Author Topic: ouch, my transmission! (Read 4705 times)

mystic_1 · « **Reply #25 on:** May 31, 2009, 10:38:43 PM »

That raises a good point. Looking back at the opening post, were you STILL at 6000 rpm when you tried to re-shift? If so a little chatter is "normal" or expected in those conditions. Shouldn't lead to a change in shifting though, that's the sign that something went awry.

mystic_1

nobody · « **Reply #26 on:** June 01, 2009, 05:31:38 PM »

Well when I missed the shift the rpms dropped. I snapped the throttle back up to try to match speed but it must not have been close enough.

Terry in Australia · « **Reply #27 on:** June 02, 2009, 08:08:54 PM »

Quote from: heffay on June 02, 2009, 09:26:45 AM

riding your bike like you stole it doesn't make you an idiot, by the way... we all missed a shift or two.

now, i'm confused... if you missed a shift your RPMs should have gone straight to the moon.
and to make shifting more easy on the bike you would've wanted to shift at lower RPMs, not way up at 6k.

And that raises an interesting point Heffy, if I actually stole a bike, the last thing I would want to do is bring attention to myself by riding it like an idiot. So the term "Ride it like you stole it" is a bit of a nonsense, like the old biker saying, "If it aint a Harley, it aint #$%*", which quite literally means that if it is a Harley, it's #$%*.

Now I suppose that if you stole a bike and were spotted "in the act" by the owner, you might well ride away as fast as you could because on your side of the pond just about everybody is apparently "packing heat", so you may want to make up as much distance as possible between you and the (now really angry) owner, but of course, if you subscribe to the mantra "Outlaw guns and only the outlaws will have them" you (the bike thief) may in fact be the armed aggressor, in which case you might just ride around in circles firing your 6 gun indiscriminately, while blowing rasberries at the disaffected owner.

Regardless, damaged gearboxes are common when motor vehicles of all types are stolen, my wifes car was stolen a few years ago, and apart from the steering column lock being damaged, the thief managed to jam the gearbox in first and reverse, so perhaps "ride it like you stole it" just means ride it normally, not trying to attract the attention of an armed and angry owner, while changing gears without using the clutch? It really is a fascinating subject..........................

City Boy · « **Reply #28 on:** June 02, 2009, 09:22:48 PM »

Hi mgab.You may want to take a close look at the shift drum.You will need to remove the oil pan and pump for this check.Trans cover needs to be off.While viewing the drum through the open bottom,move the drum back and forth a little at the linkage end and see if the whole length of the drum moves at the same moment.I had a unit once that the customer mentioned was hard shifting.The drum,which is a hollow casting had completly split near the middle.The fracture was not in a straight line so the broken end would still move,just not when it was supposed to.If your machine is shifting badly in only one gear I would think this is not your problem;however if in more than one gear this may be something to check. Rock On

Terry in Australia · « **Reply #29 on:** June 04, 2009, 04:50:58 AM »

Quote from: heffay on June 03, 2009, 01:18:39 PM

Terry... you should play more Grand Theft Auto.

Ha ha, nah mate, the last computer game I ever played was "Space Invaders", then I lost interest in that stuff, damn my short attention span!

nobody · « **Reply #30 on:** June 05, 2009, 07:13:35 PM »

Okay, I've called several mechanics and the verdict is not good. Most are saying that I should either sell it or try it on my own. They're estimating between $750 and $1200 and I just can't justify spending that much on a bike that's only worth $2000. So I'll be trying to find a parts bike or a spare engine to get parts from. What price should a parts bike or a spare engine sell for? There's a pretty beaten parts bike with only 13k on the clock for $600 but that seems a tad high. Also, any advice you may have for the job would be very helpful would be amazing.

If anybody in Denver feels like making a friend and wrenching some I could definitely use an extra hand and a knowledgeable brain.

bistromath · « **Reply #31 on:** June 05, 2009, 07:40:39 PM »

Best idea right now is to buy a used motor that runs, even if it runs like #$%*, and ride on it while learning the intricacies of transmission repair on the current motor. That way you have a usable ride while you wrench on the busted one. In no case should you take it to a shop unless you know of a shop that really loves and respects these old bikes. Most places will hack and bang at them because "it's just an old Honda", and there aren't too many good mechanics left who really know the insides of the SOHCs. Ask anyone who's taken their SOHC carbs in for adjustment. They'll tell you it's worth learning yourself.

