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I bought a set of crankcases that I think are from the earlier 175 engine series- before the 175 used the 250 crankcases. Someone decided to convert it to a 250 by boring out the crankcase mouth, but it wasn't done very carefully- even if it had been done right the bore was too big to avoid breaking into the threaded holes for the cylinder bolts- here's a picture:

I'm a fool for this sort of project- repairing an abused part, so I'll probably try to fix it. This is a model of the problem:

And this is what I'd probably do to correct the problem:

But, I've never repaired a crankcase mouth, so I'd like to know if anyone has, and if there's a better solution. I would split the collar, plug weld it into place, and drill out the old threads for a TimeSert type of thread repair. The kerf removed from splitting the collar will probably be too big for the gasket surfaces to match up, but probalby not worth the effort of making 2 collars and cutting them 'off center'.
If anyone sees a problem with this let me know- it'll probably be winter before I start fooling around with it.
I did get the entire lower end, but no cylinder or head. I took a guess that the 175 cylinder sleeve would be 3mm thick like a 250, but I don't know what the dimensions of a 175 cylinder are- if anyone has measured a 175 cylinder I'd like to know the OD of the sleeve before I repair the cases to the wrong size.
And, if anyone has a 175 engine top end cluttering up their shop...
Rick

I'd just build it up with weld then bore it and re thread the stud holes. I'd likely only build up around the stud holes then run a bead around the the top edge to increase the gasket contact surface and not bother fully building up all the way to the bottom. Depends somewhat on how easily/cleanly it welded...

Bill

I would wait till i had a barrel and head to hand as they are made to a tight clearance on the bolts on my 250 and you want it all to line up.

Bill-
I thought about doing it like you suggested, but not worrying about the building up the top gasket surface, like this:

Do you think I'd have a sealing problem if I did it as drawn? I'd need to add a spot for the locating pin.
Bevel bob-
I hear you- will try to at least borrow a cylinder before I start

Do you think I'd have a sealing problem if I did it as drawn?

That I really don't know... I guess I'd also want to find out if the barrel skirt needs support from the crankcase, where then you're sleeve method would be a possible advantage.
You need to find out the diameter of the 175 skirt, might not be as much to build up as you think...

Bill

I dont think the skirt needs much in the way of support from the cases, sealing cyl base is not usually a problem and the case is well ventillated, distorsion needs to be guarded against, cases bolted up and pre-heated before welding?.Also perhaps make up a guide plate from the bolt holes before doing any welding? ,I'm no machinist though!!.