Topic: Early 750 output shaft bearing design change

[slyguy]

I kinda wanta get my lower end back together again since everything looks amazingly clean, but I'm thinking about the outer output shaft bearing and was wondering where/what others have done & best place to get them? According to the bulletin, The output bearing was "Improved" from E-1034808 thru 1044805 before the case redesign to the dbl roller. I was told "the groove" in bearing was a fault and do believe I saw the single row w/out groove somewhere? I presume it would be #91003-300-305. If I am correct then how did they "capture" the shaft before the final fix?  I'll be eagerly interested in your responses, documentation or pics!

[Kickstart]

Ah... ok... so your engine has both the inner and outer grooved bearings?

Yeah, I would also like to know what "problem" Honda was solving for with that bulletin.

If I had to guess - and do like guessing (even if I really don't know what I'm talking about) I would theorize it was to allow the whole assembly to twist a little bit without "cocking" the bearing.  Maybe Honda was worried about the outer bearing race being twisted in relation to the inner bearing when everything flexed under heavy acceleration? 

I've attached a picture of my engine (75 CB750F) with the newer double row design (so, not like yours), with neither bearing having a groove.  It appears to be held in place between the larger outer bearing set-ring and a lip on the case where the inner bearing sits.

I believe your case looks like the left image in the bulletin, correct?

You can buy the bearings without the grooves from any good bearing distributor, but getting them with the correct grooves is more challenging.
Looks like cmsnl has the outer grooved bearing available (assuming they don't send you the superseded part number)
http://www.cmsnl.com/honda-cb750k0-four-usa_model14346/91004438003-bearing-6305hs_91003259000/#.UrOevPRDsuc
Interesting how this is a HS bearing (or an extra clearance bearing, C3).

Looking at the cmsnl parts list for your bike:
http://www.cmsnl.com/honda-cb750k0-four-usa_model14346/partslist/E21.html
It looks like they have two separate bearings options:
"up to serial number: 1048345" or "from serial number: 1048346"
And the former one appears to be the same bearing as the 6205 grooved bearing in the transmission.

Ordering them from cmsnl is probably cheaper than buying the non-grooved bearings and having someone put a groove in it (I had it done and it wasn't cheap):
http://forums.sohc4.net/index.php?topic=60026.msg1313396#msg1313396

But... to your point/question, you're looking to put the new "improved" bearings in and I'm not sure if the ones cmsnl are the "improved" ones.

It looks like the service bulletin is just replacing the outer 6305 bearing.  I wonder if it's replacing it with a non-grooved bearing and just relying on that full "snap" retaining ring to hold it in place.
Does your assembly have both the full retaining ring (like the one in my picture) as well as the bearing half ring?

[slyguy]

Thanks for the links too! The single row grooved bearings were deemed inadequate thus the "redesign" which was finally resolved starting with E-1044806 which was the wider dbl row/non grooved bearing, a new set of cases redesigned for this which also had the full groove cut into cases to hold the shaft/bearing assy in. I'm wondering what was "improved" on the bearing at E-1034808 thru E-1044805?

[HondaMan]

Thanks for the links too! The single row grooved bearings were deemed inadequate thus the "redesign" which was finally resolved starting with E-1044806 which was the wider dbl row/non grooved bearing, a new set of cases redesigned for this which also had the full groove cut into cases to hold the shaft/bearing assy in. I'm wondering what was "improved" on the bearing at E-1034808 thru E-1044805?

The early dual-row bearings were not HS (C3) rated, and they caused a LOT of lost power (and heat). They then wore the bearing capture housing oval (front-to-back) and caused the countershaft seal to come loose and leak. Sometimes it even popped out. This happened during the very end of the K2 engines, from the New Factory only. These cases (up through the K3) had dual grooves in them, so the 1-row or 2-row bearings could be fitted in production: this hinted that Honda was having a tough time obtaining the bearings they wanted/needed. Some folks even thought (in those days) that the non-C3 bearings ended up in the early ones by accident from this 'problem'.

All of the dual-row output bearings eat power, though: the details are in my book.

[Kickstart]

Not to sidetrack the thread, but are you saying the double row bearing should be a C3?  Hondaman, can you confirm?

I think I ordered normal clearances for the double row on my rebuild... but I got the 6205 bearing in C3... maybe I read that wrong in your book.

Going back to Slyguy's questions: "I'm wondering what was "improved" on the bearing at E-1034808 thru E-1044805?"  Does anyone know?  The best I can tell from the service bulletin that Dream750 posted is the change just replaced the 6305 grooved bearing with a non-grooved 6305 bearing.

[slyguy]

Not to sidetrack the thread, but are you saying the double row bearing should be a C3?  Hondaman, can you confirm?

I think I ordered normal clearances for the double row on my rebuild... but I got the 6205 bearing in C3... maybe I read that wrong in your book.

