Replacing Heat Exchanger Zinc

[Briggy G]

Universal 25.
Any suggestions on things to keep an eye out for when doing this?
Close through hull, unscrew bolt and go for it ?
Is there a standard size that I can order and have on hand before opening ? Probably need to replace gasket also, green oxidation covering exchanger.
Any suggestions much appreciated!

 

[LeslieTroyer]

Do you have a 2 or 3 inch heat exchanger(early M25's had 2"). ?? My M25 2" takes 1/8 x 2" . teflon pipe dope (tube) on the threads. - no need to pull the end plates. The zinc is the brass hex on the cylinder.

If you do pull the end plug to replace the rubber replace The o-ring on the end cap bolt

Don't forget to open the raw water before starting


Les

 

[Briggy G]

Hey Les,
Thanks for your reply. Are we talking 2 or 3" diameter? Hmmm.
I am so green that I don't actually even understand the rest of what you said.
The brass hex, I can see.... is that what I am replacing?
It appears there has been leakage based on the green oxidation and that I should replace a gasket too?
Open raw water..... Are we talking thru-hull valve?
Eek. I'm more lost than I thought!
...

 

[Briggy G]

Photo attached

 

[LeslieTroyer]

Catalina delivered both heat exchanger (HE) sizes with the M25 engines. They increased the size when toooo many folks had over heating issues.

Raw water is "sea water" as opposed to anti-freeze coolant "fresh" water. So yes I ment the thru hull that feeds you engine. Your list of what to do included closing it before removing the old zinc. I just wanted to remind you to open it afterwards.

Yes the brass hex hold the zinc. On the very small sizes like 1/8" it is a one piece part 2" long. Larger sizes are two pieces 1) brass plug with internal and external threads and 2) a threaded pencil zinc that screws into the brass plug. It is always good to have spare plugs around incase the old zinc is too far gone to remove from the plug. It is not uncommon to have to cut the end of the zinc to length. Don't force it if you bottom the zinc before the threads on the plug tightens.

The the 2" HE has one removable end cap. The 3" I've seen have both ends removeable. The end caps are held on with a central bolt. This bolt has a o-ring hidden under the big rubber gasket that seals the end cap to the cylinder. Remember th HE has both raw and fresh water and removing the caps may cause you to have to burp the fresh water side of things.

The C34.org tech wiki is a great resource for info on the engine. Stu Jackson has done a fabulous job collecting info

Les

 

[Briggy G]

Awesome, Thanks Les. Your comments and recommendations really help.

I feel a little better about tackling this. I also appreciate the c34.org tech wiki recommmendation!

Thanks!

 

[Stu Jackson]

The C34.org tech wiki is a great resource for info on the engine. Stu Jackson has done a fabulous job collecting info

Thanks, Les.

Briggy, that would be here:

http://c34.org/wikiwp/?rdp_we_resource=http://c34.org/wiki/index.php?title=Diesel_Engine

The 3" HX zinc should have an 11/16" hex head. If you still have the 2 inch HX it may be smaller.

Do NOT isolate the threads to the HX. You should check it every 3 months anyway, so it isn't going to get stuck from galvanic corrosion. Check it regularly and get a "feel" for what works for YOU, not what anybody else, including me, tells you. Start with 3 months and go from there. If you take my advice, do it at 2 months!!!

 

[Briggy G]

Wow guys- thanks so much for your help!!
Got it changed - had completely eroded !!!

 

[LeslieTroyer]

Great it always feels good when something is easier than expected.

Les