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Did a compression test tonight on 192.

Boostdtalon

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Test went ok. Just thought I would share my results.

Cyl. #1 145
Cyl. #2 120 /ubbthreads/images/graemlins/uhh.gif
Cyl. #3 145
Cyl. #4 145

Now I know the next step to see exactly where #2 is losing compression is a leak down test. I've checked with all the local auto stores and none of them seem to carry the tool nor can they order it. I know that Harbor Freight has them on their website. So I may have to make a run down to Winston Salem to get one.
 

fuel

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was that cold or hot when you did the test? did you try again squirting some oil into the bore of #2?
 

2of9

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I was told the brand of the tool for the compression tests could yield to lower comp numbers...but #2 is quite low. Let us know how it goes.
 

toybreaker

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Quoting boostdtalon:
It was hot. A buddy reminded me about putting some oil in cylinder, so I'm going to do that today.



There's a couple things you can do to ensure the best readings.

safety first Throwing spark around a cylinder that's full of fuel can lead to external combustion, and a loss of eyebrows.

Disable the fuel injectors so they don't spray fuel into the cylinders while you're cranking the engine over. Spraying fuel creates a (small, but very real) fire hazard, and it will also wash down the bores leading to lower numbers and possible scuffing of the cylinder walls. Unplugging the cas is an easy way to disable the injectors (and ignition.)

Hold the throttle open while cranking to reduce the pumping losses. This will ensure the quickest build of cylinder pressure, and the most accurate readings.

Watch the gauge as the engine cranks. You should build a substantial amount of the final reading on the very first rotation. If it slowly creeps up, that speaks volumes about the rings.

The suggestion of adding oil and repeating the test on the low cylinders is an excellent one. If the numbers increase dramatically, you can suspect the rings aren't sealing well.

On a side note, I've found that many of the hoses used on two piece compression testers use the same fittings as many shops air line fittings. This means you can do a poor man's leak down test by bringing the cylinder you want to test to tdc on the firing stroke, and then thread the hose into the plug hole. Next, just pop the gauge off and apply shop air to the hose end to pressurise the chamber. (if you air line doesnt clip on to the testers hose, you can also use a rubber tipped blow gun attachment to pressurise things.)

Setting the compressor/air line pressure to 90 p.s.i. is a happy medium between getting enough pressure to seal the rings, and having too much pressure which will definately spin the engine off of tdc.

(don't forget to remove the ratchet in case the engine spins when you apply pressure

It wont give you any readings, but you'll be able to hear where the air is escaping, and draw some conclusions from that.

Air heard leaving thru the oil filler cap or dipstick tube means rings.

Air heard moving in the intake means intake valves

Air heard moving in the exhaust means exhaust valves aren't sealing well

Good luck, and post up your results!
 
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Wizardawd

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I would do a wet test on all the cyliners, not just the low one. Variation between cylinders is important as well since it can show leaks between cylinders.

And you forgot bubbles in the coolant during the leakdown is a good indicator of a hg problem.

My money is on some valves not seating.

Wiz
 
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steve

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I don't think TB was trying to write an all-encompassing article on the leakdown test, so he may have left out many things for the purpose of getting to the point and providing details that the OP can handle without being overwhelmed.
 

belize1334

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Putting oil on the piston reduces the dome volume and will lead to artificially high compression numbers. In the extreme case it could even cause hydrolock. You want to let it seep down around the rings to help them seal but you also want to make sure that there's none pooled on top of the piston. Don't add more than a cap-full and crank the engine once or twice before you put the tester in place. Put a rag over the hole while you're cranking so that it doesn't spatter your engine bay.
 

