Topic: From Rundown & Ragged.. To A Mean, Clean & Shiny Machine - My 1977 Honda CB750 K

[Ellz10]

So I was able to remove the assembly, and upon inspection, none of the snaprings seem to be out of place nor can I see anything wrong, but I have an obvious untrained eye so Mark or anyone else, if you see something off, please don't hesitate to say something!

[Ellz10]

Well I think I may have found the problem and yes it does involve a snap ring.

I didn't see it before, but once I slid the gears over and looked more closely as well as comparing every bit of my gears to the assembly that came in the mail today off a 1978, I realize the difference and the problem. One of the snaprings jumped out of its groove and lodged itself into the side of that gear (3rd I believe).

I'm guessing that could very well be the reason behind the teeth shearing off and locking the bike in place, unable to shift out of gear?

[Ellz10]

So tonight I bought all new thrust washers and snaprings/circlips and I'm going to replace all mine correctly just to be safe.

I'll be posting pics of the new transmission assembly I got later.

[Ellz10]

So here's the new transmission assembly that I got from a 1978. Looks to be in pretty decent shape. Bike had 32k miles on it.

I'm debating whether or not to just drop this assembly as a whole into my motor or just the 4 gears that need to be replaced.

Thoughts?

[HondaMan]

I'd suggest dropping it in as-is. The gears have mated and polished their bushings and the spline on the gears have now met the splines on the shaft, so this will let them shift more easily. Otherwise, you'll be in for a new 'break-in period' while the introduced gears mate with the shaft (and vice-versa). When these bikes were new they were known for stiff shifting (and quite loud!) for about 1000 miles. I got used to the 'gripes', usually smiling to myself knowing the 'change' would get better when the owner got used to it.

The mainshaft: there will be little spacers (either none, which was a rare perfect-match) or one, or two on the left end of the (original) mainshaft. Before removing that one for good, use feeler gages to see how much clearance there is between the spacer on that end and the ball bearing there. Then when you set the new shaft (if you use the whole thing) use the feeler gages again to find out - or make - the spacing the same again. This space was +/-0.004" on average, but I've never seen an actual spec from Honda for it.

[Ellz10]

I'd suggest dropping it in as-is. The gears have mated and polished their bushings and the spline on the gears have now met the splines on the shaft, so this will let them shift more easily. Otherwise, you'll be in for a new 'break-in period' while the introduced gears mate with the shaft (and vice-versa). When these bikes were new they were known for stiff shifting (and quite loud!) for about 1000 miles. I got used to the 'gripes', usually smiling to myself knowing the 'change' would get better when the owner got used to it.

The mainshaft: there will be little spacers (either none, which was a rare perfect-match) or one, or two on the left end of the (original) mainshaft. Before removing that one for good, use feeler gages to see how much clearance there is between the spacer on that end and the ball bearing there. Then when you set the new shaft (if you use the whole thing) use the feeler gages again to find out - or make - the spacing the same again. This space was +/-0.004" on average, but I've never seen an actual spec from Honda for it.

Okay perfect!! Thanks so much Mark, I really appreciate it!

On a different, but semi-related note, I still cannot for the life of me, figure out what that noise was/is that the bike would make while driving it. You know, the sound that would get louder the faster I went and quieter the slower I went. You can hear said noise in the short video I had posted at the very end. Could it have been the gears somehow? I just can't imagine that being it, but I could be wrong.

Do you have any thoughts or ideas on what it could've been?

[jgger]

My GUESS would be yes. They were probably scrapping on each other before the snap ring let loose. Check the sides and the tips of the dogs for witnesses marks. Purely a guess though.

BTW you are doing a great job of keeping it all together through this. When you look back later it will have a greater value on the promise to your Dad.

[scottly]

CycleX did most of the machining?

CycleX sent him the under-cut trans in a supposedly ready-to-install condition.
Zach, all the glitter that ended up in the oil filter had to pass through the oil pump; you will need to take it apart, check for any damage and clean any debris from it as well as the pressure relief valve and oil passages in the case. Hopefully none of the ground up bits of metal have gotten past the filter.   

[HondaMan]

Do you have any thoughts or ideas on what it could've been?

