Author Topic: So while driving to work today...transmission fun! - total engine rebuild fun! (Read 9533 times)

SKTP · « **on:** November 18, 2009, 11:01:28 AM »

I ride a 1978 750K everyday for the last 2 years. It runs great. Today it did the first weird thing ever. From a stop, letting the clutch out like normal, it seemed under powered, then a loudish pop came from the transmission area and it seemed to slip into gear (like is was not fully engaged initially). I hoped that it would not happen again and continued driving to work. It then felt like it 'slipped gears' again going into second. I am due for a 2000 mile oil change (doing that tonight). What else would you guys check? I hope the oil change fixes all (maybe wishful thinking). If it continues, what would be your next step?

Thanks for any suppestions

SKTP · « **Reply #1 on:** November 19, 2009, 10:34:42 AM »

Well, I tried adjusting the clutch this morning and it is still clunking in first (and only first)

basically first gear starts out fine then when the clutch is fully disengaged and I'm at about half way to shifting to second it feels really under powered (maybe slippy?) and makes a clunking sound (sometimes 2 or three) then becomes normal and is completely normal in every other gear...did not have time to do the oil change, that will happen tomorrow (but the last change was about 1600 miles ago so I really doubt that will change anything drastically)

CycleRanger · « **Reply #2 on:** November 19, 2009, 10:37:56 AM »

How many miles on the clutch?

SKTP · « **Reply #3 on:** November 19, 2009, 10:40:47 AM »

at least 38,000 most likely more...not the original tach

SKTP · « **Reply #4 on:** November 20, 2009, 11:22:59 AM »

People are now telling me this sounds like a bent shifter fork?

MCRider · « **Reply #5 on:** November 20, 2009, 11:34:31 AM »

Quote from: SKTP on November 20, 2009, 11:22:59 AM

People are now telling me this sounds like a bent shifter fork?

Your symtoms are not quite what we'd expect from a bent shift fork. The lack of power thing is odd.

But problem is there is not much else it could be. The clutch is what it is and doesn't vary that much gear to gear.

So tell us, do you power shift this thing? No judgement here, I love to powershift. But its hard on shift forks, especially the 1 to 2 shift.

Usually the symptom is it goes into 2nd OK, then hops out into a false neutral.

Or maybe you like hard downshifts which would bend the fork the other less common way.

Maybe the shift linkage has come loose under the shifter cover. Someone just recently posted that happened to them. It was on a bent shift fork thread.

Has it been dropped on the shifter? That sometimes binds things up.

I've never seen an oil change fix such a problem. Nor have I seen one fix itself. Sorry.

SKTP · « **Reply #6 on:** November 20, 2009, 12:01:59 PM »

No power shifting for me...I clutch everytime...the engine sound fine and it basically click into first (kinda with a clunk, always has) then the clutch feel normal as I release it into first. I t releases all the way. Then, about halfway to second, it feels liek I sound have more power but it lags, then it makes a a terrible clunking sound (sometiem 2 or three) then grabs the gear like it should and behaves completely noramal in second and above...right now I am getting it rolling in first and shifting to second way earlier than usual to avoid the "clunk" zone....thanks for any comments, I will check out the shift linkage tip for sure

TwoTired · « **Reply #7 on:** November 20, 2009, 12:09:53 PM »

Do the drive chain sprockets still have teeth on them?

When you "lose power" is the engine revving higher without the bike going faster in relation?

MCRider · « **Reply #8 on:** November 20, 2009, 12:13:38 PM »

Quote from: TwoTired on November 20, 2009, 12:09:53 PM

Do the drive chain sprockets still have teeth on them?

When you "lose power" is the engine revving higher without the bike going faster in relation?

That's a real good point I'd forgotten. I've seen drive sprockets that were virtually toothless. And the 1st to 2nd gear area would be the spot where you're transferring the most get it going power and would make the chain skip over the worn down teeth. Less likely to skip at 3rd and above as you reach cruising speeds.

Yikes!

vanillagorilla · « **Reply #9 on:** November 20, 2009, 06:31:16 PM »

Something they taught us at school about transmission diagnostics...
"If the symptom happens in three or more gears, the problem is outside the transmission(shift linkage, shift detent, clutch). If the symptom is specific to one or two gears, the issue is inside the transmission(gears,shafts,drum,forks)."
So... I am guessing it is going to be in the trans. Could be a fork, but it may have to do with worn out dogs and slots(those are technical terms believe it or not). In any case, I think it may be a "time to take it apart" thing...

