Compression Testing Issue

[dolt]

Would you mind running my specifics through your calculator and see what you get for SCR, CCR, and CCP, just for comparison? 103 build, flat tops, 255 cams, .045 gaskets, assume 85 cc chambers.
Thanks!

Very similar numbers to your calculator; did not expect much variance as the math is pretty simplet.
103"/-1.5cc dome volume(flat top)/intake close @ 25*/85cc chambers/.045" head gasket/avg deck height .006"/1200' ASL
9.76SR/9.46CR/190.1CCP

Just for grins checked at 86cc.
9.67SC/9.38CR/188.5CCP

Variables could be deck height and chamber volume. Chambers typically are 85-86cc but tend to be closer to 86; I have seen chambers measure 90cc.

 

[Rod Stewart]

dolt;
OK thanks for that. Good to know we are pretty close!

Hose length did not make any difference, I checked my Snap On set 3 different length hoses No change

Thanks for checking that Jack.
Just a question on the tester; is the Snap On release valve on the gauge, or on the cylinder end of each hose? Presumably on the gauge.

 

[joel]

On my compression testing hoses there are Schrader valves In the end that screws into the cylinder head.
This keeps the compressed air in the hose. When the Schrader valve becomes dirty and allows that compressed air back into the combustion chamber it does affect the readings some.

 

[dolt]

On my compression testing hoses there are Schrader valves In the end that screws into the cylinder head. This keeps the compressed air in the hose. When the Schrader valve becomes dirty and allows that compressed air back into the combustion chamber it does affect the readings some.

Very good point Joel; one I should have pointed out a few posts back.

 

[dolt]

Thanks for checking that Jack. Just a question on the tester; is the Snap On release valve on the gauge, or on the cylinder end of each hose? Presumably on the gauge.

I believe you will find that all compression testers locate the release valve at the gauge; never have I seen one located anywhere else.

 

[Rod Stewart]

On my compression testing hoses there are Schrader valves In the end that screws into the cylinder head.
This keeps the compressed air in the hose. When the Schrader valve becomes dirty and allows that compressed air back into the combustion chamber it does affect the readings some.

This to me is the better system, and makes for better accuracy. JMO.

 

[dolt]

This to me is the better system, and makes for better accuracy. JMO.

I have not seen a compression tester, other than the hand held, that did not have a Schrader valve at the connecting end of the hose. Are you saying that the HF tester does not have the Schrader valve?

 

[dbmg]

I have not seen a compression tester, other than the hand held, that did not have a Schrader valve at the connecting end of the hose. Are you saying that the HF tester does not have the Schrader valve?

Harbor Freight schrader is at gauge. If you look at first kit it has the non screw type fitting for spark plug hole. I do not how you could get a accurate reading trying to hold in plug hole while opening throttle and cranking all at the same time unless you had a helper.
http://www.harborfreight.com/catalogsearch/result?q=compression+tester

 

[dolt]

Harbor Freight schrader is at gauge. If you look at first kit it has the non screw type fitting for spark plug hole. I do not how you could get a accurate reading trying to hold in plug hole while opening throttle and cranking all at the same time unless you had a helper.
http://www.harborfreight.com/catalogsearch/result?q=compression+tester

Are you sure! Looking at the picture, I think I see the tip of a Schrader valve in the threaded connectors. I have used the non screw in type compression tester back in the day and always had to have a helper and usually had to check each cylinder 3-4 times to be sure of the reading.

 

[Rod Stewart]

I have not seen a compression tester, other than the hand held, that did not have a Schrader valve at the connecting end of the hose. Are you saying that the HF tester does not have the Schrader valve?

Bingo!
The HF tester does NOT have a Shrader valve at the cylinder end of the 18" hose.
All it has is the release valve right at the stem of the gauge itself. Thus the problem I have been talking about.
It takes both hands to hold the short rubber tipped spigot in the plug hole, and a helper to activate the starter button. Its easy enough to block the throttle wide open beforehand, so at least you don't need another free hand to do that.