The Stovebolt Site Forums The Shop Area Engine Shop 261 block steam hole crack

I just got my 261 block back from magnafluxing and 2 little cracks showed up, They are on the top of the block between the small steam hole and the adjacent head bolt threads by #1 and #6

There is only about 3/16" between these two holes and this area appears to be covered with head gasket to allow for sealing.

My question is: Can I live with this? Should I try to have this welded or brazed? Can I get by with only a heli-coil?

It looks to me that these tiny cracks cannot grow because they now run hole to hole. I just worry about head bolt torque on this area in the long term.

Any suggustions?

You' should get it fixed. If it's cracked to a head bolt hole, not even a Heli-Coil is going to help on the bolt torque. The machine shop should be able to handel the repair without any problems.

Longbox55

I've got a number of a diesel repair shop in Phoenix that may be able to fix it. I'll call them Monday.

I think that crack was in the block for some time, the threads in the block show small signs of corrosion near the crack.

When putting it back together, you may want to use a stud, if that is possible. Some of the stress is absent when using a stud. This could make a difference if there is thread in the problem area. If there is no thread there, it would not help.

Yours probably isn't the only 261 with cracks,I bet a few are cracked and go unoticed.
Might be a difficult repair due to the limited space and if the crack has migrated into the head bolt threads in the block.It's a stressed area when the bolt is torqued down.Get a professional opinion and go from there.

Truckernix

There is thread in the affected area, I think the idea of a stud with thread sealant could be the answer.

I thourghly cleaned up this area today. The crack is only 1/8" long and runs from the steam hole to the closest tangent part of the threads, I put a new gasket on this on the block and the area of the crack is totally covered with the gasket. It appears to me if the stud were used and set in thread sealant,the block could be rebuilt with no further problems.

I am going to have the block decked to clean up the face as well as the head milled. This should make a good flat sealing surface.

Do the torque values change between studxs and Head bolts? If the studs have fine threads on top do I torque them the same?

One of the experienced machinists wil hopefully jump in here. My comment was meant to address the stress created in the threaded hole. With a stud, you don't get the same shear stress and the tension forces are distributed over more of the threads. Also, the tension force generated by a specific torque value is dependent on the pitch of the thread.

Just what exactly is a steam hole?


Stuart

I was thinking about retapping the 1/2"-13 head bolt threads with an oversize bottoming tap (GH5)and then silver soldering the studs to the block after the block was decked.

This operation would not require the heat needed for welding or brazing and should add substantial strength th the threads.

atomarc
There are 3 pairs of steam holes drilled on 261 blocks and heads between 1&2, 3&4, and 5&6 cyclinders. One of these holes in each pair is within 1/4" of the 3 center head bolt threads.

wags,

Thanks for the info! I wonder what the purpose of this steam hole is? The head and block are full of passages to allow water to circulate through the water jackets of the block and head...is this just another name for one of those passages.

Stuart

I think the 261 casting is thicker to allow for the 3.750 bore. This reduced the water flow between the cyclinders I mentioned earlier. These added water passages (Steam holes) were added to improve water flow in this area.

The steam holes are there to vent steam bubbles from the cylinder walls during warm-up.
Especially during cold temperatures, when the coolant is very cold, localized hot spots can form these bubbles.
Kind of works together with the original 261 bypass thermostat, that circulates the coolant through both head and block before the thermostat opens.
I heard that was more common with bigger truck engines, like the 261 originally was.

I found a picture that Tim had linked that sure helps me understand the 'siamese cylinder' deal and the need for these steam holes.

http://ares.cs.siena.edu/~lederman/truck/Documents/EngineeringFeatures/slides/orig_Page60.html

Stuart

I talked to the machine shop, they are going to furnace weld the area and machine new threads. They said they could garantee the fix if it was done this way. He said his shop is full of old flatheads and 270 GMC's with weld repairs of all kinds. Thanks for the responces