Making one engine out of two

[motoman]

Not EVEN Tod, When these cases are produced the crank journals are line bored to match perfectly. Mismatching is dodgy at best. Most likely it will produce an assembly that won't turn or an assembly that will wipe out main bearings quickly.

If you've ever been into an automotive engine you will see that all the main bearing caps are numbered (if the engine has ever been disassembled) and they all have arrows pointing to the front.

That's not because the assembler was anal.

+1!..........and original crank ASSEMBLIES were balanced, so with any piston/ring or rod change from that original crank assembly there will be some smoothness and longgivity loss.

[trbig]

Not EVEN Tod, When these cases are produced the crank journals are line bored to match perfectly. Mismatching is dodgy at best. Most likely it will produce an assembly that won't turn or an assembly that will wipe out main bearings quickly.

If you've ever been into an automotive engine you will see that all the main bearing caps are numbered (if the engine has ever been disassembled) and they all have arrows pointing to the front.

That's not because the assembler was anal.

+1!..........and original crank ASSEMBLIES were balanced, so with any piston/ring or rod change from that original crank assembly there will be some smoothness and longgivity loss.

Well, I had a new piston/ring/rod change in an engine that smacked a guardrail several years back now and slid down the asphalt,. The wreck and asphalt ground the engine case down pretty bad and ground my pickup coils off. The lip was totally destroyed that the left side cover seals to on the lower engine case so I replaced the lower case. 100+ thousand miles later, and still going strong, sorry, but both of you guys' words of doom and gloom sound a little hollow to me...

[trbig]

So thinking more about this, I'm not so sure these engines are line-bored. Just from a production viewpoint alone, it would make no sense. That would mean they'd have to bolt the two incomplete halves together with all the case bolts torqued to spec, bore the crank journals, then disassemble again so they can install all the components, then re-assemble a 2nd time. A line-bore on a regular motor where you're able to get to everything afterwards to install the crank/rods/pistons, etc.. I understand.

Then what would you do if these crank bearing halves didn't completely fit into each case half... I don't know. I wish someone here knew someone who knew a guy that had an uncle that worked on the production line of these things at some point. As unlucky as I am with everything else, I just can't believe that I got a one-in-a-million shot with swapping these case halves if the journals were all in a bit different place.

[trbig]

+1!..........and original crank ASSEMBLIES were balanced, so with any piston/ring or rod change from that original crank assembly there will be some smoothness and longgivity loss.

And this statement is incorrect. The cranks were balanced, but not with rods/pistons attached. Any swapping of any piston of any weight.. as long as they are all relatively close to each other in weight, there will be no vibration nor any loss of longevity if done right. The weight of two pistons being pushed up and forward is offset exactly by the weight of two pistons being pulled back and down. As a matter of fact, you can send your crank in to people to have it "Knife edged" and a lot of the mass taken off of it to get the motors to rev much quicker. There's no need at all to take into account of the piston/rod/pin weight as far as vibration or balancing go as long as each cylinder's components weigh equally. I think this is the reason for the writing on pistons that you see when a motor is completely stock and opened up for the first time. I think it's simply some sort of weight measurement to make sure all are the same.

[motoman]

So thinking more about this, I'm not so sure these engines are line-bored. Just from a production viewpoint alone, it would make no sense. That would mean they'd have to bolt the two incomplete halves together with all the case bolts torqued to spec, bore the crank journals, then disassemble again so they can install all the components, then re-assemble a 2nd time. A line-bore on a regular motor where you're able to get to everything afterwards to install the crank/rods/pistons, etc.. I understand.

Then what would you do if these crank bearing halves didn't completely fit into each case half... I don't know. I wish someone here knew someone who knew a guy that had an uncle that worked on the production line of these things at some point. As unlucky as I am with everything else, I just can't believe that I got a one-in-a-million shot with swapping these case halves if the journals were all in a bit different place.

trbig, interesting to hear you've had no issues mixin' matchin' case halves. A local rider here had to do the same thing with no issues on his XS11SH. I've ridden it and it runs smoothly.
I do remember reading a decade ago or so about the production of these specific motors. Alot of high performance race 'tricks' were used with their production. Rods were radioused and shot-peened, forged crankshaft with crank ASSEMBLIES being balanced, original factory pistons were forged along with use of chrome rings, five angle cut of combustion chamber so ignition in cyl. copied that of the hemi-head design. Seems there were a couple other performance enhancements, but that was way too long ago for me to remember.