Weak Blocks

[Bryce S.]

Of the articles/ posts that I've read it seems that most common issues is a bock cracks on the water outlet side of the motor (driver side) from mostly freezing it seems. Are there other known weak spots on this block that happen for other reasons such as vibration or tension? On all the picture I never see any damage on the manifold side of the engine. I wonder why this is?

[Joe Bell]

26-7 blocks are known for cracks between 2 and 3 form center soft plug inward, also from exhaust valve in to cylinders

[dobro1956]

As Joe mentioned, The 26-27 blocks are prone to having cracks between #2 and 3 cylinders. They are usually cracked in the top of the oil galley in the water jacket. Probably due to a change in cores or casting practice.

[J and M Machine]

Of the articles/ posts that I've read it seems that most common issues is a bock cracks on the water outlet side of the motor (driver side) from mostly freezing it seems. Are there other known weak spots on this block that happen for other reasons such as vibration or tension? On all the picture I never see any damage on the manifold side of the engine. I wonder why this is?

As with any engine over time wear and tear and rust take its toll on the block and iron parts.
We've seen the multitude of cracks on engine blocks/heads and Model T isn't void of those as all engines stress.
Dealing with something that is old and wasn't meant to last this long.

Common cracks are in center valve seats; due to overheating

Ones you've mentioned are caused by freezing and stress.

All of these cracks were repaired by us and engines are back on road.

[TXGOAT2]

Valve seat cracks are usually a result of overheating. Freeze damage is very common, and affects all engines so abused. I suspect that many other cracks that are often noted are the result of freeze damage or overheating damage, and the likelihood of cracking is increased by water jacket corrosion, improper cylinder head bolt torque, running engines with deposits in the water jackets, and running hard with loose bearings, leaking valves, leaking head gaskets, broken motor mounts, etc. Chronic overloading, such as might be expected in a truck engine or a car engine running in sandy or muddy or mountainous country, would also promote valve seat cracking, especially if other factors are present. Water jacket corrosion is very common in Model T engines, and most all of them have seen plenty of about every kind of abuse and neglect that can be brought to bear on an engine.

[RajoRacer]

I've seen several '26 - '27 blocks cracked in the water jacket in the front of # 1.

[Norman Kling]

A common area for a crack is between the exhaust valve seat and the cylinder wall. Many engines have had valve seat inserts and sleeved cylinders to close those areas. This is very common when the engine overheats and then cold water is poured in before the engine has time to cool off. So if your engine overheats, do not immediately pour in coolant. Let it cool off for half hour or more before you pour in coolant. Also keep the radiator and water jacket clean and check for leaks and coolant level before starting to avoid overheating. If it starts to heat up, stop and cool off before going on.
Norm

[TXGOAT2]

Running the engine with late ignition timing overheats exhaust valves and seats, especially if cooling system problems exist. Cast iron blocks can stand a lot of heat, but they do not like UNEVEN heat. Normal operation of all engines concentrates heat at the exhaust valve and exhaust valve seats, and you do not want to do anything or allow anything to aggravate that situation. Avoid overloading and keep the cooling system in top condition, and use the spark control properly. If you have leaky valves, fix 'em. Running for long periods at higher speeds/loads with a very lean mixture will also cause excessive exhaust valve and seat temperatures. Intake manifold leaks can cause high exhaust valve and seat temperatures. It's my opinion that leaky exhaust manifold gaskets and cracked manifolds can allow excess oxygen into the exhaust manifold and exhaust ports which can cause more rapid deterioration of exhaust valves, exhaust manifolds, and exhaust valve seats

[TXGOAT2]

It's best to avoid overboring flathead engines, so far as is possible. An engine needing maximum overboring would probably benefit for sleeving back to standard. Proper sleeving can prevent a hot spot between the exhaust valve seat and the cylinder bore while preventing dumping too much of the combustion heat into the water jacket.

[Allan]

Another area for cracks is the rear main bearing web, especially in early blocks, but not exclusively. The blocks are machined to accept the nuts on the rear main bearing bolts. This creates sharp stress riser, from which cracks can emanate. The end result is usually a broken block and crankshaft. It is often reported that the crankshaft broke and tore the back out of the block. I have seen evidence that the reverse is true. The blocks crack, eventually the web breaks out, and takes the crankshaft with it. It is good practice to magnaflux blocks before reconditioning, with careful attention to the back web.

Allan from down under.