# Anyone able to suggest a good Compression Tester?



## Rags2Fishes (Sep 4, 2018)

Hello, Thank you for the add to this forum.

I have been looking at Compression Testers and see quite a price variance. Can anyone suggest a good lower price tester for a basic Do it yourselfer? 

I appreciate all replies!


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## KMixson (Sep 4, 2018)

I had bought one from Sears sometime around 1980 and it has lasted me this long. It is just a simple gauge with a hose and a couple of different adapters for the different thread patterns.


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## Weldorthemagnificent (Sep 4, 2018)

Mine came from Napa auto parts. Don’t spend the Farm on a snap on or other high dollar gizmo. 


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## Rags2Fishes (Sep 4, 2018)

Thank you for your replies. I am still searching. I did look at Craftsman, my only thought is are they as good now as they were then. I see K-Mart and Lowes both sell Craftsman now. I know MAC and Snap-On are out of range as I'm not a shop. Harbor Freight's didn't have a good review. 

Anyone offer the lifetime warranty like NAPA, etc.? Still open for more suggestions!


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## DS49 (Sep 4, 2018)

If you are only going to use it occasionally and don't want to have one of your own, both Autozone and Advance have units you can borrow for free.


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## MrGiggles (Sep 4, 2018)

OTC makes some that are affordable, and are better qualtiy than what you'll find at most places.

I have a very inexpensive set from eBay, had them for almost 10 years and they still work fine. I hardly use them though.

A word of advice, if you plan to use it on small engines, get one that has a Schrader valve in the tip, right where it screws into the cylinder. If it is mid length in the hose, the volume of the hose adds to the volume of the compression chamber (lowering the compression ratio) and you will get false low readings.


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## 86tuning (Sep 4, 2018)

The snap-on gauge itself isn't that expensive. It's the box and accessory hoses that cost a mint. So if you only need ONE hose you can buy it piece by piece, and save a bunch of money for a quality gauge.

Thing that kills a gauge or any measuring tool is impact. So keep it in a box, and be careful not to drop it. Both of my snap-on compression gauges are over 20 years old, and work just fine. I have one at home, and one at the office.

I also prefer their torque wrenches.

The real question is, why do you think you need a compression gauge? Usually they are only useful for confirming that the jug is dead. Or checking an engine that doesn't run, before purchasing it.


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## Rags2Fishes (Sep 4, 2018)

86tuning said:


> The snap-on gauge itself isn't that expensive. It's the box and accessory hoses that cost a mint. So if you only need ONE hose you can buy it piece by piece, and save a bunch of money for a quality gauge.
> 
> Thing that kills a gauge or any measuring tool is impact. So keep it in a box, and be careful not to drop it. Both of my snap-on compression gauges are over 20 years old, and work just fine. I have one at home, and one at the office.
> 
> ...



Hi 86tuning, it would be for checking a few motors before purchase. I thought I would buy a couple of the same motors if possible to have spare parts on hand. I live in an area where there are many boats from fresh water lakes. Odds are good I'll find another! Plus I have some other things around where it might be good to have one handy. I live in a rural area and it might not be feasible to borrow one from Advance Auto or Autozone. They are both 25 miles each way and if I'm out on a "buy" maybe further. Thank you for replying.


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## Rags2Fishes (Sep 4, 2018)

MrGiggles said:


> OTC makes some that are affordable, and are better qualtiy than what you'll find at most places.
> 
> I have a very inexpensive set from eBay, had them for almost 10 years and they still work fine. I hardly use them though.
> 
> A word of advice, if you plan to use it on small engines, get one that has a Schrader valve in the tip, right where it screws into the cylinder. If it is mid length in the hose, the volume of the hose adds to the volume of the compression chamber (lowering the compression ratio) and you will get false low readings.


Thank you MrGiggles, I appreciate the advice. Will the description usually state there is a Shrader valve? Something I wasn't familiar with! My current Motor is a 1989 Johnson 40hp. Thank you.


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## Weldorthemagnificent (Sep 5, 2018)

Unless you are wanting to use it on chainsaws and weedwhackers, an automotive gauge will work fine. Mine gives low readings on chainsaws but works fine on outboards down to 4 hp (smallest I’ve tried) snowmobiles, motorcycles etc. don’t overthink the gauge. If one reads 5lbs low or high is not a big deal, what you are looking for is the ability to spot two cylinders at 120 and one at 80. Great deals can be had on outboards that people don’t want to bother or have means to put on a stand and run in a tank and a compression test will tell valuable information. It’s a great tool and I recommend anyone who buys motors have one... a $40 one. My advice is to go with one from autozone or Napa. If you’re a small engine mechanic spend more. If you are into very small engines such as chainsaws get a specific gauge like an Oregon. 