Going back to Slyguy's questions: "I'm wondering what was "improved" on the bearing at E-1034808 thru E-1044805?"  Does anyone know?  The best I can tell from the service bulletin that Dream750 posted is the change just replaced the 6305 grooved bearing with a non-grooved 6305 bearing.

I also believe this but also, to do that they must have also incorporated the full diam.retainer ring in case as well...yes?...and then at 1044806 they had the dbl row with eng.case mods too.

[HondaMan]

Not to sidetrack the thread, but are you saying the double row bearing should be a C3?  Hondaman, can you confirm?

I think I ordered normal clearances for the double row on my rebuild... but I got the 6205 bearing in C3... maybe I read that wrong in your book.

Going back to Slyguy's questions: "I'm wondering what was "improved" on the bearing at E-1034808 thru E-1044805?"  Does anyone know?  The best I can tell from the service bulletin that Dream750 posted is the change just replaced the 6305 grooved bearing with a non-grooved 6305 bearing.

Normally, the 6304 on the mainshaft by the clutch was/is the "HS" (or extra-clearance) bearing. The extra clearance avoids binding when the crankcases twist under power. In many ways, using C3 clearance in all of the bearings can provide less friction losses, ending up like a tranny with 40k miles on it (if the gear dogs are in good condition) which makes the bikes smoother and more torque-y in midrange riding.

The main disadvantage to having all C3 clearance bearings is: the gear alignment is slightly off, so if the teeth are crisp and not well-broken in, they will be stiffer to shift. If the tranny is well broken in, you will likely never notice, and there will be more power to the ground in fewer break-in miles. The down side: a bearing that starts at C3 clearance, if not a high-quality unit, will quickly wear to even more clearance, which can cause other issues like leading to rounded-edge gear dogs.

Honda's general intent here (and in many of their similar gearboxes) seemed to be: use tight bearings while the gear teeth are wearing themselves together, and they will all settle together in a mated set that holds its alignment for a long time. In practice, this works fine: in competition with other bikes of their day who used the less-expensive C3 bearings throughout their gearboxes (like the Kawi Fours or the Yamaha Triple, later on) the writers of magazines like Cycle or Cycle World always noted how much smoother the Kawi and Yami gearboxes shifted under power - WHEN THEY WERE NEW. Note, however, most of those bikes are now gone...

[slyguy]

So where's the best place to get the best bearing for the early output shafts?
Ya know, that bulletin shows an "improved bearing" (91003-300-305) but uses the same cases?

[HondaMan]

So where's the best place to get the best bearing for the early output shafts?
Ya know, that bulletin shows an "improved bearing" (91003-300-305) but uses the same cases?

Today, I'd use an NSK bearing, if you can't afford the SKF. KML is also good. If you're using the single-row output bearing, don't get the C3 clearance type, but the normal type. A good bearing house will be able to tell the difference, and if they can't, go to a different one.

[Kickstart]

So where's the best place to get the best bearing for the early output shafts?
Ya know, that bulletin shows an "improved bearing" (91003-300-305) but uses the same cases?

Today, I'd use an NSK bearing, if you can't afford the SKF. KML is also good. If you're using the single-row output bearing, don't get the C3 clearance type, but the normal type. A good bearing house will be able to tell the difference, and if they can't, go to a different one.

But you can't buy the bearing with the correct groove size anymore (except maybe from cmsnl).
So, if you buy the a new bearing you'll need a machinist to cut the groove... or try to cut it yourself with a steady hand and a dremel tool.

slyguy, does your final drive have both the bearing retainer ring AND the full diameter retainer ring?  If so, maybe you could just use a non-grooved bearing.

[MRieck]

I'll be honest and say there is way to much over thought into this subject....cut a groove into a bearing with a Dremel???

[mrbreeze]

two things:
- the early CB750 chain failures were primarily caused by poor battery vent tube location and/or owners fiddling with that tube: it could drip battery acid directly onto the chain. The acid eaten chain would soon part.
- 70s chains were pretty feeble. Even small bikes went through a lot of chains as they would stretch - often unevenly - and ruin the sprockets as well. Also, the market was full of 2-stroke bikes - X6, A7, RD350, H1 - that would power wheelie easily; Honda 750s wouldn't do that with their forward mounted heavy 4-stroke motors, so wheelie envious owners would do clutch dump wheelies that are pretty damn hard on the chain. Current chains are much stronger than ones from that era. Get a decent quality (not the very best $$$$ ones made for 200hp superbikes, that's overkill) modern chain and it's extremely unlikely you will ever snap it with the 750's horsepower. Just watch out for the battery vent tube location and routing!

The case design is poor at the sprocket, it does pretty much guarantee severe damage if a chain breaks. The "fix" steel plate doesn't cure it, if a snapped chain gets kinked under power... in the space something is going to break. There isn't room between the sprocket and the case to fit a thick enough steel plate to really prevent case damage.

