Heat exchanger zinc removal problem

[Bob Bradley]

I went to replace the zincs in my heat exchangers yesterday, and ran into problems. The main cause of the problem is that the bronze nut for each zinc is so large that its points nearly touch the side plate, preventing me from putting a socket over it. An adjustable wrench, and a pair of channel locks were both insufficient to remove the nut without damaging it. Does anyone have any suggestions, short of removing the 4 side plates and having them machined out? I've considered using my turbo torch with Mapp gas, but I'm not sure that a) it would help, and b) it would not cause any collateral damage.
Bob

[MikeP]

Is a box-end wrench able to get onto the bolt? If so, you can fit the box end on the bolt and, using a second large box end wrench, hook the box end portion over the open end portion of the first wrench to double the length of handle. Obviously, the quality of the wrenches will effect how well this will work.
Snap-Ons will do fine, Taiwan wrenches will probably break so be careful.

In any case, try tightening the bolt first - just the tiniest fraction of a turn is sufficient. I know that sounds odd but it usually works to break the corrosion. Then you can loosen the bolt without much difficulty. Anytime you are dealing with recalcitrant nuts/bolts/screws, try tightening them first.

[Nonchalant1]

Easy. You've got a non-original zinc cap there. Get a really large bolt extractor (like the Hanson EX-5 made for a 19/64 drill), drill the SOB and extract it like a big bolt. Be careful not to drill too deep, but the remaining zinc in the old cap should still be there enough to prevent getting any drill shavings in the fresh water system. Drill slowly, watching the hole bottom as it goes from bronze to zinc to make sure there's solid zinc there, but it's REALLY rare to not have solid zinc left in the cap.

DD original bronze zinc heads have a square cap with a Z on it, not a hex head. Boater's World, etc., "universal" zincs have hex heads. New DD heads and zincs are not that expensive and then in the future you can just replace the screw-in zinc rods. You can still use a socket to remove the square zinc caps, but it's a smaller socket for the same zinc!

[doc g]

If you can get a big pipe wrench on it and enough torque you should be able to get it out. It should be a brass plug threaded into the cast iron , it will come out without harming the casting. I would not use heat on it as I would assume there is solder in the core which you could melt and thereby ruin the core.

[Genesis]

Use PB Blaster and a pair of vise-grips.

If the vise-grips slip, grind flats on opposite sides with a dremel to the appropriate size and apply a large wrench.

Between those two methods it will come out.

PS: The original "Z" style rounds off the corners after a good long time if they are overtightened and they become useless too. Nothing wrong with the other kind so long as you don't overtorque them on install or leave them in there for too long without servicing them.

[Bob Bradley]

Thanks, all. I just got back from removing them. I went down last night and AeroKroiled the snot out of them, and used the vice grips on them this afternoon. The 2 outboard side zincs turned out to have the original square head - in perfect condition (on the outside). The zincs themselves were pretty much mush. I went to West Marine, and learned that the originals have a non-standard sized thread (figures). Based on the fact that the heads were in good shape, and that you have to pull up the floor to get at them, I suspect that they weren't maintained too regularly.

I also found that one of the non-originals had sheared off in the housing. I'm going back down later with a drill and ezout to attempt to extract it. Hopefully it's corroded in place enough for the drill to work and not just spin it.

Thanks again for the advice (also for the post on Boatdiesel, Karl).
Bob

[Genesis]

Yeah, all the flat-head ones are non-standard threading on the inside. Nice eh? You can't buy the pencils from the usual suspects (various chandlers) and expect them to fit - they won't.

All mine are generics now; I'll deal with the issues....

[captddis]

You can get the DD replacement pencils from Camp. The DD original pencils are better quality than Camp though, they wear evenly and do not crumble into pieces. If possible use the Milspec zincs. It saves lots of grief not having to clean the broken pieces out. Dave