VOLVO PENTA OUTDRIVE DROPPING INSTANTLY

[amatas08]

Hi All,

Having an issue with a volvo penta outdrive dropping instantly (within 20 seconds) . I have replaced the seals on both rams which has made no difference. There is no visible leaks. Resivour is topped up and have drove it up and down as per manual.

I am starting to expect it could be the pump passing? I have stripped the pump and couldnt see anything obvious. Can anyone dive on how to test the pump or cylinders in isolation?

Also is one cylinder sufficient to hold up the drive on its own? If so it's unlikely to have both cylinders failing especially after getting new seals.

 

[Scott Danforth]

Easy to test if it's the ram cylinder seal or the pump load holding check valve

Both cylinders are plumbed together, and act as 1 cylinder. So if one seal is leaking, they both will collapse

Really easy to shear the piston seal when inserting in the barrel

 

[amatas08]

Thanks, can you advise on how best to test the rams and pump?

 

[Scott Danforth]

With the drive up fully, pull the gland end hose. Then go to raise the drive. If oil comes out the open hose, your piston seals are bypassing. If no oil comes out, look at the HPU

Or you can have the drive all the way down and pull the blind end hose, then lower drive

 

[QBhoy]

Older VP pumps have known issues with the ball valves in the pump passing. But usually that means the drive falls down fairly slowly.

 

[amatas08]

With the drive up fully, pull the gland end hose. Then go to raise the drive. If oil comes out the open hose, your piston seals are bypassing. If no oil comes out, look at the HPU

Or you can have the drive all the way down and pull the blind end hose, then lower drive

Thanks, can you advise on how to test the pump. I have removed the pump so that i can bench test it. I have added a short section of hose to both pump outlets and put a pressure gauge on the end of each hose. When i run the pump so that pressure builds on the 'Down' outlet, the pressure on the gauge increases to approx. 90bar (1305 psi). when the power to the pump is turned off the pressure drops to 40bar and holds steady. When i run the pump in the opposite direction, the pressure in the 'UP' outlet increase to approx. 220bar (3190psi). when the pump is turned off the pressure on the gauge drops to 140bar (2000psi) and holds steady. Is this an accurate test? i would presume if the pressure dropped to zero then the pump internals were passing?

 

[Scott Danforth]

I would look at the cylinders.

 

[alldodge]

Sounds like you pump is fine
Don't have a VP manual, but Merc manual list one additional test. It connects the two lines together with gauge. Run in either direction and pressure should not exceed 13Bar (200 psi)

 

[Scott Danforth]

the oildyne 108 is usually set up for 2900-3000 psi to raise (as it has to fight the prop thrust) and only about 900-1500 psi to lower (as gravity and prop thrust help)

 

[alldodge]

 

[amatas08]

I have replaced the trim cylinder seals again and still no joy. Seems to be dropping slower but takes less than two minutes to drop from top to bottom. When I looked at pictures online of the trim cylinders there seems to a large springs on the rod, which mine does not have. Is this required?

I still am not sure if it is the cylinders or the pump. I tried the method described above as recommended with the drive up and disconnected the gland hose. I presume the gland end hose is the one on the side the rams comes out? With the drive up and hose disconnected I ran the pump and oil came out the hose. Does that confirm the ram seal is leaking.

Is the any way to figure out which ram is the problem?

 

[Scott Danforth]

if you pressurized the blind ends and oil came out the gland end. then yes, one of your cylinders is bypassing.

when you took apart the cylinders, was it the piston seal, or the piston to rod seal you found compromised?

 

[amatas08]

if you pressurized the blind ends and oil came out the gland end. then yes, one of your cylinders is bypassing.

when you took apart the cylinders, was it the piston seal, or the piston to rod seal you found compromised?

The plastic ring that goes over the o-ring on one of the pistons was damaged when I removed it. I replaced this with a new one, so unless it got damaged again as it is very flimsy. It was very difficult to get the piston back into the cylinder with the new seals

 

[alldodge]

Was the inside bore of the cylinder real smooth the entire length?

 

[amatas08]

Yes looked good. I gave it a quick run over with honing tool also just to ensure there was no sharp points

Was the inside bore of the cylinder real smooth the entire length?

 

[alldodge]

Your pump passed test i previous post, so only think left is the internal seals or piston in cylinder.

 

[Scott Danforth]

I use a bit of .005" plastic shim stock wrapped around the piston to get the seal to compress when pushing the piston in the bore.

at work, we have a tapered cone that drops in the barrel to drop in the pistons.

 

[amatas08]

Does anyone know if this spring is always installed. As there is not a spring on either of my cylinders

 

[Scott Danforth]

no, its generally not installed