Logo
FULL SITE MENU

Rolling torque Volvo Penta DP-SM

O

OskarH

New member
Hello everybody.

I have a problem with my Volvo Penta DP-SM outdrive and would be really happy with some help from you guys as I have ordered a crane for launching the boat on Tuesday.

I had som water in the oil and did a pressure test. This showed that I had a leak in the outer prop shaft seal.
I took it to the local marina to get the nut that holds the bearing carrier. I then changed the seals and o-rings.
After that I brought it back to the marina so they could tighten the nut.

The mechanic said that he had set the rolling torque to 2,5nm (1,8lb-ft).
When I got it back I tested the rolling torque by winding a thread on the input shaft and attaching a fish scale. With some calculation I only get 1nm (0,7lb-ft).
Now I’m contemplating what to do.

  1. Have the mechanic made an error and I should bring it back and retighten it
  2. Have the mechanic set it to 2,5nm but after some spinning when I was measuring, the bearings has “settled” and the measurement has changed and I should retighten it.
  3. This is normal and I should just launch the boat

I can ad that before taking the unit apart I also had rolling torque of 1nm.

Also I made a mark at 12 a clock on the bearing carrier nut and after mechanic has tighten it the mark is between 1 and 2 a clock.
 
I wouldn't rely on a fish scale being that accurate.. you need a wrench like this-


I have used cheaper beam style to set up rear differential gears and found them to be just as accurate - https://www.zoro.com/performance-to...V91lHAR1AswWrEAQYCCABEgJoL_D_BwE&gclsrc=aw.ds

also note usually for rolling torque there are two different specs one for new bearings and one for used.

Might be worth a call the the mechanic , but in all likely hood using a fish scale it is tough to get it moving a couple turns to measure as you need to get past the start up torque.
 
Yes I know the fish scale is not that accurate, but for now that’s what I have.

But i have an update.
When I was spinning the input shaft of the lower unit I could feel some resistant, almost like you could feel the teeth of the gears.
I went to the mechanic and he checked the rolling torque and as I had measured it was only 1nm, not 2,5nm as he had told me.
We tightened the nut pushing the bearing carrier so we got a rolling torque of 2,5nm.
But when we did that the grinding increased and you could really feel every teeth in the gears when I spin the input shaft.
I told the mechanic to take it apart and I had a look at home.
No damage to the two outer bearings that I can get to.
So I made my own special tool for the nut so I could torque it myself and test.

My conclusion is this:
Before I took the lower unit apart the first time I made a marking on the nut to see where it was located.
Now when I torque it to the right rolling torque this mark is turned more than 90 degrees from the original position and I start to feel the teeth of the gears.
So the rolling torque has probably been very low before I took it apart and when I tighten it to the right rolling torque something happens gear engagement and it goes rough.

I but some contact pattern paint on the gears and when I only torque it around the old mark the rolling torque is around 0,7nm I get a god contact pattern.
I took it apart and put on new paint and as soon as I increase the rolling torque I start to feel the teeths. I would still consider the contact pattern to be good.

So what could have happened?
I haven’t changed anything except the prop shaft seals.

Has it been this low rolling torque since factory?

Maybe previous owner have changed bearings and failed to shim it in a proper way?

Could it be wear on the parts and you have to re-shim the lower unit after som running hours?
 
IMG_4965.jpeg

This is contact pattern when torqued more than 90 degrees from the original marking.


IMG_4962.jpeg
This is the contact pattern when torqued like before I started the disassembling.
 
The contact pattern when torqued like before looks better. Are there not shims to set the gear depth and thus contact pattern? Not familiar with the drive you are working on but have never seen rolling torque used to set gear pattern, usually a shim behind a bearing or race.

What you may be seeing is the rolling torque diff between new and used bearings.. for example merc spec for alpha drive input shaft bearings is 7-16 in lb for new, 6-8 in lb for used bearings. Also defines used bearings as spun under load once… all that makes one think it is not as precise as it may seem. Certainly if you have smooth operation and good engagement pattern that is it. Also need to take care of if the pattern you show is drive or coast side.
 
the span for the rolling torque on this Penta is between 2 and 2,9nm and as you say with old bearings you should aim for the lower part of the span.
There are shims that you can change to get another contact pattern but the nut will also change the contact pattern when you tighten it.
So it feels like previous owners has maybe changed bearings and didn’t do it right.
Because the rolling torque was set to 0,5nm.

I think my plan right now is to leave it as it was with the torque set to 0,5nm. I will check the gear lash and also the axial movement of both prop shafts to see that i don’t have any play in the bearings.
And then I will put it tighter and drop the boat in the ocean.
The summers are quite short in Sweden and I will probably only put 50 hours on the engine on a season.
And also this is how the drive have been set up for at least two years, because the previous owner did not open the outdrive.
 
OskarH said:
There are shims that you can change to get another contact pattern but the nut will also change the contact pattern when you tighten it.
So it feels like previous owners has maybe changed bearings and didn’t do it right.
Because the rolling torque was set to 0,5nm.
Click to expand...
you are correct something is not right. Tightening preload on bearings should not change contact pattern. If it has worked the gears don't look bad, use it for the season and this makes a good project for next winter.

I had the same situation last year noticed fishing line on propeller shaft and leaking some oil at end of season. completely disassembled and put all new seals in the drive over the winter when there was no rush.
 
Back
Top