Which compression gauge should I buy?

[29er]

I'm in the market for a new compression gauge. Amazon has a bunch on sale now. Which ones do you guys like?

[Rock Hornbuckle]

One that is made in America by a well established company.

[BILL WILLIAMSON]

A cheap one with a large tapered rubber cone. It ain't ROCKET SCIENCE just to test the compression! Bill W.

[Mitch//pa]

if you want to know if you have compression put your thumb over the hole or buy a cheap guage. if you want an accurate reading buy a good compression set. the otc on amazon seems somewhat decent for 51.00 has 3 separate hoses. i use a snap on at work 215.00

[BILL WILLIAMSON]

Originally Posted by Mitch//pa

if you want to know if you have compression put your thumb over the hole or buy a cheap guage. if you want an accurate reading buy a good compression set. the otc on amazon seems somewhat decent for 51.00 has 3 separate hoses. i use a snap on at work 215.00

Accurate, Mitch?
Last time I air pressure tested my 20+ year old, cheap guage, it was just a mini-scosh OFF! With the money I saved, I bought one of them NEW-FANGLED air ratchets!! BRRRRP-BRRRRP-BRRRRP-BRRRRP You know, the sound that the SHOP IDIOT & UPSELL-ARTIST, makes EVERY time he plugs in one of them DANG things!! Same guy always tests his BLOW gun, and wasting precious AIR, before blowin' sumpthing! I'll refrain from tellin' his booger story---- Bill W.

[29er]

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Thanks guys. Plus I'll need an adapter, right?

All that BRRRRRPin' coming from Fresno! Must have had some spicy dinner!

Mike

[Reds34]

You will need an adapter, I don't think anything now will come with a 7/8 adapter.

Red

[29er]

Thanks, Red... just ordered the OTC 5606 from Amazon and will pick up an adapter from one of the Model A parts houses.

[BILL WILLIAMSON]

Originally Posted by 29er

Thanks, Red... just ordered the OTC 5606 from Amazon and will pick up an adapter from one of the Model A parts houses.

29er,
Somewhere in the carriage house, I have a diesel compression tester that I only used once. I wonder if one of the adapters might fit the 7/8" plug holes??? (I'm afraid to go out there in the DARK)
Bill W.

[CarlG]

Originally Posted by 29er

Thanks, Red... just ordered the OTC 5606 from Amazon and will pick up an adapter from one of the Model A parts houses.

Go ahead and get the set of 4. You will always find a use for the others. Or your buddy will need a stocking stuffer.

[BILL WILLIAMSON]

Originally Posted by CarlG

Go ahead and get the set of 4. You will always find a use for the others. Or your buddy will need a stocking stuffer.

Or he can carry 1 in a long sock for a SHELALEE, in case he gets mugged! (like, THONK!) Bill W.

[MikeK]

Compression tester? I have several. Fancy sets with hoses and adapters, and the rubber cone kind. If I had a 'do over' I wouldn't own any of them. Once you have a quality leakdown tester (Snap-On EEPV509) you never look back.

If you want to make your own FAA spec cylinder leakdown tester here is a "how-to" link with a parts list and pictures:LINK

[Tom Wesenberg]

Thanks for the link Mike.
I read the first question and answer after the build posting, and the guy asked if a 1.2mm drill bit was too big a difference from the required 1.0mm bit. The answer was that it was 20% larger, but since we are dealing with a HOLE the difference is close to 44% more, and that's why he saw little difference in his gauge readings.

No spec on how thick the plug should be, and I would think a plug 1/2" long would make a difference from a plug 1/8" long. I'd probably make a brass plug about 1/4" long and bore it on my lathe with a 1mm bit.

[MikeK]

Originally Posted by Tom Wesenberg

Thanks for the link Mike.
I read the first question and answer after the build posting, and the guy asked if a 1.2mm drill bit was too big a difference from the required 1.0mm bit. The answer was that it was 20% larger, but since we are dealing with a HOLE the difference is close to 44% more, and that's why he saw little difference in his gauge readings.

No spec on how thick the plug should be, and I would think a plug 1/2" long would make a difference from a plug 1/8" long. I'd probably make a brass plug about 1/4" long and bore it on my lathe with a 1mm bit.

More Info:
The FAA orifice spec for cylinders less than 5" bore- a 0.040" orifice diameter, 0.250" long, 60-degree approach angle. 5" and greater = 0.060" orifice.

The input pressure is set for 80 psi, and 60 psi minimum on the cylinder gauge (75% of the input) is the accepted standard.

The general procedure with an aircraft engine is to start at less than 20psi and have one person feel for the TDC spot while the cylinder is under pressure. Then go up to 80psi and rock the prop ever so slightly to find the highest gauge spot and read there. If you're not careful and let it slip off TDC that prop will whack you REAL GOOD. Don't ask.

[29er]

Thanks MikeK. Here's a link to a Snap-On UK video showing the cylinder leakage tester in action on a modern car:

https://www.youtube.com/watch?v=dJhsavxX6HE

In that video, 4 sources of air flow are identified along with their corresponding cause:

Source of Air Flow Cause
(1) dipstick worn piston rings
(2) radiator leak in head gasket
(3) exhaust leaking exhaust valve
(4) carb throttle leaking intake valve

Is it the same in Model A's?