226 Camshaft Timing

8NChris

Member
Hello,
I know this question can open a can of worms so take my comments at face value. Been a heavy line/drivability technician for the last 20 years but have zero Flathead experience. With that said I have a cam timing question concerning the 48 Funk. It has a Fred Jones rebuild tag from 1965. A couple of weeks ago I did a basic health check on the engine. Static (cranking) compression was 119 to 106. Due to this being an Inline 6 with the standard 8N crank pulley the timing marks don't line up so I had to find TDC using the finger over the spark plug hole method. At TDC the exhaust valve is rocking with 80% cylinder leakage. Rolling the crankshaft backwards about 10 by hand will close the valve. When the leak down gauge gets down to about 40% the crank pulley slips the fan belt allowing the piston to BDC.

Is this a characteristic of an industrial or marine camshaft? Do the tractor 4 cylinder Flathead's share this characteristic? Everything I know (or think I know) about the internal combustion engine tells me this thing should backfire instead of run smooth.

A few of my own theories:

* It is normal and I have learned something new.
* Camshaft gears are misaligned or marked wrong for this engine.


This theory only explains the roll back:
* This being a Fred Jones reman engine of 1965 they could have upgraded to some different rods that had the beam offset with the rod journal placing the beam on the backside of the compression stroke instead of dead center.

Clear as mud?
Thank's
 
After scratching my head and rechecking my self 5 times on #1 I did the other five cylinders. Found the same results, installed plugs and went back to work. Figured it had been running all these decades there was no sense in messing with it for now.
 
(quoted from post at 01:39:39 09/05/20) After scratching my head and rechecking my self 5 times on #1 I did the other five cylinders. Found the same results, installed plugs and went back to work. Figured it had been running all these decades there was no sense in messing with it for now.
, too, am a big believer in, "if it ain't broke, don't fix it", or you will 'fix' it until it is broke.
 
Thanks for the links. Going off your second link I can tell the cam profile is different from the overhead valve I am familiar with. The compression stroke (air on thumb) only happens once and is interrupted at TDC when the piston changes direction.


A detail I left out is when rolling the engine backwards by hand it is trying to roll back on its own as the exhaust valve closes. Meaning it has not completed the compression stroke (before TDC) when the exhaust starts to rock. When I do get around to doing an overhaul I'll map the camshaft and document it. There is something a builder figured out on these years ago that is out of the normal for the living. It has do do with the geography of the plug, piston, valves and combustion chamber design.
Thank's
 

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