Some Compression Numbers

[Slipknotcraig133]

Compression Tested my motor tonite and i found out its time for a rebuild. On cylinder number 1 i have a 120lbs, number 2 is 122lbs, number 3 is 120, and number 4 is 121. So its time for a rebuild. Arnt the a20a3's supposed to have like 180 stock. If 180 is correct then my motor should have 720 total lbs of compression. As is right now i have 483 total lbs. So that means that i am only getting 67% of compression compared to stock. That means that its rebuild time. Im wonder what kind of rings, bearings, and gaskets you guys are running. Also what other parts do you guys recommend changing besides oil pump, water pump, and seals.

[Busted_Blue]

I just did my compression tests a month ago and I got about 160-170 for all cylinders.

[1987HondaAccord]

how do you do a compression check? do you just get the compression guage and put it in the spark plug hole and then turn the motor over by hand?

[Busted_Blue]

how do you do a compression check? do you just get the compression guage and put it in the spark plug hole and then turn the motor over by hand?

crank the motor with the ignition.

[88Accord-DX]

Take the coil wire off the coil to the distributor also. You don't want the spark plug wires arcing anywhere.

[smufguy]

142 psi is the lowest acceptable pressure. like u said, ur motor defenitly needs help

[AZmike]

Did you remove all the spark plugs and prop the throttle open? Those numbers seem too similar to me. Why are you checking the compression?

[Blkblurr]

The compression from the factory is 10.1 to 1 I believe. If your atmospheric pressure is 14.7 psi you will get 148.47 psi. It just depends on the air pressure of the day. You can get slight variations day to day but more importantly, your altitude makes a big difference on final pressure read.

[SteveDX89]

The compression from the factory is 10.1 to 1 I believe. If your atmospheric pressure is 14.7 psi you will get 148.47 psi. It just depends on the air pressure of the day. You can get slight variations day to day but more importantly, your altitude makes a big difference on final pressure read.

A20 compression ratios are 8.8:1 - 9.3:1 depending on which model you have.

[Versanick]

Atmospheric pressure is actually usually less than 14.7. Multiplying 8.8 x 14.5 for example (a more resonable actual psi number for ordinary, still air)...

This shows that 127.6 would be pretty close to 100% optimum psi within the cylinder and head.. so whoever's showing 170psi would probably either be hauling ass, about to blow up their motor, living in Death Valley, or actually knowing the correct formula to figure this out.

Using basic physics, the 127.6 psi makes sense. So all of the compression numbers around 120, not assuming your cylinder was at PERFECT dead bottom, and that your gague isn't totally 100% accurate, and that we don't know exactly what the atmospheric pressure was when you tested it.... your numbers are DAMN good.

I would contend that all having very similar numbers, and all being around 120 is a sign of GOOD compression. I suppose I could be wrong. But I've taken a lot of physics. And I don't see how anything over 130+psi is possible here..

Busted blue got 170.... I don't know how that works, but hopefully you'll get some better input from people who have tested it like him. I guess these things don't always make sense.

[smufguy]

i dont know wtf you are talking about, but 171psi for the cylinders is the normal compression number from the factory. i pulled 154psi on all cylinders except for cyl 1.

[AccordEpicenter]

86-89 accords with the A20 engine is 9:1:1 for carb and 9:3:1 for FI. If it doesnt smoke and runs good, 120psi doesnt sound terrible awful, but maybe on the low side

[shepherd79]

120psi is way too low.
stock engine should be pushing 180 psi no problem.

you can get engine rebuild kits from autozone or advance auto or online.
they all will do just fine.
make sure you take your block to a shop and let them work on the cylinders.
plus it is a good idea to take the valves out and grind off the deposits. you may want to grind them into the cylinder head for proper seal.

[AccordEpicenter]

what kind of tester are you using tyler? Also, how many miles do you have?

[Slipknotcraig133]

Im using one of the press in testers. I did each cylinder 3 times and got the same numbers each time. My car has 181K on it and i am somthing like 4000 feet and it was around 45 - 50 deg.'s when i did the test. Yea i have a spare motor and thats the one that im going to do the work to. That way i can just rebuild that and not have to worry about not having a car for a while.

[modu03]

first off, you should always use the screw in type testers, the press in testers always leak.

it doesn't matter what altitude your at or temperature, it will not change the reading enough to matter. on the stock engine you should have 178 psi in perfect shape... i tested my old 87 hatch at about 165-170 for all cylinders with 212,000 miles on it. that's a pretty good psi for a car with even 100,000 miles on it

get a scew on type and retest... if you still get anywhere below about 140 psi, the engine definitely needs a rebuild

also, you need to disable the fuel. just pull the under hood fuse for the injectors. then prop the throttle body open, remove all spark plugs, and attach the tester

you want to turn the engine over by the starter 7 times, this will give you the most accurate measurement. if you are low on compression, try putting about a teaspoon of oil into the cylinder through the spark plug hole and run the test again. if the compression goes up quite a bit, then your rings are the problem, if it doesn't change much, it's probably a leaking valve or head gasket.

hope this helps

[Slipknotcraig133]

Thanks man ill try that out.

[AccordEpicenter]

you MUST hold the engine at WOT to test it

[FyreDaug]

Let us know the new numbers.

[3gn86lxi]

I had 160ish on all four cylenders. And thats with 240000 miles. I would definately say that 120 is low.

[rjudgey]

Re-do test as advised having the TB open is a must to accurate figures, and if you still pulling 120 than start your re-build, after i re-built and blueprinted my engines i nromally allways get around 210-220 psi after 1000 miles after the rings and valves have bedded in nicely, a stock re-built engine should still achieve 180-190 psi all that blue printing does is makes sure that the tolerances on the engine are bang on for best frictional loses and also for best compression this is done by using over sized piston rings, and gapping them by hand to the perfect ring gap size according to the size of your new bore or the honing to clean the bore up. Can make quite a lot of difference from a engine that is just quickly re-built to one thats been blue printed and had someone take their time over it to make sure it's perfect. As much as 10bhp can be gained if your engine has lots of mods.

But even if your engine has only got 120psi it's not a major failure around the corner will keep going for a while, just means the bores and rings are a bit worn, as long as your not smoking it'll be fine for ages yet long enough for you to re-build your other engine properly!!

[FyreDaug]

Worst case scenerio your car will probably just get worse milage and have a drop in power until you throw a new one in. I should do my compression, I should have about 160 across.