SKTP · « **Reply #10 on:** November 22, 2009, 03:45:05 PM »

So I was searching the forum for transmission compatibility. It seems that unless I have some certain F models....the Ks are all the same? Please confirm or point me in the right direction.

It would appear that I need to pull my trans, firgure out what is messed up and replace it/them...its for sure my 1st gear only and the drive sproket looks fine and has all teeth...any one holding a salvageable transmission in the SoCal area (an entire engine even or bike even, in a perfect world a 1978K) I want it...thanks for any info. I need my first gear back to its once perfect shifting condition ASAP...thanks for all of your help as always

ekpent · « **Reply #11 on:** November 22, 2009, 03:56:26 PM »

Holy Crap-We have Ron in Detroit---MGAB--- and a few others with 750 trannys on the blink.MC - Mystic and some of the other boyz are working overtime--

Think we need a special transmission section on this site.

SKTP · « **Reply #12 on:** November 23, 2009, 02:06:28 PM »

Sorry about this BUMP

are all the transmissions the same (69-78K) I have found a number of transmission parts on eBay and I just want to double check with you all

thanks again...looks like the engine overhaul is going to happen. I am super scared

also, it appears that to check what is messed up, the engine has to come out (to get at the tranny)

MCRider · « **Reply #13 on:** November 23, 2009, 02:24:34 PM »

Quote from: SKTP on November 23, 2009, 02:06:28 PM

Sorry about this BUMP

are all the transmissions the same (69-78K) I have found a number of transmission parts on eBay and I just want to double check with you all

thanks again...looks like the engine overhaul is going to happen. I am super scared

also, it appears that to check what is messed up, the engine has to come out (to get at the tranny)

Man I think so, but i didn't know till I read here that the Fs were different. So now I'm not so confident in what I "know".

Still I think the Ks were all the same, and some or all of the Fs were different.

TwoTired · « **Reply #14 on:** November 23, 2009, 02:25:30 PM »

Not that I have ever opened up a 750. But, aren't there gear ratio changes among the K models beginning in 77? That would seem to indicate some changes in the trans. Specifics, I don't know, outside of what I found in the shop manual supplements.

Cheers,

MCRider · « **Reply #15 on:** November 23, 2009, 02:31:22 PM »

Quote from: TwoTired on November 23, 2009, 02:25:30 PM

Not that I have ever opened up a 750. But, aren't there gear ratio changes among the K models beginning in 77? That would seem to indicate some changes in the trans. Specifics, I don't know, outside of what I found in the shop manual supplements.

Cheers,

I think it was Mystic in another transmission thread that pointed out to the OP that he had inadvertently gotten a 2nd hand transmission with a different gear in it, more teeth. It was marked different and could be identified in the picture. The OP couldn't close his case. I think Mystic said it was from a 77/78 F model.

So I'm thinking all the Ks were the same, the first 75/76 Fs were the same as Ks, and only the later Fs were different. But I'm trying to confirm that and maybe Mystic will mystically appear as well.

nobody · « **Reply #16 on:** November 23, 2009, 03:11:19 PM »

Quote from: ekpent on November 22, 2009, 03:56:26 PM

Holy Crap-We have Ron in Detroit---MGAB--- and a few others with 750 trannys on the blink.MC - Mystic and some of the other boyz are working overtime-- Think we need a special transmission section on this site.

Haha, misery loves company!

SKTP, take a minute to read through this thread, it will may help you a little with a diagnosis. It will also give you some idea of what you're in for and hopefully provide some answers when you're confused.

http://forums.sohc4.net/index.php?topic=59158.0

SKTP · « **Reply #17 on:** November 23, 2009, 03:55:38 PM »

Good God!

How did those transmissions turn out?

Would you do it again? How much time should I expect to have my bike off the road? The most complicated thing I have done is a dual disc conversion (incomplete at this point) and a wheel swap-out...

Looks like I am buying a beater car and going for it...? I guess the learning is invaluable, but I think I could just buy another bike and save a lot of head aches? Starting off in second is getting old, really fast.

nobody · « **Reply #18 on:** November 23, 2009, 04:07:44 PM »

Both of our bikes are still out of commission, Ron's will be road worthy before mine, he works at a faster pace then I do. It's been said in that thread that this job could be done in a matter of days if you really hit the grindstone. I'd expect several weeks to a month if you work at a slightly higher than average pace and are mechanically inclined, longer if you take your time and have much to learn.

