Topic: Countershaft Bearing Holder - Bearing Doesn't Stay In

[Ellz10]

Bike is a 1977 Honda CB750K. Problem is that the new NTN 6304 I installed in the countershaft bearing holder, easily pops out with a little pull and that should definitely not happen.

Now I went ahead and bought a used one off a 1978 CB750K with the thought that mine was somehow too worn for spec, however that doesn't seem to be the case.

What appears to be the problem is the bearing itself. Now I ordered the correct bearing (or so I thought) - an NTN 6304, but what I see in the used one I bought from the 1978 is a KOYO. The Koyo seems to be thicker and it actually sits in the holder tightly the way its intended.

Should I just toss the NTN on the shelf and buy a new Koyo 6304?

[PeWe]

I looked up this page today for another thread.
It might help you.

https://wrenchandspanner.wordpress.com/2014/12/16/cb750f-transmission-bearings/

[bryanj]

A 6304 is a 6304 no matter who makes it it has to be inside specified tollerances, i would fit the new one with a small amount of removeable bearing lock liquid

[Ellz10]

I looked up this page today for another thread.
It might help you.

https://wrenchandspanner.wordpress.com/2014/12/16/cb750f-transmission-bearings/

I read through that, but my issue is that the new 6304 bearing won't stay in neither the old one nor the new (used) one I bought off ebay. What's weird is that the Koyo 6304 bearing that came in the holder wouldn't budge at all as intended. I had to heat it up to get it out. And then I even put it in the old one and it stayed in. Alas, I can't reuse this bearing because it's been torched to hell and is an original bearing.

[69cb750]

https://www.ebay.com/sch?_from=R40&_trksid=p2323012.m570.l1313&_nkw=Koyo+6304&_sacat=0

Germany, usa, Japan make good bearings, china bearings are terrible.

[Tracksnblades1]

A 6304 is a 6304 no matter who makes it it has to be inside specified tollerances, i would fit the new one with a small amount of removeable bearing lock liquid

👍^^^^^

What does the counter shaft’s bearing bore look like??

Can you see the machine marks from when Honda bored it…??

Does the bore look shiny where the 6304 race transfered it’s load and heat to the case bore..?

Does the bore look like the bearing spun? Go in snug then real loose…

Here is probably more than what you want to know about a 6304.
But like above they all make them to the same standard.

https://www.skf.com/au/products/rolling-bearings/ball-bearings/deep-groove-ball-bearings/productid-6304

Click the technical tab, then engineering tab….some ball bearings don’t tolerate a lot of press fit on the outside race. Even though they do tolerate a better press fit on the iinside race, like a shaft…Most bearing have standard recommended press or slip fit tolerances published…

[scottly]

Bike is a 1977 Honda CB750K. Problem is that the new NTN 6304 I installed in the countershaft bearing holder, easily pops out with a little pull and that should definitely not happen.

The bearing holder may have been damaged when the transmission jammed, breaking the gear teeth off, which was caused by an incorrectly installed transmission snap ring. Didn't you report that you had to pry it out?

[Ellz10]

Bike is a 1977 Honda CB750K. Problem is that the new NTN 6304 I installed in the countershaft bearing holder, easily pops out with a little pull and that should definitely not happen.

The bearing holder may have been damaged when the transmission jammed, breaking the gear teeth off, which was caused by an incorrectly installed transmission snap ring. Didn't you report that you had to pry it out?

Yes I had to pry it out. That's exactly why I went ahead and bought the used one from a 1978 CB750K. But like I mentioned above, the Koyo 6304 bearing that came in the used one I bought was situated correctly in the holder, and I even took it out and put it in the holder I originally had (the one I had to pry out) and it fit in there and wasn't loose and couldn't be pulled out.

So something tells me it's this new NTN bearing. I don't have any other explanation as to how that really old Koyo bearing fits perfectly in both holders, but the new bearing fits in but slips right out with a slight tug.

[Don R]

 I'd try another bearing, if an original one fits the hole is probably fine. Or maybe have someone measure them with a micrometer? 

[PeWe]

I had to check my setup of new bearings I ordered from Yamiya750 some years ago to ensure correct parts.

2 bearings are 6304, one with groove, the other not.
Koyo vs NTN.
Link to where they sit
https://www.yamiya750.com/index.php?main_page=index&cPath=21_250_52&sort=20a&page=2

[newday777]

Yes you need to order the Koyo

South Sound Honda shows they have it available to order.

https://www.southsoundhonda.com/--xpartsstream#/s/HOM//91003-235-000//1/y

[HondaMan]

Bike is a 1977 Honda CB750K. Problem is that the new NTN 6304 I installed in the countershaft bearing holder, easily pops out with a little pull and that should definitely not happen.

The bearing holder may have been damaged when the transmission jammed, breaking the gear teeth off, which was caused by an incorrectly installed transmission snap ring. Didn't you report that you had to pry it out?

Yes I had to pry it out. That's exactly why I went ahead and bought the used one from a 1978 CB750K. But like I mentioned above, the Koyo 6304 bearing that came in the used one I bought was situated correctly in the holder, and I even took it out and put it in the holder I originally had (the one I had to pry out) and it fit in there and wasn't loose and couldn't be pulled out.

So something tells me it's this new NTN bearing. I don't have any other explanation as to how that really old Koyo bearing fits perfectly in both holders, but the new bearing fits in but slips right out with a slight tug.

Yes, I have seen this in the K7 and K8 engines before. The last one (K7) was loose enough to bother me (it was for an engine from Wyoming), so I put in another (used) bearing holder from a scrapped K3 engine instead. And this was with the OEM bearing that was in the bike! I tried 3 different bearings I had on hand (all used ones, but good) at the time, and they were also loose in the hole.

[Ellz10]

Well I ordered the Koyo tonight. We'll see how it fits. If it doesn't fit then I'll either put the bearing liquid lock in there or just get another used holder with the bearing inside and keep it in there and install it as is.