Topic: CB750 Clutch Issues

[HondaMan]

It currently has the points plate which came in it. I have a Dynatek that I was planning on dropping in…

I will recheck the spark timing. I do think it ran well and then I had to readjust the points for some reason and afterwards it didn’t run that great. Actually I had installed the coils that came from the Dynatek kit so maybe that’s what’s causing it?

OK, NOW you're scarin' me...
The 750 does not make enough electrical power (in stock form) to run a Dyna ignition with 3-ohm coils. Hopefully your coils are 5-ohm type (Dyna also makes those).

The Dyna S ignition uses 1.5 amps more power than points, and their 3-ohm coils add another extra 1.25 amps on top of that, losing 2.75 amps to the ignition system while simultaneously providing weaker spark above 5500 RPM as a bonus.

That's just the facts.

The problem is: this causes the charging system to not charge the battery below 3500 RPM, if you have a stock headlight. If it has a halogen bulb in the headlight (like 55/60w, which many are) it will be 4000 RPM before the charging system "breaks even" while riding.

The result is: unless the bike is ridden mostly at higher speeds and RPM (always above 4000 RPM) the battery will become chronically low, making the bike into a hanger queen, tied to a trickle charger, just to provide the occasional ride.

[flyingclutch]

Well I simply am so enamored with second gear to the point where I pulled the cases apart. I havent found anything substantially wrong except the male dogs on what I believe is 5th gear and the female on 2nd were pretty worn. That may be an entirely inaccurate description of what is actually going on here, so I apologize. I’m case deep right now and soaked in oil.

The rectangle holes on the shift drum also are relatively beaten up.

Anyhow, I’m trying to remove the shift drum to replace it with my shiny new K8 shift drum and the old one simply will not budge. I have not removed any components from the shift drum and it is staked at the plate like factory. I was under the impression that these just slid right out… am I missing anything??

I do not see any metal shavings in here, and the crank journals look and feel great (if anyone cared.)

[HondaMan]

Well I simply am so enamored with second gear to the point where I pulled the cases apart. I havent found anything substantially wrong except the male dogs on what I believe is 5th gear and the female on 2nd were pretty worn. That may be an entirely inaccurate description of what is actually going on here, so I apologize. I’m case deep right now and soaked in oil.

The rectangle holes on the shift drum also are relatively beaten up.

Anyhow, I’m trying to remove the shift drum to replace it with my shiny new K8 shift drum and the old one simply will not budge. I have not removed any components from the shift drum and it is staked at the plate like factory. I was under the impression that these just slid right out… am I missing anything??

I do not see any metal shavings in here, and the crank journals look and feel great (if anyone cared.)

This is the classic C2-C5 worn-gear problem. Most of the time this indicates a bent "L" shift fork, which is the one that is shifting the C2 gear into/out of the C5.
To get the shift drum out, you must remove the Neutral switch. It holds it in place.

[flyingclutch]

Well finals are over and I managed to slap the bike back together with a new-used trans and K8 shift drum from eBay. Second gear now works perfectly.

For some reason the bike is very hard to shift when the motor is running to the point where neutral is impossible to find and first and second gears sometimes will not allow for gear changes unless the bike is rolling. Interestingly, the bike has no issues rotating the shift drum when the motor is off.

I suspect the clutch is dragging a bit… the RPM’s drop noticeably when clicking into gear and it seems to have a slight pull forward in gear with the clutch pulled. I will probably pull the clutch apart once more to make sure the convex washer is installed in the right direction, and will probably switch to a 20W-40 or -50 oil as per Hondaman’s advice.

Famous last words, I suppose, but I suspect the majority of my transmission problems are behind me. Thank you once again, everyone. I had never split cases in my life and working on the CB750 to this degree would have been a near-impossible task without this forum as a reference.

[HondaMan]

Well finals are over and I managed to slap the bike back together with a new-used trans and K8 shift drum from eBay. Second gear now works perfectly.

For some reason the bike is very hard to shift when the motor is running to the point where neutral is impossible to find and first and second gears sometimes will not allow for gear changes unless the bike is rolling. Interestingly, the bike has no issues rotating the shift drum when the motor is off.

