pk 250

Good one Ted the thread has once again lost its way, This was starting to get good with the larger tires and high power being discussed, 9.5s on 11" wheels. Gonna make a lot easier to hook up that big hp. Wonder what it gonna do to the set ups? How it gonna effect the cross and weight transfer? I know the shift in domance has possible drifted to the 250 2strokes. They may be able to keep them locked down when they hit the powerband and start to scream. Maybe the Jawas got some better competation now. I know the 250s make lots of HP but controlling the comming on the pipe has been thier biggest drawback. The Jawa still has all that torque down low so thats gonna be a real competative combo to beat.
 
ABR #69 said:
I read more informative and better posts from ole Al these days than PD. Everything will ruin Karting, so go out and have fun while it lasts. Maybe we'll all be running 600's before long! I already got my engine picked out!

The 250 MX engines are at a slight disadvantage I think, not performance wise. Once your bore them once over stock that jug is done. To stay legal you have to slap a new jug on it. So, it's a toss up. I think they're a crazy good setup, but just has a slight draw back. But, almost all engine packages do. I think a slightly higher cc for the two strokes would make them more than competitive for a longer period, maybe cheaper. But, they'd never dominate.
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Agree 100%. Where's the like button. :)
 
Ted, to maintain your credibility, always mention that, if a statement is your opinion, that it is your opinion.

That, like all things I post here, is/are my opinion/opinions.
Keep in mind this is a forum ..... to say or not to say, whatever comes to mind.
None of it is appropriate to take seriously.

As I have mentioned before, Tim is just fine at the track. Always glad to help him, if needed. OK?
On this forum, Tims opinion, about me or anything else is his opinion, and can be freely expressed. This is the same for me....you...and everybody
else Bob allows to yap on HIS forum.

Now, back to tires/rims/etc.
 
I know I'm not helping the thread get back on track, but I want to know more about the boring of 250's. What does the "next" size up in bore take them to, as far as CC's? It could be that 260 cc's needs to be looked at in a future rule proposal period, whenever that comes around.

ABR #69 said:
I read more informative and better posts from ole Al these days than PD. Everything will ruin Karting, so go out and have fun while it lasts. Maybe we'll all be running 600's before long! I already got my engine picked out!

The 250 MX engines are at a slight disadvantage I think, not performance wise. Once your bore them once over stock that jug is done. To stay legal you have to slap a new jug on it. So, it's a toss up. I think they're a crazy good setup, but just has a slight draw back. But, almost all engine packages do. I think a slightly higher cc for the two strokes would make them more than competitive for a longer period, maybe cheaper. But, they'd never dominate.
Click to expand...
 
Millennium Technologies will "recoat" and repair cylinders. There should be no need to "bore". The BRC 150 is a nicasil cylinder. There is only ONE piston size available. The nicasil cylinders are very durable and will last for seasons. However if you do stick it or worse it can be repaired and Millennium does a great job and very reasonable.

http://mt-llc.com/
 
ttownwideglider said:
I know the 250s make lots of HP but controlling the comming on the pipe has been thier biggest drawback. The Jawa still has all that torque down low so thats gonna be a real competative combo to beat.
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I don't quite understand what you're getting at. The 250s are going to come off the corners at peak torque, just like the Jawa. The 250s will be turning more RPM, so the horsepower will be higher than the Jawa. This could cause more wheelspin than the Jawa, like you said. This is an instance where it might be better, with a two cycle, to set the gearing to come off the corners lower than peak torque RPM. Try to keep that horsepower under control.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley
 
Road Dog said:
I know I'm not helping the thread get back on track, but I want to know more about the boring of 250's. What does the "next" size up in bore take them to, as far as CC's? It could be that 260 cc's needs to be looked at in a future rule proposal period, whenever that comes around.
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66mm bore-246cc 72mm stroke stock for TRX250R
67mm bore-254cc 72mm stroke
68mm bore-261cc 72mm stroke

Stock CR starts at 66.4? Unsure of stroke but it's 248cc
From a calculator it says has to be 71.5 stroke to make 248cc with 66.4 bore. Going to 67 makes it 252, 67.5 would make it 256. Also, one bore size and then illegal. But, 260 would make it ok for one more bore.

These are very relative and not exact, this is assuming 72 mm stroke for the TRX. Not sure exactly what most are running but this is based loosely on TRX honda and CR's. Not sure what all bore sizes are available for other engines, half sizes or what. But as you can see a few MM and you're out of spec. 260cc rule still won't give some people a legal second bore.

Something I'm not very familiar with, how often do you "need" to bore a racing 2 cycle? I don't know. Still a viable option, but 265cc might give more options. Way less than a Wankle and you'd get more than a single bore from a cylinder.
 
Road Dog said:
I know I'm not helping the thread get back on track, but I want to know more about the boring of 250's. What does the "next" size up in bore take them to, as far as CC's? It could be that 260 cc's needs to be looked at in a future rule proposal period, whenever that comes around.
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Looking at resleaving a cylinder would give multiple pistons sizes available to the racer however current rules would only allow for 1 over size bore. So next rules session I'll propose a change in the 250 displacement allowance.

