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I haven't been able to find a lot of information on the internet thus far to satisfy my recent curiosity about pressed crankshafts. I know they're fairly common in the 2-stroke world, seem to mostly be used in single throw engines, but have definitely also been used in multi throw engines and 4-strokes as well. Looking for 4-stroke, 4 cylinder versions seem few and far between. Off hand the only I'm familiar with is the Suzuki GS550.

In theory, this seems like a potentially more affordable method for producing custom one off or very low quantity crankshafts for specialty applications. It could possibly even be DIY to a certain extent. The thought is that the crankshaft could be broken down into parts that could be easily manufactured by ordinary machine shops from primarily near-net bar stock. All that would required is a design. There would be far less material removal than for a billet crank, and the machines doing it would have a much lower cost of operation as well. By using numerous identical parts, minor economies of scale could come into play even when making only a few crankshafts. It seems like the biggest hurdle in manufacturing would be the assembly fixture(s) used to align and straighten the pieces as they are pressed together.

So I'm looking to pick up any tidbits I can from people here who might have some knowledge or background in working with these types of cranks. What would be the major shortcomings or pitfalls relating to this type of crankshaft on 4+ cylinder engines? Obviously alignment when assembling the crankshaft would be critical. And I know about the propensity for them to twist out of alignment from torsional loads if they don't have some means (often welding) to lock them in place. But what else? Would this really be cost prohibitive compared to a true billet crank? Would the performance or longevity really be that inferior to a billet crank? Or is it more a matter of perception and a lack of resources/knowledge? Basically, tell me why it would be such a bad idea in a non-production application.

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

usually when they are used in 2 stroke engines it is combined with needle bearings instead of common plain bearings as they only require an oil mist for lubrication as in premixed 2 stroke fuel where the oil sticks to them.

some very special 4 stroke porsche engines used them together with needle bearing in the fifties.

maintining oil pressure at the rod journals is the problm when using needle bearings.

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this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

I personally think you are barking up the wrong tree, there's a reason all powerful bikes are now slipper bearing and it's not the cost.

Crankshaft's Big Ends do not revolve smoothly or consistently and you can only use so much pressure and RPM before skidding occurs then everything goes bang. You can use bearings on mains and some engines still do. Note that all pre-1980 Triumph, BSA and Norton all use roller mains and slipper BE.

I have welded them but only for extreme racing use and alignment is pretty easy after you've done a couple, a good 'V' block set, a sturdy dial gage and a plastic hammer does the trick. Gee that takes me back a looong time.

2 strokes don't rev very hard nor do they have dedicated lubrication systems and they aren't very big so they still use them.

I have said this many times before, there are thousands of crankshafts in every size and shape to be had and I find it a bit strange when someone needs to make a scratch one unless one is doing it as an engineering fun project because they can, fair enough.

But anyway, search for Mercedes Grand Prix roller crankshafts, Hirth roller crankshafts and Porsche 356 roller crankshafts if you want to see how it's really done.

Yes this is just a mental engineering exercise pertaining to engine types that are neither reasonably affordable nor readily available. Like would it be possible to build engines with similar layouts and displacements to things like the Cosworth DFV or Ferrari Colombo for substantially less than the current cost of real ones by primarily using commonly available off the shelf components combined with some less-conventional manufacturing methods? When an idea pops into my head, it's very hard for me to get it out until I am able to determine its fatal flaw. Thus far I have been unsuccessful with this one. It might simply lie in one of the many differences disconnects between theory and reality. That's why I've brought it up, in hopes that somebody more knowledgeable on the subject could put it to rest for me...Plus I think it's fun to have something new to discuss every once in a while, and break up the monotony that Monday kicks off every week.

And my thoughts were centered around still using standard automotive journal bearings. Would that be any more unsuitable to use with a pressed crank than the needle/roller bearings?

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-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

Harley still presses cranks together for their Big Twins. And Honda did for all their four stroke bikes before the CB750 (my gosh, did I just write CB750? I must be older than I look).

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Locost builder and adventurer, and founder (but no longer owner) of Kinetic Vehicles

Mick Hand machined a one piece crank from solid billet, plus many othe parts for his honda 250 "little David" which ran 9.8 seconds and still holds the 250cc quarter mile record. In 330cc form, it ran 9.02

i myself not wishing to fall off a bike as i had done many times, built a 750cc triumph twin powered, shorrock supercharged go kart running on 50% nitro, that was a blast, don't think i'd have the balls to drive it now!

there was a lot of fabricated parts in use, cylinder head was converted from 8 stud to 10 stud, cylinders were aluminum shaved A.R.E. castings with kawasaki liners, lightened cam gears, tie down kit to hold the cylinder head from blowing off the top, grease lubed valve gear which was all lightened and timpken roller bearing on the drive side of the crank., the blower was reworked with Brian Parkins special teflon trunions and a big S.U. carb with no float chamber and a Bob Harman "bodkin" neddle. i must have been really keen in those days!

don't you just love those british parallel twins.

_________________
this story shall the good man teach his son,
and chrispin chrispian shall ne'er go by,
from this day to the end of the world.
but we in it shall be remembered.

All of the early Honda S-series (S500, S600, S800) http://en.wikipedia.org/wiki/Honda_S600 had pressed-up cranks, with needle roller big-ends and mains plus single piece con-rods. This was very much in line with Honda 4-cylinder motorcycle practice of the time and the motors had lots of similarities (but no common parts that I'm aware of).

Sweet little engines that revved to the sky but very sensitive to proper maintenance i.e. clean oil and correct type and quantity of it. Unfortunately many S-cars in Australia now have various Datsun etc motors in them because of poor care of the original motor.

I've owned 6 of these cars (in various states of disreputable-ness ) over the years although none at present. My last S600 Coupe sits in my brothers shed awaiting it's time for restoration.

To my mind, the pressed-up crank will have some attractions for someone building a motor from scratch i.e. model engineering etc, but little to reccomend it otherwise as the assembly and maintenance difficulties will probably outweigh the manufacture advantages.

Dominic

Dad bought an old Simar Rototiller and rebuilt it. It was an 8 hp single cylinder two stroke, did not rev very high. The crank was assembled, using a roller bearing rod and a splined rod journal to keep everything aligned. Do not remember how it was held together, I was only 10-12 years old.

Bill