Please educate me on this Snap On Engine Compression tester

[Shelbylex]

Good evening.
I recently bought an engine compression tester on a yard sale.

The attachments are
MT-6
MT-26-10
MT-26-11
MT-26-12A
MT 26-16

I do not know much about it and could not find a manual online. From my understanding the attachment goes into a place of spark plug and you check the pressures within a cylinder. I watched a few videos but am still a little clueless

1. What size of spark plugs are those attachments for?
2. What cars could they be used for?
3. Can it be used for modern cars or it is older? (I think it's an older set)
4. Honest opinion: for a DUI guy - would it ever come useful (I previously got rid of some tools which I thought I would never need and then needed them as I am slowly learning how to fix things on cars)

Sorry for such an extensive set of questions - please add as little or as much as you have time for

Thank you!

 

[B_Bimmer]

It's a nice, quality set. It's also something 98% of people would never use. Do you drive older vehicles or work on or rebuild motorcycles or small engines? Useful as a diagnostic tool for those.

 

[Shelbylex]

I have couple of older vehicles 2000s, but it's unlikely I will use it on them. Part of my tool collection/restoration/addiction is slowly creating a nice set to work on cars, things around the house and may be get a project car to work with my kid on once he is older...
Is it possible to guess which brands of cars and from what approximate age this set may be used for?

 

[engineer2]

You can use it in whatever engine you can screw the adapter into, likely 14 mm and 18mm plug holes.
If it threads in, doesn't leak, and the piston doesn't hit that long adapter, you should be good to go.
Remove all plugs, hook it up and let the gauge pump up 5 times. Compare readings.
You can also pressurize a cylinder to hear where the air is leaking out (rings, intake valve, exhaust valve, maybe the head gasket.

 

[Ricky Joe]

It is a useful tool to have. The adapters are for different sizes of spark plugs. You disconnect the coil so the engine won’t start and then replace the plug in the engine with whichever adapter matches the plug. Using a remote starter button turn the engine through with a strong battery five or six or more times. Observe how the needle comes up: small increments, big jump at first and then progressively smaller ( good), or not at all ( real bad!). Then let sit to see if it leaks down. If it comes up in small increments, you could have bad rings, valves not seating, hole in the piston or cracked piston, etc. if it doesn’t come up at all you should check the side of the block for rods, bearing cap could be dropped, valve dropped; something catastrophic. If it leaks down slowly could be valve not seating, broken rings, etc. So, as you see, you can get a good idea that there is a problem and where to look for it. Accompanying picture shows an example of no compression!

 

[Shelbylex]

Thank you, Ricky Joe, Engineer 2 and B-Bimmer
Ricky Joe, thank you for more detailed examples - it helps better understand what to look for!
I wonder what happened to the engine to cause this damage: torn belt, valve hitting the piston and the owner ignoring the knock till the engine was beyond restoration?

Please keep the information coming. I suspect that I am not the only one who would greatly benefit from your expertise and knowledge. One never knows what life brings and knowledge sometimes becomes very useful at very unexpected times. I guess knowledge also partially fuels my tool restoration and collection addiction: with time I learn which tools could be useful in which situations (I wish I knew as much when I started - I passed a lot of deals on very interesting and useful tools when I just started this hobby and joined GJ)

 

[crewchief888]

I'd guesstimate that set is from the 80s, because of the metal box. You might find a date code stamped into the box.

 

[FMB4]

That's a good comp test kit. Meanwhile, there are a bunch of online videos that cover the use of compression testers.

 

[kelpaso1]

It is a useful tool to have. The adapters are for different sizes of spark plugs. You disconnect the coil so the engine won’t start and then replace the plug in the engine with whichever adapter matches the plug. Using a remote starter button turn the engine through with a strong battery five or six or more times. Observe how the needle comes up: small increments, big jump at first and then progressively smaller ( good), or not at all ( real bad!). Then let sit to see if it leaks down. If it comes up in small increments, you could have bad rings, valves not seating, hole in the piston or cracked piston, etc. if it doesn’t come up at all you should check the side of the block for rods, bearing cap could be dropped, valve dropped; something catastrophic. If it leaks down slowly could be valve not seating, broken rings, etc. So, as you see, you can get a good idea that there is a problem and where to look for it. Accompanying picture shows an example of no compression!

What are you talking about? Compression guage hoses have a shrader valve in the end of the hose so it can't leak down.

