Topic: 2nd Gear issues and I think I need to open the case to find out. Where do we find parts?

[kaptainkid1]

I have 1975 Honda CB750F SS 26k miles and I'm guessing the 2nd gear is worn and needs replacement.
Here is my problem and let me know if I'm on the right diagnosis.
1st.When I shift into 2nd gear only and uses the throttle on a pull to get up to speed. It feels like the gear is popping out of gear for a quick second and dropping back into gear before I shift into 3rd. All other gears are find.
2nd. Next issues is I'm running across false neutral between 2nd and 3rd gears. This has recently started to happen.
3rd. Final problems when coming to a stop light I can not shift into neutral without shutting the engine off. Once the engine is off it slips into neutral no problem. I even rock the bike back and forth and it still will not go into neutral.
I'm leaning into opening  transmission case and try to fix all the problems at once.

Where do I find the parts to fix this issues.
I'm guessing a doner used engine with good gears?
Does anyone know where I can buy parts new? Or good reliable used parts?
Which parts will fix all my problems?
Can anyone give me a parts list to start from.

Thanks.
Here is the Great Pumkin looking for a little loven to get her back on the road.

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[Steve_K]

When my SIL had his 73 750 rebuilt he told the builder that 2nd was popping out of gear.  The guy undercut the dogs on the gears and now shifts fine.  I rode B4 and after and it shifts just fine.
Steve

PS make sure the clutch is adjusted, that sometimes can make it hard to find neutral

[70CB750]

My K0 developed that problem, it started like that and eventually I could not use the 2nd at all. 

[kaptainkid1]

Here is phase 2 and finding a lower end block for sale. Unknown miles Unknown issues with the block except for blow by in the Pistons. Maybe this lower end has good gears and I can use her as spare parts block.
I'm going to tear down the lower end and learn how the gears work.

Found this youtube video of a tear down and rebuild as a guide.

What do you guys think and what I should look out for when tearing down the block?

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[kaptainkid1]

My K0 developed that problem, it started like that and eventually I could not use the 2nd at all.

Did you ever get it fixed? If so what was the problem?

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[Don R]

 I take a look at cycleX and their reconditioned transmission parts. If you already got a bottom end check the shift linkage mechanism and see if it shifts all the way up and down while rotating the output shaft. 

[ekpent]

Maybe send Jerry RX a PM as he is kind of our resident F model expert. I own a few also and if I'm not mistaken they might have changed the transmission gear ratio's on those a little from the K bikes. Might be good if you don't have the old parts repaired to make sure any new ones are compatible. Jerry piped on on your clutch thread and maybe he might notice this also..

[kaptainkid1]

Does anyone here know anyone in SoCal who rebuild these engines? How much would a rebuild cost if I drop of the engine off,  opposed to dropping off the whole bike. Since I know I can save money buy pulling the engine myself. If I get the engine gears rebuild how much should this cost? Does anyone have an idea?

I'm assuming I should put new rings, timing chain/guilds, New seals and repairs of gears issues. Any ideal how this should cost?

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[newday777]

Does anyone here know anyone in SoCal who rebuild these engines? How much would a rebuild cost if I drop of the engine off,  opposed to dropping off the whole bike. Since I know I can save money buy pulling the engine myself. If I get the engine gears rebuild how much should this cost? Does anyone have an idea?

I'm assuming I should put new rings, timing chain/guilds, New seals and repairs of gears issues. Any ideal how this should cost?

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Kurt Jordan Engineering in Oceanside has been building these since the 70s (and he still has all his notes from past builds!) He is highly respected in the race field. You'll have to ask him about price.

[kaptainkid1]

I just watched 27 video series of Peter Anderson tear down and full restoration of 1978 CB750. It's a great detail resource if you are considering do this job.

https://youtube.com/playlist?list=PLSL5PUw3f6de-DyXANtaDfPQqxZbQE2LK

I've decided my bike isn't worth the full restoration at this time. It's a runner and I like it's originality. I want to just ride this until the next major issues so I'm going to just fix the 2nd gear forks or gear dogs. What ever I find after opening up the bottom end and put her back together to rider her for couple more years.

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[Jerry Rxman Griffin aka MuthaF'er]

Kenny at CycleX might be your best source for tranny stuff and advice unless, of course, you pick up other used stuff from E Bay or from our site.

Be careful when searching for parts or for a tranny. The 75 F (76 F, 77/78 K) used different ratio gears on a couple of the gear pairs vs the other earlier K's. May also pertain to the 77/78 F's being the same??

[kaptainkid1]

Kenny at CycleX might be your best source for tranny stuff and advice unless, of course, you pick up other used stuff from E Bay or from our site.

Be careful when searching for parts or for a tranny. The 75 F (76 F, 77/78 K) used different ratio gears on a couple of the gear pairs vs the other earlier K's. May also pertain to the 77/78 F's being the same??