Yep, what Jgger said ^^^.
When the gear pushed off the snapring, the gears that were trying to engage were fighting the ones that WERE engaged. They run at different speeds, which is mathematically the product of roughly
{Engine RPM * [(1st-gear-ratio / mainshaft-speed) - (the attempting-to-lock-gear's-RPM-speed/ countershaft-speed)]}
roughly speaking (or, about 1/5 the RPM of the engine). So, it would get higher pitched as the bike's speed increased.
Since only one gearset can actually engage at once, the resulting RPM difference against the attempting-to-lock gear teeth (before they broke off) made the noise, likely gnawing on the edges of the dogs and missing teeth chattering around. Then the pieces probably locked the 2 shafts together briefly before the mass of the bike tossed them back out and ate them up.

Normally, when this happens at high engine speeds like in drag races, it doesn't get the gentle throttle-off that you gave it: they just blow holes thru the bottom case with the flying pieces!

[Ellz10]

CycleX did most of the machining?

CycleX sent him the under-cut trans in a supposedly ready-to-install condition.
Zach, all the glitter that ended up in the oil filter had to pass through the oil pump; you will need to take it apart, check for any damage and clean any debris from it as well as the pressure relief valve and oil passages in the case. Hopefully none of the ground up bits of metal have gotten past the filter.

Dang, I didn't even think of that!! Ugh, what a bummer. Oh well, I have lots to be thankful for, so I'll just suck it up and make sure I clean the pump well and thoroughly and then do my best to clean the journals and passageways - would my best bet be compressed air, you think?

My GUESS would be yes. They were probably scrapping on each other before the snap ring let loose. Check the sides and the tips of the dogs for witnesses marks. Purely a guess though.

BTW you are doing a great job of keeping it all together through this. When you look back later it will have a greater value on the promise to your Dad.

Thank you for your kind words and support, that actually means something to me!

Do you have any thoughts or ideas on what it could've been?

Yep, what Jgger said ^^^.
When the gear pushed off the snapring, the gears that were trying to engage were fighting the ones that WERE engaged. They run at different speeds, which is mathematically the product of roughly
{Engine RPM * [(1st-gear-ratio / mainshaft-speed) - (the attempting-to-lock-gear's-RPM-speed/ countershaft-speed)]}
roughly speaking (or, about 1/5 the RPM of the engine). So, it would get higher pitched as the bike's speed increased.
Since only one gearset can actually engage at once, the resulting RPM difference against the attempting-to-lock gear teeth (before they broke off) made the noise, likely gnawing on the edges of the dogs and missing teeth chattering around. Then the pieces probably locked the 2 shafts together briefly before the mass of the bike tossed them back out and ate them up.

Normally, when this happens at high engine speeds like in drag races, it doesn't get the gentle throttle-off that you gave it: they just blow holes thru the bottom case with the flying pieces!

Well I suppose the silver lining is that there's not a hole in the case, right? Hah! I didn't realize the gears run at different speeds!

Question Mark - when I go to reassemble each shaft (main and counter), and I'm installing the thrust washers, spacers, and circlips, should I be installing exactly as outlined in your book and/or the parts fiche for my year of bike? I also remember you saying I need to measure the spacer spec before re-installing it.

[HondaMan]

Yep, use the pictures of the '77 K7 model from the Honda parts fiche: they appear to be correct at South Sound Honda, and probably also at CMSNL if you can print theirs. Be sure the rounded sides of all the toothed spacers are against the rotating gears, with the ground-flat sides of those spacers against the static item (usually a C-clip in some groove). If the ground-flat side of a C-clip is set toward a spinning gear, the sharp edges of the ground face can catch on the spinning gear and unseat the clip. Honda's techs didn't ALWAYS assemble this right, either(!).

