TO-20 Compression Test Results

Tractor back together I hope with the correct timing gears. After reading on here about how much a compression test will tell you about the engine I did one - actually several. Engine at operating temp, air intake non-restrictive, throttle plate open - I think, and oil squirted into the cylinders. The results - 1 is 85#, 2 is 25#, 3 is 120#, 4 is 120#. I obviously have some problems. My guess is some sort of valve problem, and/or rings need to be replaced.

Just wanted to hear what you all had to say before I started in on this.

Thanks, Stan

The correct way to do this is to warmthe engine up to operating temperature and then remove the spark plugs. Open the throttle all the way and take the compression readings dry. Record the numbers. Repeat after squirting an ounce or two of oil in each cylinder and record the readings.

Based on the way you did it,I"d guess that #1 needs rings and # 2 has a valve problem as a minimum. #3 & #4 probably are OK.

Jerry,

Sorry I did not share all the information. I did do the test dry - here are the readings for that test. 1 is 75#, 2 is 15#, 3 is 105#, 4 is 105#.

I"ll stand by my evaluation. Looks like rings on the #1 and burned valve on #2. #3  are good to go. Looks like the heads gonna" be comin" off!

Hi Stan.. Personally, I would not come to the conclusion that you need rings yet.. adding the oil to the cylinders didn't do much for any of the cyclinders and if you had serious ring issues, I would have expected a big improvement in compression after the oil was added. the low compression in #1 and #2 looks more like valves to me as neither were significantly improved by the added oil.. could be a head gasket leak between 1 and 2, but the numbers are so much different between the two, it is probably valves.. #2 probably has a severly burned valve. For me it would be: take the head off, have a valve job done, bolt it back on, run it for a while and then recheck compression.. Jim in OH

I agree with all the other guys. Might be a blown head gasket, but probably a burned, or gunked-up valve in #2. If you tear into it, check your valve lash/gap adjustment on # 2 when you pull the valve cover. If your totally lucky you just have a badly adjusted valve that is not closing all the way. I've head several stories of guys that had heavy oil/carbon build-up on valves that were able to get cleaned-up good enough to restore good operation by using one or more snake oil products. Marvel Mystery Oil or tranny fluid soaked in the cylinders for several days has been effective to loosen gunked-up compression and oil rings and valves. I've used that trick myself on my 'ol VW that burns oil terrible...After filling the cylinders and turning by hand (without spark plugs) and refilling, and letting sit over night... couple days of that, That engine ran a whole lot better.

George

Stan, Last year I had the same problem. I did as Jerry and George recomended I found that the valves were burned. Since I did not have the equipment to remove the bad ones I had them all done, It has been the best investment I have made in this tractor. Now I have great compression and plenty of power. We have a local machine shop in our area that re-worked the head with all parts and labor for about 350.00. I considered this a bargain, he also supplied the gaskets in the price. We use this tractor regulary and I believe it was worth the money. It was a good job as I have not done any major engine work since I was much younger.I hope this helps. When you have a book it makes the job real easy. God Bless, John

(quoted from post at 09:12:55 05/27/08) .... We have a local machine shop in our area that re-worked the head with all parts and labor for about 350.00. I considered this a bargain, he also supplied the gaskets in the price. .....

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Glad it was worth it, but just for the record, $350 is a lot for a valve job.. just finished mine... $80 complete head rebuild parts kit(this site).. $35 complete top end gasket kit (this site) and $120 complete machine labor including hot tank, bead blast, pressing in all new valve guides, three angle grind, and complete assembly.. $235 total... Jim in OH

As some of you experts are fond of saying, "Supply the proper amount and type of information about your problem and you'll get lots of help" I did and you all responded with a lot of useful information. Now some follow up questions that show my ignorance.

I will be pulling the gas tank and valve cover to see what I can discover about the valves from there. I am using Marvins Mystery Oil in the oil - I like what George said about letting the cylinders soak for a couple of days. Is it useful to use it in the gas? What exactly causes burnt valves? - I'd like to know to make sure I have corrected that problem. Because all of this really started last August I have not been able to mow since then. Are these problems serious enough that I need to fix them before I do any mowing with the tractor or can I at least get one mowing out of the way and then attack them? The grass is high, early summer coming on and the fire danger can get out of hand quickly is my concern.

Again, thanks for all the useful advice and diagnosis. And for any help on these follow-up questions.

Stan

Valves get cooled by contact with the seat which is cooled by the coolant circulating in the head.
There is also some charge cooling that is caused by the evaporation of the fuel in the incoming air charge on the intake stroke. That"s why you never want to run these Continentals too lean. So the valve has to be ground correctly to seal and to contact the seat and transfer heat.

The valve lash has to set correctly. If it"s too tight, it won"t sit on the seat long enough to transfer the proper ammount of heat. So if you are going to err in setting lash on the exhaust valve, err on the side of increased lash. They maybe noiser, but they won"t burn out.
The exhaust valve is made out of high temperature alloys that reduce the susceptability to oxidation at the high temperatures they operate at. But if the valves are not correctly seated and the lash is set too tight and the mixture is too lean they will literally burn. A section will literally be missing when you pull the head and look. They will also stretch at the neck and can eventually fail there. If you run them too long that way they will start to burn out the seat. The shop manual recommends never setting the power jet less then one full turn out to preclude overly lean mixtures.
Pulling the valve covers will allow you to check the lash is about all. You won"t be able to see the business end of the valves.

Hope this helps you.

(quoted from post at 19:57:51 05/28/08) ... Are these problems serious enough that I need to fix them before I do any mowing with the tractor or can I at least get one mowing out of the way and then attack them? The grass is high, early summer coming on and the fire danger can get out of hand quickly is my concern.....

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Anytime I (or anyone else) am asked "how long can it run before it breaks", it is pure speculation... First of all.. something already "is broken".. Would I mow one last time?? Probably, I would.. If doing it myself, I'd have the gasket set in hand, have talked to the machine shop (or mechanic, if not doing it yourself) to prearrange a time early in the week.. cut the grass short enough Friday afternoon to get me two weekends.. have the head off and to the shop on Monday morning (or alternatively take the whole tractor to the mechanic on Monday).. hope that they promised it for Thursday (so they will actually have it done by Friday).. try to put it together on Saturday..

Or might be a broken valve spring on No 2. It's possible to replace without taking head off if you're careful.

Thanks for all the great information and advice. I hope to have some time next week to pull the gas tank and valve cover to check out that part of it. I checked all that out before and adjusted everything to spec - cold and hot. I will let you know if I find anything.

Thanks, Stan

Finally had time to pull the gas tank and valve cover. Found just exactly what I thought I would - valve train working well. Readjusted the clearances a little. Then pulled the plugs and turned the motor to show as much of each one of the valve heads and faces as possible. They all look okay - smooth and clean except one. You guessed it - #2 exhaust valve face looks like it has some problems. It appears to all be there just not clean and smooth. It looks like it has some sort of build-up on it - gray in color and is lightly pitted.

I'll be calling my local tractor shop tomorrow to see about redoing the head and valves.

Stan