Problem removing anode plug on Bukh DV36

[johnc]

I have a 12 year old Bukh DV36 in an LM28 and wish to replace the engine anode. The anode is fitted to a brass or perhaps iron plug with a 24mm hex head. The plug is located on the side of the water jacket. I have tried to remove the plug but it won't budge. I have a 6 sided hex socket so have a secure connection to the hex plug. I Also have drilled a hole in the watertight engine box to allow me to fit a socket extension shaft into the engine box. My next step is to hire a 1/2" impact driver but I am worried that the force exerted by the impact driver may damage the cylinder block. I have run the engine up to temperature and sprayed penetration oil over the plug. So my question is, could I crack the cylinder block. Engine access is very limited in the LM28 with Bukh 36HP engine.

[jandane]

Is your DV36 raw or fresh water cooled? If it is fresh water then just leave the anode. You do not need it. If raw water cooled, try to give the hex key a hard blow with a hammer - it some times loosens the thread. Else??

[jdp]

Sometimes it's worth trying to tighten a seized nut before loosening it. A hammer in both directions should do the trick. Let us know how it goes. Good luck.

[Brian & Glenda]

I have a DV36 which was originally raw water cooled, but a former owner converted it to fresh water cooling using a non BUKH aftermarket heat exchanger. For reason known only to others, my engine is not fitted with the standard zinc in the location you describe. Instead it has a similar shaped but smaller sized cap, with an internal fitting that accommodates a 1/4 diameter pencil shaped zinc. I do find that I must replace that zinc every four years or so years, even with my fresh water cooling system, and a isolation transformer on my boat. That zinc is slow to go, but it does deteriorate. I'd rather change the zinc, than the engine. There is also a same style pencil zinc on my heat exchanger that I must replace every year or two. It is much faster to corrode.

Do you have a long handled wrench that will fit into your socket? ie 18" /50mm or longer handle? If your handle is shorter ... slip a pipe over the end of the handle to gain better leverage. (Although if it is a ratchet wrench, use a 1/2" or greater sized drive, so you don't ruin your wrench. I put a little too much stress on my 3/8" socket wrench in this manner once, and ended up having to buy a new wrench, but I also bought the larger size that I should have used in the first place, at the same time.)

As suggested above, try hitting the fitting with a hammer to loosen the rusts bond . (I suggest that hitting the socket with a hammer will not loosen the bolt, as the socket will transfer the impact to the engine block instead of the fitting. Be careful not to damage the points of the hex nut while doing so, or the socket will not fit again until you file it's corners back into shape. I did order a BUKH fitting very much like the one you describe for my engine before I determined that it would not fit. If I recall correctly, the fitting is made of bronze, and the zinc threads into female threads on the inside portion such that they are immersed in the coolant (fresh or raw).

Hammering the handle in both directions may also help, as suggested above.

If the above don't work, and you can do it without burning things up, you could consider trying to heat the engine block around the fitting, but avoid direct heat contact with the cap so that it doesn't expand as rapidly. A MAP or propane torch could be used for this purpose. (MAP yielding a hotter flame than propane.) Plumbers use MAP when soldering copper fittings.) The expansion caused by temperature differential may help.

Hope that helps,
Brian.

[Sula]

I agree with the above suggestion of hitting the fitting (by which I mean the top of it) with a hammer. (The object of the exercise is to create vibration in the fitting that might break up the crud that is sticking it to the threaded hole it is sitting in. )

Another approach to the temperature differential thing Brian mentioned (which I suspect is more likely to give a result than the hammering, but why not do both) is to run the engine up to full temperature, then douse the fitting (trying to avoid the surrounding engine blocking which it is fitted) with freezer spray (as used by plumbers). I think this will cause a greater difference in temperature between the two than trying to heat the block with a blowlamp, as the engine block will be slow to heat up by that method, during which time heat will be conducted to the fitting. The aim is to shrink the fitting by cooling it, while the hole it fits in is still expanded by heat. The greater the temperature differential, the more likely to break the jam.

I had no trouble removing the same fitting on my boat (without heat etc.), by the way, but I don't have the access restriction of the LM 28 engine box. (My problem with that fitting is that there is the thread of an old anode stuck in my fitting. An easy fix by replacing the fitting, I thought, until Bukh UK told me how much they wanted or a new one! I balked at the price at the time, and have been dithering since.

[Brian & Glenda]

I certainly like the Sula approach to achieving a temperature differential better than my own! I have to remember that just in case I ever need to do same! Thanks Sula!

I have removed the remnants of an old zinc in my zinc's fitting, by carefully drilling it out to the maximum hole size possible, then using a thread tap to clean the female threads. Worked great. Or ... you might try drilling a smaller hole of the appropriate size for using a reverse thread 'easy out' to try to remove the remnants of the zinc. Heat would probably help here too for particularly stubborn zincs, but I've never needed to use same.

For those who don't know what an 'Easy Out' is, they are typically used by mechanics to remove the threaded portion of a bolt who's head has snapped off. Drill a hole in the stuck portion of the bolt, and insert the tapered threaded easy out until it stops going round, add a wrench, and the reverse thread should thread the stuck portion out of it's hole. 'Easy out' is probably a North American trade name. I'm not sure this would work if the zinc is soft though. It would likely just strip the threads that the easy out had created, unless a large size easy out with course threads was used.

B