Compression Testers - Snap on VS Harbor Freight : MGB & GT Forum : The MG Experience

Compression Testers - Snap on VS Harbor Freight #1
Aridgerunner Bill Bussler Montoursville, PA, USA Sign in to contact 1956 MG MGA 1500 "The A" 1959 Triumph TR3A "The Mistress" 1977 MG MGB "Sweet B"	Topic Creator (OP) Dec 23, 2014 07:31 AM Top Contributor Joined 12 years ago 6,234 Posts

I posted this on the A side too because it's relevant to both A & B.

Just for giggles yesterday, after running the 1800 engine on the test stand we decided to do a comparison test between my brothers Snap on gauge and my Harbor freight gauge. The results were practically identical; varying maybe a pound between gauges.

And to dismiss the rumor that the Harbor Freight gauge did not have a check valve in the hose I have attached a picture of the end of the HF unit. You can clearly see the check valve. The piece on the right side of the hose is the long reach adapter which does not have a check valve and because it's only about 1 1/2" long it shouldn't need one. And we did use it for the test. So now I feel comfortable using the HF gauge in the future.

Bill

Si Vis pacem, para bellum

DSC_0906.JPG 24.9 KB

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Re: Compression Testers - Snap on VS Harbor Freight #2
2150john John L Nolensville, TN, USA Sign in to contact 1974 MG MGB MkIII	Dec 23, 2014 08:07 AM Joined 14 years ago 469 Posts

Thanks for the test. Good to know.

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Re: Compression Testers - Snap on VS Harbor Freight #3
riley1489 Bruce H Great White North, QC, Canada Sign in to contact 1953 Jaguar XK120 1959 Riley 1.5 "King George" 1973 MG MGB	Dec 23, 2014 08:32 AM Top Contributor Joined 14 years ago 29,256 Posts

Good test

but just a start, a sample of one does not prove much.
Let's put these testers in the commercial shops for 5 years and validate after this life cycle.
I will say however it is the delta between readings not the reading so most likely any 'quality' gauge will suffice for the masses here.

Bruce

Life's most persistent and urgent question is, "What are you doing for others?"

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Re: Compression Testers - Snap on VS Harbor Freight #4
Perdido Rut Rutledge Tuscaloosa, AL, USA Sign in to contact 1960 Austin-Healey Bugeye Sprite "Scarlet"	Dec 23, 2014 08:55 AM Top Contributor Joined 18 years ago 5,280 Posts

William,
Thanks for the valuable info! I cross check my compression gauges and find that the HF one is spot on. I have a few adapters around the shop and will be checking my oil pressure gauges...gives you confidence all is well.
Rut

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Re: Compression Testers - Snap on VS Harbor Freight #5
JWD Jim D. Gig Harbor, WA, USA Sign in to contact	Dec 23, 2014 09:01 AM Joined 13 years ago 699 Posts

In reply to # 2878918 by riley1489 Let's put these testers in the commercial shops for 5 years and validate after this life cycle.

Bruce

I seriously doubt there are many here that will justify spending $200+ for a Snap-On tester and use it once or twice a year when a $30 HF will work just fine. Comparing home use to commercial shop use is idiotic.

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Re: Compression Testers - Snap on VS Harbor Freight #6
ClayJ Clay Johnston Mt. Olive, MS, USA Sign in to contact 1972 MG MGB	Dec 23, 2014 09:26 AM Top Contributor Joined 20 years ago 20,196 Posts

X2, for most of us the HF unit is fine for once or twice a year. I check mine annually during tune-up and compare to previous year readings.

I've also found the HF leakdown tester to work reasonably well, just have to be very careful when using it to follow the procedure exactly so as to avoid pegging the needle on the output gauge. Pegging the needle (easy to do) will cause the needle to be off on the reading indexes.

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Re: Compression Testers - Snap on VS Harbor Freight #7
ohlord Rob C A tiny Island off the coast of Washington State, N.W., USA Sign in to contact 1957 Land Rover Series I "EYEYIYI" 1957 Land Rover Series I "OVRLND" 1971 MG MGB 1971 MG MGB "Bedouin 2" & more	Dec 23, 2014 09:40 AM Top Contributor Joined 14 years ago 28,879 Posts

accuracy gives a good indication of compression. Do you propose that if all the numbers read within 10% high to low and they were all reading in the 90psi range that the engine is fine because it is the delta between readings not the reading that counts ?

In reply to # 2878918 by riley1489 Good test thumbs up

but just a start, a sample of one does not prove much.
Let's put these testers in the commercial shops for 5 years and validate after this life cycle.
I will say however it is the delta between readings not the reading so most likely any 'quality' gauge will suffice for the masses here.

Bruce

LNDRVR4X4.COM
Home of Project "INCARN8'

1957 Series 1 Land Rover electric VEHICLE CONVERSION

FIXITUPCHAP.COM
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Re: Compression Testers - Snap on VS Harbor Freight #8
riley1489 Bruce H Great White North, QC, Canada Sign in to contact 1953 Jaguar XK120 1959 Riley 1.5 "King George" 1973 MG MGB	Dec 23, 2014 09:54 AM Top Contributor Joined 14 years ago 29,256 Posts

In reply to # 2878931 by JWD Comparing home use to commercial shop use is idiotic.