The 'spacer' thing is: when you drop the mainshaft into the (inverted) upper case, there will be some clearance between the last "face" on the engine's left side bearing (it will be locked into place by the little C-shaped retainer in the groove of the case) and the gear there, or the spacer(s) in between that gear and that bearing. Then use feeler gages to measure the distance between that gear (or spacer), between that and bearing's inner race's side face. This is the point at which there should be 0.001" to 0.004" (0.1mm max.) per the old manuals, which lets that last gear there 'float' slightly back-and-forth - this also sets the depth of how far the outer teeth of the gear next to it (4th) will engage the slots of the end gear, and this engagement must not be less than 3mm: 4+mm is better. If your newly-acquired gearsets are truly complete, they may contain a spacer washer(s) of thickness(es) different from your original one(s) because the shaft-set came from differently-cut cases. It is also possible that there is NO spacer in a given engine: this bearing retainer's cutting tool could vary its position slightly in the later engines due to Honda's holding fixtures for their case machining process with then- NC machines (before CNC was invented).

A side note: in the earlier engines this was done differently from the way the K7/8 cases (and F2/3) were done: the cutters in the earlier versions were (tediously) all mounted on a common shaft and dropped into place from above the [inverted] upper case using the clutch-side bearing face for reference: in the post-1976 versions these were cut from the fixtured case, which could move around about 0.1mm in their processes. That's why the spacers appeared, so as to shim-up the 5th gear toward the clutch side to fully engage with the outer teeth of the 4th gear next to it when in 5th gear.

BTW: you, too, can learn these kinds things by spending endless hours studying these cases, but if you're married it probably isn't a good investment of your time.   I learned this 'stuff' in between my 2 wives, when I had too much spare time on hand and the SOHC4 still dominated the bike-counts on the  hiways and byways around here...

[scottly]

CycleX did most of the machining?

CycleX sent him the under-cut trans in a supposedly ready-to-install condition.
Zach, all the glitter that ended up in the oil filter had to pass through the oil pump; you will need to take it apart, check for any damage and clean any debris from it as well as the pressure relief valve and oil passages in the case. Hopefully none of the ground up bits of metal have gotten past the filter.

Dang, I didn't even think of that!! Ugh, what a bummer. Oh well, I have lots to be thankful for, so I'll just suck it up and make sure I clean the pump well and thoroughly and then do my best to clean the journals and passageways -

The only way that snap ring came out of it's groove was because it was assembled incorrectly. Maybe someone's techs should be reading this?? At the very least, you should be refunded what you paid for the under-cut trans that caused the damage, and a couple of pan gaskets thrown in wouldn't hurt..

[calj737]

CycleX did most of the machining?

CycleX sent him the under-cut trans in a supposedly ready-to-install condition.
Zach, all the glitter that ended up in the oil filter had to pass through the oil pump; you will need to take it apart, check for any damage and clean any debris from it as well as the pressure relief valve and oil passages in the case. Hopefully none of the ground up bits of metal have gotten past the filter.

Dang, I didn't even think of that!! Ugh, what a bummer. Oh well, I have lots to be thankful for, so I'll just suck it up and make sure I clean the pump well and thoroughly and then do my best to clean the journals and passageways -

The only way that snap ring came out of it's groove was because it was assembled incorrectly. Maybe someone's techs should be reading this?? At the very least, you should be refunded what you paid for the under-cut trans that caused the damage, and a couple of pan gaskets thrown in wouldn't hurt..

Amen

[Ellz10]

The 'spacer' thing is: when you drop the mainshaft into the (inverted) upper case, there will be some clearance between the last "face" on the engine's left side bearing (it will be locked into place by the little C-shaped retainer in the groove of the case) and the gear there, or the spacer(s) in between that gear and that bearing. Then use feeler gages to measure the distance between that gear (or spacer), between that and bearing's inner race's side face. This is the point at which there should be 0.001" to 0.004" (0.1mm max.) per the old manuals, which lets that last gear there 'float' slightly back-and-forth - this also sets the depth of how far the outer teeth of the gear next to it (4th) will engage the slots of the end gear, and this engagement must not be less than 3mm: 4+mm is better. If your newly-acquired gearsets are truly complete, they may contain a spacer washer(s) of thickness(es) different from your original one(s) because the shaft-set came from differently-cut cases. It is also possible that there is NO spacer in a given engine: this bearing retainer's cutting tool could vary its position slightly in the later engines due to Honda's holding fixtures for their case machining process with then- NC machines (before CNC was invented).

Mark, you'll have to forgive me and I promise I'm not a complete idiot, but I am absolutely lost as to what you're trying to explain. If you have the time and don't mind, could you please break it down simpler for me, apologies!

