Volvo Penta S120C Workshop Manual

[jaybird1111]

Thanks for the info, DougR

We'll keep everyone posted on the outcome.

[jimbunyard]

Good that the drive plate is bad, you don't have to pull the boat and the saildrive.

It looks like you could still use the existing input shaft, especially if you could shim the drive back (or the engine forward) 3/8" or so (I did mine but it's an MS gear not a sail drive).

The bad thing about that route is that the drive plate, 872809, is 725.00.
I've seen them for as low as 400.00 but that's hit or miss.

It might be worthwhile to contact D.B. Marine, the conversion they show might also work with MD 2020, 30, 40 series. I suspect that the total cost for the shaft build up and machining and drive plate pricing will be about double the price of the new Volvo damper. You never know though, and it might be worth it in the long run if their damper plate is sufficiently inexpensive.

If you decide to go with the original damper, Doug's recommendations about the proper use and installation of the electrically isolating components is important for corrosion protection of the out drive, but also for properly centering the input shaft in the damper itself. The first picture shows what happens if you don't get them right, the rubber and metal separate, and that's an 800.00 mistake.

The three alignment components (shown in the 2nd picture) are items 27, 28 and 30. The difficulty comes with trying to reinstall the cover plate 29 while ensuring that the plastic gasket 28 and centering ring 27 are correctly positioned. The easiest thing to do is use spray adhesive to glue the #28 gasket and #27 ring to the #29 plate and then install them as an assembly.

By the way if the plate shown in the picture is any use to you, let me know. The splines are good, you're welcome to it if you need it.

And I almost forgot, beer is good, let me know if you're in the area, I'll do likewise.

[jaybird1111]

Again, thanks, Jim. Check your PM

[jaybird1111]

If anybody has any vibration dampeners for MD series engines with the splines stripped out but the elastomer still in good shape (similar to mine), I'd be interested in purchasing to experiment with modifications for 120 s'drives with stripped splines.

Send me an email or PM (you can email via the CF site)

Thanks
Jay

[jaybird1111]

The experiment is complete, and here are the results.

It might have been an easy thing to just hang another vibration dampener/flywheel onto the back of the engine, but then you are still left with the worn splines on the tranny input shaft, which is likely what caused the whole thing to go bad in the first place. It might bear reminding that in my case, engine was replaced, transmission was original.

Volvo would have you replace not only the dampener, but also that shaft, which would entail replacing the entire gearset @ circa $3 grand. Not that much more to replace the whole drive.

So, it takes two mech.engineers and an extremely good machinist, but we have come up with this fix. This is a very abbreviated version. If you want details, I'll have to email. You can get in touch with me via the email link provided in my CF account.

Bore out the splines in the vibration dampener and weld in a splined collar. The splined collar is tack-welded in place to limit the chance of heat damage to the rubber element in the vibe dampener. That process takes quite a bit of time, as you tack in a couple welds, let that cool, then do another couple of tacks. Limit the rubber temp to ca.200F our estimate


As for the input shaft, the machinist put it on a lathe and found that the shaft had about 2000th/inch of runout. The process of machining off the splines included truing the shaft. The prepared spline adaptor was heat-shrunk onto the input shaft. We determined the amount of heat-shrink we could get on the shaft appears to be about 20x the strength of the original splines, therefore we don't have to worry about it slipping.


This fix does not allow you to replace the input shaft seal, so you need to make sure you have a good seal in place before heat-shrinking on the spline adaptor. Also, we immersed the input shaft housing arrangement/gearset, just enough to cover the seal, as we put the hot adaptor onto the shaft to prevent damaging the seal, so it is imperative to drive out any water left in the gearset before reinstallation.

I installed this yesterday, and it is shifting smoothly, although the weather was fairly bad so I didn't take the boat off the dock. Next time we go sailing we'll find out whether this works, and if it doesn't I'll let y'all know.

This is approximately $200 in parts (splined stock), enough to do two or three of these, and the machine work was $3-400. If anyone is interested, we can short-cut the engineering work, we'll provide drawings and directions.

[jaybird1111]

Although nobody has asked here, I posted my solution in another forum, and was asked, 'what happens should the seal go bad?'


Because: the spline adaptor is shrunk, not welded on, and; it's not hardened tool steel... you can cut the spline adaptor off with a die grinder or a Dremel tool.

It is not advisable to reheat and press off. Even though the seal may have gone, the heat will compromise the bearing. Cut the adaptor off.

The $200 in splined stock, as I said, made several of these pieces, so you merely shrink on another adaptor.

[jaybird1111]

Update:

I have put my starboard through the wringer, (long story) and it is going just fine. I'm well pleased with this modification/repair and will be doing the same to my port saildrive when opportunity arises.