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## Weldorthemagnificent (Sep 5, 2018)

Mr Giggles had a good point. The schrader (tire type) valve being right on the part that screws into the motor. 


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## turbotodd (Sep 5, 2018)

I have about 10 of them. If I take one engine and use all 10 gauges, I get 10 different readings.

All a compression gauge is good for is a general idea of the condition. If it says 10 psi on the gauge after doing a proper compression test, you have a problem. If it says 90+, it's generally going to be in good enough condition to run.

I see guys on FB all the time selling motors and they'll state in the ad that cylinder #1 has 133 psi #2 had 132 psi and #3 might have 134. LOL. Then I show up with my gauge and it says 120 and they start throwing a fit saying my gauge is junk. They'll run me off quick if I ask to see their gauge. "My mechanic tested it"...let's go to his shop then. LOL...99.99% of gauges out there don't read in 1 psi increments. Most are 5 psi. Typically if there's a compresison problem, it's obvious anyway. Like 20psi difference between cylinders or maybe the one only has 20psi.

The seal between the hose adapter and the cylinder/head also plays a big part...if it leaks, the gauge will read low...and not everyone takes good care of their adapter hoses and/or adapters. 

The only true way to know an engine's condition is to do a leak down test. Better yet, pull the exhaust cover (on 2 stroke) and have a look at the pistons/cylinders-but not everyone will want to do that-and I understand & respect it. So I typically leak test them. Not real easy on 2 stroke stuff but it can be done. Real easy on 4 stroke stuff, especially pushrod 4 stroke stuff like lawn mowers. Pull the pushrods off and leak it, do not have to hold the engine from turning over.

On 4 stroke stuff, many times you can't do an accurate compression test. Why? Because many of them have decompression mechanism which reduces the load on the starter. My old F25 showed 75 psi. Guy shows up with his gauge and I just watched him shake his head when he seen 75 show up on his gauge. He questioned it and then I asked him how he was going to calculate what the actual compression was based on the decompressor built into the camshaft. Huh he says? Some Kawasaki engines (bikes mostly) will start/run with a cranking compression of 40 psi. They do it to reduce the load on the kick starter or electric starter. They have to. I've disabled them before and you cannot start them without it, period.


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## Pappy (Sep 5, 2018)

You cannot go wrong with OTC. 
As has been stated the readings will be all over the place between gauges and cranking speed, etc. 
Replaceable shrader valves is a good feature to have in one.


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## Rags2Fishes (Sep 5, 2018)

Pappy said:


> You cannot go wrong with OTC.
> As has been stated the readings will be all over the place between gauges and cranking speed, etc.
> Replaceable Shrader valves is a good feature to have in one.



Do the OTC Compressor Testors come with the shader valve near the entry point of the cylinder? I have some standard tire Shrader valve inserts and can order some new ones. I am also just learning and using my Repair Manual and best advice I can get at this point. I appreciate your reply!


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## Rags2Fishes (Sep 5, 2018)

I am currently looking at the OTC 5606 Kit. I may try and find a local mechanic who needs some heated shop space and work a deal for shop use. 

Anyone else use the OTC 5606 Kit? It looks like a good option.


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## Rags2Fishes (Sep 5, 2018)

Weldorthemagnificent said:


> Mr Giggles had a good point. The schrader (tire type) valve being right on the part that screws into the motor.
> 
> 
> Sent from my iPhone using Tapatalk



Do you know if the OTC 5606 Kit has the Shrader valve on the part that screws into the motor? I couldn't tell by the photos. Thank you!


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## Weldorthemagnificent (Sep 5, 2018)

That’s a nice kit. This is mine. You can see the valve at the end of the hose. It’s a budget kit but has served me well for about 15 years.








https://www.amazon.com/Innova-3612-Compression-Tester-Piece/dp/B000EVU89I


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## Rags2Fishes (Sep 5, 2018)

Weldorthemagnificent said:


> That’s a nice kit. This is mine. You can see the valve at the end of the hose. It’s a budget kit but has served me well for about 15 years.
> 
> 
> 
> ...



Thank you! I appreciate you taking the time to post!


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## Pappy (Sep 5, 2018)

Call OTC and ask. I would imagine they still do. Mine is ancient and still in perfect working condition. Have gone through a few Shrader valves when I forget to let the pressure off slowly but that is what they are there for...to replace if need be.


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## Rags2Fishes (Sep 6, 2018)

Pappy said:


> Call OTC and ask. I would imagine they still do. Mine is ancient and still in perfect working condition. Have gone through a few Shrader valves when I forget to let the pressure off slowly but that is what they are there for...to replace if need be.


Thank you, I'll call an ask. I would like to use a link to help this site as I buy a lot from Amazon. I'll be buying new Spark Plugs, extra Shrader Valve inserts, etc. Thanks again...


