Topic: CB750A Street ET bracket drag bike. A year to build it.

[dragracer]

Mike, I hesitate to ask this question but its already been put on this thread many times; what caused the engine/ transmission to lock up leading to Sams crash??

[MRieck]

Mike, I hesitate to ask this question but its already been put on this thread many times; what caused the engine/ transmission to lock up leading to Sams crash??

Nothing outstanding in the teardown Frank. Think it may have been either the shift mechanism or the pressure regulator. It acted like it wanted to be in high and low at the same time. I replaced both those parts. Only thing not good were the 4 springs in the cush drive unit. Primary chain was very loose too.....also replaced.

[dragracer]

I know a lot of us were curious about the cause even though it wasn't going to change the end results for Sam. Things like that could happen to any of us involved in the sport of motorcycles.

[Sam Green Racing]

Well guys, I'd given up on what might have caused it but thinking back to something I saw posted on the Internet a short while ago, I might be able to answer it myself but I need to do a little more digging first.
It seems like I wasn't the only one to experience gearbox problems when coasting to a stop, In my case, before I managed to stop. Give me some time guys as I'm having some problems posting on the site where I found this being discussed.

[underdog]

  I sure would like to see this bike back in action. It inspired me to get a 750A.

[Jerry Rxman Griffin aka MuthaF'er]

Sam, I just saw an article about a 101 year old Brit actively riding his scooter. You riding again?   

[kmb69]

Well guys, I'd given up on what might have caused it but thinking back to something I saw posted on the Internet a short while ago, I might be able to answer it myself but I need to do a little more digging first.
It seems like I wasn't the only one to experience gearbox problems when coasting to a stop, In my case, before I managed to stop. Give me some time guys as I'm having some problems posting on the site where I found this being discussed.

Sam, very, very interested to know what you find. Especially since we have a couple of automatics in the works. Keith

[Sam Green Racing]

Well guys, I'd given up on what might have caused it but thinking back to something I saw posted on the Internet a short while ago, I might be able to answer it myself but I need to do a little more digging first.
It seems like I wasn't the only one to experience gearbox problems when coasting to a stop, In my case, before I managed to stop. Give me some time guys as I'm having some problems posting on the site where I found this being discussed.

Sam, very, very interested to know what you find. Especially since we have a couple of automatics in the works. Keith

I'll get back to ya'll Keith as soon as I can find out more but like I said, I'm having big problems accessing the site where this was being discussed.
My biggest problem is the fact that never having any experiences of them, I don't fully understand how these gearboxes and torque converters work.
Despite the fact that I saw the motor at Mikes when it was originally pulled down, I didn't pay much attention to how it all worked.
Does anyone have a parts book showing an exploded view of what's in there ? I'll keep searching and ask on the Auto section here on the forum.

[kmb69]

.....
I'll get back to ya'll Keith as soon as I can find out more but like I said, I'm having big problems accessing the site where this was being discussed.
My biggest problem is the fact that never having any experiences of them, I don't fully understand how these gearboxes and torque converters work.
Despite the fact that I saw the motor at Mikes when it was originally pulled down, I didn't pay much attention to how it all worked.
Does anyone have a parts book showing an exploded view of what's in there ? I'll keep searching and ask on the Auto section here on the forum.

Torque converter is a pretty much standard 3 component design - pump, stator, and turbine. Both gears are always engaged, but the clutches are "switched" on and off by hydraulic valve.
This section of the shop manual does a pretty good job of describing how it all works:

[Sam Green Racing]

.....
I'll get back to ya'll Keith as soon as I can find out more but like I said, I'm having big problems accessing the site where this was being discussed.
My biggest problem is the fact that never having any experiences of them, I don't fully understand how these gearboxes and torque converters work.
Despite the fact that I saw the motor at Mikes when it was originally pulled down, I didn't pay much attention to how it all worked.
Does anyone have a parts book showing an exploded view of what's in there ? I'll keep searching and ask on the Auto section here on the forum.

Torque converter is a pretty much standard 3 component design - pump, stator, and turbine. Both gears are always engaged, but the clutches are "switched" on and off by hydraulic valve.
This section of the shop manual does a pretty good job of describing how it all works:

It makes sense now Keith, if the motor dies for any reason, get on the front brake as quick as you can.
If the motor is not running, no oil is getting to the converter and more importantly, no line pressure if being fed to the two clutches so its only a matter of time before they can't make up their minds which one should be working, hence both trying to work at the same time and both gears being engaged at the same time.

[kmb69]

.....
It makes sense now Keith, if the motor dies for any reason, get on the front brake as quick as you can.
If the motor is not running, no oil is getting to the converter and more importantly, no line pressure if being fed to the two clutches so its only a matter of time before they can't make up their minds which one should be working, hence both trying to work at the same time and both gears being engaged at the same time.

Almost, but not quite. The clutches are both open by default - they both slip so the gears are not engaged at the same time. It requires oil pressure to one or the other for it to engage.

[dragracer]

.....
It makes sense now Keith, if the motor dies for any reason, get on the front brake as quick as you can.
If the motor is not running, no oil is getting to the converter and more importantly, no line pressure if being fed to the two clutches so its only a matter of time before they can't make up their minds which one should be working, hence both trying to work at the same time and both gears being engaged at the same time.

Almost, but not quite. The clutches are both open by default - they both slip so the gears are not engaged at the same time. It requires oil pressure to one or the other for it to engage.

So when running an auto, sounds like its imperative to always have clean oil in the motor. This would mean regular oil and filter changes and periodically pulling the pan and clutches to clean out debris. Yeah, and no synthetic oil because its killer stuff at a drag strip. Causes prolonged cleanup after a catastrophe.

