Texas Two Step Taco

teazer

Well-Known Member
DTT BOTM WINNER
The issue that John raises is important. Given that side loads are relatively low ( as yet undefined), what is the rated axial load on that roller thrust bearing? It will cycle as load (revs) increase in say each gear, but that's not a lot of cycles.

I suspect that a hardened steel washer each side would work just fine. We put 100HP through a GT750 clucth which is a similar design - but with two hard thrust washers.
 

John Murray

Member
No. It won't cycle at all. The load will shift the basket out on the bearing until the washers are loaded, and that's where it will stay. Don't put any washers in there, just stop the bearing from moving and let it work the way it was designed to work. Forget about the damn washers - there's a very good chance they'll end up blue and burnt from the continuous load and poor lubrication.
 

Texasstar

Can't is a four letter dirty word
The thrust washer is a bad idea. What's going to happen is the forces on the gear are going to make the basket creep back very slightly on the main bearing, just enough to load up the thrust bearing. This position is where the basket will stay, and both the main bearing and the thrust bearing will remain permanently loaded. If you're lucky the Torrington will survive and won't scatter a hundred hard little rollers throughout the primary drive.

Putting a retainer over the original bearing adds no more moving parts and doesn't add a permanent axial preload to a bearing that isn't meant to take one. You're overcomplicating things and adding complexity where it isn't required.
The thrust washer is a bad idea. What's going to happen is the forces on the gear are going to make the basket creep back very slightly on the main bearing, just enough to load up the thrust bearing. This position is where the basket will stay, and both the main bearing and the thrust bearing will remain permanently loaded. If you're lucky the Torrington will survive and won't scatter a hundred hard little rollers throughout the primary drive.

Putting a retainer over the original bearing adds no more moving parts and doesn't add a permanent axial preload to a bearing that isn't meant to take one. You're overcomplicating things and adding complexity where it isn't required.
It’s been a problem all my life...over thinking things.

The washers that are coming are 47mm od and 1mm thick. We have 1.27mm between the basket and the clutch holder. We will be able tack the washer and use it as a retainer. Done.


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Texasstar

Can't is a four letter dirty word
Now to lighten the front. 18” shouldered bultaco hub, Buchanan spokes.
12 lbs
IMG_7719.jpg



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John Murray

Member
It’s been a problem all my life...over thinking things.
You're not alone there, Pat ;). I don't know how many times my solutions have created more problems than they solved..

Just remember the washer and the gear will both be hardened, so preheat them a little before you tack them. A mild steel ring would work just as well.

PS. Very impressed with the weight savings. I think this thing is gonna be quick.
 

Texasstar

Can't is a four letter dirty word
You're not alone there, Pat ;). I don't know how many times my solutions have created more problems than they solved..

Just remember the washer and the gear will both be hardened, so preheat them a little before you tack them. A mild steel ring would work just as well.

PS. Very impressed with the weight savings. I think this thing is gonna be quick.
The great thing is now that we are set up for a honda rear end we have more options. We also have a 19” shouldered cb175 hub we can swap to and it is easy to swap to 520 sprockets.

Thinking about going 15/35 sprockets now that our rear tire circumference has dimished to 78 inches. Should put us at 95 @ 8500 rpms.


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teazer

Well-Known Member
DTT BOTM WINNER
John knows a lot more about Bultacos than I do but I'm not sure I agree with that logic.

Every time the engine unloads - think engine braking- the thrust is reversed and as the motor creates a cyclic thrust so the basket will feel forces inward and outward. On a drag bike there should be zero reverse thrust so to speak, but after each gear change, the primary drive becomes loaded again causing a new thrust pulse.

Bottom line is that a GT750 and most other bikes from the era use hardened thrust washers without any issues. One difference though is that on a Suzuki the clutch shaft bearing is not retained in any way. It's just a roller bearing, so the basket will be subject to greater side loads than a Bultaco. On the GS and GT series, that isn't a problem because as John mentioned in an earlier post, the side thrust forces are not huge

BTW, how do you have enough space behind the clutch drum to weld on a plate/washer? On my bikes there is almost zero clearance between drum and basket. The drum sits hard up against the outer thrust washer and that's hard up against the drum. Does the drum but up against that step in the shaft, leaving some clearance?

