Calibrate a compression tester

[Iplayfarmer]

This post is somewhat incidental to my "Black Smoke" thread.

How would I calibrate a compression tester? Is it common for shops to test compression testers?

I have a compression tester that I picked up at a yard sale a while back for something like $3. I want to make sure it's giving me good readings before I scrap an engine based on its reading.

 

[MrJimi]

For $3, I may have doubts also, how about you check it on a good engine that you know has good compression or compare it with a friends tester on the same engine

 

[kevinj]

This post is somewhat incidental to my "Black Smoke" thread.

How would I calibrate a compression tester? Is it common for shops to test compression testers?

I have a compression tester that I picked up at a yard sale a while back for something like $3. I want to make sure it's giving me good readings before I scrap an engine based on its reading.

Are you sure the tester will read high enough for a diesel?

 

[slowrev]

Just get a tee to hook it up on the same line as a known good gauge and compare readings.
when pressurizing the line with compressed air. Should be close enough.

 

[CATMAN]

The couple of diesels that I have used a compression tester on, were in the 410-450 psi range. I would think that some of the older diesels(non-turbocharged) are going to register higher than this. How high does that gauge go? How strong is the hose, tube or adapter that you will be using? Be safe.

 

[Marlowe]

A compression gauge at best is an indicator,not conclusive evidence. What I mean by that may be best explained by an analogy. Let's say your teenage son drives a pickup. One Saturday morning you walk out to get the morning paper and find an empty beer can in the bed of the truck. That's an indicator that he's been drinking and driving, but it sure isn't conclusive evidence, and neither is the reading on a compression gauge. The best way to read any compression gauge is a comparison between cylinders. They should be fairly close. If not, it's an indication of a problem.

 

[Iplayfarmer]

The couple of diesels that I have used a compression tester on, were in the 410-450 psi range. I would think that some of the older diesels(non-turbocharged) are going to register higher than this. How high does that gauge go? How strong is the hose, tube or adapter that you will be using? Be safe.

When I posted the question I was at work, and for some reason I thought that this one went higher than it does. Now that I am home I took a closer look at it and it only reads up to 200 psi. That won't do since my engine compression spec is 455 psi.

The question still stands, though, for future use on gas engines. I think the best option is to just test it on a good engine against another known working tester.

Now, I guess the question is what's a good diesel compression tester?

 

[john_bud]

THe one in the picture is garbage. I hate them. For a couple bucks more get one that screws into the spark plug hole. Press in is junk, garbage and other adjectives and invectives that are best not used on a site like this.

At harbor freight you can get a diesel compression tester for diesels cheap. Yeah, it's a HF unit, but it will tell you something. And for 35 bucks nothing.

Otherwise, you are looking at multi-hundred dollar units. Snap on, Matco etc.

If you get one, get one that can also do leak down. Then you can compress the cylinder and determine how long it takes to leak. That will tell you a lot about rings and valves. Use your ears and you can tell which is leaking.

jb

 

[DieselPower]

I own a Snap On diesel compression gauge kit. Back when I was wrenching full time I would send it in every 2 or 3 years along with my torque wrench's to get calibrated. Last time around I think they charged me something like $25. But considering it was a $500 plus diesel compression kit I figured it was well worth it.

 

[Iplayfarmer]

THe one in the picture is garbage. I hate them. For a couple bucks more get one that screws into the spark plug hole. Press in is junk, garbage and other adjectives and invectives that are best not used on a site like this.

At harbor freight you can get a diesel compression tester for diesels cheap. Yeah, it's a HF unit, but it will tell you something. And for 35 bucks nothing.

Otherwise, you are looking at multi-hundred dollar units. Snap on, Matco etc.

If you get one, get one that can also do leak down. Then you can compress the cylinder and determine how long it takes to leak. That will tell you a lot about rings and valves. Use your ears and you can tell which is leaking.

jb

JB, could you be a little more clear about whether or not you like this style or not.

I think I've gotten the $3 out of it that I paid.

I was just looking through another HF ad last night and saw the diesel compression tester. I'm going to be in the vicinity of a store tomorrow night, and I thought I may pick one up.

Has anyone used the cheapo HF diesel tester? I see they have two. Is the cheap one adaptable enough to work with these smaller diesel engines?

 

[wedge40]

Just curious.
Would something like this work?
Surplus Center Item Detail
Sure you'd have to find an adapter to fit.

Wedge

 

[TimC]

To answer your original question, yes, you can have your tester calibrated. Search your local yellow pages and you should be able to find a local industrial calibration service that will do it for you. All a compression tester is is a pressure gage really.
Just for example, this is who we use where I work Davis Calibration Services - Instrument Calibration Services On-Site or Pick-up & Return
I don't know wether or not they'll do one gage for a consumer or not, but you get the idea.

It's most effective to "calibrate" a gage near the middle of its range, so in theory, you should "check" that gage near 100 psi. Near either the upper or lower limit of the gage you'll see some "end effects" and will not get great results. Keep this in mind when purchasing any gage, and don't ever use a gage that is undersized to the pressure. ex: 100 psi gage on 200 psi. This will ruin your gages. You could very easily use your home air compressor to fill up an appropriate pressure vessel to a known pressure, then plug your compression tester up to the known pressure and you'd know how close it was. It might take a few adaptors to do so, but you should be able to do this for little or no cost.

 

[john_bud]

JB, could you be a little more clear about whether or not you like this style or not.

?

I'll try. don't like them.

They can easily show a 30-50 psi variation due to leakage and operator technique. Bad data is much worse than no data as it allows you to confidently make horrendous decisions.

While you can statically cal the tool (plan on it being $100+), you would be better served to test an engine once a day for a month and determine the variability in test method using the tool. Very accurate calibrated tools can give wildly erratic results due to technique. That one is about the worst.


Or was that a rhetorical question? we get so little of that .... around here the specialty is more in line with snide quips and sarcasm.

 

[Iplayfarmer]

Or was that a rhetorical question? we get so little of that .... around here the specialty is more in line with snide quips and sarcasm.

Yep. Sarcasm just doesn't translate as well in writing. Winking smileys can only do so much.

 

[AKfish]

Come on guys.... most folk's aren't really mean-spirited. Emails and forums are difficult venues with which to promote genuine communication.

I can imagine that I've ruffled feathers when attempting to be flip --- I've flopped --- and didn't have a clue until later on.

I like a good ribbin' and try to figure that many comments are attempts to be in jest and not take 'em too seriously.

Bye the Bye --- you get that Bolen's goin'?? I'm waitin' with baited breath.... to smell diesel fumes again!

AKfish

 

[john_bud]

Come on guys.... most folk's aren't really mean-spirited. Emails and forums are difficult venues with which to promote genuine communication.

AKfish

I HOPE all understood that my reply was full of jocularity (or an attempt there in). My feathers are smooth! Slicked back in fact.

jb

 

[Iplayfarmer]

Bye the Bye --- you get that Bolen's goin'?? I'm waitin' with baited breath.... to smell diesel fumes again!

AKfish

Nope. I'm waiting on more shims to adjust the timing on the pump. Plus I've been busy lately. Not going to work on it tonight! I don't think that would go over well... "Happy Vallentine's Day Honey. Here's a flower. I'm going to spend the night tinkering in the garage."

I don't know if the shims are going to do the trick, though. That's why the questions about a compression tester. I'm worried that even with the timing right it may not run. I want to check the compression and see if I'm due for an overhaul.