[HondaMan]

The 'spacer' thing is: when you drop the mainshaft into the (inverted) upper case, there will be some clearance between the last "face" on the engine's left side bearing (it will be locked into place by the little C-shaped retainer in the groove of the case) and the gear there, or the spacer(s) in between that gear and that bearing. Then use feeler gages to measure the distance between that gear (or spacer), between that and bearing's inner race's side face. This is the point at which there should be 0.001" to 0.004" (0.1mm max.) per the old manuals, which lets that last gear there 'float' slightly back-and-forth - this also sets the depth of how far the outer teeth of the gear next to it (4th) will engage the slots of the end gear, and this engagement must not be less than 3mm: 4+mm is better. If your newly-acquired gearsets are truly complete, they may contain a spacer washer(s) of thickness(es) different from your original one(s) because the shaft-set came from differently-cut cases. It is also possible that there is NO spacer in a given engine: this bearing retainer's cutting tool could vary its position slightly in the later engines due to Honda's holding fixtures for their case machining process with then- NC machines (before CNC was invented).

Mark, you'll have to forgive me and I promise I'm not a complete idiot, but I am absolutely lost as to what you're trying to explain. If you have the time and don't mind, could you please break it down simpler for me, apologies!

Yeah, this is pretty far 'into the weeds', but makes or breaks the operation of 4th & 5th gears, and was never explained in Honda's manuals. I suppose that's because few people ever needed it, or because Honda was walking away from the 750 toward building cars instead with the Yen they had made from the 750.

The mainshaft is a fixed-length piece, but the crankcases were not so perfectly made so as to be fixed-width in the F2/3 and K7/8 bikes. So, the inside width of the cases between the 2 ball-bearing seats for the mainshaft varied a little bit in production. At the same time, the clutch pack got slightly thicker because of the double-sprung steel plates they added, so both the clutch cover and the crankcases needed some special treatment. The clutch cover for the K7 doesn't fit the earlier bikes at the result. And, the mainshaft, being a fixed-length piece, needed to be pushed toward the clutch cover side of the engine. Doing this then could leave some extra space on the left end of the mainshaft, which could let the last gear on that end (5th) float away from the 4th gear, which reduces the engagement of the outer teeth of the 4th gear and the inner teeth of the 5th gear on that end of the mainshaft. This can (and has) make insufficient tooth-engagement depth with those 2 gears on the end of this shaft when in 5th gear.

So, take a look at the 2 gears on that far end of the mainshaft (opposite the clutch end) and you'll see the far gear if in a fixed position, set there by the snapring and spacer. The next gear in on the mainshaft has 2 sets of teeth: the far left ones engage the inside of the 5th gear. This is where the spacers set that depth: if the teeth do not mesh at least 3mm when in 5th gear, they will wear quickly and the bike will then jump out of 5th. The spacers ensure the 5th gear can't get too far away from the 4th gear, and at the opposite end the clutch pressure plate can't get too far away from the clutch lifter.

[Ellz10]

The 'spacer' thing is: when you drop the mainshaft into the (inverted) upper case, there will be some clearance between the last "face" on the engine's left side bearing (it will be locked into place by the little C-shaped retainer in the groove of the case) and the gear there, or the spacer(s) in between that gear and that bearing. Then use feeler gages to measure the distance between that gear (or spacer), between that and bearing's inner race's side face. This is the point at which there should be 0.001" to 0.004" (0.1mm max.) per the old manuals, which lets that last gear there 'float' slightly back-and-forth - this also sets the depth of how far the outer teeth of the gear next to it (4th) will engage the slots of the end gear, and this engagement must not be less than 3mm: 4+mm is better. If your newly-acquired gearsets are truly complete, they may contain a spacer washer(s) of thickness(es) different from your original one(s) because the shaft-set came from differently-cut cases. It is also possible that there is NO spacer in a given engine: this bearing retainer's cutting tool could vary its position slightly in the later engines due to Honda's holding fixtures for their case machining process with then- NC machines (before CNC was invented).

Mark, you'll have to forgive me and I promise I'm not a complete idiot, but I am absolutely lost as to what you're trying to explain. If you have the time and don't mind, could you please break it down simpler for me, apologies!