[Sam Green Racing]

Well I guess that's me told then, hahahaha.

[kmb69]

I'll get back to ya'll Keith as soon as I can find out more but like I said, I'm having big problems accessing the site where this was being discussed.
.....

Sammie, keep trying to get that info. Inquiring minds want to know!

[Sam Green Racing]

I'll get back to ya'll Keith as soon as I can find out more but like I said, I'm having big problems accessing the site where this was being discussed.
.....

Sammie, keep trying to get that info. Inquiring minds want to know!

Well Keith, I thought you had solved the problem with your diagram.
I have been reading on an Automatic page where people have been having gearbox problems after killing the motor and rolling to a stop or knocking it into neutral and killing the motor before stopping and also when being towed with a dead motor.
I guess with either of these situations, the motor is off and not pumping oil but the gearbox is still being spun up by the rear wheel, your thoughts on that my friend.

[MRieck]

So.....the engine died when you were halfway through your run?? You probably don't remember BUT that bike was blowing main fuses at Bradenton. Wilbur found one intermittent short but maybe another occurred.

[kmb69]

So.....the engine died when you were halfway through your run?? You probably don't remember BUT that bike was blowing main fuses at Bradenton. Wilbur found one intermittent short but maybe another occurred.

That's true, but the engine was still running after Sammie went down, laying on the ground, and had to be turned off.

[kmb69]

.....
Well Keith, I thought you had solved the problem with your diagram.
I have been reading on an Automatic page where people have been having gearbox problems after killing the motor and rolling to a stop or knocking it into neutral and killing the motor before stopping and also when being towed with a dead motor.
I guess with either of these situations, the motor is off and not pumping oil but the gearbox is still being spun up by the rear wheel, your thoughts on that my friend.

Yep, the hi clutch and countershaft are turning if the bike is rolling. One or both clutches would have to be dragging badly to lock the rear wheel. Neither clutch should be engaged or dragging without the engine running and producing oil pressure. This is the predicted action per the design. Doesn't mean something can't go wrong. But like I said above, your bike was still running laying on the ground and had to be turned off. I do not have any explanation and that's why I was hoping you could find out more info from your other forum.

I guess a faulty low clutch could not release properly when the hi clutch is engaged and essentially have both gears engaged at the same time. That would lock up the rear wheel.
 

[Sam Green Racing]

So.....the engine died when you were halfway through your run?? You probably don't remember BUT that bike was blowing main fuses at Bradenton. Wilbur found one intermittent short but maybe another occurred.

Yes Mike, I do remember what happened at Bradenton in November 2013 but I don't remember what Wilbur found other than a blown fuse.
The bike ran faultless at Valdosta in the following Spring race and I made 10 passes on it with no issues.
At Virginia, going off what I was told and off the timing slip, the bike reached about 80mph at the 330 foot mark and then the fuse blew. After that I was just coasting with a dead motor hoping to make it to the first turn off.
I went through half track at 48mph and that's when it locked up and high sided me.
I seem to recall Bill saying that it was a wire joint not fully covered that might have touched the fork leg, perhaps his memory is better than mine but he told me several weeks later when I got out of the Hospital.

Sam.

[Sam Green Racing]

So.....the engine died when you were halfway through your run?? You probably don't remember BUT that bike was blowing main fuses at Bradenton. Wilbur found one intermittent short but maybe another occurred.

That's true, but the engine was still running after Sammie went down, laying on the ground, and had to be turned off.

Not what I was told when I got out of hospital Keith. I was told it had blown a fuse again. If the motor was running, why was I coasting when it spat me off ?

[kmb69]

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Not what I was told when I got out of hospital Keith. I was told it had blown a fuse again. If the motor was running, why was I coasting when it spat me off ?

Sammie, I'm not sure you were coasting. I was there literally seconds after you went down. The first guy there, who we didn't know, told me he had to kill the engine. I did not hear it with my own ears, but that what I was told at the time.

Somebody had a video of that run. Please repost it.

Where is Bill Benton? Not answering email!

[MRieck]

 Hmmmmmmmmm. Keith and I didn't see the actual run....just the aftermath. Personally I can't remember what the track people said.
 Billy rode the bike later at Valdosta and experienced a mechanical problem and got out of the run. He must have coasted to the finish line. I assume he put the bike in neutral. I have towed the bike back to the pit and there were no problems (bike in neutral).
 I just hope there are no problems now. I went through the engine throughly.

[kmb69]

.....
Billy rode the bike later at Valdosta and experienced a mechanical problem and got out of the run. He must have coasted to the finish line. I assume he put the bike in neutral. I have towed the bike back to the pit and there were no problems (bike in neutral).
.....

If I remember correctly, Billy said it was lurching and making a "clacking" sound. But I'm also pretty sure he was "skeered" at the time to take any chances and I don't blame him. Pretty sure something mechanical happened that made it go down. If I remember the video correctly, the rear end just started washing out right then left left then right (memory failing I guess). Definitely interested in determining the cause if at all possible and learning what Sammie finds out on the other forum.

I would have bet money that Mike would have found something at teardown as I was speculating that both gears had engaged simultaneously.

[MRieck]

Yeah....I was really hoping to find something definitive but no luck other than the cush drive springs being all f'd up. That and the very worn primary chain.

[dragracer]

Just my thoughts, but for good measure  I hope Bill would consider stripping ALL of the wiring off the bike and starting all over again with just the basics needed to run the bike. Perhaps the wiring wasn't what lead to the mishap in Virginia,  but I've pushed that bike off the end of the track myself because of a blown fuse.  At this point there's no reason to leave any part of the stock harness in place unless the bike retains the full charging system.

It'll be nice to see Sam Auto racing again.