Texas Two Step Taco

[teazer]

That's good. I used to have a set of micrometers in inch measurements. Haven't used them in donkey's ages. It's so much easier to work in metric. Just sayin'

And the new piston should be larger close the bottom than at the top because they are tapered to allow for the fact that the top (crown) gets hotter and expands more. They are also cam ground so the dimensions side to side are less than front to back. It is possible that the piston you used might have insufficient taper for your application.

 

[Texasstar]

“The worst kind of racers are those that listen to everyone and those that listen to no one.” -Bill Baxter

We have found the limits of one particular piston. Talked with two other bultaco racers today that had the same problem with this particular Wiseco piston. Both have stuck this piston.

After sticking his first Hughes Wiseco Piston, Flat track racer number one found a solution by ceramic coating the top of the piston and running .006” piston to wall. He likes it because it is the lightest piston available.

Bruce Reynolds of
http://www.brbultacos.com/ designed his own and has sold over 100 to flat track racers without one seizure problem. He also races a Bultaco Bandido.

I shared with him how we were cold starting and going WOT. He said this is going to sound crazy but we run .005” piston to wall clearance. He says the box says .005” but you can run 5...lol. We would run .006”

Both laughed when I told them the box of my piston said .003” piston to wall. Flat track racer one originally used Bruce’s piston and never had a problem until one time Bruce was out of stock.

So the BRbultaco Wiseco piston has an older semi keystone ring design and the rings are moved further away from crown. The piston is coated. They are heavier than the other Hugh’s and are about the same weight as the original mahls. Bruce said the lighter piston leaves the crank unbalanced and he prefers the heavier piston. Optimization.

Bruce also said the cylinders distort easily and become barrel shaped. He said that he has USChrome Nikasil plate the cast iron bore. BB has done this before but says it is a pain if you stick the piston and it will come off...if not it lasts a long time. BB suggested I wait on the Nikasil until we get the chamber and carbs dialed in.

Enter racer number 3. I received an email from the nitrous burning Bultaco and he said, “get rid of the forged Wiseco and go back to the original cast piston.” But we are running 14:1 compression. He thinks that is a bad idea also.

In no way is this a bad review of Hugh’s pistons and I think the world of Tim. When you are pushing the limits you just have to find the right parts that will be optimized together.

I may have buyers remorse later but going with the BRBultaco Wiseco. A non seizure seems worth 250.00 bucks. By the time I get the Hugh’s and coat it we are back to 250 bucks. Will take it to Wells racing and have it bored to .006” and we will be back on the dyno. We are cold starting and going WOT. It is also important to get back on the dyno to ensure we keep killing the virus and do our part to save humanity.

Call me Ratllin’ Tex.






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[teazer]

That all makes sense. BB is right about plating after you get the rest dialed in. They say that timing is everything in life.

.006" (6 thousandths on an inch) is a good place to start but I suspect that you will need more with a forged piston. Is there a suitable cast piston available by any chance? They typically expand less. Do the calculation on barrel versus piston expansion just to see what the numbers look like. I was surprised.

And what fuelil ratio are you running now? I'd start at 25:1 or maybe even 20:1 to let the oil transfer a little of the heat away. I wouldn't go as far as Gordon Jennings and 16:1 but he was on the right track.

I normally like teeny tiny thin rings to stop ring flutter but I wonder if thicker rings might help to transfer heat to the barrel.

Who do you know that can cast you an aluminum barrel with extra transfer ports and no fins?

You may want to think about a larger stinger diameter to reduce exhaust pressure and heat build up and try the next run with EGT and CHT tied to a data logger so you can see how fast they rise.

Time to design a pipe while you wait for "My Corona" to stop playing on the national jukebox.

 

[Texasstar]

That all makes sense. BB is right about plating after you get the rest dialed in. They say that timing is everything in life.

.006" (6 thousandths on an inch) is a good place to start but I suspect that you will need more with a forged piston. Is there a suitable cast piston available by any chance? They typically expand less. Do the calculation on barrel versus piston expansion just to see what the numbers look like. I was surprised.

And what fuelil ratio are you running now? I'd start at 25:1 or maybe even 20:1 to let the oil transfer a little of the heat away. I wouldn't go as far as Gordon Jennings and 16:1 but he was on the right track.

I normally like teeny tiny thin rings to stop ring flutter but I wonder if thicker rings might help to transfer heat to the barrel.

Who do you know that can cast you an aluminum barrel with extra transfer ports and no fins?

You may want to think about a larger stinger diameter to reduce exhaust pressure and heat build up and try the next run with EGT and CHT tied to a data logger so you can see how fast they rise.

Time to design a pipe while you wait for "My Corona" to stop playing on the national jukebox.

Thank you I got carried away with the zeros. I haven’t found a modern cast piston to replace it yet. But if I find one will be a buyer. BB thinks if we go back to a NOS bultaco cast piston we will to need to drop rev’s. Ralf looked for wossners for us but to no avail.

What do you think about heating the forged piston in boiling water and then measure it to determine necessary clearance?

I do know somebody who can make us a billet cylinder. I hear you loud and clear and will make the calculations. The heat transfer on the thicker rings makes sense.

So oil fuel ratio was what was in BB’s weed eater gas can. I suspect it was typical 50:1. I have lost 3-500 dollar hedge trimmers this past summer mixing 40:1 because they were run WOT for long periods of time and just changed my fleet to 32:1. Will make sure we richen up the mixture. 10-4 on the EGT and CHT.

Time for some pipe dreams...thanks again.

Making a check list before getting on the dyno.










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[Texasstar]

side by side BR Bultaco Wiseco 86.5 mm Hugh’s Bultaco Wiseco 86mm


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[Texasstar]

BRBultaco Wiseco in the House for a Bultaco Bandido Montadero

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[Texasstar]

hugh’s Bultaco Piston , stock Bultaco Piston, BrBultaco Piston


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[teazer]

Looking at the first picture, nice looking piston (on the left). The one on the right not so much.

.006" for a properly warmed up motor that is on and off the throttle so it warms properly and stays warm without a lot of full throttle. How much for one that starts almost cold and its run at WOT for 12/13/14 seconds?

Street, dirt, motocross etc are all part throttle applications with periods of cool down between blasts. Drag is full on from start line to winning line.

I'm thinking that 6 thou will be fine for the dyno as long as the motor gets a few heat cycles first and is warmed up before winding it open and allowing cool down between runs to avoid a heat soak situation. If that all works. then you could warm it up to race it but that will be less powerful (but more reliable) than keeping it cool. It's all a balance.

They say that to finish first, one must first finish, so in this application maybe warm up might be better than peak power and sticking pistons. Alternatively add an extra couple of thousandths clearance. BB has been through all those issues and can probably guide you there.

I see gas (cooling/lube) ports in that stock piston to keep the bridge cool and lubed. That might help on the new piston too. More accurately, it might keep the bridge cooler. The idea is to stop the bridge from heating up and expanding into the bore. You could also relieve the bridge slightly to add more clearance at that spot.

 

[Texasstar]

Bruce Reynold said to not pay attention to the box and use .005 but they are warming up their flat track engines. Another flat rack racer that used this piston told me he used .0055

BB and I are debating he thinks .008 is too loose so we may go for .0065” that would give us .0015” over what Bruce said to use.


The top of the piston is coated, rings are moved down, rings are wider to transfer heat. Looks like somebody else had seizure problems with their Bultaco’s with design of this piston.


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[Texasstar]

Just talked with Doug he originally bored the Hughes piston to .0055” piston to wall clearance. He recommends we go .007” on the BR Bultaco piston.

He thinks we were not “wet” enough on the top end.

Making progress with piston to wall divination process. Taking it to Wells racing tomorrow to have it bored .007” piston to wall.

7 days a week. 7 notes in a diatonic scale.

“The number 7 is the seeker, the thinker, the searcher of Truth (notice the capital "T"). The 7 doesn't take anything at face value -- it is always trying to understand the underlying, hidden truths. The 7 knows that nothing is exactly as it seems and that reality is often hidden behind illusions.”




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[Texasstar]

With 14:1 compression Ralf suggested we start with our timing at 20 degrees BTDC. That is 2.44mm BTDC and not the 3.15mm BTDC that we used from the Bultaco manual. We are running C12 race fuel next time.


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[teazer]

I like 19 degrees but that's because that's what a TD3 or TZ used to run. That doesn't necessarily mean it's right for a much larger bore, but 20 degrees sounds like a good place to start. If teh motor is OK with that, you can always add a degree or two and see the results on teh dyno.

C12 shouldn't detonate at that setting. It's pretty tolerant - if a little flat in terms of throttle response. Once you get it dialed in, see if you can get your hands on a pail of U4.4 We are not allowed to run that in S/E but I ran it in tnt and dumped a load into our old truck and it really perked that thing up. It just feels crisper - an I don't mean DNA sequencing CRSPR...

 

[Texasstar]

I like 19 degrees but that's because that's what a TD3 or TZ used to run. That doesn't necessarily mean it's right for a much larger bore, but 20 degrees sounds like a good place to start. If teh motor is OK with that, you can always add a degree or two and see the results on teh dyno.

C12 shouldn't detonate at that setting. It's pretty tolerant - if a little flat in terms of throttle response. Once you get it dialed in, see if you can get your hands on a pail of U4.4 We are not allowed to run that in S/E but I ran it in tnt and dumped a load into our old truck and it really perked that thing up. It just feels crisper - an I don't mean DNA sequencing CRSPR...

I get it so U4.4 is like a disruptive technology say CRSP. I own both CRSPR and Intellia but currently don’t have any U4.4. Looks like next week will be a good week to take stock of all three on weakness.

So cooler heads and excellent timing prevail in such times. I asked Ralf if he thought the taco was too far advanced and he said it would have been much worse with a hotter head. The flat track guys keep saying words like “we have never seen that much advance in a Taco.“


According to the spreadsheet we were running somewhere between 22-23 degrees BTDC. We had no detonation and it looks like we now know our lImits for our Piston. So let’s go to the sluggish throttle side of timing and find an optimum. I think it was Lynn Mobley that said a Bultaco will run between 1mm and 4mm BTCD with 1mm being sluggish on the throttle and 4mm being very snappy or Crisp . Then we will add the U4.4.

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[teazer]

No doubt he was right. The problem with timing a two stroke is that at low revs and small throttle openings, the effective compression is quite low, so the motor needs a lot of advance to get the fire going.

As revs rise, the pipe becomes more effective as it stuffs gas back into the cylinder. As revs rise, so does teh speed at which the mixture is "squished". Combine those two and you have faster moving more turbulent mixture under higher compression so the flame propagation rate is much higher so it needs less advance.

In most applications we want a quick throttle response at low to mid revs and at less than WOT, so we use more advance. But that extra advance adds heat at higher revs and because the peak pressure rise is now too early, it adds extra pressure which adds extra heat before TDC.

That's where programmable timing helps. Ask BB about his Zeel and how guys set the timing on those.

On a low compression low load street motor, none of that matters too much but the more effective the pipe and ports are at filling the cylinder, the more timing matters.

People think that Bultacos are hot Spanish bikes, but when they are tuned they need to keep a cool head.

VP have way too many fuels to make any sense of. They say that U4.4 is the best and they also say that C12 is best for old air cooled motors, but yu could try any number of them and see minor differences. C12 is cheap (relatively) and a known winner, so maybe stick with that for the moment rather than chasing through different fuels from VP and Sunoco.

 

[Texasstar]

rotary table dialed in and making a plate for the electronic ignition sensor


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[idahofrank]

Tex, Please don't disregard what Teaser said about fuel/oil mixture ratios. I am old and it's been decades, but I remember the dyno testing that Gordon Jennings did in regards to fuel/oil mixture ratios. He found as the oil ratio went up, HP increased along with better engine lubrication. I have always run 20:1 with excellent results in all my two stroke engines.

Jet sizes will have increased to compensate for the displaced fuel.

It will smoke more.

Plug life may be shorter.

Teaser, do recollection agree with mine?

Former El Bandido owner ........... of course, I did not drag race it.

 

[teazer]

You are right.

Cycle did a test on that showed a clear power rise with more oil. The same has been shown to be true by various other magazines.

Back in the day, Gordon Jennings did a series of tests on the TZ350E - or was a it a 250 - that Mark Homchick (sp?). I have a copy of that article "somewhere", but as I recall it he tested a variety of Oil:Fuel ratios and preferred 16:1 using the best oil available. Many people derided his results and claim his bikes stalled and fouled plugs and had all sorts of other unproven tales, but Jennings did tests and that was his result.

We used to run our RS125 road racer on 20:1 or 24:1 I don't remember which and never had any troubles with that.

Back in the day Castor oil form CAstrol was the best oil in terms of lubricity and shear strength, and every test I have seen, suggests that's still true, but it's messy stuff. A747 was what we ran years ago but got used to using high grade Silkolene that MotoLiberty supplied for the Aprilia Cup bikes we raced around the year 2000. They are in the Dallas area and still supply it. www.silkolenestore.com


I have tried a huge range of oils over the years and never has any trouble with any, but prefer Silkolene or Motul but even Yamalube R will work.

 

[teazer]

Just to put things in perspective, these are 125cc cylinders from a Honda RS125 race bike, TZ250 racer and RS250 Aprilia Cup bike

And this is an older RM250 Suzuki.

So much more port area.

 

[Texasstar]

Tex, Please don't disregard what Teaser said about fuel/oil mixture ratios. I am old and it's been decades, but I remember the dyno testing that Gordon Jennings did in regards to fuel/oil mixture ratios. He found as the oil ratio went up, HP increased along with better engine lubrication. I have always run 20:1 with excellent results in all my two stroke engines.

Jet sizes will have increased to compensate for the displaced fuel.

It will smoke more.

Plug life may be shorter.

Teaser, do recollection agree with mine?

Former El Bandido owner ........... of course, I did not drag race it.

Thank you, I bought some C12 fuel yesterday and will definitely go with 20:1 to start with!


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[Texasstar]

You are right.

Cycle did a test on that showed a clear power rise with more oil. The same has been shown to be true by various other magazines.

Back in the day, Gordon Jennings did a series of tests on the TZ350E - or was a it a 250 - that Mark Homchick (sp?). I have a copy of that article "somewhere", but as I recall it he tested a variety of Oil:Fuel ratios and preferred 16:1 using the best oil available. Many people derided his results and claim his bikes stalled and fouled plugs and had all sorts of other unproven tales, but Jennings did tests and that was his result.

We used to run our RS125 road racer on 20:1 or 24:1 I don't remember which and never had any troubles with that.

Back in the day Castor oil form CAstrol was the best oil in terms of lubricity and shear strength, and every test I have seen, suggests that's still true, but it's messy stuff. A747 was what we ran years ago but got used to using high grade Silkolene that MotoLiberty supplied for the Aprilia Cup bikes we raced around the year 2000. They are in the Dallas area and still supply it. www.silkolenestore.com


I have tried a huge range of oils over the years and never has any trouble with any, but prefer Silkolene or Motul but even Yamalube R will work.

20:1 it is to start. I will check out the silkolene.


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