There are some who would like to resleave rather than replate.
Replating with nicasil is a great option like Chris says its pretty reasonable. How ever I've found brand new cylinders on some engines available for the cost of a replating.
Again there are so many options available to the racer now that the new age of open kart racing has come into effect.
 
alvin l nunley said:
I don't quite understand what you're getting at. The 250s are going to come off the corners at peak torque, just like the Jawa. The 250s will be turning more RPM, so the horsepower will be higher than the Jawa. This could cause more wheelspin than the Jawa, like you said. This is an instance where it might be better, with a two cycle, to set the gearing to come off the corners lower than peak torque RPM. Try to keep that horsepower under control.

From the desk of Al Nunley
Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley
Click to expand...

The 250's apply the power different. They don't make quite as much HP/torque as the 500cc Jawa but they make more than enough. Tuning the pipe in my opinion would be better than gearing the engine in and out of the pipes performance.
 
The ATC/TRX engines have bore sizes from 66mm-68mm in .25mm increments, with the 72mm stroke this will make a max of 262cc's. The CR's from 86-01 are 66.4mm-68.5mm in .50mm increments, with the 72mm stroke this will make a 266cc max. I don't believe the cc's need to be increased to equal the power out but it would be nice to be able to use all the available bores. The ATC/TRX is a sleeved cylinder from the factory, the CR's are all plated from the factory according to Wiseco. Hope this info helps.
 
Also, as 270cc's is a "common" microsprint class, it would open up more parts suppliers and pipe options for the PK and other 250's
@Stephen Gleason -- where are you sourcing your pipes for the 250 at this point?
 
270ish would open up a big range of options, keeps it well under the Wankle too.

I know it's all in available bore sizes, but either way certain engines would be left behind. One might get 3-4 another might get 5 bores in 270. But, I think it could definitely be considered to be raised. I don't know enough about it to be the one suggesting as to what the max CC allowed should be though.

Also, thanks for the info Brian. I wasn't exactly sure what was available.
 
Criss are you saying that you never bore a nicasil cylinder? Do you use cast iron rings to get a seal. Dont know much about this type of coating. How do the rings seat if there is no cross hatch ? I like the idea of never boring ,then I could go to max bore size on a say 125 cylinder and possibly get the piston swain coated and reuse the piston and cylinder several times. Never have to resleeve. Just buy new rings when it starts loosing compression. Check ring groove in piston thats about the only thing to wear out. How about some more info on these coatings and how it works.
 
http://mt-llc.com/
Most of your questions can be answered on this site. In short, Nicasil is very porous and retains lubrication better than the best cross hatch can. Our BRC cylinders are nicasil over aluminum. There is no liner. So thermal transfer is very efficient. That's why most all modern day cylinders, especially water cooled, are nicasil.
 
Ok that answers what Nicasil is which I knew it was nickel silicon. But it does not answer any of the other questions I ask. Do you have to replate the cylinder at every refreshening. That would be more expensive than just reboring and putting a new sleeve in after max is reached? What type of rings do you use? I have been told that the Swain coating on the piston will last for several runs and almost completly cuts out piston and cylinder wear. Has anyone tried this combination of coatings , and what were the results? This is extremely interesting , added preformance and cost savings at every refreshening. Think of the savings on pistons. If the nicasil coating last for several refreshings then it could be a cost saver also, just buy one piston and run it until clearence needs adjusting then recoat cylinder and piston.
 
Interesting...... I read of what is considered dominance back when because of the sheer numbers of Sudams. A statement made to sound as if Sudams are a thing of the past. If so, Jack & Mike sure still know how to win a Championship with one as well.

Anyone seen any signs of that elusive "Wankle Biter" run with other folks' stuff that gets so openly criticized? I'd looove to see how it matches up with one of Tim's 250's. Kinda like Tim's 250 vs. Sasquatch. Innovation vs. something we hear exists, but thats about it. :)
 
Unless you gouge it in a seize, the nicasil has indefinite life unless it's a bad plate job and flakes somewhere. No need to "refresh" the bore per se, but a light hone to remove any deposits from the piston or rings that could be there. The lifespan of the piston is usually determined by fatigue due to revs, in addition to wear. If Swain-coated, the revs probably dominate that equation and the piston should be replaced once the wristpin hole elongates or other damage becomes apparent. I do not know whether Swain coating and nikasil are compatible -- a good question for Swain's tech dept. AFAIK, standard rings are used. Yes, assuming the Swain-coating isn't too abrasive for the nikasil, long cylinder/piston lives would result, RPM dependant. Please report back any findings.
 
Thanks ted for the info I will be checking with Swain on the compatiblty of the two coatings. Yes wrist pin hole elongation and ring groove wear will be the determining factors to the piston life. But this combo sounds very interesting for an increase in preformance and savings on rebuilds. Plus a guy can go to max bore size to gain the extra cc and not worry about resleeving and buying many piston sizes.
 
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