Compression

[DickC]

What is acceptable? I have a 25 coupe and the compression for each cylinder is 38-39 pounds. Engine runs smooth and seems to have enough power for tours. I took the compression in hopes of finding an answer to oil consumption. Have checked all areas for leaks, no drips, rear end for oil seepage passed 4th main, etc.

[TXGOAT2]

How much oil does the car use?

[Charlie B in N.J.]

Was that hot or cold? Hot I’d say it’s on the low side. Did you do a wet/dry test? That would tell you if it’s valves or rings. If the test was done cold and it’s the rings the comp might come up a few Lbs. taking you into the low 40’s. If it’s the valves eng temp doesn’t matter to compression. There wouldn’t be a change.

[TXGOAT2]

What procedure are you using to check compression?

[Scott_Conger]

most compression testing rigs for "T"s are generally inadequate and tend to give low readings. If your setup does not gather multiple compressions and have a release valve, you will get low readings. Your T runs well so I would not obsess over the readings.

Your complaint is excessive oil consumption...given that and the fact that Model T's do not have oil control rings on the pistons, or seals on the valves, I would have to ask this: When on tour of 150+ miles per day, how much oil do you consume? My experience has been that anything other than a brand new engine will tend to consume somewhere in the neighborhood of 1/2 quart or so of oil per day at sustained 35 MPH and 150 miles distance.

[Art M]

Maintain the oil level at or below the upper valve.
How oily are the spark plugs and are they all oily or just some.
Is the exhaust smoky at idle when the engine is hot.

I wouldn't worry about either the low compression or the oil consumption, but if it bothers you, do a ring and valve job .
Warning. Once you get into the engine you will probably find a lot of other issues.

Art Mirtes

[JTT3]

Some people forget to open the throttle fully when doing a compression test which if not done will effect the readings negatively. Best John

[Norman Kling]

A few drops of oil in each cylinder and a good compression gauge will tell you what the compression is. If you don't have one, you need some sort of adapter to fit the pipe threads on one end and the threads on the tester. Usually those on the tester are metric for modern spark plugs. I have a tester with a rubber cone shaped end on it which works with two people. One to hold the tester in the head and the other to either turn the crank or starter. Best way to test is to remove all spark plugs and open the throttle to full throttle to get as much air into the cylinders as possible and also relieve the pressure on the cranking mechanism so you can get the fastest spin possible. even jacking up the rear wheels with the parking brake off helps.
Most important things to remember are that even compression between cylinders is desired and that the compression varies with altitude above sea level, so if you are on a mountain it would be lower than at the coast. Also the type head on the engine changes the compression. The standard high head for your engine will be the lower compression, usually about 45 to 50 lbs. The aluminum high compression heads or the older standard iron " Low" head will also have higher compression. These were stock only on the engines before world war 1 and the high head used the remainder of the production.
If the engine has been rebuilt with modern pistons, they do have oil relief rings and also compression rings. and all rings are above the wrist pins, so there would be no leakage around the wrist pins.
One way to tell if your engine is a severe oil burner, is to go downhill in compression or even a stop from a high speed long slow down on compression, then start out with open throttle and if a lot of blue smoke comes out the exhaust, you are burning oil. Note on a cold day, with a cold engine, you will get what looks like white smoke, which is actually steam from condensation in the exhaust system. So make your test with the engine warmed up.
Norm

[DickC]

Thanks for the replies. I will try the drops of oil and open throttle technique to see if it makes a difference. In regard to the question on oil consumption,
the last tour we took this T on was fairly flat,(rolling hills) that required frequent compression slow downs as I try to keep the speed around 32 to35 mph. If I find I am too close to the car in front I will let off on the gas and let the engine slow me down. In about 100 to 110 miles I used a little over a quart. No noticeable smoke but sometimes when starting from a light a puff will be apparent. That amount of oil will not drive me to do a "rebuild" as the engine is smooth and has plenty of power.

[TXGOAT2]

That's a little on the high side on oil consumption. But if the car runs well and does not leak or blow oil out the oil filler cap, I would run it. As for compression tests, the speed the engine is cranked when making the test, among other things, can affect readings. Note that the oil level in the crankcase can affect oil consumption. The oil level must be kept at or above the lower test cock on the crankcase. It is not necessary to keep it up to the upper test cock, and it should never be above the upper test cock. You might try parking the car on a level surface for an hour or so, or overnight, then placing a pan under the crankcase and opening the lower test cock to allow oil to drain down to its level. (Which might take a while) Once that's done, add one pint of oil and go drive the car. Warm it up well, and see if you can make it smoke. Ford sugessted running the oil level halfway between the upper and lower test cocks. That's about 1 pint above the lower test cock. If you have a high volume accessory outside oiler installed , they can make a tight motor smoke at idle. Rod dippers might do the same thing.

[Scott_Conger]

From this last description, I will bet in a few years it will start to smoke at idle but not while on the road. At that time, you'll be in the market to do a valve job, with oversize valves and that's about it. I'll bet your plugs still run clean, too. You're pretty much describing my nearly all original '19 and I wouldn't dream of doing anything but add oil or change oil until it starts smoking, and then, I'd take my own advice and drive it another 10 years.

You can fret over compression if you want, though I cannot imagine what that will gain you, and I'm sure there are those who would advise you to refresh an engine that is "smooth and has plenty of power". I wouldn't, but hey, if you decide to, to each their own.