Yeah, this is pretty far 'into the weeds', but makes or breaks the operation of 4th & 5th gears, and was never explained in Honda's manuals. I suppose that's because few people ever needed it, or because Honda was walking away from the 750 toward building cars instead with the Yen they had made from the 750.

The mainshaft is a fixed-length piece, but the crankcases were not so perfectly made so as to be fixed-width .in the F2/3 and K7/8 bikes. So, the inside width of the cases between the 2 ball-bearing seats for the mainshaft varied a little bit in production. At the same time, the clutch pack got slightly thicker because of the double-sprung steel plates they added, so both the clutch cover and the crankcases needed some special treatment. The clutch cover for the K7 doesn't fit the earlier bikes at the result. And, the mainshaft, being a fixed-length piece, needed to be pushed toward the clutch cover side of the engine. Doing this then could leave some extra space on the left end of the mainshaft, which could let the last gear on that end (5th) float away from the 4th gear, which reduces the engagement of the outer teeth of the 4th gear and the inner teeth of the 5th gear on that end of the mainshaft. This can (and has) make insufficient tooth-engagement depth with those 2 gears on the end of this shaft when in 5th gear.

So, take a look at the 2 gears on that far end of the mainshaft (opposite the clutch end) and you'll see the far gear if in a fixed position, set there by the snapring and spacer. The next gear in on the mainshaft has 2 sets of teeth: the far left ones engage the inside of the 5th gear. This is where the spacers set that depth: if the se teeth do not mesh at least 3mm when in 5th gear, they will wear quickly and the bike will then jump out of 5th. The spacers ensure the 5th gear can't get too far away from the 4th gear, and at the opposite end the clutch pressure plate can't get too far away from the clutch lifter.

Perfectly explained!! Thank you very much! Sorry you had to break it down further, but I really appreciate it!

[Ellz10]

I'm struggling to realize and understand which direction these circlips go in pertaining to the flat side and chamfered side. I MOST DEFINITELY do not want to install them incorrectly, less I find myself right back in this same situation. So, can someone help me here. I do better by looking at photos, so I've attached a screenshot of the parts fiche with pointers.

[HondaMan]

I'm struggling to realize and understand which direction these circlips go in pertaining to the flat side and chamfered side. I MOST DEFINITELY do not want to install them incorrectly, less I find myself right back in this same situation. So, can someone help me here. I do better by looking at photos, so I've attached a screenshot of the parts fiche with pointers.

I'll see if I have a shaft of those that I can take pix of tonight: I think I have 6 trannys around here(!) - the kind with gears, that is...
In the meantime a general rule: if the gear next to the spacer is free to spin on the shaft, the rounded side of the spacer faces it. This lets the oil seep in and prevents suction from pulling the spacer against the rotating part, as flat-to-flat surfaces under light closure pressure will push oil to the surface of such interfaces, then causing a suction that pushes them together. That's how the troubles start!

[Ellz10]

I'm struggling to realize and understand which direction these circlips go in pertaining to the flat side and chamfered side. I MOST DEFINITELY do not want to install them incorrectly, less I find myself right back in this same situation. So, can someone help me here. I do better by looking at photos, so I've attached a screenshot of the parts fiche with pointers.

I'll see if I have a shaft of those that I can take pix of tonight: I think I have 6 trannys around here(!) - the kind with gears, that is...
In the meantime a general rule: if the gear next to the spacer is free to spin on the shaft, the rounded side of the spacer faces it. This lets the oil seep in and prevents suction from pulling the spacer against the rotating part, as flat-to-flat surfaces under light closure pressure will push oil to the surface of such interfaces, then causing a suction that pushes them together. That's how the troubles start!

The tranny part absolutely had me dying, I literally had tears in my eyes from laughing so hard lol.

On a more serious note - I want to clarify - when you say 'spacer' are you referring to the circlip?

And if you were able to help me by sending pics, I would be so very grateful - I'll donate to the forum extra next month on top of my monthly donation!

[grcamna2]

Good to see it going together smoothly.

[Ellz10]

Good to see it going together smoothly.