Ask Ralf what he would do. :)

Good to hear that you are saving more weight. It all helps.
 
Last edited:

John Murray

Member
John knows a lot more about Bultacos than I do but I'm not sure I agree with that logic.

Every time the engine unloads - think engine braking- the thrust is reversed and as the motor creates a cyclic thrust so the basket will feel forces inward and outward. On a drag bike there should be zero reverse thrust so to speak, but after each gear change, the primary drive becomes loaded again causing a new thrust pulse.

Bottom line is that a GT750 and most other bikes from the era use hardened thrust washers without any issues. One difference though is that on a Suzuki the clutch shaft bearing is not retained in any way. It's just a roller bearing, so the basket will be subject to greater side loads than a Bultaco. On the GS and GT series, that isn't a problem because as John mentioned in an earlier port, the side thrust forces are not huge

BTW, how do you have enough space behind the clutch drum to weld on a plate/washer? On my bikes there is almost zero clearance between drum and basket. The drun sits hard up against the outer thrust washer and that's hard up against the drum. Does the drum but up against that step in the shaft, leaving some clearance?

Ask Ralf what he would do. :)

Good to hear that you are saving more weight. It all helps.
The forces shifting the basket back - the combustion hits that lasts less than 90 deg - are much bigger than the forces in the opposing direction. They must be or else the shifted bearing wouldn't be a problem, it'd just be oscillating back and forth harmlessly. In practice it knocks the bearing out but not back in. The engine braking forces wouldn't be anywhere near enough to move the basket on the bearing.

I know full well I come across as an opinionated old fart - and I am - and a smart-arse and possibly even a know-it-all. And I agree that what works on the Suzuki should work on the Bul as well. I'm not being intentionally argumentative. More than anything I'm basing my advice on my experience that the simplest possible fix that lets the device work as intended is the one least likely to cause unintended side-effects. Without seeing the parts I don't know how much room can be made for a retainer, but if it can be done it would be my first choice if not the only choice. Of course I may be proved wrong. Cheers.
 

Texasstar

Can't is a four letter dirty word
John knows a lot more about Bultacos than I do but I'm not sure I agree with that logic.

Every time the engine unloads - think engine braking- the thrust is reversed and as the motor creates a cyclic thrust so the basket will feel forces inward and outward. On a drag bike there should be zero reverse thrust so to speak, but after each gear change, the primary drive becomes loaded again causing a new thrust pulse.

Bottom line is that a GT750 and most other bikes from the era use hardened thrust washers without any issues. One difference though is that on a Suzuki the clutch shaft bearing is not retained in any way. It's just a roller bearing, so the basket will be subject to greater side loads than a Bultaco. On the GS and GT series, that isn't a problem because as John mentioned in an earlier port, the side thrust forces are not huge

BTW, how do you have enough space behind the clutch drum to weld on a plate/washer? On my bikes there is almost zero clearance between drum and basket. The drun sits hard up against the outer thrust washer and that's hard up against the drum. Does the drum but up against that step in the shaft, leaving some clearance?

Ask Ralf what he would do. :)

Good to hear that you are saving more weight. It all helps.
You had me at welding!

There is 2.5mm (using feeler gauges) between the aluminum casting and the back of the basket. I put a 3mm washer in and pulled it and the basket dropped.

We did not have this problem until we put the Magee pipe on. Big pulse.

Here is what Ralf said,
A brass washer is good
A brass washer and a steel washer for support is better.
An axial needle bearing would be best if you have room.


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John Murray

Member
Brass isn't a bearing material. Bronze is.
Neither will wear well against aluminium - it's surprisingly abrasive. The mating face needs to be hardened steel.
The aluminium face is narrow and hollow - it's a seal housing with very little strength.
I'm done.
 

