Case VAC running poorly

Hi guys i'm having a few problems with my 51 Case VAC, I just readjusted the valve clearances that worked their way out almost double the clearance that they should've been... after doing that I ran the tractor for about an hour just to have the number three exhaust valve loosen up on me to the point where it almost stalled the motor... After the motor cooled I readjusted the valves and have been running the tractor ever since.... The problem that I'm having currently is that the motor stumbles and misfires regardless of where it's at whether it be idol or full throttle... i'm just wondering if this may be due to a bent pushrod? Or fuel/carb? or ignition timing?

Why would it be timing? Once the timing is set on an engine, it doesn't just wander around by itself.

There's a little spring loaded button inside the distributor cap. Make sure that isn't kaput.

If the abof mentioned items seem to make no difference, Check the distributor shaft for looseness (toward and away from the rubbing block, not in and out). If it is loose at all. it is too loose. It will cause the tractor to have erratic timing. Jim

Did you see any reason for the ex valve to loosen?

If the jamb nut was left loose, that is an obvious and correctable reason. But if the adjustment was still where it was set, and there was a major change in the lash setting, the change had to come from somewhere.

A bent pushrod is easy to determine, just spin it and watch for wobble.

Also check for a broken valve spring, or a sticking valve.

Another cause though can be a valve seat loose and falling out, holding the valve down. Sometimes they will go back in place temporarily then come out again.

Doing a compression test will show some loss if the seat is loose, total loss if it comes out.

As Janicholson said, check the distributor bushing, point condition and gap. Check for spark quality at the plugs.

There is a drain plug in the bottom of the carb. With the engine off, fuel valve open, pull the plug and catch the gas in a clean glass. The flow should be a solid stream, slow to a trickle as the bowl empties down, but continue to flow as a trickle, not stop or slow to a drip. Look at what was caught, check for water or trash. If contaminated, the tank may need to be cleaned, whatever was in the glass will also be in the carb.

Thank you all for the informative replys I'm really happy to have a second opinion with this problem. It looks like I have a good amount of info to work with now. One other follow-up question if you guys wouldn't mind, what would be a good compression range for this motor?

I assume you know each piston has to be on the compression stroke when you set the valve clearance.

had similar problem Saturday. Check this thread.
Richard in NW SC
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That is a low compression engine, so don't expect much, maybe 80-90 PSI.

What to look for is consistency between cylinders.

The best test is to get the engine up to operating temp, pull all plugs, throttle open, battery fully charged.

Use a screw in type tester, spin the starter until the pressure is at it's max, usually about 6 to 10 compression strokes, write down the results.

Then add about a teaspoon of oil to each cylinder, repeat the test.

The results will be slightly better with the oil, as the oil helps seal the rings.

Any low cylinder that gets dramatic results from the oil has ring problems. A low cylinder with little improvement has a valve or gasket problem.

Do some simple trouble shooting like I tell many people on here

#1 check and make sure you have a good blue/white spark at the center wire of the distributor and at the 4 plugs that jump a 1/4 inch gap or more
#2 pull the carb drain plug and make sure you have a good steady flow of gas that will fill a pint jar in less then 3 minutes.
#3 when was the last time you serviced the air cleaner and dumped the mud and water out and fill with new oil.

Thanks to all of you for the good advice also to Steve@Advance, I'm going to run it through a compression test tomorrow to see just where the engine is at... I'll be sure to update my findings on this thread once the test is done....

Ran a compression test thankfully it was an even 90 psi in each cylinder... but I have found the problem and I'm almost embarrassed to admit it BUT on the number three cylinder I noticed the crush washer from the old plugs was still there meaning I doubled up on washers on the number three so removed the old washer put the plug back in and it runs fine.... ahhh! :roll: