Texas Two Step Taco
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Texasstar
Can't is a four letter dirty word
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The day the music died.......
Could hear it tighten on the first run and stick tight on the second. Also sounded like a touch of clutch slip on the second run about 2/3rds up the rev range. Stuff happens. It's unfortunate, but I'm sure you will be back stronger than ever. Clutch slip is a good sign that you are making more power, so you have that going for you.
You are right that helical primary gears cause side thrust (which also absorbs power). Is there a model with straight cut gears? If not, you may need a different design of thrust bearing behind the basket to stop it moving.
Does that piston need more clearance or did it just overheat? The crown has no piston wash and is way too light, so i agree that it's too lean at least wide open.
The other confusing thing is that it sounded like it was held wide open at peak revs when the revs stopped climbing and just before the throttle was chopped and it nipped up (on the first roll on). That may have contributed.
Has BB got a spare A:F wide band sensor and plug and gauge just to keep an eye on general conditions or a spare EGT or CHT gauge just to keep watch. I usually try to wire up a fresh motor on its first few runs because I canNOT afford new pistons. After that it's too much to watch on a run and happens too fast. With data logging it makes it easier to see what went wrong.
At least no signs of detonation. It was a simple overheating and negative piston to bore clearance. Muriatic acid will probably clean the bore but the piston goes into the collection. We all have a few of those - even Bill I suspect.
Could hear it tighten on the first run and stick tight on the second. Also sounded like a touch of clutch slip on the second run about 2/3rds up the rev range. Stuff happens. It's unfortunate, but I'm sure you will be back stronger than ever. Clutch slip is a good sign that you are making more power, so you have that going for you.
You are right that helical primary gears cause side thrust (which also absorbs power). Is there a model with straight cut gears? If not, you may need a different design of thrust bearing behind the basket to stop it moving.
Does that piston need more clearance or did it just overheat? The crown has no piston wash and is way too light, so i agree that it's too lean at least wide open.
The other confusing thing is that it sounded like it was held wide open at peak revs when the revs stopped climbing and just before the throttle was chopped and it nipped up (on the first roll on). That may have contributed.
Has BB got a spare A:F wide band sensor and plug and gauge just to keep an eye on general conditions or a spare EGT or CHT gauge just to keep watch. I usually try to wire up a fresh motor on its first few runs because I canNOT afford new pistons. After that it's too much to watch on a run and happens too fast. With data logging it makes it easier to see what went wrong.
At least no signs of detonation. It was a simple overheating and negative piston to bore clearance. Muriatic acid will probably clean the bore but the piston goes into the collection. We all have a few of those - even Bill I suspect.
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Texasstar
Can't is a four letter dirty word
Bill said, “I can’t find the Magee pipe with the bung.” I said, “I have it at home.”
As a musician that is exactly how I felt! Your lyrics are expertly crafted and I need your listening skills.
I am going to post the first run where I only had it in second gear and then shut it down. I was watching the little tach on the tank on it said 8500 rpms. BB didn’t think it sounded like it rev’d high enough.
Need to find a better solution than this 200.00 piston. The first clue was the wrist pin problem. Going back to our original posts where you did some research on the different pistons.
God I love DTT makes it so easy to archive the progress and the musings.
Cue Joe Cocker With a little help from my friends...
BB said that they had to go to straight cut gears for such a problem on the Zx14???
When we pulled the head and spun the crank it was not spinning cleanly. The clutch gear was misaligned with the crank and was in a bind. We pressed the bearing back in and I am going to make two tiny tach welds 180 degrees out from each other to see if it will hold the bearing in place on the clutch basket. It took a lot to press the bearing in place. Otherwise we will be making our own custom set of straight cut gears as there is nothing that I know of for the taco and if we go that far we might as well make a slipper. Cue the Beatles BILLY ShEARs. Ralf is our Billy.
I am learning to trust and am very grateful for my friends. Thank you!
