Compression readings not so good on gas engine.

[JimR]

All the above items are good suggestions. I do have to put my 2 cents in. I spent 10 years of my life as a mechanic and the next 20 years as a machinist. If you are going to do the rings. You really should do the bearings and valves while you have it all apart. Unless of course the bearings are like new and show no wear. The valves should at the bare least be lapped. This is a real easy job using a small suction cup like tool you can buy for under $10.00 at any local parts place. They also sell valve-lapping compound. Buy the finest that they have. Check the valve stems for slop by pushing the valve side to side when it is about 1/4 open without the springs on them. Also look at the valve stems for any noticeable wear on the shaft. Why the rings would be gone with only 1300 hours is beyond me. Maybe the rings are stuck. I would not think they are worn out. Do another compression test by squirting 2-3 squirts of 10-40W oil into the bad cylinders to see if it is in fact the rings. If it is the rings, I would do the following to see if they are in fact stuck. First I would spray a lot of rust buster/nut loosener fluid into the 2 bad cylinders. In a few days I would do the following. Drain the oil and put in 3 quarts of kerosene and 2 quarts of oil. Run this for about 20-30 minutes at 1200 rpm's. Dextron II or III will do the same thing. I like Kerosene because it is lighter. If the rings are stuck this will surely free them up. (I did this on a Chevy 350 that was cooked from overheating. Lady didn't realize it until the motor froze up. The oil drained like mud and the motor had very little power. After I did my thing it was purring like a kitten once again.) Then change the oil filter and oil using 10-40W oil afterwards. Riun your tracotr for a good few hours and take another compression test on the bad cyclinders. If they are stil low. Drain the oil and put 20-50W in it. The heavier oil will help to seal the rings a little bit better but not much. This of course will make your tractor harder to start in the winter. I use to run 20-50W in my old Ford 8N because it smoked really bad. The change to heavier oil cut the smoke down to about 50%.

 

[Keoke]

Roto, when doing compression test, if you are doing one cylinder only then you must hold throttle open. You have to take in air before you can compress it. However, if all the other plugs are also out then there is no need to hold throttle open since air for tested cyl will come from the other open holes.
If you want to be sure as to what the leakage problem is take an old spark plug break out the porcelain and braze in a male air chuck fitting. Get testing cyl on exact tdc compression (both valves closed). Put air hose in bench vise or use a vise grip to regulate air flow into cyl. The Pro's do this with a pressure regulator for fine control. Now listen at blocked open carb for intake valve leak (stuck?) exhaust pipe (burnt/stuck) and oil fill or crankcase breather (rings). Take radiator cap off and look for bubbles (head gasket).
The toughest part of this test is getting cyl on exact tdc (dead rock) to keep the engine from turning backward or forward when applying air. If you have a hard time with getting dead tdc you can cheat by getting close and then putting tractor in gear and locking the driveline with brakes. Be sure both valves are closed. And be real sure that the brakes will hold the vehicle solid when letting the air in for this is dangerous business.
To find tdc on cyl other then #1, measure circumference of front pulley from tdc mark. Use cloth tape for this and convert fraction measurement to decimal reading. Divide this figure by number of cyls and mark on pulley (eg, 12 inches divided by 4 cyls = 3 inches) so every 3 inches (twice around) equal's one cyl on tdc. Remember, it takes two turns (720 deg.) of crank turn to fire a cyl. Firing order on most 4 bangers is 1-3-4-2. Be sure to turn engine in the right direction. This procedure will get you close, but not necssarily right on tdc for tested cyl. All mentioned of tdc here refers to top of compression stroke not exhaust stroke.
Enough all ready, good luck.

cheers,

 

[JimR]

You do not need to be at TDC to do a leakdown test. All you need to do is to be on the compression stroke. The easiest way to find that is by putting your finger in the plug hole and turning the motor over with a ratchet until you feel or hear air hissing by your finger.

 

[normde2001]

"Sorry I cant figure out how to change colors so these questions and answers are same color."

Just use quotation marks around the copied and pasted quotes.

