35, 35, 36, 35 and then...

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Model T Ford Forum: Forum 2015: 35, 35, 36, 35 and then...
Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Thursday, January 22, 2015 - 03:03 pm:

Cold compression test on the 23 touring. I didn't want to run the engine indoors enough to warm it up. With all the plugs out and the carburetor off, I cranked about a half dozen times on each cylinder. The 35, 35, 36, 35 was cranking dry. After a couple of squirts of oil in each cylinder, the numbers became 37, 38, 40, 47. I guess there's some leaking of both rings and valves, and the big change on #4 means rings more than valves on that one. Does that make sense?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Robert G. Hester Jr., Riverview, FL on Thursday, January 22, 2015 - 03:10 pm:

Time for a ring and valve job. :-(


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Thursday, January 22, 2015 - 03:15 pm:

The numbers before you squirted oil are all very close, so for there to be a valve seating problem all the cylinders would have to have it (seems unlikely to me). Why #4 went up more than the other cylinders after the oil is a bit of a mystery, was that the cylinder that you oiled first? Maybe its oil had more time to spread around the rings and seal them up before you checked the compression again.

Since you're checking the compression cold, your numbers don't seem out of line to me, here are a couple of earlier threads on compression testing:

http://www.mtfca.com/discus/messages/179374/227110.html?1312211952

http://www.mtfca.com/discus/messages/411944/491665.html?1415259822


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dennis R on Thursday, January 22, 2015 - 03:53 pm:

Are you turning it over with an electric starter? If you are, be sure you have the throttle wide open. If you don't, you're compression readings will be artificially low as you will be pulling a slight vacuum in the cylinders and not getting a full charge of air to compress. Just my 2 cents...


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Thursday, January 22, 2015 - 03:53 pm:

Why don't you start the engine and warm it up, then repeat the test and see what you get? Seems to me to run a test on a cold engine that's been sitting for a while could have a lot of variables mixed in the results.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Thursday, January 22, 2015 - 05:26 pm:

I don't know what your altitude is but the compression will be lower at higher altitude. I don't think you will get a very good reading when the engine is cold. This would especially be true if it hasn't been run for a long time. It could also vary according to how much oil you squirted. The oil is only supposed to coat the rings to help them seal. If you put too little in cylinders 1-3 they could still read lower. Likewise if you put in too much in #4, you could have decreased the size of the combustion chamber and the reading would be high.

Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Tillstrom on Thursday, January 22, 2015 - 07:56 pm:

When doing a compression test make sure the throttle is wide open. With them all being as even as they are I wouldn't do anything to it without running it down the road a few miles and repeat hot (with throttle wide open). It also helps to remove all four plugs.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Thursday, January 22, 2015 - 08:48 pm:

RE read Steve's post.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Thursday, January 22, 2015 - 09:15 pm:

Yes, the throttle position is irrelevant when the carburetor is off the car. :-) I'll take the car outdoors and warm it up, then see how it tests.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Thursday, January 22, 2015 - 09:30 pm:

The warmed-up compression readings will be interesting and useful as a baseline for future comparisons.

If the car runs smooth and pulls well with four good plugs in it, that sure sounds like victory to me, drive the car and enjoy it! :-)


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