Battery vs. hand crank compression test

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Model T Ford Forum: Forum 2016: Battery vs. hand crank compression test
Top of pagePrevious messageNext messageBottom of page Link to this message  By tt newbee on Sunday, September 18, 2016 - 03:21 pm:

I just did a compression test on TT

Using the battery and turning her over 4 times I got 49 - 47 - 47 - 49.

So I decided to try it with the hand crank. The readings were in the mid-20's.

The readings were all taken with the spark plugs and carb removed.

This is a mystery to me. What am I doing wrong?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Sunday, September 18, 2016 - 05:46 pm:

Should be the same either way.


Top of pagePrevious messageNext messageBottom of page Link to this message  By tt newbee on Sunday, September 18, 2016 - 06:38 pm:

I thought they should be the same.

The engine was cold.

I checked by cranking with the battery, then with the hand crank. I did not remove the compression tester or change anything between the tests. I got a much lower reading on every cylinder using the crank.

I have since done a search and found the following:

Beg, steal or borrow a battery and recheck - you'll probably be pleasantly surprised by the readings.
http://www.mtfca.com/discus/messages/80257/92612.html?1243907565

Are you cranking over the engine with the starter Susan or just using the hand crank? You may get lower results with the crank.
http://www.mtfca.com/discus/messages/80257/112802.html?1257115774


Top of pagePrevious messageNext messageBottom of page Link to this message  By John E Cox on Sunday, September 18, 2016 - 08:12 pm:

If you have leakage(rings or valves) it would be lower when hand cranking I would think.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Sunday, September 18, 2016 - 08:24 pm:

You are most likely cranking slower by hand. If you had bad rings or valves you wouldn't be getting #'s in the high 40's. You're OK. Don't sweat it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave Young in Mays Landing, NJ on Sunday, September 18, 2016 - 08:44 pm:

What matters is that you got excellent numbers. The high 40's are great and may even improve a little once you get some time on it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, September 18, 2016 - 09:01 pm:

Because on battery you are going rurr-rurr-rurr-compression, rurr-rurr-rurr-compression, rurr-rurr-rurr-compression, rurr-rurr-rurr-compression =47. By hand it's like; ug,ug,ug, comprssion, ug,ug,ug,comprssion (dripping sweat about now) =20's LOL :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Thomas Mullin on Monday, September 19, 2016 - 02:08 pm:

I was surprised how fast compression drops. Got a gauge with a hold feature and now I can crank faster and still get a reading. I also use the crew in adapter.

When I tried running back and forth to the gauge, the readings were very low.


Top of pagePrevious messageNext messageBottom of page Link to this message  By tt newbee on Monday, September 19, 2016 - 02:35 pm:

Has anyone else tried checking compression both by hand cranking and using the starter? If so, what were your results?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Philip Berg on Monday, September 19, 2016 - 02:52 pm:

On my freshly rebuilt engine in my 16 coupelet via handcranking I achieved 50psi cold.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dewey, N. California on Monday, September 19, 2016 - 05:04 pm:

My compression tester is inherited from my father--he had a service station before WWWII (and one when I was first married in '76)--yep, I was a "Petroleum Distillate Transfer Engineer"!.
Anyway, back to my compression tester; its a Boyce Compresso-Meter and has a valve that keeps the read compression on the gauge, then you push a little button to release it. Very handy for checking compression by oneself.


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