My crankshaft broke Tuesday June 30. I pulled the engine and took it to Kevin Prus Sr. that afternoon. He called me this morning July 3 to tell me my engine was repaired and ready to pick up. That is what I call fast turnaround.
Amazing what can be done with double-sided sticky tape!
You're lucky. Mine broke the rear main out of the block.
Oops! I think I see the source of the problem though Bob - the block to pan bolts were upside down!
I'll remember that.
Jim, so what all did he have to do? No damage to the block I guess?
Bob, are you sure your crankshaft broke and took out the rear main, or did the rear main break out and take the crankshaft with it?
If you look closely at the break in the casting, you may find polished areas, perhaps near the land where the main bearing bolt heads rest. Then there may be fresh break areas further out. I have seen 3 blocks where this is the case plus another which was cracked but not yet broken out.
I would be interested to hear what you find. Photos may help us all.
Allan from down under.
I really think the block broke first and took out the crank.
There are shiny spots along the sides of the break and it looks like the top part broke last as it's a pretty clean break.
It was a fresh rebuild with maybe a thousand miles.
It made funny noises and there was cast iron in the trans screen.
I pulled the bottom cover once and looked around but didn't see any cracks but I never thought to really inspect the back end.
I think I heard when the block finally broke and the crank broke about a hundred feet farther down the road.
Made the most noise I ever heard come from an engine...Scared the hell out of my wife following behind. (she could stand to lose a little hell so it wasn't all bad!)
i ponder whether using the rear main as a thrust bearing coupled with the strain of the clutch pulling on the rear of the block and the weight of the flywheels causes the block to break first?
Bob G, I am glad that you can have a sense of humor about it! (Might as well. It is a part of the model T experience, although one I have not personally experienced. Yet.)
James B, I am glad that your damage was not so severe! If you are going to do it? That IS the better way. I just hope you do not later do like Bob G's?
Do drive carefully, and DO enjoy! W2
Bob, thanks for the feedback. It looks like the block cracked first. Finding the cast iron bits in the screen would indicate this. There are so many broken crankshafts, which do not break the block. But I can't imagine a broken block not taking out the crankshaft.
Kep, it is my opinion that the cause of the rear main breaking out of the block is due to poor machining practise from new. The rear main cap bolt heads register on a machined surface which is at right angles to the block web. The sharp angle between two machined faces is a perfect stress riser. If this was a decent radius, I feel many of these breakouts would not occur.
I have seen at least two blocks with cracks emanating form this sharply machined area, these being detected before the block broke.
It has come to the stage where I will not re-build a block without first having it crack tested, with special attention to this area.
Others may have different opinions.
Allan from down under.
Should i radius the shelf thing where the bolts go on my own engines?
Here's that sharp corner on mine.
Pretty clean break across the top and some shiny spots along the sides.
Bob, your second and third photos clearly show where the cracks had been 'working' before letting go. This is probably the source of the cast iron debris in your trans cover screen. It also shows shiny spots in the first photo.
Kep, in Bob's first photo you will se that the casting at the rear of the block is not very thick. I had wondered if there was a way we could radius that area. I would be loathe to make the radius by taking more material from the vertical face of the machined area which is already on the thin side. However, there should be no problems machining down the horizontal surface on which the main bearing bolt heads sit, leaving a generous radius to the vertical face. You might have to tickle up the heads of the bolts a little to match the radius.
Others may be able to shed a more enlightened comment.
Allan from down under.
All the breaks I have seen like that were on replaced babbitt jobs, that came from a K.R. Wilson Babbitt hammer improperly used, broke the same exact way, and following the same lines, and that is more then one.
I just checked 3 blocks looking for a sharp corner to the front of the rear main bolts.
An '18 block has a pretty sharp corner.
'25 and '26 blocks have about 1/32" radius.
Mine that broke is a '23 and has a very small radius...you could probably call it a sharp corner.
It would be a simple machining operation on a bare block to cut the horizontal face the bolts sit on to get a bigger radius.