Boostdtalon

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Thanks for the info TB. Lol I ran the wet test today and the difference was substantial. So I'm going to take my other block to the machine shop to get it checked out. Gonna stick with the original plan of stock rods and wiseco or JE pistons. Thought about Evo pistons but for the money I don't think it's worth it.
 

turbowop

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Is the engine acting funny at all? Any reason why you did the compression test in the first place? I know 503 has one cylinder that is a bit lower than the others, but it runs and drives fine, gets good fuel mileage and power to boot, so I don't worry about it. If you're trying to gain some power for racing or the engine is acting weird or missing due to the lower compression in the one cylinder, by all means fix it. But if it's just a number on a gauge and the car runs fine otherwise, just let it be, IMO.
 

belize1334

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The only problem with that is the possibility of crank damage due to consistent imbalance between the force exerted on the rod journals. This MAY lead to warping of the crank. Also, bad rings lead to blowby which can have it's own effects such as popping dip-sticks and contaminated oil.
 

Quoting turbowop:
Is the engine acting funny at all? Any reason why you did the compression test in the first place? I know 503 has one cylinder that is a bit lower than the others, but it runs and drives fine, gets good fuel mileage and power to boot, so I don't worry about it. If you're trying to gain some power for racing or the engine is acting weird or missing due to the lower compression in the one cylinder, by all means fix it. But if it's just a number on a gauge and the car runs fine otherwise, just let it be, IMO.



True dat!

In the quest for perfection, you'd better not drive your car. As soon as you fire it up, perfection goes out the window. If all feels well behind the wheel, and you actually want to drive your car, wait for it to get worse before you tear it apart.
 

turbowop

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Quoting belize1334:
The only problem with that is the possibility of crank damage due to consistent imbalance between the force exerted on the rod journals. This MAY lead to warping of the crank. Also, bad rings lead to blowby which can have it's own effects such as popping dip-sticks and contaminated oil.



I suppose all of this could happen in theory, but I've never heard of anybody complaining about such things happening to them on the forums.

The one cylinder isn't quite down to the service limit yet. The comparison between that cylinder and the others is out of spec, but so is the one cylinder in my car and It's been going strong for a few years now. I think guys have been in the 9's with stock engines that have compression like this even. /ubbthreads/images/graemlins/rofl.gif
 

Boostdtalon

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Quoting turbowop:
Is the engine acting funny at all? Any reason why you did the compression test in the first place? I know 503 has one cylinder that is a bit lower than the others, but it runs and drives fine, gets good fuel mileage and power to boot, so I don't worry about it. If you're trying to gain some power for racing or the engine is acting weird or missing due to the lower compression in the one cylinder, by all means fix it. But if it's just a number on a gauge and the car runs fine otherwise, just let it be, IMO.



Yeah the car smokes quite a bit at times. Thats why i ran the test to see what it was. Other than that it runs fine. If all it was was low compression without the smoking I'd leave it alone for sure.
 

turbowop

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It's possible that the smoking could be caused by leaky valve stem seals though, which won't show up on a compression test. This is dependent on when the smoking occurs though.
 
Last edited:

Boostdtalon

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Well it's mainly visible at idle and it's never consistent on when it happens. I've suspected valve stems, I'm going to try and run a leak down test before I do anything else. That will help me see if it's valve stems or the rings.
 

turbowop

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Leak down test won't show an issue with stem seals. It will show problems with valve seat sealing, piston rings, or headgasket.

If the problem is mainly at idle, I'd put money on it being valve stem seals.
 
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Boostdtalon

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Since I have the means and the money to do a rebuild on the bottom end. I might as well. I can drive the car as is for now. I'm not trying to make the next high hp monster; just something that is a joy to drive. I may occasionally take my car to a road course or autox. Once I get this stuff fixed I plan on fixing the suspension and paint.
 

atc250r

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Based on the history of these motors (and Mitsu's in general) I would say its bad valve stem seals that are causing the smoke. The low compression number could be from several things but like wop said, if its running good then leave it alone.

John
 
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fuel

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smoke on idle could also be a turbo seal too, which you'll also see smoke on de-acceleration. A good indication of weak valve stem seals is smoke on first startup after sitting for a while as oil weeps down onto the back of the valve head.
 
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