roller crank
- Thread starter lyonsy
- Start date
That would have low friction but poor service life, I'd have thought.There are 2 inherent problems:
1) putting the thing together. You have to build the crank in pieces as you assemble the rollerized rods to each throw. Requires splined or similar connections ans press fits. Lots of effort involved. They've done this on modded VWs for years. The result is very high RPM potential but at a very high cost.
2) inability to withstand high compression ratios and absolutely NO ability to withstand detonation.
1) putting the thing together. You have to build the crank in pieces as you assemble the rollerized rods to each throw. Requires splined or similar connections ans press fits. Lots of effort involved. They've done this on modded VWs for years. The result is very high RPM potential but at a very high cost.
2) inability to withstand high compression ratios and absolutely NO ability to withstand detonation.
rust collector
Active member
Tatra made diesel trucks with roller bearing cranks, but they are kinda big, so I doubt you could use the same system in a car engine.
They had a crank throw part for every cylinder, and used a conventional rod bearing, and had a separate main bearing part, with the roller bearing(or ball bearing???) that bolted to the crank throw part.
That system takes a lot of room, and I think it needs to be BIG to be strong enough, but it does work.
Here you have a pic of the throw part:
Sorry, but I could not find a pic of the roller mains part
They had a crank throw part for every cylinder, and used a conventional rod bearing, and had a separate main bearing part, with the roller bearing(or ball bearing???) that bolted to the crank throw part.
That system takes a lot of room, and I think it needs to be BIG to be strong enough, but it does work.
Here you have a pic of the throw part:
Sorry, but I could not find a pic of the roller mains part
73GreenMachine
Well-known member
Thats interesting. I was talking to someone the other day about different bearing types and was under the impression that roller bearings were a bit of a problem when used in this type of application mainly due to oiling issues. That is, when the bearing rotates, it creates a wavefront of oil infront of the roller needle or ball, which could cause uneven oil distribution and may lead to premature bearing failure. The reason I understood that the plain bearings work well in this application is due to the fact that the oil forms an even barrier around the crankshaft journal so they are better lubricated and have a higher surface life. (Note: Correct me if I am wrong here but this is what I picked up from the conversation)
International and White both had truck engines in the 1920's that used ball bearing mains. They were four-cylinder flatheads with only two main bearings and a HEAVY crankshaft. Low horsepower, low compression, low speed engines. They worked just fine but weren't suitable for higher power output so were discontinued. Wisconsin built millions of their venerable V-4 air-cooled industrial flatheads with only two mains and a stiff crankshaft, these were tapered roller bearings which were shim adjustable for proper clearance. Very durable.
Joe
Joe
Hi compression ratios and high costs killed them off.
Porsche used them in the special stroked and bored versions in the 356 back in the 50's. The whole crank was indeed built up, at enormous cost.
A quite a number of motorcylce makers used built up roller cranks too.
Roller bearings have no place in a modern mulitple cylinder engine unless its a two stroke Orbital Combustion Process engine. Torsional vibration and twist make it impractical to make roller crank sixes at the moment. Somw one will figure out how to make carbon fibre or diamond grade crank throws, and mechanically link all six together one day. Untill then, don't bother, brother!
Porsche used them in the special stroked and bored versions in the 356 back in the 50's. The whole crank was indeed built up, at enormous cost.
A quite a number of motorcylce makers used built up roller cranks too.
Roller bearings have no place in a modern mulitple cylinder engine unless its a two stroke Orbital Combustion Process engine. Torsional vibration and twist make it impractical to make roller crank sixes at the moment. Somw one will figure out how to make carbon fibre or diamond grade crank throws, and mechanically link all six together one day. Untill then, don't bother, brother!
hey
nah i wasent going to do it.
its just in a rule book the class iam in says no roller cams and cranks.
the only way i could see it whould be on forged cranks with needle roller bearings.
but couldent see how you whould get past the lack of ristriction causing low oil psi.
more curosity then anythng
drift
nah i wasent going to do it.
its just in a rule book the class iam in says no roller cams and cranks.
the only way i could see it whould be on forged cranks with needle roller bearings.
but couldent see how you whould get past the lack of ristriction causing low oil psi.
more curosity then anythng
drift
A
Anonymous
Guest
Vintage roller cranks used to pop up every once in a while when I was tooling around on aircooled VW's. I know they were made for Beetle engines in stock stroke and one stroker size, I think by SPG. Here's a Porsche roller crank on evilBay, just for kicks:
http://cgi.ebay.com/ebaymotors/Porsche- ... dZViewItem
http://cgi.ebay.com/ebaymotors/Porsche- ... dZViewItem
A
Anonymous
Guest
No, you don't have to have a multi-piece, pressed-together crank to use roller bearings. Outboard motors don't. What you do need is a case-hardened crank, and case-hardened and split outer races for the rollers to run on (split so you can assemble them around the crank throws). This is done in crankcase-scavenged two-strokes that are primarily lubricated by oil in the fuel. Roller bearings don't need much oil to work. Waste of time in a 4-stroke where you have a good supply of oil pumped into the bearings. The hydrodynamic wedge of oil that the crank runs in probably has little more resistance than rollers, esp. if you use a lightweight or synthetic oil.
Guys: Early Millers and Offys also used roller (or ball?) main bearings supported by a "diaphram" main bearing support system. I can't find my reference books (we just moved and most of that stuff is still packed) but I suspect roller bearings were used at that time because more traditional babbit bearings were not up to the task in those days. If I recall correctly, the later (Drake) Offys moved to a more traditional main bearing but still used the diaphram design. So it seems that at least some high performance engines used roller bearings successfully.
A
Anonymous
Guest
I'm not saying you couldn't or shouldn't use roller cranks, roller camshafts, roller whatever. Kawasaki's first big four stroke, the 900cc Z-1, had a roller crank. I just don't think you gain anything much, for all the trouble and expense.
As far as aircraft engines, I suppose you can find examples of anything, but I know that the WW2 engines used soft plain, short-life bearings of high "imbedability," meaning that they would break in fast and could survive a certain amount of particles in the oil, from battle-damage or whatever.
Particulate matter is deadly for rolling element bearings. Go down to your local machine shop and look at the plain bearings they have pulled from car engines; I think you see why an ability to survive particles and scratching is a good quality to have in automotive bearings.
As far as aircraft engines, I suppose you can find examples of anything, but I know that the WW2 engines used soft plain, short-life bearings of high "imbedability," meaning that they would break in fast and could survive a certain amount of particles in the oil, from battle-damage or whatever.
Particulate matter is deadly for rolling element bearings. Go down to your local machine shop and look at the plain bearings they have pulled from car engines; I think you see why an ability to survive particles and scratching is a good quality to have in automotive bearings.
Similar threads
All Small Six
Roller cams
