Rebuild or Conversion

[David Erik Sneed]

I have a failed MG-5075SC behind a 6BTA.  Considering a rebuild of the existing unit, however am also considering a conversion to a comparable ZF.   Any insights or recommendations?   Unit drives a Doen 105 jet and is 1:1 ratio.  One item that is driving the conversion question is the apparent damage to the Twin Disc – lots of metal in the oil and strainer following a low oil condition due to seal failure – may or may not be rebuildable.  Thanks for your help.

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[Tony Athens]

You don’t screw around.. You needed to get it done and you did.. Good for you..

Not that it matters now, but for the 5075 to fail at such early hours and then looking at the pics says volumes–The gear was installed with some type of interference on the input applying thrust pressure on the gears input shaft–Not a fault of the gear–A Lousy mechanic put it together..

Anyway, seems all is good now..

Tony

[David Erik Sneed]

Here’s a pic of the hydraulic pump setup.

[David Erik Sneed]

Velvet drive solution. Working great!

Thought I’d circle back and share the ultimate fix for this boat. I’ve had this all together now for a couple of months and have sorted out the bugs. She operates great and we’ve been using her continuously managing our floating houses on Fontana Lake.

Installed a Velvet Drive conversion from Seaboard.

Worked with BAM to build a 1500 DSL modified Velvet Drive.

Custom built a shift linkage in my own shop.

Had to install an electric clutch driven hydraulic pump for the reverse bucket on the Doen jet. Deweze makes a great setup for a snow plow on 12 valve Dodge trucks. Appropriately modified that kit for the marine engine with my own custom mounts.

The boat is now setup for easy maintenance. Simple replacement parts if needed.

Thanks for supporting these engines so well. The Velvet Drive kit is fantastic.

1 user thanked author for this post.

Scotth

[David Erik Sneed]

Continuing to research options and noted the Seaboard kit to convert to a Velvet Drive.   So many options out there for new and performance units by Velvet Drive and third parties.  Is this an option worth considering?   This is a 1:1 application.  Did get the MG-5075 pulled and photo of the input shaft attached.  Severe damage.  

[David Erik Sneed]

Trying pics again. Too large first time around. 

[David Erik Sneed]

Thanks Tony.   There is always more to the story and here it is.  This vessel is a military surplus 2003 Seaark VC Commander.  Low hours (187 on both engine compartment and dash meters) which based on my experience with other surplus purchases doesn’t mean much.  At any rate I’ve been sorting her out over the past few months a bit at a time and trialing her on our local lake.  All has gone very well until she suddenly showed a pressure spike on the trans pressure gauge of over 400 (gauge maxes out at 400 and it was to the stop).  My initial reaction was that this was suspect since all seemed well and then suddenly she lost drive power.  A quick inspection revealed a bilge full of oil and nothing on the stick.  I had changed the trans oil a few weeks earlier with SAE 30 and had run several trips with no issues.  Assume an front seal failure since nothing visible elsewhere.  Nursed her back to the dock with oil on hand (20w50) and a tow.  Pulled the control valve to see if there was any trash that could have created a pressure regulator issue and found fine metal debris.  Pulled the strainer and a hand full of metal came out including some larger chunks that appear similar to bearing cage components. Not entirely sure at this point as I’m still in the process of pulling the trans for inspection.   Pics attached of the current status (turbo pulled and lines, etc working out).

[Tony Athens]

David,   It would be very unusual for a MG5075SC to fail behind a 6BTA 5.9.. This is a very good gear w/ a good track record.. With that said, are you leaving some history of operation out?   As to a replacement, NOTHING made by ZF would be an easy change out.. The ZF301C would be the closest (it a coax gear) .. The ZF280  is and very popular 1:1 gear for engines like yours using jets,  but it would raise your engines crankshaft center-line about 5″. In some cases this is a good thing.. Post some pics your you engine installation & Boat.. Tony

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David Erik Sneed

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