If you have a block that has some cracks, should you use it? If you do, how should you repair it?
The blocks for our Flathead Ford V8s are getting more difficult and expensive to find.
Many times a block that "should be good" will be cracked. You have bought a few engines, busted knuckles to take them apart, then paid to have them cleaned and magnetic particle inspected. Finally you get the call from the machine shop -- "It's cracked".
First of all, it is not the machine shop's fault and they have earned their pay by finding the cracks. Remember, they would like the block to be good also; that way they can go ahead with the machine
work and parts sales.
If it is a structural crack, say through a main bolt or stud hole, it probably doesn't make sense to try to repair it. It would be difficult to add the strength needed while maintaining the dimensions required in the main bearing bore, and at the main cap to block parting line.
If it is a combustion chamber crack it is a higher risk repair because of the high pressures and temperatures. I have successfully repaired these cracks with the tapered thread
cast iron pins. Irontite and Loc-n-Stitch are two brands that work well.
The procedure is to identify the ends of the crack and drill the proper size holes through the casting wall. This hole is reamed tapered, then tapped tapered. The threads are very fine to give a better chance to seal. The tapered pin is coated with a ceramic sealer and screwed into the hole fairly tight.
These end pins are cut off and dressed almost flush as necessary. Then more holes
are drilled through the casting wall, to just barely intersect the end pins. The process is continued until the crack is completely pinned.
The pins are then machined to match the surrounding castings. Sometimes at this point, the area is peened. The repair area can then be machined normally.
If this crack repair has gone through a valve seat or into a cylinder, a seat insert or a sleeve is usually installed.
Frequently an oversize seat
is installed to get a "clean-up" cut on all sides of the seat counter bore. The stock seat OD is usually 1-5/8" plus maybe .008" for the crush fit. Oversize seats, still with the normal ID, are available 1-11/16" and 1-3/4" ODs.
Some shops peen or stake the area around the seat inserts after installation. This is an attempt to enhance seat retention.
My opinion is that if the seat and counter core are sized correctly, you don't need staking and if they are not, staking won't do the job.
A deck crack or cracks in ports, or cracks in the outside of the block, could be repaired in much the same way.
If the pan rail is split by freezing, the cracks may total many inches, making pinning too expensive to consider. I have seen blocks brazed and silver soldered sucessfully in this area.
The problem with brazing and welding
is that there may be stresses bound into this complicated casting. The heated repairs can cause a bore to become unround or a surface to not be flat at operating temperature, even though they are as they should be at ambient temperatures.
Another problem with some types of welding is a very hard transition layer between the weld and the parent material. This does not machine well with normal cutters, although it may be ground.
There are furnace welding processes
that can save almost any casting, including building up worn area. One of these is Cyclone Excels weld. This is quite expensive but may be worth the cost in some instances.
A final thought on crack repairs. There's a lot of talk about the French flathead blocks and engines that were made will into the 1980's for the French military.
There surplus stock is now available in the US as well as Europe. Although a new Flathead block seems very expensive to most flathead owners, and there are some minor differences in the castings, the potential is all there in a new block; there are no repairs new or old that might create problems.
Most reputable automotive machine shops should be able to make lasting repairs on the Flathead blocks, but we have to weigh the expense, the time, and the nagging doubts when we
encounter certain crack situations.