Sometimes you can find a "parts bike" in which the motor still runs fine, and get a better deal on that than a "running when I took it out" ebay find.

Terry in Australia · « **Reply #32 on:** June 06, 2009, 03:15:06 AM »

Quote from: mgab on June 05, 2009, 07:13:35 PM

There's a pretty beaten parts bike with only 13k on the clock for $600 but that seems a tad high.

G'Day Mate, well over here 600 bucks for a CB750 with only 13K on the clock is a bargain, so if it runs I'd say, "BUY IT!". You should be able to offset the purchase by selling off the remaining parts that you don't need, so if you can't get half of that money back, you're probably not trying. Just make sure you get to ride the beater to make sure you're not getting something worse that you've already got. An engine swap should only take an afternoon, and a 6 pack. Cheers, Terry.

nobody · « **Reply #33 on:** June 06, 2009, 06:18:58 PM »

Yeah, the only issue with this parts bike is the guy hasn't had it started for ten years and it's somewhat stripped... No way to know for sure if it runs. New development though, I just remembered that I met this guy a while back who claimed to have a friend with 20-30 engines. So I called the guy up about it, says he's got a k model engine and a 78ss engine that I could have for $350 each. Both supposedly have good compression. Should I buy the ss engine or both? Might be a good idea to have a third engine to use for parts when rebuilding the trasmission currently in my bike right? What would you do?

(fyi, that's a collective "you", it's all encompassing, everybody)

nobody · « **Reply #34 on:** June 06, 2009, 06:22:01 PM »

Oh, also, he mentioned something about maybe burning off some clutch, says adjusting it some may fix my hard shift. Would adjusting it fix the neutral light though? Seems to me like it's something more than just an out of adjustment clutch.

mystic_1 · « **Reply #35 on:** June 06, 2009, 07:32:00 PM »

Quote from: mgab on June 06, 2009, 06:18:58 PM

Yeah, the only issue with this parts bike is the guy hasn't had it started for ten years and it's somewhat stripped... No way to know for sure if it runs. New development though, I just remembered that I met this guy a while back who claimed to have a friend with 20-30 engines. So I called the guy up about it, says he's got a k model engine and a 78ss engine that I could have for $350 each. Both supposedly have good compression. Should I buy the ss engine or both? Might be a good idea to have a third engine to use for parts when rebuilding the trasmission currently in my bike right? What would you do?

(fyi, that's a collective "you", it's all encompassing, everybody)

The 78ss engine won't interchange with your 74K engine. If the K engine he has is 76 or earlier, I'd buy it, chuck it in the bike, and run it while I rebuilt the original motor. You probably don't need a third parts motor, once you get into your just replace the parts you need.

mystic_1

manjisann · « **Reply #36 on:** June 06, 2009, 08:14:33 PM »

Quote

Now I suppose that if you stole a bike and were spotted "in the act" by the owner, you might well ride away as fast as you could because on your side of the pond just about everybody is apparently "packing heat", so you may want to make up as much distance as possible between you and the (now really angry) owner, but of course, if you subscribe to the mantra "Outlaw guns and only the outlaws will have them" you (the bike thief) may in fact be the armed aggressor, in which case you might just ride around in circles firing your 6 gun indiscriminately, while blowing rasberries at the disaffected owner.