I luck out on a used 1975 CB750F ss bottom end engine block with low mile. It seems the lower case was never opened except for a new clutch. I checked engine Vin numbers and we are only 7714 products numbers apart
Cb750E- 2511164 and CB750E-2503450 parts block.
It seems the old bike was dropped or had an accident and a cracked bottom end by the points. It never ran after that and I'm guess it sat outside rotting away. It had chromed Shifter plate cover and clutch cover. I'm guessing prior ownership made expensive changes and love it when it was running.
My conclusion it's a low 10k-20k because the the clutch was replaced so it had be over 10k but the engine sprocket was clean and had very little to no wear. The paint on the block is clean and not much grease or oil leaks. The piston seems to have minor carbon build up and had very minor carbon deposit. Checking the Shifter springs it seems the clips and springs are functioning very well. Another good sign. I feel this block with gears is my solution for a quick fix.
$80 for used offer up block. Can't beat that price. I can sell off parts and make my money back.

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[Kevnz]

That case could be repaired by a competent welder; I had a similar job done on mine many years ago. had actually ground away the bolt head boss. (PO) You could probably get away with a patch up using JB Weld as an interim solution if want to get the bike going and come back and address it properly later. Shame to part out what might be a good motor.

[david 750f]

4th and 5th gear have different ratios on the F’s

[PeWe]

If using later transmission in an earlier engine:
K final shaft where the later last gear to be used. That gear is a must with later trans.
#
#
Later final gear on earlier shaft sit in earlier case. Here serial matching US K5. K2 here.

Later trans will go into this case.

[HondaMan]

The 1st and 2nd gear ratios changed in the F0/1 bike as compared to the K0-K6.
The shifter drum may have a worn/chipped "Neutral Bump" Check pages II-34 and II-41 in my book for inspection details.

[kaptainkid1]

If using later transmission in an earlier engine:
K final shaft where the later last gear to be used. That gear is a must with later trans.
#
#
Later final gear on earlier shaft sit in earlier case. Here serial matching US K5. K2 here.

Later trans will go into this case.

I luck out on a used 1975 CB750F ss bottom end engine block with low mile. It seems the lower case was never opened except for a new clutch. I checked engine Vin numbers and we are only 7714 products numbers apart
Cb750E- 2511164 and CB750E-2503450 parts block.

The has same gear for same years and same model.

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[PeWe]

If using later transmission in an earlier engine:
K final shaft where the later last gear to be used. That gear is a must with later trans.
#
#
Later final gear on earlier shaft sit in earlier case. Here serial matching US K5. K2 here.

Later trans will go into this case.

I luck out on a used 1975 CB750F ss bottom end engine block with low mile. It seems the lower case was never opened except for a new clutch. I checked engine Vin numbers and we are only 7714 products numbers apart
Cb750E- 2511164 and CB750E-2503450 parts block.

The has same gear for same years and same model.

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That's good.
I thought you had an earlier engine you had a later trans to.
Now matching engines with their content inside
Good to have spares!

[kaptainkid1]

If using later transmission in an earlier engine:
K final shaft where the later last gear to be used. That gear is a must with later trans.
#
#
Later final gear on earlier shaft sit in earlier case. Here serial matching US K5. K2 here.

Later trans will go into this case.

I luck out on a used 1975 CB750F ss bottom end engine block with low mile. It seems the lower case was never opened except for a new clutch. I checked engine Vin numbers and we are only 7714 products numbers apart
Cb750E- 2511164 and CB750E-2503450 parts block.

The has same gear for same years and same model.

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That's good.
I thought you had an earlier engine you had a later trans to.
Now matching engines with their content inside
Good to have spares!

Well I found a weird drive line sprocket from the spare motor that didn't fit my CB750F ss.
I wanted to run the newer sprocket from the spare engine and noticed they were very different. Same gear tooth 18 teeth. The cleaner one had a huge spacer in the back.

I also had a spare 17 tooth sprocket which seems to be a mod I can do later if I want higher end gears. I think 17 tooth came off the SS when I first bought the bike.

Can anyone explain the thicker sprocket off a stock cb750f ss block. Was that a factory sprocket? Is sprocket a spare part I can use in the future?

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[Don R]

  Some late models had the 630 chain but would have fewer sprocket teeth than a 530 chain. Like maybe 15.

[newday777]

  Some late models had the 630 chain but would have fewer sprocket teeth than a 530 chain. Like maybe 15.

That would be the K7 and K8 along with the 77 F2 and 78 F3 that had the 630 chain and offset final shaft to move the sprocket away from the case for the bigger chain thickness.

kaptainkid1
The 75 and 76 F model(SS) are different output shafts from the 77/78 F2/F3 as this picture Per posted shows.

[Jerry Rxman Griffin aka MuthaF'er]

From your pictures/description it looks like an aftermarket 10mm offset sprocket to me??? Check the offset and compare the lengths of the final output shafts.

The 77/78 models that used the double row output shaft bearings were factory offset by 10mm as was the front sprocket cover, swingarm, upper shock mount and the rear sprocket carrier along with a different chain guard in order to align the rear end with the longer output shaft.   

[newday777]

 I'm going to just fix the 2nd gear forks or gear dogs. What ever I find after opening up the bottom end and put her back together to rider her for couple more years.

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Have you gone any further on your transmission? Almost a month since your last post on it.