It's been a lot of work so far but none of it has really been too difficult, these bikes have a pretty straight forward design. It may have been easier just to sell it and find another 750 but I didn't want to lose money selling the bike for half of what I bought it for. I certainly wasn't about to pay a mechanic $1200 or more to fix it either, might as well buy another one if I'm spending that much.

It's your call, whatever you do. Just know that it's no cup of tea to repair the transmission. If you attempt it and begin to struggle this site is usually pretty good at providing an answer to your question.

Don R · « **Reply #19 on:** November 23, 2009, 06:34:30 PM »

mystic_1 · « **Reply #20 on:** November 23, 2009, 06:38:08 PM »

My understanding is that F models and K7/K8 have the same transmission, which is different than K0-K6.

mystic_1

MCRider · « **Reply #21 on:** November 23, 2009, 06:43:14 PM »

Quote from: Don R on November 23, 2009, 06:34:30 PM

My brother once put 75 F gears into a K engine to get the different (close?) ratios.

Yes in my readings tonite (John Wyatts CB750 book) there was the reference that all Fs had the new closer internal gearing. I could find no reference that the later Ks changed though.

The discussion went along the lines that the Ks were to be left alone as touring bikes and the Fs were to be the sportier competition for the dual cam Kaws and Suzis until Honda could bring there dual cams on line.

Still no absolute confirmon the Ks trans though.

Thanks Mystic, your post kept mine from getting posted. I'll look for more confirm tomorrow. Maybe the microfishy lists the number of teeth on the gears?

SKTP · « **Reply #22 on:** November 23, 2009, 06:53:03 PM »

I still need to go through all part by part, but my initial part number searches at BikeBandit.com seem to indicate the Ks are all the same

mystic_1 · « **Reply #23 on:** November 23, 2009, 07:28:56 PM »

Speaking of part numbers, I was just off compiling this list based on CMSNL.com:

The K0-K6 manual on the main website says:

Gear ratios

Primary reduction: 1.708
I   2.500
II   1.708
III   1.333
IV   1.097
V   0.939

The K8-F3 manual says:

Gear ratios

Primary reduction: 1.708
I   2.500
II   1.708
III   1.333
IV   1.133
V   0.969

Transmission gear part numbers

K0:

Item	Part Number	Superceeded By
GEAR,LOW	23421 300 050
GEAR,SECOND THIRD	23431 300 010	23431 392 000
GEAR,SECOND	23440 300 010	23440 410 305
GEAR,MAIN FOURTH	23450 300 010
GEAR,THIRD	23460 300 010	23460 410 305
GEAR,FOURTH	23471 300 010
GEAR,MAIN TOP	23481 300 020
GEAR,COUNTER TOP	23491 300 010
GEAR,FINAL DRIVE	23501 300 030

K7:

Item	Part Number	Superceeded By
GEAR,LOW	23421 300 050
GEAR,M.2.3	23431 392 000
GEAR,CT/SHAFT 2ND	23440 392 000	23440 410 305	Upto Serial#: 2719994
GEAR,CT/SHAFT 2ND	23441 410 000	23441 431 000	From Serial#: 2719995
GEAR,M/SHAFT 4TH	23450 392 000
GEAR,CT/SHAFT 3RD	23460 392 000	23460 410 305	Upto Serial#: 2719994
GEAR,CT/SHAFT 3RD	23461 410 000		From Serial#: 2719995
GEAR,FOURTH	23471 300 010
GEAR,MAIN TOP	23481 300 020
GEAR,COUNTERSHAFT	23491 392 000
GEAR,FINAL DRIVE	23501 392 000

F0:

Item	Part Number	Superceeded By
GEAR,LOW	23421 300 050
GEAR,M.2.3	23431 392 000
GEAR,CT/SHAFT 2ND	23440 392 000	23440 410 305
GEAR,M/SHAFT 4TH	23450 392 000
GEAR,CT/SHAFT 3RD	23460 392 000	23460 410 305
GEAR,FOURTH	23471 300 010
GEAR,MAIN TOP	23481 300 020
GEAR,COUNTERSHAFT	23491 392 000
GEAR,FINAL DRIVE	23501 392 000

So the K7 transmission has different ratios and different part numbers than the K0, particularly in the upper gears.

mystic_1

SKTP · « **Reply #24 on:** November 24, 2009, 09:48:31 AM »

Option #2: engine swap...are all the years the same? how about Fs and Ks? I think I could nab an F motor with like 12,000 on it for around 200 bucks. That sounds way easier (I have a 78K)

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Author Topic: So while driving to work today...transmission fun! - total engine rebuild fun! (Read 9533 times)