I suspect the clutch is dragging a bit… the RPM’s drop noticeably when clicking into gear and it seems to have a slight pull forward in gear with the clutch pulled. I will probably pull the clutch apart once more to make sure the convex washer is installed in the right direction, and will probably switch to a 20W-40 or -50 oil as per Hondaman’s advice.

Famous last words, I suppose, but I suspect the majority of my transmission problems are behind me. Thank you once again, everyone. I had never split cases in my life and working on the CB750 to this degree would have been a near-impossible task without this forum as a reference.

Generally, the bike needs to be rolling to change gears, except from N to 1 or 2.
This is the classic 'constant mesh' gearbox, so oil drag and slight (normal) clutch drag make it almost impossible to shift gear-to-gear if sitting still. All this is perfectly normal for these bikes.

If you are not using the correct type of oil, shifting will be MUCH harder.You can't use common car oils in these bikes. The best non-synthetic I know of today is the Bel-Ray EXL Mineral in 20w50 weight, which is an almost identical copy of the mineral-based Castrol XLR that was developed expressly for this bike, in Britain (circa 1970). Spectrol makes an excellent synthetic oil: do NOT use their synthetic (or any oil) labelled "For V-Twin motorcycles" or "For H-D motorcycles". You need a 20w50 non-detergent, high-zinc oil. Valveoline is NOT on this list: the cheapest oil that kind of works (but not in summertime, too light) is the Shell Rotella 15w40 for diesels. Many other diesel-rated oils also contain the zinc (ZDDP) that is required. If the oil label says things like "Cleans your engine while you drive" do NOT use it in this engine, as it will foam at high speeds and reduce the oil pressure severely in the process, sometimes even to 0 PSI when pulling off freeway offramps and stopping.

[flyingclutch]

Well finals are over and I managed to slap the bike back together with a new-used trans and K8 shift drum from eBay. Second gear now works perfectly.

For some reason the bike is very hard to shift when the motor is running to the point where neutral is impossible to find and first and second gears sometimes will not allow for gear changes unless the bike is rolling. Interestingly, the bike has no issues rotating the shift drum when the motor is off.

I suspect the clutch is dragging a bit… the RPM’s drop noticeably when clicking into gear and it seems to have a slight pull forward in gear with the clutch pulled. I will probably pull the clutch apart once more to make sure the convex washer is installed in the right direction, and will probably switch to a 20W-40 or -50 oil as per Hondaman’s advice.

Famous last words, I suppose, but I suspect the majority of my transmission problems are behind me. Thank you once again, everyone. I had never split cases in my life and working on the CB750 to this degree would have been a near-impossible task without this forum as a reference.

Generally, the bike needs to be rolling to change gears, except from N to 1 or 2.
This is the classic 'constant mesh' gearbox, so oil drag and slight (normal) clutch drag make it almost impossible to shift gear-to-gear if sitting still. All this is perfectly normal for these bikes.

If you are not using the correct type of oil, shifting will be MUCH harder.You can't use common car oils in these bikes. The best non-synthetic I know of today is the Bel-Ray EXL Mineral in 20w50 weight, which is an almost identical copy of the mineral-based Castrol XLR that was developed expressly for this bike, in Britain (circa 1970). Spectrol makes an excellent synthetic oil: do NOT use their synthetic (or any oil) labelled "For V-Twin motorcycles" or "For H-D motorcycles". You need a 20w50 non-detergent, high-zinc oil. Valveoline is NOT on this list: the cheapest oil that kind of works (but not in summertime, too light) is the Shell Rotella 15w40 for diesels. Many other diesel-rated oils also contain the zinc (ZDDP) that is required. If the oil label says things like "Cleans your engine while you drive" do NOT use it in this engine, as it will foam at high speeds and reduce the oil pressure severely in the process, sometimes even to 0 PSI when pulling off freeway offramps and stopping.

Currently it has three quarts of some Lucas 10W-40 motorcycle oil I think I had found at Walmart. Usually I run the Mobil 1 motorcycle oil in my bikes and I had run it in this bike previously as well and it worked fine.

I will try stepping up to the Rotella or a 20W-50 moto oil. And I will be absolutely sh*t-my-pants happy if that’s the cause of the extremely hard shifting.

Is there a digital version of your book for sale, HondaMan?