I keep running across discussions on this forum about cracked blocks. I know a block might crack if it overheats. I also appreciate that we are using engines that are roughly a century old, but I really am not familiar enough with engines to know why so many forum members have experienced cracked blocks.
Is there something that we should be doing to lessen the risk of cracking one of these precious blocks?
Eric, Several things are to blame. Age is one of them. Years of heating and cooling cycles can also contribute to stress in the blocks leading to cracks. Broken crankshafts can cause some serious damage and is often discussed on the forum. Then the 26-27 blocks had a design flaw in the way the casting is made and stress cracks form between cylinders two and three in the top of the valve spring oil galley. They are also subject to crack around the valves near the same area between pistons two and three. I believe a lot of the 26-27 blocks were cracked from day one. but the cracks were small and rusted shut. A lot of times when we vat clean, and oven bake our engine blocks, or heads, it can open up some cracks that were rusted shut or laying "dormant" for all those years. Antifreeze will go thru a crack that would never leak with plain water. I had a small hairline crack open up in the top of the oil galley on my new overhauled 27 engine. (it did not show up during magnafluxing) It just barely leaked antifreeze into the valve spring chamber, but it would put about a teaspoon full of antifreeze in there in about a month. So I removed the antifreeze, and ran an entire summer with plain well water. The crack "rusted shut" and I no longer have a crack that leaks. I have decided that I will never oven bake another 26-27 engine, because I think the chances of opening up a crack are too high (in my personal opinion) Another thing that can bust the castings is rust. Rust creates a massive hydraulic type of pressure when allowed to severally rust. Im not sure if it is because of the rust or the rust allowing water into the threads or seams and then that water freezes. I have seen old blocks busted around the bolt holes from years of neglect. A lot of our old blocks are salvaged from years of sitting outside. Then there are the normal things like running out of water or oil, letting it freeze with no antifreeze (or too little antifreeze), overtightening some of the bolts. That could be what caused the 25 engine block to crack at the main bearing bolt boss that Mike Bender is discussing on another thread. I have also seen the threaded bolt bosses at the rear of the block or front timing cover cracked by uneven tightening of the bolts when installing the parts. So many things can cause the cracking. The only thing I can think of to help, is just use good judgment and be gentle as a person can be when cleaning or assembling. Clean and chase all threads, and take care of the parts you have with decent storage and maintance. OK that was my two cents worth and probably overpriced. Have fun and be safe Donnie Brown .... OH yea, disclaimer notice for the "forum police"... These are my personal opinions and observations from too many years of working on old rusty stuff.
Donnie B, I think that was way more than two cents worth!
The big thing is, there are many different causes and types of cracks. It really depends on where the crack is and what caused it before a significant discussion is warranted. Many cracks do very little real harm to an engine, and many millions of engines are run every day with cracks known or mostly unknown. Each and every known or discovered crack needs to be looked at individually to determine whether it is a serious problem or not. That determination depends on whether the crack affects the structural integrity of the engine? Will it continue to grow significantly? Will it result in a significant leak? Of what and where to?
ANY crack can be repaired, by someone that really KNOWS how to do it. Many blocks are not worth the cost to repair some cracks because of the value of the time it takes and the materials and energy needed to do the job correctly. Many cracks can be adequately patched by most anyone of average skill levels with a little simple instruction. Some very rare and extremely desirable early engine blocks and other parts should only be repaired by one of the few well known professional cast iron welders with an excellent reputation.
Drive carefully, and enjoy the holidays! W2
Eric- I don't disagree with anything Donnie or Wayne wrote here. My additional 2 cents:
1. Generally speaking nobody makes any mention here when they find the block they are about to use in an overhaul has NO cracks. The 27 T engine I rebuilt back in the early 80's had none. It only comes up when someone is needing advice on how to handle a crack repair. That can skew one's perception of the "problem" of cracked blocks.
2. Side valve engines such as Ford used exclusively up until the early 1950's are much more complicated and difficult to cast. When you think about it the 1936 Lincoln Zephyr V-12 engine (single casting, valve in block) is to my reckoning the most complicated automotive casting ever made. Mass production of such a complicated casting will inevitably result in some core shifting which can leave some areas thinner than intended by the designers. Also along the same lines, there are large differences in temperature within a side valve block when running. Very cool around the intake valve ports and seats, and very hot around the exhaust seats and ports. All of that has to be endured by a single casting. Talk to the flathead V-8 guys about cracks in blocks. Little known fact: Ardun heads for the flathead V-8 were originally designed for trucks, to eliminate their tendency to crack the stock blocks in the area of the center siamesed exhaust port. A loaded truck runs at a higher duty cycle meaning a lot of heat in that area. The switch to OHV and OHC engine designs moved all of those problems to the heads. When you think about it, other than freeze cracks, have you ever heard of a Model T head to be cracked? I'm not saying it can't happen, but it's very rare.
another 2 cents---
I expected people to comment on freeze cracks. Many of the motors we have today were left or stored in areas that got cold in the winter.
Some of them got water in them and the ice expanding ice cracked them.
I believe that this is prevalent in the area just over the valve cover or in the top of the valve chamber, but others may know more than me
Wayne, I do agree that every crack is its "own story" and has to be addressed as to each crack and how it happened. It is a way deeper subject than I could give for my "2 cents worth". Christmas is almost upon us. Merry Christmas to all ...
Thanks for adding that crack by freezing. Prior to anti-freeze for the coolant, water was left and guess what, block cracks at the water jackets.
Most common spot in just below the top of the block, underside of the lip above the cylinder casting, driver side most times.
Many blocks have these seeping cracks, small and large.
My father used to "stitch" cracks in cast iron.
Using soft metal machine screws usually around 3/16ths in diameter. Then drilling and tapping holes at each end of the crack. Then installing the machine screw at each end. Once it was screwed deep in the hole he cut it off and peened it over. Once that was done he drilled another hole 1/2 into the 1st screw and 1/2 in the line of the crack and then tapped that hole. Another screw was installed cut off and peened over, then repeated the drilling and tapping and installing the screw and peening until you reached the end of the crack and the machine screw you installed in the beginning.
Now the entire crack is filled with overlapping machine screws peened over. Once that was completed he would use "water glass" or now known as sodium silicate available on amazon. This liquid was poured into the radiator usually about a quart then water added, and the motor was started and let run hot. Once the motor got good and hot and ran for a while the solution was drained from the cooling system. After the motor and cooled naturally water was added and the crack was sealed. After a while of running the screws and crack would rust over and a perfect seal was obtained.
The reason you installed screw at each end of the crack 1st is to stop the crack from expanding as the screws are installed and peened.