Texas Two Step Taco

So with a little help of the Bultaco group on Facebook we have found out what the spring and cam are on the front of the crank. Gear driven primaries have some form of drive to protect the transmission and that spring on the crank is a shock absorber. It is a Cush drive.
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we have found out about this...


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Nice cylinder head. Ralf is a smart cookie for sure. And the torroidal combustion chamber is sweet. 14:1 is easy to start - just add more exhaust timing to drop the effective (dynamic) compression at low revs. A strong leg would also be useful. :)

That form of cush drive was common on older bikes. Triumph twins used it for years as did Norton on their singles and many others. It's a spring loaded face cam and it won't disintegrate the way that cush drive rubbers do.
 
teazer said:
Nice cylinder head. Ralf is a smart cookie for sure. And the torroidal combustion chamber is sweet. 14:1 is easy to start - just add more exhaust timing to drop the effective (dynamic) compression at low revs. A strong leg would also be useful. :)

That form of cush drive was common on older bikes. Triumph twins used it for years as did Norton on their singles and many others. It's a spring loaded face cam and it won't disintegrate the way that cush drive rubbers do.
Thank you I hope we get to race together one day! So..:speaking of the Cush life...Ralf and I have been talking about a 123 auto transmission and he said, “Ah I see. The outer clutch basket is one piece with the gear. Thats where most manufacturers put the cush / damper.
What jumps in mind..... it could be modified rather easy to an overrunning pulley if u ever want to use some 1-2 or 1-2-3 auto transmission mod for drag-race.
The overunning pulley will protect the selector forks in case u have to close throttle for some reason.... Usually stock gears and the shift drum get modified for auto tranny. Dogs on gears get a ramp and shiftdrum little slot mods.
Suggest start with stock tranny and lets see where u get.” A little more involved than a lock out...but how will we get to that .002 R/T ?


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185 degrees exhaust duration for the Bultaco Montadero M51 https://youtu.be/RZic1EmCxOY


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Dyno for grins straight header no muffler 5k rpms...raining outside humidity was high! https://youtu.be/bOD42gNbmZk


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That no pipe run was in first gear and it revealed this issue. 47mph in first gear.
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This is the dyno run. High humidity aftermarket 70’s expansion chamber 80 plus MPH in second gear. https://youtu.be/wF8sLHN4lP8


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we were getting huge RFI interference but the RPMs on the monitor matches my gauge on the bike. After this run the Bultaco wouldn’t start so we did a compression test and had 60 psi.


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We rebuilt the taco while we tried to remove some heads for a H2 he just bought. Geeze now I know why H2 heads are so expensive.
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we measured the bore 85.35 mm the pistons were .50 over stock which made them 85.50. We had some marks where Zeke had seized the bike before.
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With no base gasket and throwing reckless abandonment to checking the correct squish. We put it through two heat cycles and then did a dyno run with the Dr. John Magee designed chamber. Now this chamber was designed for a Kawasaki H2 Drag bike @ 9500 rpms. BB said his bike has never made more power the only problem was it also liked to seize the piston.

The bultaco just wanted to keep revving. Probably should have changed the jets in the carbs...well should have change the carbs. We made the most HP we have made 28 whp. We also seized the piston twice. Made runs until we had no compression again.

We turned the chamber a light blue on the taco. https://youtu.be/kZLeR1PbXTU


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“You start by determining, mathematically, an upper limit for piston speed.” And you get rid of Mahle non forged pistons that seize tighter than John Calvin’s theology.



Piston Speed

.166 X 2.519 (64mm) X 8500 rpm = 3,555.72

.166 X 2.519 (64mm) X 9000 rpm = 3,764.88 ft/min

Piston speed limit 4000 ft/min


What do you think 9k redline?


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If you're still making power and don't mind tearing down the engine on a frequent basis, you can go even higher. Short skirt forged pistons can often get you over the 5000 ft/min mark (especially on a drag motor, which will only be running these speeds for short periods of time).

Abnormal wear on the skirts will be a signal that you're near/past your limit.

Depending on how deep you want to go down this rabbit hole, longer con rods will also help, but will also bring a new set of problems with them.
 
Sonreir said:
If you're still making power and don't mind tearing down the engine on a frequent basis, you can go even higher. Short skirt forged pistons can often get you over the 5000 ft/min mark (especially on a drag motor, which will only be running these speeds for short periods of time).

Abnormal wear on the skirts will be a signal that you're near/past your limit.

Depending on how deep you want to go down this rabbit hole, longer con rods will also help, but will also bring a new set of problems with them.
The Mahles we had in both of our engines had wear.
I have been reading the KJV of Jennings two stroke tuning and he warned me of the same con rod peril.

Have a Pro Lite forged Wiseco 86mm piston coming from Hugh’s Bultaco. Kinda pricey at $180.00

Found an XL1200 Yamaha Watercraft piston that may work on the Bultaco 360. Has th same 20mm wrist pin but trying to find piston height diagrams and pin to dome measurements are harder with two strokes than 4 strokes. Center wrist pin to crown is 36mm and wristpin to top edge is 31mm
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Haven’t got to the section on reed boxes.
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I have been obsessing about reed valves and port velocities...found this picture from a highly modified Bultaco Pursang. Thought to myself now that makes sense. Vertical mounting of a reed valve.
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I wouldn't have thought there was enough csa with the reed mounted that way, perhaps that's why it has had such a huge seize. Is that a crack in the liner as well?
 
Pete12 said:
I wouldn't have thought there was enough csa with the reed mounted that way, perhaps that's why it has had such a huge seize. Is that a crack in the liner as well?
That is not my reed nor engine...this guy bought this bike and forgot to put oil in his fuel.


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Texasstar said:
That is not my reed nor engine...this guy bought this bike and forgot to put oil in his fuel.


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Oh yeah, I knew it wasn't yours as it's a Pursang, not a Montadero. Forgot to put oil in his fuel, tragic mistake.
 
Pete12 said:
Oh yeah, I knew it wasn't yours as it's a Pursang, not a Montadero. Forgot to put oil in his fuel, tragic mistake.
Don’t you find this intake port interesting? Aren’t the two reeds basically two individual Venturi ports? And he has it dumping into finger ports cascading down into the cylinder. I wonder if there is a port plug on the other side.


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Texasstar said:
Don’t you find this intake port interesting? Aren’t the two reeds basically two individual Venturi ports? And he has it dumping into finger ports cascading down into the cylinder. I wonder if there is a port plug on the other side.


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Sure do find it interesting, but it doesn't seem like the cross sectional area of the two reed petals would be large enough, but I've been wrong before. There would have to be two matching windows in the piston for it to work correctly.
 
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