Is it worth putting a racing crank into a polini 3 port motor to run in the super production class? What would I get out of it if I do run a racing crank? Looking for some good advice.
Is it worth putting a racing crank into a polini 3 port motor to run in the super production class? What would I get out of it if I do run a racing crank? Looking for some good advice.
Why do you say that? So if the guy next to me on the track is running a race crank he won't be faster in all power ranges? Is the race crank lighter than an a stock crank? It's stuffed and won't it rev better in all power ranges over a stock crank? If the polini 40cc 3 port motor is 6.2 hp and you add the race pipe that bumps the hp to about 8 hp to 8.5 hp. Now if I add a race crank that should get me to about 10 hp? I'm I right or I'm I wrong?
No, stuffed crankshafts are definitely not lighter than standard crankshafts. BZM crankshafts are particularly heavier based on the fact that they incorporate aluminum inserts into their "race" crankshafts. The lightest would be the Polini crankshaft with the tungsten inserts, but still heavier than a standard crankshaft.
A stuffed crankshaft decreases volume in the crankcase, which cycles the piston to TDC at a higher velocity. In the end, you may gain a few RPM's on the top-end, but usually, it's not noticeable on a Super Production engine.
The best thing you can do with the bottom-end is have the crankshaft trued and precisely centered on a set of high-speed bearings. Without the added weight of a “race” crankshaft, your engine will spool up far faster.
Some of the fastest engines I’ve assembled were built with standard crankshafts.
Thanks minimotopilot now that's the kind of info I was looking for. I can learn alot more from an answer like this than just telling me no. Now woudn't having the crankshaft tured be against the rules? I didn't think we could do work on the inside of the motor in the super production class? Thanks again minimotopilot,
not sure with pocketbike racing, but blueprinting an engine is definitely allowed and a "must do" to be competitive in superstock bike racing. All you are doing is bringing the bike up to original factory tolerances and specs, you are not modifying anything.
So the blueprinting falls under these rules? I underlined the section I'm still alittle confused about it so I'll just have to contact the league about it. Hey coax maybe you could jump in here and straighten me out some on this subject if you would? Thanks guys and sorry about being a noob but these guys have a couple years or more on me and just trying to catch up some. 1.5 – SENIOR (B) SUPER PRODUCTION (Ages 16+)
Must be a 40cc 3-port, two-stoke engine and cannot have any engine upgrades
with the exception that any production race crank may be used. No material may be
removed from any part of the exhaust, carburetor or engine. Porting, polishing,
matching, balancing, etc. are not allowed in this class. Bikes may be air- or water-
cooled and can have up to 14-14mm SHA carburetor. Non-programmable ignition
systems must be used. Any production clutch, flywheel, exhaust, reeds, air box,
wheels and tires may be used. No combustion enhancers such as NOS may be
used and all bikes must be naturally aspirated.
Chinese C1 Replicas or Banshees may race in the Super Production Class. No
part of the pocketbike may be altered in any way except for the following:
The bike may use any clutch currently in production.
The bike may use up to a Dell'Orto 14-14mm SHA carburetor. (Banshees
may run with stock carburetor.)
The bike may use any pocketbike tires currently in production.
The bike may utilize a race crank.
The bike may utilize race pipes. (Added 3/1/06)
Bikes suspected of utilizing bigger carburetors or having porting, polishing etc. will
be torn down and tech inspected.
That reads like only "out of the box" bikes will be allowed in that class.. i think that is the same place i wanted to run a banshee since they are placed in the super proddy class (50cc w/ 18.5mm carb & polini parts... woohoo)..
No, having the crankshaft trued is definitely not against the rules. If you had the crankshaft balanced, that would be a violation, but that in itself is an extremely expensive service.
Stangely enough, most of the crankshafts that I've come across arrived out of true, brand new out of the box. In my opinion, and I'm sure any engine builder would agree, it's the equvelant of receiving a broken part. Having the crankshaft trued translates to simply having it fixed.
If I'm not mistaken, Team Calamari Racing (the Squids) charges about $60 for this service, which is extremely cheap and their turn-around time is absolutely amazing.
After that, center the crankshaft on a set of high-speed bearings. If you can't do it yourself, employ the services of someone who knows exactly what they're doing.
If you're still interested in decreasing the volume in the crankcase, omitting the crankcase gasket during reassembly of the bottom-end would yield the same results of having a stuffed crankshaft, if not better. In that case, you'd use a high temp sealer like Yamabond or Permatex in place of the gasket, but the case halves need to be perfectly flat, with no nicks or gouges on the mating surfaces.
If you're still interested in decreasing the volume in the crankcase, omitting the crankcase gasket during reassembly of the bottom-end would yield the same results of having a stuffed crankshaft, if not better. In that case, you'd use a high temp sealer like Yamabond or Permatex in place of the gasket.
I've been pondering doing just that for a while now. I finally tore down one of my China engines and pulled the gasket out to try it out, but I haven't run it yet, TBH because my Euro is so good that I always take it to the track. By my math, you save a few cubic centimeters of volume which is roughly equivalent to the stuffers.
What do you think about skimming the cases? I have noticed that on some engines (admittedly Chinese, but I really like to play) even with the gasket removed I will still have more than .5mm clearance on the crank wheels. By the same logic, I should be able to skim a few tenths of a mm, eliminating the wasted crankcase volume.
Great advice, BTW. That is why I keep coming back to this site.
