850 Engine Compression Results, Now What?

Bought a 1957 850 this week, an improvement from the 2N I restored last year. I did an engine compression test and could use some help in diagnosis and plan of action. The test result are as follows, First No. is Cold Engine, Second No. is Cold Engine with a squirt of oil, Third No. is Hot Engine no oil. They are for cylinders moving from dash to radiator in a row (not firing order), Cyl 1 120/125/110, Cyl 2. 75/85/75, Cyl 3. 92/88/95, Cyl 4 107/91/102. No Oil in coolant, no water in oil. Plugs all have equal amounts of carbon, but not caked on too bad. No plug or insulator damage. No smoke in exhaust, even on cold start-up. Engine is covered in oil from years of use and probably bad gaskets. Oil pressure 50 lbs. Hours on what is probably the original proofmeter is 6900 hrs. Engine sounds fine, no rattle, pings, etc. No history on tractor other than it was a working tractor and ran fine on my purchase. No real rust, original hood, 801 replaced fenders and foot boards. WHY is hot engine compression lower than cold engine, I thought rings would expand when hot? What is typical reason for such a large difference between cylinders? Oil did not significantly improve compression. What is going on with Cylinder 2 (is this valves, rings, or other?) I assume no blown head gasket as fluid are not mixing. What should I do next, what can I expect, ie. full rebuild, just valves, valves & rings??? Thanks all, REALLY appreciate any suggestions, experiences, etc. Larry
 

You've got your cylinders numbered backwards. #1 is next to the radiator.

Be that as it may, you possibly have a head gasket issue between cylinders 2 and 3.
 
Braze a air chuck to a spark plug and with 2 at TDC pressurize the cylinder. Hiss in #3 cylinder or not will verify gasket.
Leak down test will verify valves.
 
As others have said possible head gasket compression leak between 2&3. But another thing i have run into on these is that the valve adjustments seem to get neglected. Ive pulled the tank and then the valve cover and checked the valve lash before getting to excited about pulling a head..
 

What I would do would depend on what I want it to do for me. The two holes that are low, when put together with how it runs, aren't low enough to be a really bad head gasket. If I needed to depend on it for high dollar crop work I would want to make it more reliable. For more usual life for that age tractor I would just clean it up, use it, and monitor it. The tractor is designed for you to be able to remove the valve cover without removing the tank.
 

A Cylinder leakage test will tell you where the leakage is at...

What I have to say about it is in this post...



https://forums.yesterdaystractors.com/viewtopic.php?t=1392134

When you do a compression test you need to record the first five hits on each cylinder. The fist tell you the ability of the valves to seal the rest tell you the ability of the cylinder to build compression..

Because we don't know where the piston is at you will have to replete the test several times to find your highest number for the first hit... That is the one you would record all five hits...

In your test use Cyl 1 120/125/110 as a good one it looks good and compare it again #2 & 3 record all if your 5 hits from the check that showed the highest first hit...

Once you add oil it will help a leaking valve that has a dirty/rusty seat seal it won't help a burnt valve... About all the increase you will see tho is 5psi on the first hit if it greatly increases the other hits on a cylinder with low numbers its more than likely a piston seal issue..

We need those 5 best hits to make a good judgment call from there we determine what test to use to find zacky where the leakage is lost before we tear into it in the blind...

If we cannot build a first good hit all the rest of the numbers are moot that first hit is the magic number we work off of :wink:
 
Wow, some great help offered. I cant do it today, but tomorrow, Wed, I will go back and re-do the compression tests and record the "first
hit" on each cylinder, and I will do it as suggested several times for each cylinder to get the highest first hit number. I did actually
watch the pressure gauge while turning over the engine, but I did not record the first hit for pressure build up, only the final number.
I will record these numbers and get back to the forum before I start playing with the valves. I am going to do a restoration on this
tractor, and will want to replace the gaskets anyway to stop the oil leaks onto the engine, and for preventative maintenance, so eve if it
needs a new head gasket, that was going to be done anyway. Thanks, Larry.
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top