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## Rags2Fishes (Sep 6, 2018)

According to OTC Tech at Customer Service I was told the Shrader Valve isn't necessary for Compression testing. The Tech said even when using the extension I will get a good reading. I imagine because of turning over the motor 5 times or so? I'm not sure but the 5606 Tester Kit is a mid-line tester that has most Gasoline adapters. Any thoughts before I make my purchase?


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## MrGiggles (Sep 6, 2018)

Rags2Fishes said:


> According to OTC Tech at Customer Service I was told the Shrader Valve isn't necessary for Compression testing. The Tech said even when using the extension I will get a good reading. I imagine because of turning over the motor 5 times or so? I'm not sure but the 5606 Tester Kit is a mid-line tester that has most Gasoline adapters. Any thoughts before I make my purchase?



He's full of crap.

Without the valve the needle just bounces up and down as cylinder pressure oscillates. Yes, you can decipher a reading, but it works much better with the valve.


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## Rags2Fishes (Sep 6, 2018)

MrGiggles said:


> Rags2Fishes said:
> 
> 
> > According to OTC Tech at Customer Service I was told the Shrader Valve isn't necessary for Compression testing. The Tech said even when using the extension I will get a good reading. I imagine because of turning over the motor 5 times or so? I'm not sure but the 5606 Tester Kit is a mid-line tester that has most Gasoline adapters. Any thoughts before I make my purchase?
> ...



I wish I could tell by the photos. Does anyone have the OTC 5606 that can verify if there is a Shrader Valve at the tip? What your sharing makes sense. OTC has a good rating by a lot of people. :-k


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## MrGiggles (Sep 6, 2018)

Rags2Fishes said:


> MrGiggles said:
> 
> 
> > Rags2Fishes said:
> ...



From what I have seen, gauges that have a quick coupler usually have the valve right behind it, essentially in the middle of the hose.


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## KMixson (Sep 7, 2018)

I believe you are over thinking this too much. An OTC 5606 would be a quality gauge. It is designed to measure compression. It will measure compression. The schrader valve or some other form of check valve is there keep the needle stabilized while cranking over the engine. If it does not have a schrader valve the intake stroke would pull the needle back down every time making it hard to get a good compression reading.


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## Rags2Fishes (Sep 7, 2018)

KMixson said:


> I believe you are over thinking this too much. An OTC 5606 would be a quality gauge. It is designed to measure compression. It will measure compression. The schrader valve or some other form of check valve is there keep the needle stabilized while cranking over the engine. If it does not have a schrader valve the intake stroke would pull the needle back down every time making it hard to get a good compression reading.



Thank you. I appreciate all replies. I don't believe I was overthinking this because I simply didn't have any experience with a Compression Tester and a reply here said to be sure it has a Shrader Valve. I had no idea if the one I was looking at did. I took the advice above and called OTC and was told I didn't need it. However, as mentioned above and your reply, it is obvious the Shrader Valve should be there to avoid the fluctuation of the needle. I ordered the next one up from the OTC 5606 that comes with more adapters so I'll be all set now. I was only trying to confirm there was a Shrader Valve and unfortunately, the online photos and OTC Tech didn't help. Again, I appreciate all replies as I now ordered what I was looking for thanks to the help here!


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## DaleH (Sep 7, 2018)

I may be wrong, but ‘Schrader valve or no Schrader valve‘, one with a button to release the pressure will hold the reading. I’ve been compression testing OBs using a Craftsman model for 40+ years now and I never even gave it one thought about whether or not it has a Schrader valve or not ... in fact, I’m not even going to go bother looking at it.

I’ve also only seen one bad gauge in my life ... no small surprise that Haba Freight sold it ...


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## Rags2Fishes (Sep 7, 2018)

DaleH said:


> I may be wrong, but ‘Schrader valve or no Schrader valve‘, one with a button to release the pressure will hold the reading. I’ve been compression testing OBs using a Craftsman model for 40+ years now and I never even gave it one thought about whether or not it has a Schrader valve or not ... in fact, I’m not even going to go bother looking at it.
> 
> I’ve also only seen one bad gauge in my life ... no small surprise that Haba Freight sold it ...




Thank you DaleH, I appreciate the reply. I ask where I need to learn and will gladly share when I'm able. I have MANY tools, but never bought a Compression Tester so asked some questions and took suggestions. I learned right away H. Freight had many bad reviews so knew I needed to look elsewhere. I believe the OTC will serve me well. With past measurement tools, I learned to always use the same tool to compare readings before and after. There are too many variations using different tools for the same Job. That isn't to say that there isn't a "better" tool but I'm happy landing somewhere in the middle.


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