So what your saying is the 2 crank halfs are not equal to each other that there alittle offset? Well maybe you could tell me how I can get to around 10hp And stay within the rules? That's my goal. I see people claiming 10hp to 11 hp and turning like 16000 + rpm's with 3-port motors. I'm getting 14200 rpm's. That's on a real long straight but it is still winding up before the corner. So I really don't know my true peak rpm's but it is'nt to far away. Atleast I don't think that there is another 2000 rpm's there that is. Now my setup is just basic polini blue reeds & polini race pipe, clutch set at 8500 rpm's, 7/70 gears, squish .63mm, polini motor.
Wouldn't truing a crank technically be the same as removing material from the engine, even if you call it a fix?
No material may be removed from any part of the exhaust, carburetor or engine. Porting, polishing, matching, balancing, etc. are not allowed in this class.
Wouldn't truing a crank technically be the same as removing material from the engine, even if you call it a fix?
No material may be removed from any part of the exhaust, carburetor or engine. Porting, polishing, matching, balancing, etc. are not allowed in this class.
Truing doesn't involve material being removed from the crankshaft. In most cases, the crankshaft can be trued by simply placing it on jig and smacking with a brass hammer until the crankshaft wheels are running perfectly parallel to one another.
Truing free's horsepower, eliminates engine and chassis vibration and basically, your engine will hum like a European sewing machine. How's that analagy?
If you want to talk about testing the limits of cheating and outright cheating, we can talk about Frank Giannini.
I've been pondering doing just that for a while now. I finally tore down one of my China engines and pulled the gasket out to try it out, but I haven't run it yet, TBH because my Euro is so good that I always take it to the track. By my math, you save a few cubic centimeters of volume which is roughly equivalent to the stuffers.
What do you think about skimming the cases? I have noticed that on some engines (admittedly Chinese, but I really like to play) even with the gasket removed I will still have more than .5mm clearance on the crank wheels. By the same logic, I should be able to skim a few tenths of a mm, eliminating the wasted crankcase volume.
Great advice, BTW. That is why I keep coming back to this site.
Sure, I'd definitely recommend skimming the cases, but this is definitely an instance where having a trued crankshaft would be absolutely mandatory, in addition to a set of bearings with a C3 radial play rating to eliminate any radial movement of the crankshaft. Otherwise, an untrue crankshaft would definitely seize against the interior walls of the crankcase.
A good example of the benefits of skimming would be when I did this with a stock air-cooled engine, which belonged to one of the Moderators here (Eric). I skimmed the cases for a crankshaft clearence of .25, installed a trued BZM standard crankshaft (no inserts) on a set of high-speed SKF's and precisely assembled the engine.
The end result was an air-cooled engine that easily kept up with a BZM Super Production engine.
The engine was installed in Eric's refurbished Polini GP Steel. We met at the track (Adams Karting), I took the air-cooled Polini for a test spin and he rode a BZM powered DM. When we hit the 750ft straight, I stayed right on top of him the entire time and I weighed 190 pounds at the time. If he catches this thread, I'm sure he could tell you about it.
This is a prime example of what an engine can do when assembled correctly. I seriously cannot emphasize this enough.
So what your saying is the 2 crank halfs are not equal to each other that there alittle offset? Well maybe you could tell me how I can get to around 10hp And stay within the rules? That's my goal. I see people claiming 10hp to 11 hp and turning like 16000 + rpm's with 3-port motors. I'm getting 14200 rpm's. That's on a real long straight but it is still winding up before the corner. So I really don't know my true peak rpm's but it is'nt to far away. Atleast I don't think that there is another 2000 rpm's there that is. Now my setup is just basic polini blue reeds & polini race pipe, clutch set at 8500 rpm's, 7/70 gears, squish .63mm, polini motor.
Yes, exactly. The wheels on an untrue crankshaft are not running parallel to one another. Basically, one or both are slightly out of true and in laymans terms, basically wobbling. Something as simple as tightening the flywheel nut with a clutch holding plate on the clutch will contort the crankshaft out-of-round.
There's tons of stuff you can do with an engine and stay within SP rules. The possibilities are endless and it really depends on what you want to do and of course, how much you can spend.
To give you an idea and what can be done, towards the end of our PB racing days, we were having pistons, cylinders and crankshafts cryogenically treated. We'd also have the piston crowns and combustion chambers ceramic coated and the piston skirts coated with dry-film lubricant.
The rules say you can't remove anything from the internal parts, but nothing about adding material to internal parts.
To give you an idea and what can be done, towards the end of our PB racing days, we were having pistons, cylinders and crankshafts cryogenically treated. We'd also have the piston crowns ceramic coated and the skirts coated with dry-film lubricant. Ceramic coated combustion chambers too.
Would all this need to be done with all new parts? Because of the oil film that's inside of the used motor? I think it would be wise for me to get some more wrench time rebuilding a couple more motors before I spend that kind of money. Thanks for taking the time to post in my thread minimotopilot.
Yes there is cag. But I'm sure there is more that can be done to these motors that are between my setup and doing high dollar mods like this. I'm sure there are more great tips and tricks like truing the crank. I have been going back the the start to present of some of the forums and reseaching for awhile now but no one really posts about them much. Everybody has SP bikes it seems but once they get the carb tuned and the clutch set and a few other problems taking care of not much else is talked about. Now talk about upgrading to a 50cc open type bike it's a whole new ball game.
Last edited by StrayDawg63 : 01-30-2008 at 07:52 PM.
I can't believe I found this thread lol. But Freddie's right. That polini motor he put together for me was a BEAST. Easily kept up with my BZM powered motor, and I think I had that motor geared pretty high as well.
If you decide to build a motor similar to what Freddie did, I highly suggest running a ratio of 32:1 vs. 50:1. You want more oil to coat the internals and to lower engine temps.
