This month, I'm passing on some varied advice from contributors to the internet
Stationary Engine Mailing List to solve the problem of a cracked water jacket:
* We've had numerous discussions on welding cast iron in the past. People that I know to be knowledgeable have
posted detailed descriptions on what to use and how to use it. All that aside, I still don't feel enough confidence
in my ability to tackle an engine. We've got a 6hp FM Z with a thin crack in the water jacket that extends from
the head back to the base directly below the cylinder. It's virtually non-existent when cool, but as the engine
runs, a steadily increasing stream of water begins to make its appearance. It's pretty bad after a while. Anyway,
because it's in a high-stress area, I figure it will have to be welded. My problem is that I haven't had much luck
locating someone in my area that is experienced in welding cast.
* For the last 7or 8 years I have been using a welding rod designed for dirty castings. No preheat, no grinding
or cleaning, no stress relieving, machinable (unlike Ni) and it welds right through rust and dirt!!!
It takes a different technique but saves a lot of work and has a higher success rate. I have had great luck with
it. The rod is Weld Mold 706 - the manufacturer is in New York but I get mine from a small specialty weld supplier.
* This rod seems to burn right through the rubbish. I have done as much as 6 inches of continuous weld without
trouble. The only place I have had much trouble is right next to the exhaust valve or on an exhaust manifold. The
first pass always looks a little bubbly but just chip and brush and weld right over it. Comes out smooth as satin.
The results are the same color as iron and can easily be drilled and tapped. I think the reason it works so well
is that the expansion and contraction of the weldment matches that of iron. (Ni and stainless contract so much
during cooling that the weld pulls from the iron).
* The best cast iron rod that I have ever used is the Palco 808 rod made by Precision Alloy Company of Scottown,
Ohio. They really "flow" well and are easily machinable. You can use them to weld steel to cast with
good results (those of you that are familiar with alloys know that this can be difficult).
* The primary concern of welding such a project is the condition of the metal. I'll bet it's rusty, thin, and most
likely will be difficult to weld.
* I have used radiator repair epoxy putty successfully, I have a particular patch on my car radiator that is going
on four years old and doing fine. It is on the top (hot) tank, and goes through a lot of expansion and contraction
cycles plus vibration. It cost less than $3 for material, and it took about an hour to prepare the crack and apply
the stuff. Almost all the different brands and kinds of patching materials available are all the same basic epoxy,
they add fillers, colors and perfumes to fool you into thinking they are all different and unique from each other
when they are not. I would try radiator epoxy first because it won't keep you from welding it later if it comes
to that. As far as welding goes, ask the welder to consider either Ni-Rod or a stainless steel rod meant for thin
cast iron sections, with a preparation of grinding out the crack to a shallow depth. Follow the welding with thorough
peening of the bead to eliminate all stresses from shrinkage.
* Depending on how big the crack is , you can open it up with a die grinder and a cone shaped carbide burr. Knead
up a batch of the epoxy putty as mentioned in the previous post. With the tiniest bit of effort you can fill the
crack , smooth it out and have a nice smooth homogenous surface. It'll set up in 10 minutes and will take paint
* We used Araldite (epoxy) to repair the leaking water jacket on my father's A Model Ford about 20 years ago. We
ground out a groove where the block was cracked and filled it with Araldite. Once it had set we ground it smooth
with the block and painted over it. The car has done a LOT of mileage (it has been round Australia) and has had
the engine rebuilt recently. We are still using the same block we repaired all those years ago and it has never
* The heating and cooling on the water jacket is minimal - about 200 degrees. Epoxies are somewhat plastic, allowing
the expansion and contraction of the metal, so I don't think that's a big concern.
* I have an engine with a crack in the bottom of the water jacket. Several years ago I put radiator stop leak in
the water and finally the leak stopped and hasn't shown back up for a few years now.
* If you don't want to or can't weld it, metal stitch it. This works as good or better than a weld.
* Metal stitching is an old art of repairing cast iron before the days of welding. Small holes are drilled along
each side of the crack and from side to side a slot is cut in. The side holes are fairly close together, something
At each end of the crack, a small hole is drilled through to stop the migration of the crack.
The end holes are plugged and peened. In the side holes, a bowtie or staple-like item is inserted and also peened
in, then the length of the crack peened to seal it.
I've seen some of the old big engines and compressors repaired this way and with excellent results.
* I have two cracks in my 6 hp Z on the bottom side of the head that I vee'd out with a small dental grinder, cleaned
very good and put JB Weld in them. It is the engine I once used to pull a molasses mill for two days, full rolling
boil most of the time, and never leaked.
* In my reproduction copy of the McCormic-Deering operating instructions, under "repairing water jackets"
it says "Where the crack is a very small one, not over a thirty-second of an inch in width, the patching can
be done by means of what is termed a "rust joint." .......... Drain the jacket. put a coat of putty or
tallow over the crack, being careful not to fill the crack, with it. Fill the jacket high enough to cover the crack
with salamoniac solution (one pound to a gallon of water) let stand thirty minutes, drain, and run engine five
minutes to warm jacket. Stop engine put solution back into jacket and repeat process three or four times. If the
crack is not too wide, you will thus form a rust joint that will never leak."
Salamoniac is Ammonium Chloride.
So there were a good variety of solutions to the original question, and hopefully the outcome will be as positive
as the engine owners response!
* Thanks to all who responded on and off-list concerning my "crack problem".
Everyone seems to recommend an epoxy without hesitation, but I still have my doubts in this case. I mean it is
just below the cylinder after all. Those of you who have a 6hp FM Z probably know that they do tend to get pretty
Prior to posting my question I was concerned with the stress of expansion breaking up the epoxy fairly quickly,
but maybe not. Perhaps I'll try some of my favorite epoxy on the outside and try to get a liquid epoxy settled
into the crack from the inside. I've just never had this exact problem before so I'll defer to your collective
judgment and give it a shot.