Texasstar

Can't is a four letter dirty word
Brass isn't a bearing material. Bronze is.
Neither will wear well against aluminium - it's surprisingly abrasive. The mating face needs to be hardened steel.
The aluminium face is narrow and hollow - it's a seal housing with very little strength.
I'm done.
He is German so it probably got lost in translation lol! He hasn’t seen what you have seen nor does he have your knowledge and nobody knows the limits of Spanish metallurgy until you have had one...or have thrown a leg over one knowing it!


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Texasstar

Can't is a four letter dirty word
Btw we have gone through 2 gallons of c12 with BeNOL 20:1 and it has been a blast!


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teazer

Well-Known Member
DTT BOTM WINNER
John,
I agree that the bang force will always be bigger than engine braking force. And I also agree that pushing up against the aluminum can't be good for anything.
Most of my bike racing was done in VIC with the odd trip up to Oran park to run in a customer CR93 and my CB77racer. The only Bul I worked on was a customer water cooled TSS for the same customer and that was so long ago I don't remember much about it. I certainly didn't try to redesign the transmission and to be honest I don't remember if the primary was straight cut or helical.

My experience is different than yours so it's not too surprising that I come at things from a different direction. All input is welcome and I am learning from your comments and ideas and I love the things you have done with your bikes.

Pat,
C12 is good, safe gas. Once you get it running right, swap that for some U4.4 and see what difference it makes, if any, on the dyno. It's not particularly high octane but it seems to burn faster, so don't go mad with ignition advance. And do not leave the rest of the drum for BB. His bikes are fast enough already......

The new pipe may create longer stronger pulses...
 

Texasstar

Can't is a four letter dirty word
John,
I agree that the bang force will always be bigger than engine braking force. And I also agree that pushing up against the aluminum can't be good for anything.
Most of my bike racing was done in VIC with the odd trip up to Oran park to run in a customer CR93 and my CB77racer. The only Bul I worked on was a customer water cooled TSS for the same customer and that was so long ago I don't remember much about it. I certainly didn't try to redesign the transmission and to be honest I don't remember if the primary was straight cut or helical.

My experience is different than yours so it's not too surprising that I come at things from a different direction. All input is welcome and I am learning from your comments and ideas and I love the things you have done with your bikes.

Pat,
C12 is good, safe gas. Once you get it running right, swap that for some U4.4 and see what difference it makes, if any, on the dyno. It's not particularly high octane but it seems to burn faster, so don't go mad with ignition advance. And do not leave the rest of the drum for BB. His bikes are fast enough already......

The new pipe may create longer stronger pulses...
Haven’t forgot about the U4.4 and drag racing started this past weekend in Texas and the place was PACKED. No social distancing there... Didn’t go and stayed home working on the Taco. Dave took his two Harley’s and couldn’t even make a pass because it was so packed.

I also have the other chamber on the list to make for testing. Need to install the O2 and EGT in this chamber before heading over to BB. I know this is getting drawn out but just wanted to make sure this piston is knocked into shape and we are dialed in. BTW i picked up a drum of BB’s favorite fuel not long ago. Truth be told it smells even better than BeNol and C12. I really like the smell of U4.4! My wife doesn’t like any of it and keeps making comments how great I smell after I put on freshly laundered clothes. Need to see if I can find a fuel that smells like fresh laundry ;)


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Texasstar

Can't is a four letter dirty word
We have done a lot of polishing aluminium and here is what I have found that works for me. The little harbor freight d/a with the 3m oversized 3” discs. Start with 200 400 600 and then the polishing wheel.
IMG_7734.jpg

IMG_7735.jpg

IMG_7736.jpg



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Texasstar

Can't is a four letter dirty word
So I have been watching this championship gal launch this RD. I think her name was Lisa. She blips the throttle like a two step and feathers the clutch. This rd had a six gear auto transmission.




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