See Terry, that's whats wrong with foreigners, they overgeneralize. I for one do not own a 6 gun! (mine holds 7 and slides out at the push of a button

)

mgab, wishing you good karma. I honestly think if you could do an car tranny a bike tranny is within your mechanical abilities. Just take lots of pics, notes, and take it slow. But my opinion isn't worth much

Brandon

Terry in Australia · « **Reply #37 on:** June 07, 2009, 04:52:11 AM »

Quote from: mystic_1 on June 06, 2009, 07:32:00 PM

The 78ss engine won't interchange with your 74K engine. If the K engine he has is 76 or earlier, I'd buy it, chuck it in the bike, and run it while I rebuilt the original motor. You probably don't need a third parts motor, once you get into your just replace the parts you need.

mystic_1

Well, with respect, that's not entirely correct. The F2 and F3 engine will go in, but there are several differences. You'll need the F2 carbs, throttle cables and choke lever and cable assembly and you'll need pods as the F2's airbox is slightly wider and will crack your sidecovers. (although you could modify a K4 airbox to fit)

If your bike has them, you'll need to swap over your header "stubs" and screws, and carefully remove the F2 exhaust studs, ("double nut" it) and you'll have to work out what you're gonna do about the drive sprocket. The F2/F3 runs a 630 chain, while your bike runs a 530. Your front sprocket will slide over the splines on the F2/F3 output shaft, but you'll need to use the F2/F3's lockbolt assembly, and you'll need to make up some spacers to ascertain your chain alignment.

The value of the conversion is questionable, while the F2/F3 engine has another 4 BHP than yours, it is also quite fragile. If I had to choose between the two, I'd take the K engine, there's always more of a chance that it won't be buggered. If it is a really good F2/F3 engine though, and you're feeling adventurous, you won't be disappointed. Cheers, Terry.

Quote from: manjisann on June 06, 2009, 08:14:33 PM

Quote

See Terry, that's whats wrong with foreigners, they overgeneralize. I for one do not own a 6 gun! (mine holds 7 and slides out at the push of a button )

Brandon

Ha ha, fair enough mate, although an auto with a 7 round mag is a waste. After all, auto's were designed specifically for folks who couldn't hit a bull in the butt with a banjo, the theory being, the more shots you can get off, the more chance you have of hitting something! My advice is, if you're the kinda guy who needs an auto, you already know your limits, so get one with a bigger mag!

manjisann · « **Reply #38 on:** June 07, 2009, 05:18:11 AM »

Quote

Ha ha, fair enough mate, although an auto with a 7 round mag is a waste. After all, auto's were designed specifically for folks who couldn't hit a bull in the butt with a banjo, the theory being, the more shots you can get off, the more chance you have of hitting something! My advice is, if you're the kinda guy who needs an auto, you already know your limits, so get one with a bigger mag!

Haha, touche.

Brandon

nobody · « **Reply #39 on:** June 07, 2009, 08:55:04 AM »

Wow, this guy was telling me that the sprocket would need to be changed but didn't mention any of the other parts not matching up. I don't know if I want to go through all that work for a measly four horsepower. Being that it's my first engine swap it may be a good idea to keep it somewhat simple too.

754 · « **Reply #40 on:** June 07, 2009, 09:07:57 AM »

Actually,
The F motor will fit
You can swap to your old sprocket on the engine, BUT shaft in engine is longer, so you will need to shim your rear sprocket out.
Your 76 and down carbs will fit, just use the rubber manifolds for those years.
Depending on which exhaust you are running, you may have to change out studs to flanges.

..................................................................................

Why not just buy a spare motor, split your cases, and use the trans out of the other one.

goon 1492 · « **Reply #41 on:** June 07, 2009, 10:48:24 AM »

I too think if you can and have been into car trannys you can do this simple bike, almost sounds like a syncronizer or this drum thing that city boy talks about. Hondman lives out there in colorado land and is very good at tranny's from what I have read, you might check him out for his advice and maybe services.

nobody · « **Reply #42 on:** June 10, 2009, 09:01:46 PM »

So I started the tear down today, didn't get much done but made some progress. Took off the seat, tank, battery, and removed the exhaust... HOLY HELL THAT EXHAUST WAS HARD TO GET OFF!!!! So I got to thinking, I was going to buy the k model motor for now and maybe the ss engine for a project bike or maybe mod it and swap it in this winter. This reminded me of the fragility comment about the ss engine, how fragile is it? What on it is weaker than the k engine? Is it going to blow on me after only a small amount of tooling around? Will the extra power even be noticeable over the k engine? The black paint certainly looks cooler but if it's going to be significantly less bullet proof I may want to avoid it...

