strokes when compression testing are needed, what happens on the first and second full compression stroke tells you more about the health of the engine than what number you can get as the highest number.
Another thing I rarely see mentioned when there is talk about compression testing is proper spark plug removal in preparation for testing --it may not matter if the plugs were just out, but if the plugs have been in a long time there is some carebon built up in the nooks between the plug and the head (some oil burning engines it is almost art there is so much), --if the plug is just removed, then the test is done some of those chunks can get caught under the valves causing a false low reading ---the proper preparation procedure would be to loosen the plugs a turn then restart the engine, rev it a few times to blow loose pieces out of the combustion chamber ---then do your compression test.
Throttle open, or closed doesn't matter much as long as all the plugs are out and all cylinders are done the same ---the reason is that with all the plugs out intake valves that are open in other cylinders allow air into the intake manifold ---if you are only checking compression in 1 cylinder and only have that plug out then having the throttle open will make a difference.
When checking compression on a modern fuel injection car the injecters should be disabled so fuel isn't sprayed causing lower and lower readings because fuel washed down the cylinders( on a 12 cylinder engine it is so bad that most all compression goes away by #10).
Most all compression testers read different, some with a long fabric corded rubber hose from $$$ tool company read lower than ones with a short steel corded hose, I have a German graphing tester that has wire inside the hose to reduce the space in the hose because the space in the hose is added to the space in the cylinder head when checking compression ---makes for a stiff hard to bend hose---this gauge prints a bar graph on a little card,( http://www.samstagsales.com/motometer.htm ) I have another tester for wankel engines, it has a roll of paper and prints a graph on moving paper, a normal gauge won't work on a wankel engine, each pulse is a seperate face (cylinder) of the rotor---every 3rd pulse is the same cylinder
The "highest" reading from spinning 10 compression strokes is only good if you are in a contest ---one has to remember that the engine only gets ONE compression stroke to run, no more than 5 compression strokes when compression testing are needed, what happens on the first and second full compression stroke tells you more about the health of the engine than what number you can get as the highest number.
Another thing I rarely see mentioned when there is talk about compression testing is proper spark plug removal in preparation for testing --it may not matter if the plugs were just out, but if the plugs have been in a long time there is some carebon built up in the nooks between the plug and the head (some oil burning engines it is almost art there is so much), --if the plug is just removed, then the test is done some of those chunks can get caught under the valves causing a false low reading ---the proper preparation procedure would be to loosen the plugs a turn then restart the engine, rev it a few times to blow loose pieces out of the combustion chamber ---then do your compression test.
Throttle open, or closed doesn't matter much as long as all the plugs are out and all cylinders are done the same ---the reason is that with all the plugs out intake valves that are open in other cylinders allow air into the intake manifold ---if you are only checking compression in 1 cylinder and only have that plug out then having the throttle open will make a difference.
When checking compression on a modern fuel injection car the injecters should be disabled so fuel isn't sprayed causing lower and lower readings because fuel washed down the cylinders( on a 12 cylinder engine it is so bad that most all compression goes away by #10).
Most all compression testers read different, some with a long fabric corded rubber hose from $$$ tool company read lower than ones with a short steel corded hose, I have a German graphing tester that has wire inside the hose to reduce the space in the hose because the space in the hose is added to the space in the cylinder head when checking compression ---makes for a stiff hard to bend hose---this gauge prints a bar graph on a little card,( http://www.samstagsales.com/motometer.htm ) I have another tester for wankel engines, it has a roll of paper and prints a graph on moving paper, a normal gauge won't work on a wankel engine, each pulse is a seperate face (cylinder) of the rotor---every 3rd pulse is the same cylinder
Mitch//pa
BANNED
compression readings will be the same at different cranking speeds. you might see a 1 or 2 lbs difference but nothing noticeable. even if you start it up with the gauge in one of the cylinders the readings will be the same...
that being said i give it 3 compression strokes to obtain a reading
the BEST way to document an engine for future reference is with a leak down test using a proper leak down tester.
that being said i give it 3 compression strokes to obtain a reading
the BEST way to document an engine for future reference is with a leak down test using a proper leak down tester.
Ed in Maine
Well-known member
Since this engine has such low miles on it, I think you may have lost the head gasket. I have found that after having the engine apart, that on restart you can see the torque drop off as much as 10-15 pounds when the motor gets hot. Do all the checks mentioned above then before you start to take everything apart I would go with a new copper head gasket, Permatex Head Gasket Sealer and then torque to 55 ft-lbs. Then after 5 minutes of running, retorque again. After 10 minutes of running, repeat the procedure. You should re-torque until there is no change in the torque values. Good luck. Ed
BILL WILLIAMSON
Well-known member
But, car's not running BAD, he was just doing a compression test to establish a baseline for future tests.
If a headgasket was that bad, stuff would be squirtin' out everywhere & it most likely WOULDN'T even run.
Let's not have the man tearing down his engine, since it's probably due to a bad compression guage or procedure. Bill W.
Last edited:
Mike V. Florida
Well-known member
Anyone else notice that it's been 4 days and no other word from cape codder on what if anything he's done to double check his readings?
tbirdtbird
BANNED
ha, happens all the time!!!
BILL WILLIAMSON
Well-known member
Patrick L.
Well-known member
That happens all the time too. Its just the way we are, we try to help. There are some that show no respect or courtesy toward others, but, they are in the minority. So, we continue to help because thats the way we are.