Crankshaft needle bearings

[kspringer80]

I'm working on a new design and was thinking about using needle bearings at the rod end of the shaft and a ptfe bushing/seal at the prop driver end. I haven't seen many instances of this combination being used, am I missing something on this train of thought? I'll also make a traditional plain bore main bearing to be on the safe side.

 

[MachineTom]

Needle bearings have been used in many small engine , 2 stroke Motocross engines 80, 125, 250cc come to mind. The downside of then is you need large and many to carry high loads in performance engines. THe second is assembly, all the engines that use them need a build up crankshaft as you can not have a parting joint in the big end of the rod when using needle bearings. These all have caged needle bearings, uncaged needles are only for low rpm, or oscillating loads. A 600 cc sport bike engine uses standard type insert bearings, they redline a 17,000 rom.

There is no magic.

 

[kspringer80]

Thanks for the reply, I think I'll keep pushing forward with it then. I'm looking at quite a small. 375 I'd bearing with a. 5625 of and length. Definitely no parting point in my single cylinder design. Going to machine a single piece main as a backup plan though.

 

[mu38&Bg#]

Needle crank bearings are not common. The shaft bends while running and needles don't work so well. If the needles are to run on the crank itself the hardness and surface finish must be appropriate. There are only a couple model engines that I can think of which used rollers on the the crank. Ball bearings work well. Needles in rod ends are standard in utility engines.

Greg

 

[kspringer80]

If I go with the needle set-up I'm sticking with a rather oversize crankshaft. For the same bearing od I can go with a larger I'd. With the needles running on the shaft do of think I'll have an issue with 1144 or should I make it from O1, harden and grind to size after hardening?

-Kyle

 

[mu38&Bg#]

I think last time I checked needles wanted Rc 53-57 to ride on. That large of a bearing is overkill for a 1.5cc.

 

[wildun]

all the engines that use them need a build up crankshaft as you can not have a parting joint in the big end of the rod when using needle bearings.

TOM.
I have worked on a lot of two stroke motorcycles and agree with most of what you say, but I also worked with other types of engine.

Eg. - Tecumseh two stroke lawnmower engines and the old Johnson Iron Horse engines (to name two of many types) used needle rollers for their conrod big end bearings using a solid (not built up crank ) and a split conrod as in a car engine.
Instead of the usual soft bearing shells they used a hardened steel shell with a "V" shaped join where the two halves met, in order to allow the rollers safe passage as they travelled across the joint. These were very successful and lasted for many years of extreme torture!

Crowded rollers were used on the older Iron Horse (which were very successful) and I think the Tecumseh may have used cages ( in two halves), but there were probably others who used this system successfully.

The important thing to note is that these worked well under very arduous conditions, to say the least!

However, a 1.5cc engine is a different matter!

Will.

 

[dnalot]

Two stroke outboards use needles in the large end of the con-rod without using a built up crankshaft. The rod end is machined to its final finish and then what will become the cap is snapped off the rod with a clean break. When carefully fitted back together you can not see or feel the joint. Special car bust be taken during assembly, if the rod cap is tightened without the grain of the joint aligned properly the rod is ruined.

Mark T

 

[kspringer80]

Thanks Guys, I'll shelve the needle bearing idea for now. I mocked up a crankshaft out of O1 this morning and tried to harden it... The warping wasn't too bad, but was more than I want to try to grind true again. I'll stick with the plain bearing for now.

 

[skyline1]

Hi guys

If I may chip in

Sorry Diatribe But,

I've been using silver steel shafts ( drill rod ) in plain cast iron bearing shells for years

needle rollers are probably at their best below about 5000 R.P.M. , low friction , low inertia, and they handle shock loading well and have been doing so for years

higher speeds need a different approach !

Very hard steel shaft running in a cast iron bearing

 

[mcostello]

I used home hardened 4140 and ran needle bearings on it and it did not last long. Don't know how hard it was but will not do it again.

 

[wildun]

If you use a steel suitable for nitriding, (and there are quite a few), there will be little or no distortion, - this is a much lower temperature process and is equal to or better than normal case hardening and may not even require grinding afterwards - the parts which don't require hardening can be masked. -
It would be well worth while checking out!
Will.