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Discussion Starter #1
Ever wonder how the oil pressure relief valve worked in the old T head engines? Well wonder no more...

This is a high pressure oil system relief valve.

Relief valve (1024x731).jpg

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Part E is a jam nut to lock the setting of part F. Part F is screwed into the body of part A against the ball and spring. The more part F is screwed into the A body, the higher the oil pressure needed to pass some oil through the relief valve which lubes the F/R planetary and the PTO.

The rubber O-ring just seals the threads between the A body and the adjusting component when the lock-nut is locked against the A body.

Roger,
 

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Good stuff!
 

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Excellent information! Thanks for posting.
 

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And the pressure reading that you expect the relief valve to kick in at is?
 

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Discussion Starter #5 (Edited)
I do not know Gravely's original specification, but 25 psi sounds good to me. The low pressure systems only developed about 10 to 15 psi.

If you adjust a relief valve, remember to check for oil escaping to lubricate the F/R and PTO. The piston displacing crankcase air will blow that oil all over inside.

If you cannot achieve both decent oil pressure and a escaping stream, then it is time for some bottom end work, the connecting rod bushing, the drive pinion bushing, and even the pilot bushing in the H/L sun gear. I forget to check the sun gear bushing at times.

Click to enlarge

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Oil enters the hollow drive pinion shaft via the big bushing and then enters the front flywheel and the crank pin, the other end of the drive pinion rides inside the high/low sun gear to lube the high/low assembly. There is a plug in the very end of a drive pinion shaft.


Roger,
 

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Good stuff Roger and thank you for putting it together. This thread is now stuck. :fing32:
 

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Discussion Starter #7
A little more info about the drive pinion. Oil to the internal sun gear bushing is under pressure, oil to the pin plate bushing is via a weep hole.

Click to enlarge

Drive pinion.1 (1024x731).jpg

Drive pinion.2 (1024x731).jpg

Drive pinion.3 (1024x731).jpg

Drive pinion.4 (1024x731).jpg

Drive pinion.5 (1024x731).jpg

Roger,
 

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Discussion Starter #8
Stories about the crank pin and connecting rod coming soon to a theater new you.
 

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Discussion Starter #9
The oil system starts with the pick-up in the bottom of the chassis which feeds the oil to the pump behind the fan belt pulley. The first low pressure systems fed oil straight back into the crankcase without being filtered, oil that was not pumped into the bottom end went to the filter and then to the relief valve. The early pick-up tubes had fairly course screens on them and some fine debris was pumped into the engine. Oil sludge was a problem in the early crank pins.

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oil.jpg oil.2.jpg

Later with the high pressure oil systems and full flow oil filters, oil was fed to the filter first and then plumbed to the side of the case and drive pinion shaft. What was not pumped into the bottom case escaped through the relief valve lubing the F/R gears and PTO.


Oil in the drive pinion shaft heads either to the H/L sun gear or through the front flywheel to the crank pin. The crank pin has an oil inlet galley cut into the forward end and a hole drilled through that galley allowing oil to enter the inside of the crank pin. Another hole through the center of the pin allows oil to escape lubing the crank pin bushing. With the 6.6 and 7.6hp engines there are oil squirt holes in the connecting rod. When the hole in the crank pin aligns with the hole in the connecting rod, oil squirts out lubing components in the bottom cases. The 5hp engine connecting rod has no squirt hole, but with a wet sump oil was always being thrown around by the flywheels. The piston pin has a splash hole in the top of the connecting rod, since the piston pin does not turn all the time, just a little oil sufficed for the rocking motion.

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Roger,
 

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Thanks Roger
I was wondering why I didn't have a lot of oil in the PTO area of my C8. Thanks to your relief valve explanation I have adjusted the oil pressure from 55 psi to 30 psi and i now have a generous stream of oil exiting the valve. I adjusted my valve while it was on the engine. I loosened the oil lines just enough so the fittings could move but not leak too much. Started the engine and turned the adjustment until I had the pressure I wanted and then locked it down. I also replaced the O-ring before I made the adjustment. The P.O. must have just snugged everything down so the relief valve was almost closed off.
 

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Discussion Starter #11
About that sludge in the crankpin, orientation of the holes in the crankpin during installation into the flywheel can help. The crankpin is pressed into the forward flywheel. If the holes in the crankpin align with the center of the flywheel, then there is a better chance of the sludge being squirted back out when the holes in the connecting rod align.

Look at this pin which was mounted with the exit holes almost 90° out from center,

Click to enlarge

20120830_9 (791x630).jpg

Roger,
 
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