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Hi Brad...I have someone working on my 1985 HD 1000 Sportster and he is looking for what the proper compression reading should be. We have a complete maintenance manual, however, are unable to track it down. He has a compression tester and is reading around 140.....He is thinking it should be around 180. My understanding is those readings are "psi". All we have been able to find is "ratio". I hope I am saying this correctly...and thank you very much for your reply. David

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In the absence of a specific compression pressure, you can right down all the pressure reading on each cylinder. The lowest reading should be within 75 percent from the highest cylinder press reading and your engine is fine.

Posted on Jun 12, 2014


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Posted on Jan 02, 2017

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In reality, you do not need to know the ratio to check compression. Normally you are looking for compression readings of about 120psi with no variations of more than 20%. Testing should be done with ignition disabled and throttle held wide open. Use same number of revolutions for testing each cylinder.

Posted on Apr 29, 2009

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My car run by fuel and Natural Gas, when I convert the fuel function from gas to fuel the malfunction signal appear, but by do not stop after some time this signal off. my car is toyota.

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Ckeck the ground wire located near the sensor... this causes this problem

Posted on Feb 28, 2009

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The fault may very well be with the tester itself: The compression tester should have a check or "HOLD" valve which causes the needle on the gauge to REMAIN at it's highest recorded point. For example, my 1993 Isuzu Rodeo had a compression of 160 psi. The gauge "holds" the needle at the measurement UNTIL THE VALVE IS RELEASED-(mine had a button that needed to be pressed to release the pressure) then there will be a slight discharge of the pressure contained within, the needle should drop back to zero, and THEN you should be able to remove the tester. What I am getting at is if the pressure drops that fast, I think the "HOLD" valve on it may be defective, OR the tester is not properly sealing on the combustion chamber (stripped threads?). Might be worth buying another one for 20$ just to be sure.

A four cylinder engine, you say? Very rarely will you have ALL of your cylinders exhibit the same pressure loss symptoms. How did the other three cylinders test?

Here are the components required for a running engine to fire:
1-good spark (adequate voltage, good plugs/wires)
2-dedicated fuel supply (fuel pump with adequate pressure)
3-timing (slack in timing chain/belt?)

If the timing belt broke or maybe even jumped a tooth or two, it COULD cause DAMAGE to your engine-pistons hitting valves-if it IS what they call an "INTERFERENCE" engine.

Hope this helps.

Posted on Dec 31, 2009

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SOURCE: 1968 beetle over heated and now it wont start,did

This sounds like a classic case of blown head gasket.

You seem to know some about cars, however I will attempt to give you my best answer.

You have a gasket that seals the engine to the head, when you over heat this gasket gets punished and in some cases the head can get warped and the seal between the engine and head is lost resulting in your loss of compression.

You need to remove the head for a better look, take the head to a machine shop and have them check it for warped condition, if so see if it can be machined flat, also look into a rebuilt head, it may just be cheaper to do that then the work to fix your original.

As well your going to have to find the reason the car over heated in the first place..

This might be a good time to see if the car is worth fixing?!

Posted on Dec 29, 2010

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The compressions you mentioned...Good?
No. Not at all.
Those compression reading indicate either really bad/worn piston rings, or valves that are not sealing properly, or both.
Normal compression readings should be at or above 140 PSI, +/5 5 PSI difference, no more.Save your money, and look for another unit. This engine is going to cost you a lot of money to make it right.

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