 

[Shelbylex]

Thank you. It appears that 4/5 adapters are 14mm and one 18mm.
I tried to find on the internet which cars used those size sockets and only found reference to 1980 Honda (model not specified) and 14mm to BMW 3.0 (12 point plug) May be they are too common to mention, but does anybody know where I could get this information or may be write down some cars which use this size sockets.

 

[APEowner]

I'm guessing that set is from the '70s because I bought mine in the early '80s and it's essentially the same but has a blow molded case.

As for what it can be used on the vast majority of spark plugs have 14mm threads. There are some older ones that have 18mm threads which this set covers and some newer ones with 12mm threads. There are also some with 10mm but they're very rare.

If you think you might keep this and use it occasionally the odds are it'll work on anything that you're working on. If you want to sell it anyone who's looking for a compression gauge is likely to know what applications it'll work on.

Also, I think you're confusing sockets and threads. The socket is the tool used to install and remove the plugs and fits on the hex of the spark plug. The threads are the part the goes in the hole. To use this tool you remove the plug and thread the adapter into the hole where the plug was.

 

[kbeefy]

Thank you. It appears that 4/5 adapters are 14mm and one 18mm.
I tried to find on the internet which cars used those size sockets and only found reference to 1980 Honda (model not specified) and 14mm to BMW 3.0 (12 point plug) May be they are too common to mention, but does anybody know where I could get this information or may be write down some cars which use this size sockets.

It's not the socket size, it's the thread size.

I have only seen a couple newer BMW's and Mini's that use the 14mm plug (I think the thread is actually 12mm) you are referencing, and that is one that this tool would not work on. At least, not without an additional adapter.

That tool will work on 95% (or more) of the gasoline vehicles on the road today.

 

[Ricky Joe]

Ford is 14mm

 

[engineer2]

There are four standard SAE spark plug threads, all metric:
M18 x 1.5
M14 x 1.25
M12 x 1.25
M10 x 1.0
Older cars are going to be 18 and newer cars usually 14 depending on the year and the manufacturer.
I think 12 and 10 are more for small engines, but some can be 14.

Some cars from the 30's? and older use inch size spark plugs like 3/4" or 7/8", even 1/2 NPT.
Don't know about industrial engines, but likely metric unless very old.
Spark plug taps are different than regular taps because the thread tolerance is different. Got to be a bit looser so they don't seize.

 

[Ricky Joe]

What are you talking about? Compression guage hoses have a shrader valve in the end of the hose so it can't leak down.

Mine does not.

 

[Wrench97]

Late 60's into the 70's, the issue with that set and newer cars is the adapters don't fit in the spark plug tubes of a lot of the over head cam engines. The newer sets have black hoses smaller top fittings and the hoses are longer.

 

[Shelbylex]

Thank you, Gentlemen!
Sorry about confused post - by sockets I meant the size of sockets for the spark plugs for the unit. Thank you for clarifying it to me - I guess adapters had to be showing thread sizes (should have thought of that!)

There are two opposite views: Wrench97 -wrote that this would work only on 60s-70s cars and I will need black adapters while Kbeefy wrote that it would work on 95% on cars on the road today. Does anybody have experience of trying this set on more modern cars than 60s-70s?

 

[Wrench97]

Thank you, Gentlemen!
Sorry about confused post - by sockets I meant the size of sockets for the spark plugs for the unit. Thank you for clarifying it to me - I guess adapters had to be showing thread sizes (should have thought of that!)

There are two opposite views: Wrench97 -wrote that this would work only on 60s-70s cars and I will need black adapters while Kbeefy wrote that it would work on 95% on cars on the road today. Does anybody have experience of trying this set on more modern cars than 60s-70s?

Not 60's and 70's cars, that appears to be when the set is from.
Not all cars today have over head cams, but the for some of ones that do have a tube in the valve cover those adapters will be too short, some that may work on depends on the depth, they will work a Chevy LS motors, the GM V6's most of the cylinders on the Ford Modular V8's though the longer length is nice on the rear ones.

 

[Shelbylex]

Thank you, Wrench97. Sorry I misunderstood you. Thank you for explaining it in more details!
I wish somebody in my family taught me how to work on cars (My grandfather did, but never involved me. I never knew he did maintenance himself till he told me and by this time he was already in late 80s and stopped driving...). I have to learn it all from GJ and internet videos!

