SCV adjustment settings

[Glen D Anderson]

Good day!

Attempting to adjust the valves on a set of SCVs from an early model 3020.

I built a copy of the JDH-15 plate and am able to bottom the pressure and return valves and balls into their respective seats as well as bottom the flow control spool against the centering cam.

The problem that I'm having is that I find there is at least a .020" variance in where the control valve lever comes to rest in the neutral position after cycling it when attempting to measure clearance. This is even with putting full pressure on the detent spring plug. The handle simply does not return consistently to a zero set point.

With the factory clearances listed at .020" for the return valves & .060" for the pressure valves I see a fairly good chance of the valves leaking. At least on the return valves.

It seems to me that setting the return valves at something like .050" and the pressure valves at .090" would be better.

Thoughts / suggestions?

TIA

 

[Cliff Nelson]

Did you replace the roll pin that holds the rocker to the lever? Sometimes that helps to tighten things up. I just center the dial indicator in the neutral range, in your case .010" each side of zero. You could add .010" to each of the valve settings if you are worried about it. I normally see .005" or less when centering the dial indicator and just zero in the middle and go from there with the given settings. I also double check the zero setting after adjusting to make sure the indicator didn't move during adjustment. Hope this helps.

 

[Glen D Anderson]

Did you replace the roll pin that holds the rocker to the lever? Sometimes that helps to tighten things up. I just center the dial indicator in the neutral range, in your case .010" each side of zero. You could add .010" to each of the valve settings if you are worried about it. I normally see .005" or less when centering the dial indicator and just zero in the middle and go from there with the given settings. I also double check the zero setting after adjusting to make sure the indicator didn't move during adjustment. Hope this helps.

The levers & roll pins are new. The rockers are also in good shape. When assembled there is no movement between the lever and rocker and the fit between the lever and housings is pretty good too.

I ended up setting it more or less the way you explained by just splitting the difference of the neutral rest position. I set the return valves between .040" - .050" and the pressure valves between .075" and. 085".

Tested it a bit yesterday and it seems to work OK. Holds a load for at least a couple of hours compared to dropping the minute the engine is shut off. Also have some feathering control now which is an improvement over the "all or nothing" it had before. The feathering is still not as good as it I recall it being years ago and I think it might be due to the spread in clearance between the pressure and return valves. Thinking it might be better with a .015" - .020" spread.? Probably won't bother taking it apart to find out though....LOL

Anyway, thanks for the info. Cliff.

 

[Cliff Nelson]

Adjusting with a wider neutral range gives you just that - A wider neutral range on the control lever. As to feathering, I'm not sure if the pressure/return spread will affect that. The purpose of the spread is to insure that the return valve opens before the pressure valve, preventing over pressuring of the return porting and helping with smooth operation. My thought is that the detent cams have more to do with feathering as you are trying to move the rocker partially over the cams when trying to feather the valve. Those cams are so small that any rough spot will change the 'feel' of the lever.

 

[Bob Bancroft]

Good day!

Attempting to adjust the valves on a set of SCVs from an early model 3020.

I built a copy of the JDH-15 plate and am able to bottom the pressure and return valves and balls into their respective seats as well as bottom the flow control spool against the centering cam.

The problem that I'm having is that I find there is at least a .020" variance in where the control valve lever comes to rest in the neutral position after cycling it when attempting to measure clearance. This is even with putting full pressure on the detent spring plug. The handle simply does not return consistently to a zero set point.

With the factory clearances listed at .020" for the return valves & .060" for the pressure valves I see a fairly good chance of the valves leaking. At least on the return valves.

It seems to me that setting the return valves at something like .050" and the pressure valves at .090" would be better.

Thoughts / suggestions?

TIA

It's been long enough that I can't remember the numbers, but I did just as you describe- left myself some extra "wiggle room", one might say.

 

[Glen D Anderson]

Adjusting with a wider neutral range gives you just that - A wider neutral range on the control lever. As to feathering, I'm not sure if the pressure/return spread will affect that. The purpose of the spread is to insure that the return valve opens before the pressure valve, preventing over pressuring of the return porting and helping with smooth operation. My thought is that the detent cams have more to do with feathering as you are trying to move the rocker partially over the cams when trying to feather the valve. Those cams are so small that any rough spot will change the 'feel' of the lever.

Cliff,

I hear what you're saying about the detents affecting the ability to feather the flow.

That said, I think the fine feathering action that is done with these early style SCVs comes from the narrow window of lever travel where the followers/pins push the balls off their seat, just before they unseat the main valves.

When testing on bench with air you can feel that narrow window where you're unseating the ball but not the valve. The lever is easier to push and control but as soon as the follower/pin hits the valve, it becomes harder to push and as soon as the valve is pushed off it's seat, there's a big increase in flow.

With a larger spread(or lever travel) between the return and pressure valves opening I think you loose the light feel on the control lever because you are starting to push the return valve off of it's seat well before you are even pushing the pressure ball off of it's seat.

Long story short, I think the lighter pressure you feel on the SCV lever at the beginning of it's travel is the balls being unseated and that's where the fine feathering comes into play.

Just to clarify, I'm not arguing here. Just thinking out loud. LOL

Thoughts?