PeachParts Mercedes-Benz Forum - anyone has trouble with harbor freight compression tester?

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anyone has trouble with harbor freight compression tester?

Hi all!

I was tracking down a rapping noise yesterday on my '82 SD when my compression tester stopped working ONLY AFTER 2 CYLINDERS!

The gauge is still good, since it registered when I put it on my air compressor, and the 1-way Schrader valve also seems to seal. It is in the fitting that screws into the injector adapter. there is no obstruction in the flex hose. I'm suspecting the quick disconnect, but I can't be sure.

The gauge needle moves, it just won't build pressure.

Have any of you experienced this?

I know U get what U pay for, but I really expected better-

I have not had any issues with mine. Take it back, they will give you another. I'm not that brand sensative anymore - even Snap-on has issues with quality anymore.

the release button on mine has to be fiddled with on each test... kinda strange that it sticks in the open position...

Mine worked only once. My tester is a U.S. General, on the end there is an "o" ring that came off, perhaps when I removed the tester before releasing pressure, and I didn't realize, got another one. I bought it from here http://**************.com Just took a look at it, can't see the where the "o" ring resides, but it's been working ever since.

John, thanks for the reply. I lubed my release valve with light machine oil, and it seems to hold pressure-

Toomany,
the O-ring idea has merit. It was getting late in the day and it may have slipped off- since you got another one, could you please tell me where it goes?

Thanks,
Nate

yep, it's that O ring-

it resides deep down in the quick-disconnect fitting, beyond the tiny ball bearings that secure the mating fitting. It must've flown off just like toomany's did, because I remember releasing the QD before bleeding the pressure on the last cylinder I used it on.

remember kids, bleed pressure first, disconnect quick release second.

300sd knocking sound (big bump)

OK guys, troubleshooting time. THis all started when I got a knocking / rapping sound on the way home from work one day almost 2 years ago.

I was doing a compression test when I lost the O ring on the tester's quick release, NOW- I got another tester, values were:
#1 395
#2 385
#3 200
#4 365
#5 360

The noise does not get deeper with increased engine speed.

Oil pressure is fine, though I believe a malfunctioning gauge sender gave me a false positive and I may have run the engine low on oil for a short time. Once I heard the noise, I limped to an auto parts store and topped off the crankcase. It was at least 3 qts low. This engine does have a lot of blowby.
SOOOO,
I drained the oil today and pulled the pan. I found:

1) the O ring from the compression tester
2) some tiny bits of what appear to be plastic or gasket cement
3) No, repeat, NO bearing fragments or metal debris of any kind. \

I cut apart the oil filter, found the usual sticks and cotton waste in the upper section, and some tiny metallic fragments, no more than .010" -.020" in size in the lower section. Total qty may have been 50-70 evenly distributed thru the pleated filter.

I have yet to yank the head, but will do so soon. In trying to rule out the lower end bearings, I have 2 questions:

1) Is that sort of debris in the oil filter normal for a high mileage engine?

and

2)has anyone ever lost a rod bearing or main bearing and NOT had any metal debris in the oil pan?

Any insight based on experience here will be most welcome.

Thanks and best regards,

see if you can borrow a small camera like snap on and look into your cyl that is bad. maybe one of your buddies have a bore scope.

Good suggestion. I don't have one but maybe I should crank the engine so number 3 cyl is at bDC and yank the head.

[QUOTE=Nate Stanley;2235428]OK guys, troubleshooting time. THis all started when I got a knocking / rapping sound on the way home from work one day almost 2 years ago.

I was doing a compression test when I lost the O ring on the tester's quick release, NOW- I got another tester, values were:
#1 395
#2 385
#3 200
#4 365
#5 360

<<< #3 is very low - likely failed piston or rings - recheck valve adjustment for that cylinder and retest - try adding a squirt of oil before testing to see if reading goes up.>>>

SOOOO,
I drained the oil today and pulled the pan. I found:

1) the O ring from the compression tester
2) some tiny bits of what appear to be plastic or gasket cement
3) No, repeat, NO bearing fragments or metal debris of any kind. \

<<< I can think of no way an o-ring from a compression tester could make its way into the oil pan>>>

Good Luck,

Joseph

Got a compressor? Go to a hydraulic hose shop, bring the injector adaptor for your compression tester, say you need the bit or two to put a 1/4" male quick disconnect on it, cost maybe $3-4. Find TDC on the cylinder under test, LOCK THE FLYWHEEL w/ screwdriver in teeth, put light air pressure (start low, 10 PSI) on the cylinder till you hear leakage at the air cleaner (intake valve) , exhaust (exhaust valve) or oil cap (rings/piston).

Remember to check valve lash and LOCK THE FLYWHEEL. Alternative to locking the flywheel would be cinching the PS belt tight and keeping that from rotating instead. The bolt on the main pulley is a possibility, but I've heard of it not working as well.

Quote:

Originally Posted by Nate Stanley (Post 2235428)

Unfortunately you most likely dumped the Oil drained from the pan. Otherwise, after finding metal fragments in the oil filter I think an Oil Analysis would have been helpful.

I believe the Analysis might tell you for sure. But, I do not know if you can still take a sample if it is dumped into a drain pan. I know my draing pan is a nasty mess.

I don't believe the O-ring on the Compression Tester got inside of the Engine as the tip of the Precombustion Chamber has small holes. It must have been somewhere on the exterior and fallen into the drain pan.

The only place I can think of that an O-ring could get into the Oil Pan is from the Stem on the Oil Filter Cap. Where it seals goes back to the Oil Plan.
The other place would be if you had the Oil Fill Cap on the Valve Cover open and the O-ring managed to go through the Hole.

Quote:

Originally Posted by Nate Stanley (Post 2235428)

. . .I drained the oil today and pulled the pan. I found:

1) the O ring from the compression tester . . .

An O ring could not get past your rings and piston inside the cylinder. It may be from the spindle in your oil filter housing. Next time you change your oil, check to see if that O ring is missing. If your oil pressure needle is shaking, that O ring is worn out or missing.

You might loosen each injector line one at a time and retighten to see if you can isolate the knock to one cylinder.