 

[normde2001]

"If you want to be sure as to what the leakage problem is take an old spark plug break out the porcelain and braze in a male air chuck fitting."

You can buy that adapter at any autoparts store for about $2, It's used to pressurize, and hold valves up for assembly.

 

[Roto]

Ok guys here is what I found out, I checked the vacuum and it held 18 throughout the rpm band which seems good to me. Now for the best advice I got so far from Nasty135 and that is to do compression test at normal operating temperature. When i checked it last I did it when cold and today I let it run until it warmed up and much to my surprise that bad cylinder was 145 instead of 70 like it was before. I put plug back in put tools away and said thats enough messing with that!! I didnt even bother to try the oil or the other cylinders. Why do you suppose it improved that much just becasue it was warmed up? must have been the oil that was flying around in there from running it. I am much happier now thats for sure. As far as oil goes I have been running staight 30 weight and If I wanted to go a little heavier what would be the next step? 15/40? I should have mentioned in earlier post that it did NOT burn any oil either which makes sense that it couldnt have been only 70 on that cylinder. Anyway, I really want to Thank all of you for your help. </font><font color="blue" class="small">( testing the color thing )</font>

Mike

 

[Keoke]

Hi Jim, if you are not at TDC the air will drive the
piston down and rotate crank forward or backward to the bottom of the stroke.
Also, the intake valve stays open for a good
part of the compression stroke. It closes only
towards the end of the compression stroke.
True TDC has the connecting rod straight up with no lead
forward or backward on the crank throw. It is like
putting the pedal on a bicycle crank straight up and
droping a load on it. With no off center lead on crank all force
will be vertical and thus pedal wont move forward or
backward and load will be absorbed by crank main bearings.
And yes, you can buy and air to cyl adapter instead of making one. It will likely cost you more then $2.00, but not a **** of lot more.

cheers,

 

[JimR]

</font><font color="blue" class="small">( Ok guys here is what I found out, I checked the vacuum and it held 18 throughout the rpm band which seems good to me. Now for the best advice I got so far from Nasty135 and that is to do compression test at normal operating temperature. When i checked it last I did it when cold and today I let it run until it warmed up and much to my surprise that bad cylinder was 145 instead of 70 like it was before. I put plug back in put tools away and said thats enough messing with that!! I didnt even bother to try the oil or the other cylinders. Why do you suppose it improved that much just becasue it was warmed up? must have been the oil that was flying around in there from running it. I am much happier now thats for sure. As far as oil goes I have been running staight 30 weight and If I wanted to go a little heavier what would be the next step? 15/40? I should have mentioned in earlier post that it did NOT burn any oil either which makes sense that it couldnt have been only 70 on that cylinder. Anyway, I really want to Thank all of you for your help. </font><font color="blueclass=small">( testing the color thing )</font>

Mike )</font>

Yes, you are right that your rings were dry when you did your compression test. The oil had drained off the walls and rings and you got a low compression reading because of it. Just a little note about oil burning. Low compression does not mean your engine will burn oil. The oil ring if it is working properly will keep the oil out of the cyclinder. You say your running 30W oil. Is that detergent or non-detergent oil? If you are running detergent oil then 10-40 or 15-40 would be the next step up.

 

[Roto]

Jim, Im running straight 30 detergent oil because i think that is what manual said in 1969 so i stuck with it but maybe 15/40 would be the better way to go Im not sure. That 15/40 means its like 15 weight when below freezing and is like 40 weight when its hot? that how it works? Anyway, i do see a little smoke when i start it for a few seconds and noticed at pto rpm's i do see a little smoke coming from breather tube but feel no air. Even though the cold check was not the way to do it, It probabbly suggest that cylinder is warn a little more then the others and needs the extra oil to get good compression so just wondering if overall the 15/40 oil may be thicker and get better compression or just stick with the straight 30w.

Mike

 

[Soundguy]

Did you do the compression test dry on a warmed engine, and then wet? Try a wet test if you didn't. Worn rings will come up more than 15-20 psi.. and if no increase... be looking at yer valves.

Anti-foul adapters are pretty cheap for the fouled cyls.. if you are looking for the cheap way out..

Soundguy