Gearbox corrosion, temporary permanent repair?

[stav]

Hi All,

Not been here for a while busy with family life etc. But I had the opportunity to have the boat in a marina for a few weeks so decided upon a few jobs one of which was to flush the engine and replace antifreeze, job done and pleased.

However, I noticed some corossion around the water cooling connectors on the gearbox, which I looked at today, bad news.....

It is a TMP gearbox on the back of a mercedes om636. I had been in touch with Thames Marine Products a couple of years ago and bought some 3/4" plastic tails to replace the brass tails in the gearbox. Which shouldn't be brass due to corossion problems..... However it was not a job that came to the surface until today and the old fittings came out surprisingly easy and the photo shows why, 1/3 of the thread has wasted away.

A new gearbox is in the order of £1500 and the boat would be up for sale if I need a new gearbox. So I need to effect as good as possible temporary repair that might keep it going for a couple of seasons (sounds better than years).

I have been and bought some metal epoxy resin and some epoxy putty. I intend to clean the metal as best as possible, coat with epoxy resin as feel this might flow better and get in to nooks and crannies. Then build up the wasted area with putty until a little below threaded part. Then build in a layer to make the thread. Let all this set and fit the plastic tail with silicone sealant.

I then have the choice of reconnecting to sea water (more corossion) or running the sealed antifreezed water from the engine through it, less corossion but under pressure. Writing this it has to be sea water under less pressure.

Any other ideas/thoughts appreciated, anybody have a second hand TMP gearbox in the garage? Ideas about better products/ more specific products for this sort of repair? Any chemicals to etch/clean the surface for a better bond?

Thanks in advance.

 

[RichardS]

To be honest, I don't think you will ever repair that inner thread properly.

The simple answer is to metal epoxy the spigot connector into the hole using plenty of epoxy as a fillet on the outside as well as between the gearbox and the connector. However, that would never come off if you should ever need to remove the connector ..... so you might see whether you can epoxy a threaded collar onto the gearbox and then screw a threaded spigot into the collar perhaps with a rubber O-ring. You'll never be able to remove the collar but you could unscrew the spigot if necessary.

Richard

 

[bristoljim]

Grasp the nettle & make up a new ally boss with a decent size flange to increase the glue area , male spigot to locate it,take the grinder to the casing & bond it on with your epoxy,even paying a commercial rate to have it made it should be worth it.
It would be interesting to know what temperature the gearbox runs at without cooling.

Jim

 

[sailorman]

Been there, phoned TMP June as he was going on holiday. His temp solution was epoxy metal & it worked for 6 months until i sent the box to him for repair & that cost £1100 due to new castings.
thy issue i had with the Duffield marinised 4108 was their use of copper pipes in the system & the gearbox being ali castings

 

[RichardS]

Grasp the nettle & make up a new ally boss with a decent size flange to increase the glue area , male spigot to locate it,take the grinder to the casing & bond it on with your epoxy,even paying a commercial rate to have it made it should be worth it.

Jim

Just to clarify, isn't that exactly what I said in post #2 or are you suggesting something slightly different?

Richard

 

[stav]

Thanks for the suggestions guys, yes making a bush with a large flange seems to be the route to go. Will consider enlarging the hole to get to more solid metal. Been a while since I cut a thread on a lathe but will have to give it ago I guess......

Having done some more research found this link:

http://www.epotek.com/site/files/Techtips/pdfs/Tech_Tip_24_-_Bonding_to_AL.pdf

Citric acid would also seem to be the way to go.

Thanks again, any more ideas welcome.

 

[bristoljim]

Richard - yes as your post but as the first choice plus with larger bonding area.

Stav - much easier with a tap - surely someone on Jersey has some BSP taps you could borrow

Jim

 

[superheat6k]

You could try these aluminium brazing rods. I have done several very successful repairs using these, including one today to the end casing of my windlass motor.

Not sure how they will fair with sea water passing though, although I doubt any worse than the crap your box has been cast from.

http://www.ebay.co.uk/itm/ALUMINIUM...694419?hash=item2a73290493:g:lscAAOSwirZTwXyC

 

[stav]

Thanks superheat6K, will have a look at those. In fact pack bought, must be worth a try? Will report back in a week or two (or not at all if I just metal a bigger hole in my gearbox!!!!)

 

[PCUK]

How about making a fitting like Eberspacher use on fuel tanks. They have a slot in the inside flange so it can be fitted inside and rubber seals inside and out. No welding and removable!

 

[Topcat47]

I don't know what metal the gearbox casing is made from, but I"d be tempted to remove it, strip the gearbox and have a boss welded to the outside of the casing. It could then be drilled and tapped to take a new spigot.

 

[TQA]

If it were mine I would de grease thoroughly then epoxy the fitting back in with a good big external fillet. JB Weld would be my choice of epoxy.

Then start looking for used box that you can rob the casing from.

 

[bristoljim]

Avoid stripping down & (amateur ) welding at all costs - as many of the posts have said, with correct surface preparation bonding on a boss will be a sound permanent repair.

Jim

 

[stav]

Thanks for all the suggestions, have been and bought a short length of 2"aluminium bar and ordered some JB weld. Just have to wait for it to arrive. Still need to decided best way to clean it, was going to try some clutch and brake cleaner?

 

[bristoljim]

As my first post use a grinder on the gearbox - degrease with your brake cleaner - then grind again just before bonding.Use rough emery on the turned surface just before bonding after degreasing.Probably best if you slightly warm the the metals before bonding & keep a reasonable temperature while curing.
Best of luck Jim

 

[RichardS]

As my first post use a grinder on the gearbox - degrease with your brake cleaner - then grind again just before bonding.Use rough emery on the turned surface just before bonding after degreasing.Probably best if you slightly warm the the metals before bonding & keep a reasonable temperature while curing.
Best of luck Jim

Jim's suggestion is fine but personally I wouldn't use a grinder as it's a bit too fierce and access might not be that great. I would either hand use wet and dry, used wet to keep filings to a minimum, or if that was taking too long, a Dremel type tool with a sanding head.

Richard

 

[TQA]

Slight thread hijack but relevant.

What is the best degreasing solvent that is easily available. I use acetone now that trichloroethylene is banned and hard to find.

Never used brake cleaner, what is the active constituent?

 

[RichardS]

Slight thread hijack but relevant.

What is the best degreasing solvent that is easily available. I use acetone now that trichloroethylene is banned and hard to find.

Never used brake cleaner, what is the active constituent?

Acetone is as good as you will find. I usually use meths or white spirit as they are cheap and easy to obtain. However, I have a litre of Acetone which is reserved for the really critical jobs.

Richard

 

[stav]

Hi, guys thanks for the additional thoughts.

I have started making my aluminium boss and cut the thread today and was quite tight on the non corroded connection but loose on the corroded one. Will still go ahead with this and have decided to make it with a male 3/4" bsp thread, leave the 'body' of it at 50mm to give a large bonding surface and cut a female 3/4BSP thread for the plastic spigot.

Have bough a dremel to try and get inside a little also was intending to use a fein multimaster to flatten and rough up the mating surface.

I have also contacted TMP to ask if possible to take gearbox apart in place?

Will update as progress is made.

Thanks

 

[superheat6k]

Abrade clean the aluminium a few minutes at most before applying the heat and weld rods, otherwise the oxide layer will form and will reduce adhesion of the rods. You need to get the aluminium to the melting point of the rods for it to fuse to the surface, do not allow the flame to directly melt the rods, otherwise it will just run away as blobs when it meets the aluminium surface.

I would definitely suggest some practice on some waste material first.