Compression Tester - Recommendations?

[SteveSr]

Hello,

Well, after just wasting an inordinate amount of time because I don't have a good compression tester it is time to replace the KD tools POS I have that consistently reads really low and it even has a non-changeable Schrader valve in the tip.

I am looking for something that is accurate with small engines and won't break the bank like the truck vendors. The specs don't usually specify Schrader valve in tip or the extra volume it adds to the compression chamber which lowers the reading affecting accuracy.

Here are the contestants in no particular order:

Bosch - Owatonna (OTC) model-5605 or 5606
https://www.otctools.com/products/compression-tester-kit

Made in China. Don't know where the schrader valve is. Looks like the fixed long hose on the gauge could mean a LOT of rope pulling to get maximum pressure reading.

ATD-5639 / Lang Tools TU-30A
https://atdtools.com/5639
http://www.langtools.com/sku-tu-30a-compression-tester-set/

Country of manufacture is unlisted. Does anyone know which (if either) of these companies is the actual manufacturer? The photos look pretty much identical except the ATD comes in a red case and the Lang comes in a gray case.

Location of the Schrader valve is unspecified. Extention hose is optional which would make for less pullling. This set also has a dedicated small engine gauge (TU-21) with the Schrader valve right in the tip. The gauge looks sort of cheap and it won't do the newer 10mm plugs in 4-mix engines without a compression lowering adaptor. Will a Schrader valve even fit in a 10mm spark plug footprint?

Does anyone have any personal experience with any of these testers and could help fill in some of the missing information? I haven't done a lot of price shopping but it doesn't look like there is much of a price difference between any of these.

Thanks,
Steve

 

[Larry B]

For chainsaws I like the Stens 752-311

http://www.stens.com/752-311-compression-tester

No experience with the ones you linked to.

 

[CJ Brown]

I have this one. It even comes with a spares kit of new valves and o-rings. The thick rubber around the gauge is a nice feature when working on a cement floor.
https://www.google.ca/url?sa=t&rct=...p/B0002WSC0G&usg=AOvVaw0ccndiFDYIDsYQ7DoCzevA

 

[SteveSr]

I have this one. It even comes with a spares kit of new valves and o-rings. The thick rubber around the gauge is a nice feature when working on a cement floor.
https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwi7o6nGpJTaAhVE7oMKHeFuDYQQFgg-MAM&url=https://www.amazon.com/Mityvac-5530-Professional-Compression-Tester/dp/B0002WSC0G&usg=AOvVaw0ccndiFDYIDsYQ7DoCzevA

This one looks like it could be another contender. Rubber boot around the gauge is a must. My KD tester bought it early because of no boot and I replaced the gauge with an Ashcroft equivalent.

Have you ever used the 10 or 12mm adapters? Do either of them have Schrader valves in them? The issue with adapters without valves is that they increase effective combustion chamber size thus lowering the reading.

Thanks,
Steve

 

[Larry B]

Pretty much every automotive compression tester with the interchangeable hoses i have seen has the Schrader valve on the gauge. The 2 i have give me lower readings than the Stens. I have compared all 3 guages with my air compressor and they are all 3 very close but the 2 automotive ones are around 20 psi lower than the stens on a chaimsaw. YMMV

 

[CJ Brown]

This one looks like it could be another contender. Rubber boot around the gauge is a must. My KD tester bought it early because of no boot and I replaced the gauge with an Ashcroft equivalent.

Have you ever used the 10 or 12mm adapters? Do either of them have Schrader valves in them? The issue with adapters without valves is that they increase effective combustion chamber size thus lowering the reading.

Thanks,
Steve

There is no valve on the adapters. There is a valve at the threaded end of each different hose.

 

[SteveSr]

Pretty much every automotive compression tester with the interchangeable hoses i have seen has the Schrader valve on the gauge. The 2 i have give me lower readings than the Stens. I have compared all 3 guages with my air compressor and they are all 3 very close but the 2 automotive ones are around 20 psi lower than the stens on a chaimsaw. YMMV

Automotive vs. small engine seems to be an accuracy issue due to the much smaller combustion chambers on most small engines. Losses due to hose and adapter volumes are much less significant with automotive size engines.

BTW, which automotive gauges due you have?

Thanks,
Steve

 

[Larry B]

I have a chineeseium Ebay special. OK for what i paid for it and an old Sears Craftsman one from the mid 70's. Came with a noninductive timing light and dwell tach.

 

[SteveSr]

I have a chineeseium Ebay View attachment 118420 special. OK for what i paid for it and an old Sears Craftsman one from the mid 70's. Came with a noninductive timing light and dwell tach.

Bet that timing light (neon bulb) and dwell tach haven't seen much use in the last several decades!

 

[Larry B]

Yeah been a few years. In the drawer with the point file, vacum gauge and flexible allen wrench for GM distributors

 

[agee.ronaldj]

I was actually wondering about this subject. I have a nice MightyVac Digital compression tester. Could never get it to register any compression on any of the two-stroke engines I have. The $30 compression tester from Napa registers compression on all of my two stroke engines, I’m not sure it’s accurate at all though.

 

[AlfA01]

I've just taken a look at mine and I concur that adding adapters would essentially increase cylinder volume in err. The standard hose and fitting on my tester has the only Schrader valve, so is essentially the only true reading component of my test kit, as the Schrader valve extends into the spark plug port on the cylinder eliminating void space that can give false readings. I have four or five adapters that do not have Schrader valves and have varying volumes of void space, depending on the size needed for the spark plug port. The largest adds a volume of 10mm x 12mm or 9.42mm^3.

What would that calculate into for loss of cylinder pressure? Well, its way too early for me to be wearing that math cap. If you know each cylinder volume, you can work out the math and compensate for the additional volume. Or, you can buy a much better tester and forget math.

Cheers,
Dan

 

[SteveSr]

I've just taken a look at mine and I concur that adding adapters would essentially increase cylinder volume in err. The standard hose and fitting on my tester has the only Schrader valve, so is essentially the only true reading component of my test kit, as the Schrader valve extends into the spark plug port on the cylinder eliminating void space that can give false readings. I have four or five adapters that do not have Schrader valves and have varying volumes of void space, depending on the size needed for the spark plug port. The largest adds a volume of 10mm x 12mm or 9.42mm^3.

One thing that you could do would be to fill the adapter up with epoxy of some sort and then drill a small hole through the middle of the epoxy. This would remove a lot, but not all, of the extra volume that the adapter adds to the measurement. Once you get close to the max pressure reading there wouldn't be much flow through the adapter so the small hole shouldn't affect the reading.

 

[CJ Brown]

You could also modify the adapter to accept a schrader valve.

 

[SteveSr]

You could also modify the adapter to accept a schrader valve.

I thought about this but don't you need a specially machined seat to accept the colored (black, white) gasket on the valve itself?

Anybody got an old inner tube that they can section the valve stem? I believe that they are almost always brass and pretty soft. A propane torch would burn the rubber off and out of the way.