Ford 640 pistons

Ramseyer35 · Dec 15, 2022

I have a ford 640 with the 134 engine. I measured the pistons when I pulled them and got 3.496 inches so I ordered rings for the 3.5 inch over bore and I have no compression. Tried squirting some oil in the cylinder and still no compression. Anyone have any ideas or has rebuilt one of these engines?

wore out · Dec 15, 2022

How far did you tear the engine down beyond R+R'ing the pistons?

Did you check the ring end gap with a ring squared up partway down a bore?

Even with a HUGE endgap there should be halfway decent compression!

Ramseyer35 · Dec 15, 2022

I did not check end gap. This is my first engine and I just put the rings on and bolted everything up

J Hamilton · Dec 15, 2022

(quoted from post at 20:09:36 12/15/22) I did not check end gap. This is my first engine and I just put the rings on and bolted everything up

I take it you did not check/adjust the valve tappet gap upon reassembly?

Fritz Maurer · Dec 15, 2022

If you just bolted it back together without checking
the valves, you may have a few standing open.
Loosen all the rocker adjusters and try it again.

used red MN · Dec 15, 2022

Well you really like to go about things the hard way. Did
you crack a repair manual at all? My first question is
did you set the resting valve clearance? Looks like the
spec is 0.015 inches. Easy way for a beginner is when
one valve on a cylinder is all the way open set the
clearance on the other one. Get a tire chalk or marker
to mark them when completed or draw a diagram on
paper 1 - 8 and mark them off as you go. You are using
a feeler gauge and adjusting the screws and set nuts
on the rocker arms until a wee bit of drag is pinching
the feeler gauge blade. Do not put the valve cover and
everything back together because that is the hot
setting. So you need to run the tractor and warm it up.
Then you will want to retorque the head bolts and then
do your final valve set with the engine warm. And on
second thought did you pull the camshaft out? It has
to be in time with the crankshaft. Oh so many things to
learn dear grasshopper! ; > ) Find you a you tube on
settling the valves.

M-MAN · Dec 16, 2022

Not if you put all those gaps in a
nice straight line. I've seen it
done.

showcrop · Dec 16, 2022

Zero compression cannot be rings it has to be valves. I once got my cam timing off as I removed the crank multiple times fighting with evil rear main side seals.

used red MN · Dec 16, 2022

M-Man in my opinion if you put all the ring gaps in a straight line it will not change your compression. But to add a stipulation this would be true if you had the ring gap set to the proper spec. Even when the ring gaps are not aligned the gases or pressure which ever you prefer, follows the void allowed by the space between the rings and cylinder wall to piston clearance to flow over to the next ring gap down. And remember that the gas can flow both directions around the piston to the next ring gap down. Not aligning the rings is more for the purpose of eliminating the possibility of a burn down notch forming on the piston ring lands at the spot of the aligned ring gaps.

Ford 640 pistons

Ramseyer35

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wore out

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Ramseyer35

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J Hamilton

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Fritz Maurer

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used red MN

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M-MAN

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showcrop

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used red MN

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