signs of low compression and proper compression values ?

[rick 48 cub]

Hi All - I can't believe how fast people are responding - must be rush hour.

I suspect that I might not have enough compression on my 1948 cub tractor. What are the signs of low compression. What are acceptable compression values ?

Thanks again.

[Donny M]

Low power, hard to start, and blue smoke are a few. If you have doubts about the compression of your engine give it a test. Compression testers are reasonably priced and are also easy to use

[Jim Hudson]

120 pounds is like new anything less is less power. Blue smoke is oil burning. Breathing oil filler cap is a sign of clogged breather tube and or low compression.
Also check this out. http://www.cleancomputes.com/Cub/Blue%20Ribbon%20Service%20Manuals/GSS-1007%20Engine/index.html

[Eugene]

Lack of power, blow by from the crankcase filler tube, excessive oil smoke from the exhaust.

What is good compression? Even. When the compression gets below 60 or 70 pounds consider an overhaul. 100 to 110 PSI would be great.

What is acceptable? As long as the tractor is working OK I'd prolong the overhaul. If the tractor is using considerable oil I'd overhaul.

The Cub is definately under powered when compared to a 40 horsepower tractor. However, you have to consider that the Cub has 10 horsepower.

Just my opinion.

Eugene


Added. Do the compression test. If you haven't done so a tune up will do wonders even for an old tired engine.

[pgmrdan]

"Compression testers are reasonably priced and are also easy to use."

Who makes a good compression tester and who sells it? I wouldn't recognize a good brand at the auto parts stores any more.

This is one thing I should really get soon.

Thanks,
Dan

[beaconlight]

Any auto parts place. Sears, Harbor freight has them you can order e-mail. I don't think I have ever run into one that was so far off as not to be usable.

Bill

[Bigdog]

One other thing that needs to be mentioned is that the variation from cylinder to cylinder should be minimal - within 10% across the board. This is as important as the actual compression values.

[Dan England]

I often see statements that the four cylinders should have similar compression readings and am wondering why more than ten percent variation is bad. Would a compression reading of 87-87-90-90 be better than 100-83-100-100 and, if so, why? Thanks, Dan

[Bigdog]

Dan - whether one or the other is better is really hard to say. What the information tells you is the overall condition of the engine. The readings of 87-87-90-90 would indicate to me an engine that was overall showing conditions of wear. The readings of 100-83-100-100 indicate a possible mechanical failure on number 2 cylinder. Overall,even though the first set of readings indicate a tired engine, if it was not using / burning oil or showing other issues, you might run it for years before you need to do anything even though it would be somewhat under-powered. The second engine indicates a mechanical problem that if not corrected could lead to additional failures and major damage to the engine. The second engine might only have a burnt or carboned valve or might need a head gasket and might be cheaper to fix but you really won't know for sure until you look into it.

[Dan England]

B.D. That makes sense. Thanks, Dan

[beaconlight]

BD hit that one right on the head. I don't see how any one could have explained it better. When you listen to him you have the benefit of the ages.

Bill

[John *.?-!.* cub owner]

BD hit that one right on the head. I don't see how any one could have explained it better. When you listen to him you have the benefit of the ages.

Bill

And we do mean AGES!

[Bigdog]

Hey now!

[beaconlight]

Hey give me a break. Say something nice and look what happens. I can get into enough trouble all by my self. I don't need any help.

Bill

[Dave in Md]

I finally got to a compression check on my 53. I recorded 90, 90, 115, and 95. From the reading I've done here and other places 90-95 lbs is acceptable, nothing to worry about. I suspect the 115 lb reading I got on #3 is because of help that cylinder is getting. The plug is always a bit moist so everything else in that cylinder has a little extra sealing capacity due to the extra oil. Before I go tearing into the engine in the next few weeks, can you guys give me an idea what might be causing this? I'm thinking along the lines of a valve issue as opposed to rings since the compression is high compared to the other cylinders. Am I on the right track?
TIA
Dave