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Discussing Stan's crankshaft truing process has inspired me to finish the press that's been 90% done for several years. It's modeled after a photo of the factory press, but looking around on YouTube I've found these are common- especially with 2 stroke dirt bike mechanics.
Mine is a Danly die set- 4 posts are pressed into corners of the bottom plate(shoe) and 4 bushings are pressed into a mating top shoe- the top shoe slides on the posts extremely accurately- it's hard to measure any play when the posts and bushings are in good shape- these die sets cycle hundreds of thousands of times in industry with little maintenance.
The drawings I made were for a Ducati twin crankshaft, but it will work fine for a single with some reducer bushings.

The holes in the top and bottom plates are line bored to fit the bearing journals on the crankshaft. There's a small pocket in the shoes for the protruding flange on the crank flywheels to nest into- keep the pressure applied in a straight line to the pin. Press the pin into one flywheel, put both flywheels into the press with the connecting rods and press the crankshaft together.

The shafts on the flywheels should stay aligned as accurately as the plates were bored, which should eliminate lots of hammering on the crankshaft.

This is my bottom plate, a post , and a few different styles of bushings- steel, hard anodized, and a ball bushing.

Someone who works on crankshafts every day can probably get the same result with just a press and a hammer, but I feel better when there's not so much left to chance.
I don't have access to the kind of machinery needed to do the final drill/bore/ream, so I'm going to take this to a shop when the blizzard blows over- will report back how it works.
Rick

Very interesting Rick. I saw a crank press similar to that concept on ebay some time ago. It was made to accommodate Ducati single crankshafts. Sure would make things proceed a lot quicker. On the last Ducati crank I trued (a 200), I chased a few thousandths for a couple of hours on a truing stand, still never got it as close as I'd have liked. On Ducati, it's especially critical since the end of the crank runs in a bushing on the timing side. If that end doesn't run true, it will wear the bushing in short order. Matt

Rick,
That's a nice CAD drawing of the crank & press parts.


Stan

Stan-
The models were done in Rhino- during an introductory offer it only cost $300.00. I like it for technical drawings- it will generate vector output of perspective views, so I'm not stuck with bitmaps. Solidworks models are much better- I used Inventor at work, but the prices for that level of software are out of reach for a hobbyist. You're lucky to have Solidworks- my models aren't much more than pretty pictures.
Matt-
Even though it's Standard Operating Procedure, I have a hard time accepting that I have to beat on a crankshaft with a big hammer- I'm hoping this will be a better way- remains to be seen. The die set cost a few dollars at an auction, so not much invested.
I want to build a rig to use the crankcases/main bearings to guide a tool to ream the outrigger bushing in the timing cover- still in the planning stage if anyone has suggestions.
Rick

Rick wrote: Even though it's Standard Operating Procedure, I have a hard time accepting that I have to beat on a crankshaft with a big hammer ..

FWIW, Rick, I've seen Tony Brancato truing bevel twin cranks by dropping them on to a big lump of wood, i.e. using the weight of the beast to do the work. He said it was trick he'd seen being used in the factory ...

I’ve considered the same tool for the timing side bushing. A plug that fits in the right side main bearing with a hole reamed to the size of the journal on the crank. Then just fasten the timing cover to the center case and run a reamer through the pilot hole in the plug. Could even make the plug fit through both main bearings and assemble the cases, then ream the bushing.

I’m not keen on beating flywheels with big hammers either. I bought a set of copper faced knockoff hammers that don’t dent the flywheels but it’s still an art rather than a science. Perhaps a tool that holds one flywheel securely, held in a hydraulic press so the other flywheel can be aligned by using the press and a dial indicator measuring the movement? Matt

The problem with using a press is that you run into what the machine tool builders and operators call stick slip. It is a situation where two surfaces have enough friction between them that it takes much more energy to get them unstuck and moving relative to each other than it takes to keep them moving. Which makes it difficult to move them a precise distance consistently, since the force needed is dependant on a lot of variables on a microscopic level.
The whack with a hammer, soft faced, of course, has the advantage of applying a initial shock to break the initial friction hold, and then to apply a certain amount of force to move the surfaces a certain distance, depending on how much force was in the hammer blow.
A press with absolutely no give, or spring back, would do a good job, if the pressure applied was volume restricted, but most presses have an inherent springy-ness to them, and once the "stick" is over come, the spring "slides" the parts till the spring is unloaded, which may be as much , or not, as you needed the parts to slide.
A man with a hammer can judge how hard to hit, the initial shock to over come the stick, and the remaining kinetic energy to induce just the right amount of slide.

I'm in the BFH camp, CZ

There was a photo in a '70s magazine, taken at a Kawasaki 3 cylinder engine assembly area.
It showed someone using a lead hammer on a crankshaft.
Even then I thought, wow - looks crude but if it's good enough for Kawasaki...

Capton brings up a good point about pressing parts with an interference fit. The Ducati single cranks are easy to press together, since the pins are shouldered. The slide starts and stops dead on the shoulder. On straight pin cranks, I cut short lengths of feeler gauge and stack both under the pin and above, so that the slide stops dead on the pin-shim stack. If the crank width was measured before disassembly, just match this measurement in your pin- shim stack height. Works like a charm.

I've thought about building a fixture that may be similar to the one Matt described- it won't work on the 175 crankshafts that are my interest, but it should work with the 250 crankshafts that have holes bored through the flywheels.
The fixture is a plate with 2 rods and a lever with the same 2 rods- the holes in the flywheel fit over the rods on the fixture base plate and the lever with rods is used to apply torque to the other flywheel.


Beating a round flywheel with a hammer doesn't apply much of the force to rotating the flywheel, but this fixture should apply the force where it should do the most good.
I've got a scheme for a fixture that will work for the crankshafts without the holes in the flywheels- will draw it up soon.
Rick