Thanks Jim,

I guess I am an idiot then. confused smiley

B

Happy Christmas to you and yours smiling smiley

Life's most persistent and urgent question is, "What are you doing for others?"

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Re: Compression Testers - Snap on VS Harbor Freight #9
JWD Jim D. Gig Harbor, WA, USA Sign in to contact	Dec 23, 2014 10:03 AM Joined 13 years ago 699 Posts

I was referring to your statement, not you as a person. Sorry if I offended you. That wasn't my intention. Have a Merry Christmas. smileys with beer

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Re: Compression Testers - Snap on VS Harbor Freight #10
Aridgerunner Bill Bussler Montoursville, PA, USA Sign in to contact 1956 MG MGA 1500 "The A" 1959 Triumph TR3A "The Mistress" 1977 MG MGB "Sweet B"	Topic Creator (OP) Dec 23, 2014 10:20 AM Top Contributor Joined 12 years ago 6,234 Posts

In reply to # 2878959 by ohlord accuracy gives a good indication of compression. Do you propose that if all the numbers read within 10% high to low and they were all reading in the 90psi range that the engine is fine because it is the delta between readings not the reading that counts ?

Here's my backyard understanding of this. First, please keep in mind that I was doing a comparison test between two gauges to look for differences. I wanted to make sure that my Harbor Freight gauge was giving accurate readings.

When doing a compression test of this type you are looking for two things. One, are the readings all within that 10% range? Actually, I don't even like that. 10% of 90 psi is only 9 pounds. But on a high compression engine of say 200 PSI now your looking at 20 PSI difference and that is too much for me. Two, you want to see if your readings are close to the factory specification or close to what you got when you first rebuilt your engine. Significant differences tell you there's a problem somewhere.

Bill

Si Vis pacem, para bellum

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Re: Compression Testers - Snap on VS Harbor Freight #11
riley1489 Bruce H Great White North, QC, Canada Sign in to contact 1953 Jaguar XK120 1959 Riley 1.5 "King George" 1973 MG MGB	Dec 23, 2014 10:48 AM Top Contributor Joined 14 years ago 29,256 Posts

In reply to # 2878979 by JWD I was referring to your statement, not you as a person. Sorry if I offended you. That wasn't my intention. Have a Merry Christmas. smileys with beer

Jim,
No apology needed and no umbrage taken I was just trying to set the record straight, ( I have very thick skin winking smiley

). In my post I fully agree that any low cost 'quality' tester is for most of us just fine.

Bruce

Life's most persistent and urgent question is, "What are you doing for others?"

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Re: Compression Testers - Snap on VS Harbor Freight #12
davester Dave Diamond Berkeley, California, USA Sign in to contact 1965 Austin-Healey Sprite 1971 MG MGB GT "Dad's Car"	Dec 23, 2014 10:58 AM Joined 15 years ago 2,204 Posts

In reply to # 2878945 by ClayJ I've also found the HF leakdown tester to work reasonably well, just have to be very careful when using it to follow the procedure exactly so as to avoid pegging the needle on the output gauge. Pegging the needle (easy to do) will cause the needle to be off on the reading indexes.

I disagree. The HF tester is only good for testing a lawn mower because it operates at about 20 psi, not 100 psi as it should. I bought one and realized that they are designed incorrectly, with a 100 psi gauge on the compressor side and a 25 psi gauge on the engine size. I fixed mine so it works correctly by chucking the stupid "test" gauge and substituting in a 100 psi gauge. Adding to that problem, the fitting to connect to the air compressor was machined incorrectly on mine and wouldn't fit. I substituted a fitting from the hardware store. After those two mods it works like it should.

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Re: Compression Testers - Snap on VS Harbor Freight #13
billh1963 Bill H Albemarle, NC, USA Sign in to contact 1963 MG MGB MkI 1967 MG MGB GT 1968 MG MGC GT 1969 MG MGC GT & more	Dec 23, 2014 02:23 PM Joined 13 years ago 1,201 Posts

I bought a Snap On kit for well under $200 on ebay. Yes, they are more expensive. However, I like to only buy once. I learned my lesson about cheap tools years ago ....

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Re: Compression Testers - Snap on VS Harbor Freight #14
Rod H. Amity, OR, USA Sign in to contact 1964 MG MGB 1968 MG MGB GT	Dec 23, 2014 02:38 PM Top Contributor Joined 22 years ago 33,653 Posts

Compression gauges are a pretty simple device. I have one that my dad was given by a friend about 45 years ago, used. Later I bought one from Mac Tools when I was a professional mechanic. They both still work fine and read very close to each other.

"If I knew where the good songs came from, I'd go there more often."

Leonard Cohen

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Re: Compression Testers - Snap on VS Harbor Freight #15
B-racer Jeff Schlemmer Shakopee, MN, USA Sign in to contact 1950 Willys Jeep Pickup "Ratrod" 1964 Land Rover Series IIA 1971 MG MGB	Dec 23, 2014 03:50 PM Top Contributor Joined 19 years ago 20,902 Posts

A lot of "Snap-On" tools are not even manufactured by Snap-On. Especially gauges and electrical testers, as well as many machining tools like drill bits, taps and dies, etc...
I would not guess that the compression gauge is made by Snap-On. MityVac makes a kit that looks surprisingly similar to the Snap-On. Hmm... They may also make a cheaper version for other companies.

jeff@advanceddistributors.com

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