I know this is off topic but thought I would mention........somewhere I heard (and I'm pretty sure it was on this forum) that the main reason for so many chains breaking was due to the early bikes having a 15 tooth sprocket and that they went to an 18 tooth to cure the problem. The 15 tooth suppossedly put the chain into too much of a bind. Anyone else heard of this?

[Kickstart]

I'll be honest and say there is way to much over thought into this subject....cut a groove into a bearing with a Dremel???

Hondaman mentions this in his book as an option.
I had the grooves cut in my new transmission bearings by my machinist, but that cost me a lot.

Slyguy wants to replace his final drive bearings and wants to know what his options are (and if he needs to "upgrade" anything based on the service bulletin) - I don't think he's over thinking this...  what are we missing?

[slyguy]

Thanks HM & kickstart, the engine has the 1/2 groove retainer as well as the stock original grooved bearing. So at this point with this set of early diecast cases, I realize my only choice for the outboard output shaft bearing is just the stock 6305 grooved. Now at this point I wish I could just run down the street to the Honda dealer and pick one up like the old days...& what were they..like $5.00! LOL 

[HondaMan]

two things:
- the early CB750 chain failures were primarily caused by poor battery vent tube location and/or owners fiddling with that tube: it could drip battery acid directly onto the chain. The acid eaten chain would soon part.
- 70s chains were pretty feeble. Even small bikes went through a lot of chains as they would stretch - often unevenly - and ruin the sprockets as well. Also, the market was full of 2-stroke bikes - X6, A7, RD350, H1 - that would power wheelie easily; Honda 750s wouldn't do that with their forward mounted heavy 4-stroke motors, so wheelie envious owners would do clutch dump wheelies that are pretty damn hard on the chain. Current chains are much stronger than ones from that era. Get a decent quality (not the very best $$$$ ones made for 200hp superbikes, that's overkill) modern chain and it's extremely unlikely you will ever snap it with the 750's horsepower. Just watch out for the battery vent tube location and routing!

The case design is poor at the sprocket, it does pretty much guarantee severe damage if a chain breaks. The "fix" steel plate doesn't cure it, if a snapped chain gets kinked under power... in the space something is going to break. There isn't room between the sprocket and the case to fit a thick enough steel plate to really prevent case damage.

I know this is off topic but thought I would mention........somewhere I heard (and I'm pretty sure it was on this forum) that the main reason for so many chains breaking was due to the early bikes having a 15 tooth sprocket and that they went to an 18 tooth to cure the problem. The 15 tooth suppossedly put the chain into too much of a bind. Anyone else heard of this?

In the beginning (sometime after the Earth cooled and Eve had already screwed things up..), the 750 had 16T front and 45T rear sprockets, and chains made by RK, which were the same type as used on the 450 twins. The sprockets were also cut in then-standard JIS profiles. This combination caused the chains to be stressed to nearly maximum loads and the trip around the countersprocket was too fast for the oil from the chain oiler to penetrate the links. This, combined with the average American's propensity for never adjusting chains (which frankly came from the earlier Hondas having much-too-strong chains for any given bike, so we had learned to ignore them pretty well) caused a lot of failures, and many crankcases being destroyed in the process.

This ultimately led Honda do redesign the sprockets (starting with severely tapered teeth tips and 0.5mm larger-than-JIS base circles, among 5 other things) and use endless chains, along with switching to 17T countersprockets coupled with 48T rears. In 1970, Honda bought 51% of AMF, who then owned Harley-Davidson, for one stated reason: to obtain the rights to use the Diamond XL series chains, which Diamond had designed expressly for the Harley V-Twins. They took that tech to RK (who didn't do a REAL good job of copying, but at least improved theirs with it) who in turn made the chains that became the Honda part in early 1971.

In late 1971, starting with the K2 model, Honda installed 18T countersprockets against the same 48T rears. This was when the [in]famous "power drop" in these bikes occurred: it was easily fixed by installing a 17T front sprocket by the knowing street racers, though. Although, the 18T front does make the 750 into a sweet touring machine at speeds in excess of 80 MPH.

[mrbreeze]

Thanks for that Hondaman. Sounds like some very detailed info. I don't know where I got 15 tooth sprocket from but the main thing is that it was smaller and caused problems.

[slyguy]

Hey guys..I'm back! I wanta get an output shaft bearing(the outer) & could use some help. I would like to get the best bearing with the groove already cut, Is this even possible these days? I believe I need a 6305 normal clearance & grooved but will also need the new circlip too. TU!:)

[edwardmorris]

Hey guys..I'm back! I wanta get an output shaft bearing(the outer) & could use some help. I would like to get the best bearing with the groove already cut, Is this even possible these days? I believe I need a 6305 normal clearance & grooved but will also need the new circlip too. TU!:)

Yamiya may have some precut NTNs. I replaced all mine with SKFs and had to get the grooves widened at a shop http://forums.sohc4.net/index.php?topic=126735.msg1506804#msg1506804

Look here http://forums.sohc4.net/index.php?topic=60026.0 for more info on the engine bearings.

[slyguy]

Thanks Ed!