Kawi2strokes.com Forum

And another endorsement, he sent us a set of wheel bearings and in his instructions he said to prop the wheel up, give it a good spin and time how long it took to stop, do it with the old bearings and again with the new Silicon bearings. Old bearings, about five to six revolutions, not too bad. New Silicon bearings......it spun for an HOUR !!!!!!

In the period 1996 to 2011 I have had five bearing cage failures on my own H1 cranks and I have seen at least another three cage failures on core cranks I have bough for rebuilding. When the last failure occurred late summer 2011 I really felt I had enough of this. I contacted Chris Ritchie and asked him if he was willing to rebuild a crank for me where I supplied the bearings. I told him what I had in mind and that it was to be an experiment. He was genuinely interested and accepted the job.

Next I contacted a local bearing supplier and ordered the following SKF bearings:
3 ea. 6205 ETN9/C4
3 ea. 6305 TN9/C4
1 ea. 6305 N/C4

The TN9 designation means the bearing has a glass fiber reinforced Polyamide (PA66) cage.
I could not find a 6305 bearing with both TN9 cage and a snap ring groove, and I didn't want to use one steel caged bearing, so I came up with the following;
I removed the plastic cage from one of the 6305 TN9 bearings, then put aside the cage and tossed the rest. Then I drilled out the cage rivets in the 6305 N bearing and carefully removed the steel cage, took the bearing apart and cleaned the parts thoroughly before putting it back together with the plastic cage.

Now, why TN9 and why C4 clearance?
This choice was based on some research I did on more or less modern 2-strokes (at least when compared to the triples). I noticed that most of these (KTM, Cagiva, etc...) used plastic caged bearings with C4 clearance (often SKF) and I also learned that the 6205 ETN9/C4 was one of the most commonly used crankshaft bearings in go-karting.

I then sent a good core crank and the bearings to Chris, and I remember telling him to locate the bearings with the open side of the cage away from the crank webs (it just felt like the right orientation). A couple of weeks later the rebuilt crank returned with a note from Chris saying that he was very happy with the result.

It's now been 2 1/2 years and approximately 12000 miles. I have deliberately given it a hard time with 10 000+ RPM several times daily (it's a wonder I still have my license). All my dyno runs have been close to 11 000 RPM. Peek HP is just shy of 70 RWHP from 8500 to 9000 RPM and from there it falls off to 60 RWHP at close to 11 000 RPM. The crank is still holding so I think I'm on to something here.

You may have noticed that the small bearings (6205) were ETN9 and big ones were TN9, and about a year ago I learned the difference. The designation E has the following meaning (quoted from SKF site):

Deviating or modified internal design with same boundary dimensions; as a rule the significance of the letter is bound to the particular bearing series; usually indicates reinforced rolling element complement.

Now this was a lucky coincident as it turns out that these bearings are significantly stronger than standard 6205 bearings. I have always felt that Kawasaki made a poor decision when they stepped down the bearing size on the H1 crank. I believe the 6205 is a bit on the weak side and that it would have been better with 6305 for all six bearings.

Here is a data table from the SKF site:



As you can see the ETN9 bearings have significantly higher Basic load ratings than a standard bearing.

Anyway, I just though I'd share.


PK