CB750F2 · « **Reply #43 on:** June 10, 2009, 09:29:31 PM »

mgab. I have been away from this thread for awhile. I would not be buying anything until I could see what is wrong with the transmission in your current motor. I suggest that you have some one with you, who is experienced in motocycle transmisions, when you arrive at the stage of splitting the crankcases. He/she will be able to assist you in diagnosing the problem. The problem bay be as simple as a bent shift fork. If the trouble is serious then you can decide the best way to proceed -repair your transmission or replace with another motor. Take plenty of photos as you go along.
The above comments are made assuming that the rest of the bike is in good condition. If your go down the track of replacing yours with another motor whose condition is unknown you may be buying a lot of trouble. Better the Devil you know than the devil you don't know. Pat

222CT · « **Reply #44 on:** June 10, 2009, 09:39:51 PM »

dude jsut get ahold of the shop manual and start tearing it apart...keep everything in boxes, marked with what is in there. get the spare motors....youll need the parts....trust me.

mystic_1 · « **Reply #45 on:** June 11, 2009, 05:09:58 AM »

Quote from: Terry in Australia on June 07, 2009, 04:52:11 AM

Quote from: mystic_1 on June 06, 2009, 07:32:00 PM
The 78ss engine won't interchange with your 74K engine. If the K engine he has is 76 or earlier, I'd buy it, chuck it in the bike, and run it while I rebuilt the original motor. You probably don't need a third parts motor, once you get into your just replace the parts you need.

mystic_1

Well, with respect, that's not entirely correct. The F2 and F3 engine will go in, but there are several differences. You'll need the F2 carbs, throttle cables and choke lever and cable assembly and you'll need pods as the F2's airbox is slightly wider and will crack your sidecovers. (although you could modify a K4 airbox to fit)

If your bike has them, you'll need to swap over your header "stubs" and screws, and carefully remove the F2 exhaust studs, ("double nut" it) and you'll have to work out what you're gonna do about the drive sprocket. The F2/F3 runs a 630 chain, while your bike runs a 530. Your front sprocket will slide over the splines on the F2/F3 output shaft, but you'll need to use the F2/F3's lockbolt assembly, and you'll need to make up some spacers to ascertain your chain alignment.

True, what I actually meant was that teh 77ss motor won't work as a parts motor for the 78K motor, i.e. the transmission gears are different.

mystic_1

754 · « **Reply #46 on:** June 11, 2009, 08:41:32 AM »

I am not sure the F has different gears.

The entire trans should be able to be swapped, if that is the case.

The only thing is the countershaft, its longer on 77/78..and the bearing that the shaft sits in got wider around 73ish. So use the right shaft/bearing.

Some differences in the clutch, just make sure what you have when you order plates.

.........................................................................

Keep in mind that when you split the cases, trans parts are in both 1/2s.. so depending on problem, you may not even be touching the bottom part (if it is say shifting drum or fork gone bad).

So just go slow & make sure you understand each step of the process as you take apart...
AND,, bench test the trans thru the gears, before you install motor.. or button up the covers on the sides of the motor..

crazypj · « **Reply #47 on:** June 11, 2009, 08:57:11 AM »

Missed gear chips dogs and slots.
They become 'ramps' as they round off
Rounded dogs/slots put side loading on selectors when power is applied
Selectors bend/break.
Shift drum slots get damaged.
do it a couple of times and you need a bunch of new parts.
Easy fix, put new bits in.
Don't check any gears for engagement, it will only scare you
I have yet to see a 60's/70's Honda where ALL the sliders have close to 60% engagement, some have 90%, others 40%.
If you had a 'low engagement' one it wouldn't take much to screw things up
Sometimes it can be corrected by shimming but usually you only get 0.010"~0.015" more engagement without grinding bosses on free-wheeling gears and moving shims around

PJ

754 · « **Reply #48 on:** June 11, 2009, 09:02:51 AM »

Yeah, looking at that can be scary.

What I meant by bench test was, after cases are bolted back to gether, before engine meets fram... make sure it shifts thru (all)the gears..

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Author Topic: ouch, my transmission! (Read 4705 times)

222CT