VP DP-G Duo Prop refitting question

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Roughcut

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I've just had my Stainless Steel DP-G props rebushed and the new kits have each come with a large (around 7cm) but thin, annular nylon washer. The re-bushing engineer says they came with the Volvo kits, and he thinks it might be because VP have changed the metal in the bush and this is to insulate it from the shaft (and the rest of the leg) to prevent electrolysis. Whilst that sounds perfectly feasible, when refitting the props - I can't see any obvious place that they can fit and stay in place prior to everything being torqued up. They'd clearly have to go on the "nut" side, rather than the thrust washer side of each prop.
I've drawn a blank with my local engineering experts - does anyone have any knowledge about these? Where they might fit and what they're for?
(Just to note - I'm not referring to the plastic washer that locks into the prop spinner - that's all fine.)
Any relevant wisdom gratefully received!
 
I got new props 2 years ago from Volvo - dont recall any nylon washers that you describe but I am interested on other comments.

Jon
 
A couple of pictures :)
My guess would be that the three nylon parts together are meant to provide insulation between the bronze hub and the stainless prop.
The flat washer is probably there to to keep things neat and keep the inner angled nylon ring in place once the cone or prop nut is screwed on.


s-l1600.jpg


IMG_6199__19957.1584639042.png
 
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I did ask but they said they couldn’t tell me without the exact part number - which I’m waiting to get from the prop refurbishers who ordered it. It seemed like a simple generic question for VP - but apparently not!
 
jon and michie said:
I got new props 2 years ago from Volvo - dont recall any nylon washers that you describe but I am interested on other comments.
Click to expand...

My experience too. My 15 year old (C4) rear (?) prop has a nylon washer. The new (C3) do not. Like you I wondered, but nor could I find a suitable place had it needed to be transferred like the thrust washers.
 
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I've managed to speak to a technical advisor at the VP parts supplier, and whilst they also don't know what these washers are, their best guess is that the washer might be some sort of protective covering to assist in the prop re-bushing process. ie when the rubber bush is hydraulically pressed into the prop housing - so nothing to do with refitting the props themselves onto the outdrives. That's the most likely theory I've heard so far, but enquiries deeper into the Volvo Penta void are ongoing....
 
That ~7cm washer as pictured in @FlowerPower photo. If that is what you are describing it goes in the rear prop. There is a metal spacer, then that plastic washer then a crenelated spacer then the cone. This is to isolate the prop from the cone. Like @Anjens said I noticed my newer C4vs olderC4 either had or didnt have them. The newer C4's dont have the internal anode, the older one's do / did
 
Thanks Bruce - that's helpful and very interesting. (Not least because I now know what 'crenelated' means!)
Yes that 7cm washer is the one. I don't appear to have a metal spacer - my parts are just as on the attached image which doesn't show the 'new' 7cm washer or spacer.
DP-G Props.jpg
So it's just the 2 x thrust washers and the crenelated spacer onto the cone with its bolt and small plastic washer.
Checking the parts again on Marine Parts Europe (Volvo Penta Exploded view / schematic Propellershaft DP-G 1.68, DP-G 1.59 - MarinePartsEurope.com) there's no spacer or washer shown there either. So I can't even try and order a spacer without a part number.
Incidentally - as the crenelated washer (love that word now!) is plastic - doesn't that isolate the cone from the prop anyway? What extra electrical isolation would another plastic washer next to it add?
I'm grateful for your comments. Thanks.
 
I often wondered about the functionality of this crenelated washer (6). It sits in a peripheral recess in the cone (7) and has no physical contact with the rear propeller (5) at all. It is definitely only the core part of the cone holding the propeller in place. Furthermore it is made of rather flimsy plastic definitely not suitable as a washer under any pressure or torque. The crenellations made me think its purpose is to catch any fishing line, but that doesn’t make much sense as there is no seal to protect there.

Why is the crenelated washer (6) there at all?? Will it be missed if broken?
 
Anjens said:
Why is the crenelated washer (6) there at all?? Will it be missed if broken?
Click to expand...

It could be to improve the water flow in a small way, to smooth out turbulence created by the vanes on the underside of the cone as it spins at 1500rpm.
 
Roughcut said:
Thanks Bruce - that's helpful and very interesting. (Not least because I now know what 'crenelated' means!)
Yes that 7cm washer is the one. I don't appear to have a metal spacer - my parts are just as on the attached image which doesn't show the 'new' 7cm washer or spacer.
View attachment 114792
So it's just the 2 x thrust washers and the crenelated spacer onto the cone with its bolt and small plastic washer.
Checking the parts again on Marine Parts Europe (Volvo Penta Exploded view / schematic Propellershaft DP-G 1.68, DP-G 1.59 - MarinePartsEurope.com) there's no spacer or washer shown there either. So I can't even try and order a spacer without a part number.
Incidentally - as the crenelated washer (love that word now!) is plastic - doesn't that isolate the cone from the prop anyway? What extra electrical isolation would another plastic washer next to it add?
I'm grateful for your comments. Thanks.
Click to expand...

PentaParts zoom

part 45 is a metal washer-spacer. the picture is misleading as it's circumference is smaller and fits inside the crenelated plastic washer. At least, mine has them and so the presumption yours too............?
 
Anjens said:
I often wondered about the functionality of this crenelated washer (6). It sits in a peripheral recess in the cone (7) and has no physical contact with the rear propeller (5) at all. It is definitely only the core part of the cone holding the propeller in place. Furthermore it is made of rather flimsy plastic definitely not suitable as a washer under any pressure or torque. The crenellations made me think its purpose is to catch any fishing line, but that doesn’t make much sense as there is no seal to protect there.

Why is the crenelated washer (6) there at all?? Will it be missed if broken?
Click to expand...

It's to insulate the prop cone (7) from the prop. The props are galvanically isolated from the prop hub and hence from the drive. Without that washer the prop with be electrically connected to the cone and, through the bolt (9) to the drive shaft and you'll get electrolytic corrosion.
 
Thanks to everyone for all the replies and accumulated wisdom. Just as an update, I've had a call back from the regional Volvo Penta dealer, who's been in touch with someone technical at Volvo Penta UK - and.... it's still a mystery! There's a single prop Aquamatic Sterndrive with a line cutter that does show a similar/identical? plastic washer on the exploded parts diagram - but that's not much help reassembling a DuoProp. I'm planning to try some continuity testing to confirm the hub / props / drive shaft are electrically insulated with the existing set up. But I think from what I've gleaned so far, the boat can safely go back in the water, and the plastic washers go back in the box. It does though seem a little odd that VP would spend money buying/making washers that have no clear purpose. So I'm not sure the casebook is fully closed yet...
 
I think I may have the answer - first its not for insulation from galvanic corrosion etc.
I had my props off last Thursday after a nagging doubt and found that the Nyloc Nut on the front propeller only had 1mm of thread past it
see here for the explanation Dp-G Ring Anode and Prop nut help

anyway to your answer The Hub is Brass which when you tighten the Nyloc nut up against it - it will bite into the brass so that thin nylon washer protects the brass from getting chewed up by the nut.

Jon
 
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