 

[joel63]

Good evening.
I recently bought an engine compression tester on a yard sale.

The attachments are
MT-6
MT-26-10
MT-26-11
MT-26-12A
MT 26-16

I do not know much about it and could not find a manual online. From my understanding the attachment goes into a place of spark plug and you check the pressures within a cylinder. I watched a few videos but am still a little clueless

1. What size of spark plugs are those attachments for?
2. What cars could they be used for?
3. Can it be used for modern cars or it is older? (I think it's an older set)
4. Honest opinion: for a DUI guy - would it ever come useful (I previously got rid of some tools which I thought I would never need and then needed them as I am slowly learning how to fix things on cars)

Sorry for such an extensive set of questions - please add as little or as much as you have time for

Thank you!

Collecting Snap-on - 1978 Catalog p253

I don't know if this will narrow down things for you.
Maybe it will give you a start.
I got from a 1978 catalog.
One problem is that Snap-on has changed the numbers of the adaptors a couple of time since then.
Also the newer gauges read Kilopascal as well as PSI.

 

[Shelbylex]

Thank you, Joel63. This helps a lot!

 

[rustyzman]

I have that same set as well. Yes, it works on many new cars as well as older ones. I also have the older red hoses and a universal solid adapter with a tapered rubber end. I know I looked it up long ago and thought it was 50's era, but I really don't remember for sure.

I used this professionally on cars until 2010. Up to that point, I never had a vehicle I needed to use it on that it did not fit. Old flatheads to new DOHC imports, for me it fit them all. I have picked up a couple of the newer black hose adapters too over the years as well. I am sure that there are cars it will not, but I did not run into them myself.

It is a great tool, best compression tester made IMO. The hose crimps are nice and solid, so when you try to unscrew the hoses from a deep, otherwise inaccessable hole, the hose does not just spin on the hose barb and not unthread the end from the engine (thank you MATCO for that lesson...).

Each of those hoses has schrader valve in it, or it should. If that schrader valve is leaking or missing, the gauge will not hold a reading and will drop right back to zero. Sometimes just taking them out, cleaning them and reinstalling them will fix that issue.

Also, If you choose to use those hoses with a cylinder leakage detector (a snap on one), or to pressurize a cylinder to do valve seals you will need to remove the schrader valve first or it will not let the compressed air through. Don't want to learn that the hard way and drop a valve by accident.

Nice score!

 

[Shelbylex]

Thank you, Rustyzman! Appreciate the information! I thinks it's a keeper. I will keep my eyes out for black adapters.

...GJ is addictive and dangerous: the more I learn about tools the more I understand how much more I need to learn!

 

[asavage]

More info:
The metal case is KRA-124A (that's probably embossed on the bottom; mine is). You'll see this set listed on eBay every so often using the case number, because it's all the seller can find.

The gauge set + adapters is MT-308x-x, where the 'x' varies over the years. Popular is MT-308F and MT-308G-B, but there are others.

From pg. 252/253 of the 1978 catalog referenced above (MT-308H-B):






I think Joel's correct in that some of the adapter numbers have changed or been swapped over the years; I got to this thread because I'm working with an old Ford, using taper-seat 18mm plugs, and I have an 18mm hose adapter stamped "MT-26-11B", but according to the page above, that should be 14B, and the 11B should be the short non-hose adapter.

HTH

 

[SteadyC]

Have the same kit. The old script is on my gauge.

 

[signcrafter]

I bought the same set about 20 years ago used. The gauge was damaged so I ordered a new one from snap on. I emailed them to see if they knew if the new gauge would work on the old hose and they didn't know. I took a chance and it did thread right on and wasn't too expensive. Think around 25 bucks with free shipping back then. Not sure what they are now. I've used mine probably 20 to 30 times over the years on mostly 2000 and up vehicles and it's worked good on everything I have tried it on. I would replace the Schrader valves being it's old and they are really cheap. One less thing to worry about when using it for diagnostics. Diagnostic tools are one thing you want to make sure are accurate or they will lead you the wrong way. If you are doing compression tests you are chasing a complicated issue usually. Compression test can rule out major internal issues when chasing things like misfire or running rough. Once you know the engine is good then you can focus on the stuff attached to it. There's a lot more to it but from my experience that is usually when I pull mine out.

 

[Wrench97]

I have a set bought in the late 70's metal case but only came with 2 hose adapters, had to buy the long 14mm and 12mm hose adapters later....