Exhaust Valve Leakage - Help Needed

[oliver2-44 10,445]

I picked up my 1974 C160 Auto  about a year ago and got it running this spring.

The PO said he bought it to restore, put it in the barn and never got to it. So after cleaning fuel system and changing engine and Sundstrand black slug oil it came to life. I’ve added the seat, temporary muffler and 2nd hydraulic valve. Tranny is strong and engine ran good at idle but would backfire every couple of minutes at 1/2 or more throttle New Plug was black quickly so I leaned it out but it would then bog down under load. So I decided it was tune up time. New points installed and adjusted using ohm meter came out to 0.18. Opened the carb and someone had taken taken a screw driver  to the main jet and it was shot so I ordered an aftermarket carb. While I waited for  the carb  I pulled head to decarbon and since carb was off good time to check valve adjustment, all was good so I put it back together and no improvement. 

 

ive been wanting a Cylinder Leakage Tester and my Oreilly store made me a good match sales price.  I hooked it up..... .

At 50 psi input I had 9 ypsi leakage or  20% which is to much. I found I had excessive exhaust valve leakage and some cylinder leakage back into the crankcase.  The intake valve seems to be sealing good 😀

Rechecked valve stem to lifter clearance and exhaust had 0.017 and intake 0.007 clearance, right on spec. I re pulled the head and exhaust valve. I lapped valve some more then checked it with machinist prussian blue and have a good 0.60 this or more sealing contact.. I also took a new exhaust valve and checked contact and it was good 

     I  checked valve stem size and it is worn but still in spec.  I put exhaust valve and spring back in and sprayed  some wd40 around the top of the valve and it did not leak through. I put head back on and retested and still have the same exhaust leakage

     I’m at a loss, what am I missing

[Tuneup 1,441]

Sounds to me that you ruled out the valves so, rings? Warped head? I'll show my inexperience using that tool and suggest that you seal around the piston edge with some grease and try again. Same leakage and I'd say head gasket or warped head. OK guys, your turn

[squonk 42,886]

Are you positive your engine is staying at TDC when applying air? Every one I've done a leakage test on the piston will move some. I mark the flywheel at TDC  and make sure it at the right spot before reading leakage.

[oliver2-44 10,445]

I hadn’t though about that @squonk I’ll check that in the morning. 

[cleat 7,123]

That engine might have a compression release causing your issues.

 

[oliver2-44 10,445]

My internet has been out for a few days, so I'm slow getting back to this.

 

Lesson #1. @squonk was correct in that my piston was rotating backwards when I applied air to the cylinder for the test. I rechecked it (engine cold) making sure the piston stayed TDC and previous exhaust valve leakage went away.  Intake and Exhaust valve now have no "hearable" leakage cold.  But cylinder leakage continued.

 

Lesson #2. After reading many pieces of information on "Cylinder Leakage Testing"  several have said this test needs to be done with the engine hot, because you will get an inaccurate indication of piston blow-by with the engine cold.  Makes sense, since the piston expands during operation.

 

My #3 son is getting married this weekend so my hoped for  tractor reassembly time over this past 3 day weekend didn't materialize.  But lots of good family preparation and togetherness!  I may not have daughters, but the remains of my checkbook will still dance at his wedding    

[oliver2-44 10,445]

Closing out this old thread.

I did recheck the leak down with the engine hot and the valves were still good, but I had  even more leakage 12psi from the cylinder. I pulled the head one more time and measured the cyl bore (which I should have done the very 1st time) and it has some out of round wear. So I guess this out of round is getting worse when hot.

I did a static timing which indicated I needed to adjust the points some.  After this points adjustment the engine runs good, but  will black foul a spark plug after 10-20 hours of use. it smokes a touch at startup, and very hard working (pushing dirt with dozer blade), but I don't see any smoke with normal usage.  I can tell it's burning some oil by monitoring the dipstick  An overhaul with over-size rebore of the cylinder is in its future. 

 

Lesson #3 Whenever I pull a cyl head I measure cyl top and bottom, at 0 and 180 degrees and record it on a spreadsheet I've started on all my engines..