Kawi2strokes.com Forum

One of the highest revving two strokes are the Parilla kart engines, the 100cc ones regularly operate at 18,000 rpm, and those have similar bearings, phenolic cages i recall. The 125cc direct drive engines don't rev as hard but make 40 hp fwiw....

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1974 Kawasaki H2B 750, 1981 Yamaha XV750 Cafe, 1986 Kawasaki KDX200, 2003 Honda XR100, 2004 SDG140. 2006 Ninja 500R Turbo intercooled fuel injected.

The phenolic is quite different from Teflon/plastic on the ball guides. I use the Teflon/plastic, never had a problem with them. Haven't tried the phenolic ones as of yet, but, they aren't as pliable as the ones I use, would like to see those that have been run on the cranks

Removed these from my H1 crank with close to 50 000 km on it.
Felt like new bearings. Cages are glassfibre reinforced Polyamide (PA66).

What caused the blue ring on the outside of this one? It looks like it got hot at the ball groove.

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If it surges, that's normal, upshift.

It's been spinning in the case. That particular bearing was #1 (ignition side) and the cases was pretty worn.
That crankcase probably had 100 000 km on it when this crank was taken out in 2017. After that the same case did another 54 000 km with a different crank.
I had to retire it this summer due to a rather large crack.

P.K.

Interesting, thanks.

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If it surges, that's normal, upshift.

Interesting, that is what i usually see, good, to great results.

Info: All Kawasaki ball bearings had/have a specific "fit" within them. Ball bearings have various fits, which is literally the "slop" of the bearing itself. In terms, Kawasaki uses a "C-3" fit. This C-3 is also the same as the fit "EMG" (Electric Motor Grade).

Bearings with a tighter fit are C-1, C-2, all the way to C-5. C-1 is the 'tightest' fit, C-5 the loosest. This "slop" has a purpose, in that it is like a flat bearing clearance. Too tight, the bearing can cause drag, and binding when used with multiple bearings in a single shaft. Engine heat from operation, expansion snd contraction from heat and cool cycles, and rolling friction also changes the fit, too, as the engines run.

It is 'complicated - simple'.

Why C4?
For bore alignment?

cliff

Partly availability, but also researching parts manuals for modern high output 2 strokes (KTM, Cagiva, lots of karting engines, etc...).
It seems they all use bearings with C4 clearance, and most often plastic caged bearings.
Also, my H1 is putting out around 103 crank HP with peak power at 9500 rpm so it seemed appropriate.

I just started rebuilding my own cranks and did the first one 10 weeks ago. I used C3 bearings on that one. Got 5000 km on it now.

I use some special types of bearings from SKF that has higher load bearing capacities. Typically 22% higher for 6205 and 15% higer for 6305.
These have larger ball bearings in them.
- For 6205 they are 3/8" instead of the normal 5/16".
- For 6305 they are 1/2" instead of the normal 11.5 mm.

I had to grind a snap ring groove in one of the 6305 bearings. A tool post grinder in the lathe with a CBN grinding wheel was used to do the job.
Due to the larger ball bearings there is less material in the outer race. I didn't want to make the outer race to thin so I opted to make the groove shallower.

P.K.

Cool, Per! You've been busy.

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If it surges, that's normal, upshift.