Just curious to know what difference does it make while using multi piece crankshaft instead of single piece crankshaft?
It was helpfull.One-piece cranks are mainly found on older American-made bicycles, and children's bicycles made for the U.S. market. Most one-piece cranks use a single metal forging as left crank, right crank and bottom bracket axle.
Bicycle bottom bracket (crank hanger) shells fall, in general, into two groups, threaded and threadless. One-piece cranks fit only the unthreaded shells 51.3 mm (2.02") in diameter.
One-piece cranks are the easiest type to service, and require no special tools. All you need is a large adjustable wrench and a screwdriver.
The types of engine that commonly use this method of construction are either single-cylinder four-stroke engines such as we find in motocross machinery, or two-stroke engines. Two-stroke engines find common use in motorcycle racing - although sadly even the 125 cc Grand Prix class is soon to disappear - and karting.
In conventional two-stroke race engines, crankcase lubrication is looked after by oil that is either pre-mixed with the fuel or metered in some proportion to the fuel by a pump from a tank. After it has fulfilled its lubrication task, the oil passes into the combustion chamber where it is combusted with the fuel. Given the marginal lubrication, the needle roller is a natural choice for such engines.
The crankshaft for a single-cylinder engine can typically be made in two or three pieces. The two-piece crankshaft has one main bearing, a crank 'cheek' and the crankpin as a single piece, and a second piece which is a main bearing journal and a crank cheek. The crankpin is a heavy interference fit into the cheek of the second piece. A three-piece single-cylinder crank has a separate crankpin.
The main problem with a multi piece Crankshaft...is lost motion...hence newton's cradle....whenever there is two much play in the crank bearings...Motion is being transferred to the wrong areas, instead of being transferred to the critical mass thats being accelerated. Don't get me wrong a two piece Crankshaft may be the answer to get more power in a over-square engine design.Just curious to know what difference does it make while using multi piece crankshaft instead of single piece crankshaft?
Lets look at the traditional methods to manufacture crank shafts
Starting with cast cranks, there are three options in increasing order of strength:
Cast iron, , Nodular cast iron, Cast steel
Cast iron is not pure iron at all. Pure iron is too soft to carry the load so we have to add graphite for strength.
In regular cast iron, the graphite particles are flakes. In nodular cast iron, they are spherical nodules. These nodules gives the cast iron more strength and flexibility.
Cast steel is stronger than “ Iron” simple because steel is much stronger than iron. As with iron...different alloys of steel will give a crank different levels of strength. To make a cast crankshaft, we heat iron or steel to its melting point then pour it into a mold. The up side is that this process really cuts down machining costs compared to the machine cost of a billet crank shaft.
Forged steel cranks begin with a metal bar that is heated until it is soft enough to pounded into the rough shape of the crankshaft. Then it is machined into the final shape.
The billet steel crankshaft starts with a large bar of steel is forged into a cylinder shape as large as the finished crank shaft.
I could go into which is strongest and why ..but that is another post. Lets just says the forged billet is the top of the line and the cast iron crank is the weakest.
When we talk about multi piece crank shafts, I guess they would be ok but introducing the welding process can introduce a lot of unwanted stress points, really messes up grain structures, undetected stress cracks, hidden grind burns. A lot of hot rodders made their own Stroker crankshafts back in the day but the horsepower was way under 500 hp back then.
Yes you can weld up a crank shaft and it will probably work if you don’t go too big on the torque and horsepower.
A major reason I've seen for multi-piece cranks is to allow roller/ball bearings instead of (2-piece) journal bearings. I think early Porsches used them - they were bolt-together. But one-piece cranks are stronger, and I'm sure easier to machine to maintain alignment of all the main bearings (unless it's machined after assembly).
How large is this engine? Is there a specific reason for considering an assembled crank?