Help needed with new compression tester

[ian_uk1975]

Bought a new compression tester recently because my old, trusty Gunson Hi-Gauge was too bulky to fit into #8 and #7 plug holes of my Chevy 350 with new, aftermarket, heads.

My new tester has a very useful extension tube and various adapters. I have to use the extension tube, as the thread size on the of it is the size I need. The tube is a snap-fit into an adapter which, in-turn, screws-on to the larger spark plug thread on the end of the business end of the tester. The problem is, the gauge, when in this configuration, is not holding ANY compression and I can hear the air 'chuffing' out of the gauge. I'm positive ths air is escaping from the area where the extension tube snaps onto the adapter, as there's play in this fitting and no rubber O-rings in that area. Seems like a totally barmy design, as I fail to see how it can possibly be air-tight. However, maybe I'm doing something wrong? I've had another look on eBay and, it seems, even a Snap-On tester uses a similar design looking at a pic. However, I haven't had the opportunity to inspect one 'in the flesh'.

Here's the tester I've got...




Any ideas?

Cheers,
Ian.

[GreenV8S]

Can't work out from the words/pics which bits you're trying to fit together or whether they're supposed to fit in the way you're using them.

Is there just the one snap-fit connection in your kit, or do you have other bits that can be connected in a similar way? If you have any others, see if they produce an air tight connection and then see what the difference is between the ones that work, and the others. Perhaps you're missing an O ring? The only snap fit connections I've used have been mechanically locked together by a sprung part of the fitting that had to be released before they could be disconnected, with an O ring to seal.

[leorest]

ian_uk1975 said:

...I'm positive ths air is escaping from the area where the extension tube snaps onto the adapter, as there's play in this fitting and no rubber O-rings in that area...

Is the snap fitting you refer to the part in the top right of the picture? Are you sure this is being connected fully? It has a cylindrical collar which needs to be pulled back (foreskin if you like) to allow the male part to be pushed home. Some of these style of connector can require a firm insertion force.

[andy-xr]

I know what you're talking about and you're missing a rubber o ring I think

[ian_uk1975]

leorest said:

Is the snap fitting you refer to the part in the top right of the picture? Are you sure this is being connected fully? It has a cylindrical collar which needs to be pulled back (foreskin if you like) to allow the male part to be pushed home. Some of these style of connector can require a firm insertion force.

Yep, that's the bit. The outer collar is sprung-loaded and has to be pulled-back to allow the extension tube to fit. However, once the extension tube has snapped into place, there's quite a bit of play in the connection. The end of the extension tube that fits into the adapter at top right is the same as the end on the adapter at bottom right. There are 3 small ball bearings in the adapter that are pulled-back when the outer collar is pulled-back, enabling the extension tube (or the threaded adapter at bottom right) to snap into place. The ridge in the adapter then prevents removal, as it bears against the ball bearings inside the adapter. However, the connection is not air-tight and I can't see how it ever could be given the design.

All this is very hard to desribe in words, but very simple to see! Maybe I'll upload a YouTube clip.

There are loads of compression testers being sold using the same design, so I'm confused!

[ian_uk1975]

GreenV8S said:

Can't work out from the words/pics which bits you're trying to fit together or whether they're supposed to fit in the way you're using them.

Is there just the one snap-fit connection in your kit, or do you have other bits that can be connected in a similar way? If you have any others, see if they produce an air tight connection and then see what the difference is between the ones that work, and the others. Perhaps you're missing an O ring? The only snap fit connections I've used have been mechanically locked together by a sprung part of the fitting that had to be released before they could be disconnected, with an O ring to seal.

Yep, the threaded adapter at bottom right is the same snap-fit design. However, I can't test it as the thread size is wrong for my spark plug holes. I've looked at pictures of other compression testers using the same design and they do not have any (visible) O-rings around the snap-fit connections.

[GreenV8S]

ian_uk1975 said:

Yep, the threaded adapter at bottom right is the same snap-fit design. However, I can't test it as the thread size is wrong for my spark plug holes. I've looked at pictures of other compression testers using the same design and they do not have any (visible) O-rings around the snap-fit connections.

I'd have thought if the thing isn't sealing at all then just sucking/blowing on the end would show you whether there was any sort of seal; I doubt you need to actually connect it to the engine to show the problem.

[Pumaracing]

These are standard high pressure airline snap fittings. Looks like the female connector has its internal O rings missing. Send it back under warranty.