ZF68IV / ZF63 IV / HSW630V - low / unstable oil pressure

[ArranP]

video of stable pressure - ran for 15 minutes in neutral, then shift gear forward and reverse without applying revs.
https://photos.app.goo.gl/2f3cyJ8dnEiL28vB9

video of unstable pressure - ran for for 15 minutes in neutral, then shift gear forward and reverse and apply revs.
https://photos.app.goo.gl/2SdTN5zADeCFcDb76

If in neutral and apply revs oil pressure is 320 psi and remains stable.

The oil pressure becomes unstable and drops after applying revs whilst the transmission is in gear, also can hear a hissing sound but uncertain from where it is coming.

[FPNC]

Shift pressure relief valve or segment rings.

Be aware, you are in danger of burning the clutch plates when you load the prop shaft and rev the engine with low clutch oil pressure.

[ArranP]

Originally Posted by FPNC

Shift pressure relief valve or segment rings.

Be aware, you are in danger of burning the clutch plates when you load the prop shaft and rev the engine with low clutch oil pressure.

Where is the shift pressure relief valve located ?

[FPNC]

Originally Posted by ArranP

Where is the shift pressure relief valve located ?

In the control valve assembly. You would need to get a hold of some manuals to get into the control valve and segment rings. The control valve is removed to access the segment rings at the end of the input shaft.

[ArranP]

Originally Posted by FPNC

In the control valve assembly. You would need to get a hold of some manuals to get into the control valve and segment rings. The control valve is removed to access the segment rings at the end of the input shaft.

I have the repair manual
https://www.harbormarine.net/pdf/zf-...3a-80a-85a.pdf

I have replaced the piston rings on this shaft with new.
https://photos.app.goo.gl/1YT33Ty9Agi7YvULA

I have the control block here at home with me, I am about to begin to dismantle it.
https://photos.app.goo.gl/o31ndSjXea3Unx3E9

What item # is the shift pressure relief valve ?

[ArranP]

The transmission works fine for the first 15 minutes then after that there comes hissing and the pressure becomes unstable. I'm unable as yet to locate the source of the hissing.

[s/v Jedi]

Originally Posted by ArranP

The transmission works fine for the first 15 minutes then after that there comes hissing and the pressure becomes unstable. I'm unable as yet to locate the source of the hissing.

Is this after cold start or also after 15 minutes when already at work temperature.

You need to find the hissing sound; maybe start with a new oil filter?

[ArranP]

Originally Posted by s/v Jedi

Is this after cold start or also after 15 minutes when already at work temperature.

You need to find the hissing sound; maybe start with a new oil filter?

Ordered new oil filter, awaiting delivery.

Could a Mechanic Stethoscope find the source of the hissing ?

[s/v Jedi]

Originally Posted by ArranP

Ordered new oil filter, awaiting delivery.

Could a Mechanic Stethoscope find the source of the hissing ?

Yes, probably. You can try a big screw driver… I tried that and could hear valves but not sure if it would locate hissing…

[ArranP]

Originally Posted by s/v Jedi

Yes, probably. You can try a big screw driver… I tried that and could hear valves but not sure if it would locate hissing…

Thank you.

Here is a diagram of the control block
https://photos.app.goo.gl/o31ndSjXea3Unx3E9

Do you know which item # is the shift pressure relief valve ?

[s/v Jedi]

Originally Posted by ArranP

Thank you.

Here is a diagram of the control block
https://photos.app.goo.gl/o31ndSjXea3Unx3E9

Do you know which item # is the shift pressure relief valve ?

I wish, I’m not a mechanical engineer. But I think the diagram shows have a list of every item that is on it, incl. it’s name and part number.

Hopefully someone who suggested the valve is the cause comes back with more info…

[ArranP]

I am considering installing the new engine mounts. It is a V driver transmission , is there an acceptable amount of engine movement ? it maybe that the lift and lowering the engine in currently doing in forward/reverse is putting fritction on the shaft making it behave similar to an over proped configuration and in my case is the cause of the black smoke the engine produces after 1500 rpm and maxes out at 1900 rpm instead of its intended max of 3200 rpm.

[ArranP]

Oil pressure seems be stable now after 15 minutes.

I changed the fluid filter and o-rings, replaced the o-ring on the temperature sensor, was careful to clean the housing where the large o-ring goes above the filter.

But I think it was the new oil filter that probably got it working.