Yes, most definitely! It could've been worse, and I'm grateful it wasn't. Though there's a lesson to be learned here and I always yearn for knowledge, so now in the future I have the information to do this correctly and know what to look for in any future builds! Silver lining I suppose!

[HondaMan]

I'm struggling to realize and understand which direction these circlips go in pertaining to the flat side and chamfered side. I MOST DEFINITELY do not want to install them incorrectly, less I find myself right back in this same situation. So, can someone help me here. I do better by looking at photos, so I've attached a screenshot of the parts fiche with pointers.

I'll see if I have a shaft of those that I can take pix of tonight: I think I have 6 trannys around here(!) - the kind with gears, that is...
In the meantime a general rule: if the gear next to the spacer is free to spin on the shaft, the rounded side of the spacer faces it. This lets the oil seep in and prevents suction from pulling the spacer against the rotating part, as flat-to-flat surfaces under light closure pressure will push oil to the surface of such interfaces, then causing a suction that pushes them together. That's how the troubles start!

The tranny part absolutely had me dying, I literally had tears in my eyes from laughing so hard lol.

On a more serious note - I want to clarify - when you say 'spacer' are you referring to the circlip?

And if you were able to help me by sending pics, I would be so very grateful - I'll donate to the forum extra next month on top of my monthly donation!

I had to spend last evening taking care of some dogs, arf...it seems a couple of our neighbors suddenly had to go out of town and my wife volunteered to take care of their pups for a few days, so I have to 'pitch in' to help walk everyone (and tonight). When I get back from that, I'll dig thru some more of the gearboxes: I have a K7 set in there somewhere amongst the (7 or 8 ) others.

The 'spacer' is just a round washer-like gizmo that has teeth on the inside of the hole so it won't spin on the shaft. While most of them were bronze, Honda switched to using cast iron in some of the K7/8 and F2/3 engines, seemingly at random. Those with the iron bushings inside some of the gears (instead of the bronze bushings) usually have iron spacers, too, so you could possibly have 2 kinds of spacers now as you have more than one tranny     on hand.

Edit: Later (dogs are sleeping!!)
Here is a couple of shots of the assembled F2 mainshaft at the 5th-gear end. The spacer in this one is an iron type, not the bronze type, so it is black and on the far side of the snapring. 5th gear is on the far (right) end in these pix and 4th is closer to you. The spacers I've mentioned would be placed onto the mainshaft on the far side of this one's 5th gear, in between the gear and the bearing on the end. This shaft has one, though, so it fit together as-is.

While hard to see here, the flat side of the snapring is toward you, and the rounded side of it toward the spacer washer's flat side. The rounded side of the spacer washer is toward the (far) 5th gear on the end of the shaft. Note that this is always the same situation in the several places on these 2 shafts where clips and spacers are used: there is a non-sliding gear in each place that is mated with a sliding gear to select the different drive ratios. Some lock together with dogs and slots: the 5th gear uses splines and gear teeth.

If your shaft has spacers (or needs them) they will go on the opposite side of this 5th gear, in between it and the ball bearing. Normally there will be no binding occurring when the proper spacer(s) are installed there. Those spacers will push the 5th gear (toward you in the picture) toward the clutch end of this shaft while at the same time ensuring the inside teeth of this 5th gear will engage fully with the sliding 4th gear, which is closest to you in these shots. This is where the "3mm minimum" rule comes into play: there must be at least 3mm of engagement when these 2 gears are meshed in top gear.

[Ellz10]

Perfect! Thank you so very much Mark, I really appreciate it!

With all the information in hand, I'm going to go ahead and start reassembly and I'm going to record the whole thing and then I'll upload it to YouTube and post it here so that you and others can see how I assembled it and let me know if I did indeed so it correctly! I absolutely will not close the cases until I get the go-ahead that the trans was assembled correctly! I DO NOT want to be back here in this same situation, especially not on this bike!

[HondaMan]

I DO NOT want to be back here in this same situation, especially not on this bike!

Especially with that Sump Thing! That makes it so hard to reassemble/reprime the oiling system each time, too.
Clever gadget, though, and well made.

[HondaMan]

This bike is amazing.

Yeah, I particularly like the 'tribute' to the original paint styling on the tank, in the long-swept stripes. Classy thought!