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Texasstar
Can't is a four letter dirty word
Just some highlights put the C12 race fuel in the Bultaco and it started backwards from the Kickstarter every time. Had to push start all night. The rpm tell tale said 10,800 was max so I was twisting off a little too much probably why I had the detonation.
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Stay tuned we are checking the Tell tale...
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Something horribly wrong with that last chart. How come it's dropping where the other chart shows power rising?
Before it's run again, I'd check the timing with a timing light to make sure it's not advancing or retarding way too much when it's running, and start with a much larger main jet just to play safe. I would also check piston to bore clearance and set it on the wide side of the recommended range. An air cooled motor with such a large piston is likely to have clearance issues because the piston will heat up and expand a long time before the barrel gets to operating temperature. With a forged piston and cast iron barrel, that's the worst possible combo of different expansion rates.
That clutch basket is a really nice piece of machining, but is the bearing really a press fit with no flange behind it? On many bikes there would be a hardened thrust washer behind the basket to stop it moving inwards and there is also a hardened washer between the basket and hub so that clearances are maintained on the overrun too.
There would need to be a shoulder on the gearbox shaft that it presses against and the gearbox shafts would need to be positively located to prevent lateral movement. Or go to a straight cut set of primaries with an aluminum clutch basket. I wonder if there's something that could be tweaked to fit like say a TZ350. But with less than 50HP the stock helical gears should be OK as long as the basket is restrained.
Before it's run again, I'd check the timing with a timing light to make sure it's not advancing or retarding way too much when it's running, and start with a much larger main jet just to play safe. I would also check piston to bore clearance and set it on the wide side of the recommended range. An air cooled motor with such a large piston is likely to have clearance issues because the piston will heat up and expand a long time before the barrel gets to operating temperature. With a forged piston and cast iron barrel, that's the worst possible combo of different expansion rates.
That clutch basket is a really nice piece of machining, but is the bearing really a press fit with no flange behind it? On many bikes there would be a hardened thrust washer behind the basket to stop it moving inwards and there is also a hardened washer between the basket and hub so that clearances are maintained on the overrun too.
There would need to be a shoulder on the gearbox shaft that it presses against and the gearbox shafts would need to be positively located to prevent lateral movement. Or go to a straight cut set of primaries with an aluminum clutch basket. I wonder if there's something that could be tweaked to fit like say a TZ350. But with less than 50HP the stock helical gears should be OK as long as the basket is restrained.
Texasstar
Can't is a four letter dirty word
I went back and red your previous assessment of the Magee pipe and this run proves your assessment to be true.
“Horribly wrong with the chart.” Agreed. That first chart is the mph chart.
“Check the timing with a light” we didn’t do this but we checked the static timing with the dial indicator and it was 3.15 mm btdc write smack dab in the middle of the Bandido spec 3-3.25 mm however we will install the Zeeltronic next time and set the rev limiter and make sure everything is conservative to start with.
New tm38 will be here Monday and will up the Jet size.
I ordered a cheap 99 xl1200 Yamaha two stroke watercraft piston off amazon to measure it to see if it will work. It will be here Monday. It has the same wrist pin as the taco at 20mm and if it is in the ballpark I can buy those a lot cheaper than the Wisecos at 180.00 ea
I will post the clutch basket parts fiche for your review. Yes it is a press fit and there is no flange on both of the taco baskets. I pulled the other basket yesterday to double check.
TBC...
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Texasstar
Can't is a four letter dirty word
In exactly the same way that my GT750 recorded 16,000 rpm and 263mph.
Both are obviously impossible unless it was strapped to a space shuttle.
Hobbs just came buy to take a look. Didn’t like the idea to tack weld the bearing. He suggested red loctite on the clutch basket bearing and thrust washers between the basket and the inner case riding on the spacer. Here is the video
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Texasstar
Can't is a four letter dirty word
Ok, I’m gonna very optimistically say I’m understanding a tad better than half. But I’m full on board with my ignorance being completely fascinated.
Guys, can I send y’all some spark plugs? You need Loctite? Maybe some 2T oil?
I’d send some Bourbon but I don’t want to corrupt Zeke
