Topic: 1/8 mile ET's and flywheel discussion.

[Don R]

 How much 750 would it take to be competitive in a street bike bracket race with a maximum 8.50 dial?
  It's a nice track, we always have good 60' times there with the car. I'm guessing it will take a high 12 second quarter mile bike at least.
Gerald Kramer is doing three street legal bike races next year at Eddyville Ia. 

[dragracer]

How much 750 would it take to be competitive in a street bike bracket race with a maximum 8.50 dial?
  It's a nice track, we always have good 60' times there with the car. I'm guessing it will take a high 12 second quarter mile bike at least.
Gerald Kramer is doing three street legal bike races next year at Eddyville. 

Don. In my experience it won't take much to run 8.50s. I ran 8.20s with a basically stock 736cc K8. I did lower the bike quite a bit by sliding the forks through the triple rees and i made adjustable rear struts to drop the rear of the bike. I used a stock seat and had it cut down a lot to lower my center of gravity. I put drag bars on the bike. I installed a sidewinder and rejetted the stock PD carbs but left the airbox on with drilled holes. At one point i had a simple "kill" switch set up on my foot shifter to momentarily cut fire to the dyna S to make full throttle shifts. Otherwise,  that was it. In hindsight i wish i had bought shortie shocks and installed a decent airshifter.  I was mainly using the bike as a test bed to figure out if i wanted to actually spend the time and money to build a purpose built Honda 750 dragbike. I learned a lot from that basic set up that i carried forward into my F3 dragbike i built over 25 years ago. The F3 is still kicking so i must have figured something out.

[dragracer]

I forgot to add that the bike was geared for stop light to stop light. I wanted to keep the engine revving on what feltvto mecwas its ideal torque/horsepower curve.

[Don R]

 Thanks for the info, I've managed to not make a pass on a bike yet, when I'm at the track I don't want to take away from running the dragster and talk myself out of it. The Kawasaki refused to run twice, once because some dummy forgot which way the choke worked and fouled a plug, once it just wouldn't start. Now it's gone to a new home.
  I'd like to go at least to see the owner Gerald, he's a former cb750 drag guy and why not make a lap or two just in case I can use my crew chief skills bracket racing a bike.
  I'd for sure want a lightened flywheel and the 17 tooth front sprocket back on. I have light flywheels for charging or starting or neither but not both. I'm not big on kick starting.

[dragracer]

Thanks for the info, I've managed to not make a pass on a bike yet, when I'm at the track I don't want to take away from running the dragster and talk myself out of it. The Kawasaki refused to run twice, once because some dummy forgot which way the choke worked and fouled a plug, once it just wouldn't start. Now it's gone to a new home.
  I'd like to go at least to see the owner Gerald, he's a former cb750 drag guy and why not make a lap or two just in case I can use my crew chief skills bracket racing a bike.
  I'd for sure want a lightened flywheel and the 17 tooth front sprocket back on. I have light flywheels for charging or starting or neither but not both. I'm not big on kick starting.

Don. You're making me now think about pulling that old bike out of the storage shed to get it started again. I'm curious if i can duplicate those numbers or maybe lower the ET some. I had an issue with it occasionally jumping out of 3rd gear so the transmission problem would need to be addressed before I would take it down the track. Of course if i pull the engine to split the cases, my high performance tendencies will overtake my stock motored mind and the whole experiment will blow up. Hahaha.

[scottly]

  I'd for sure want a lightened flywheel and the 17 tooth front sprocket back on.

No, you want more flywheel to launch off the line, and I would use a 16 tooth on front, unless you are running a rear sprocket with more than 48 teeth.
BTW, the rule of thumb is to multiply the 1/8 mile ET by 1.57 to estimate the 1/4 mile ET.
8.5 X 1.57 = 13.345

[dragracer]

I don't feel there's anything to gain from a lightened crankshaft in a dragbike engine personally. I can say i run a lightened rotor with the magnets removed on my mono shock bike. There just enough to bolt the starter clutch to it with sufficient taper to tighten the bolt to the crank. I  don't run a charging system so theres no need to have that weight hanging off the end of crankshaft.  I do agree with trying to use a smaller sprocket on the front, you get more benefits from the front than changing the rear.

[Don R]

 My old Honda guru Tom told me that he twisted the end off of his crankshaft running a stock flywheel,  that's where I got the lightened flywheel info.
  Tom told me once his bike ran .02 off the national class record, NHRA asked him to decide if he was willing to tear down if he went below it. I have that bike, but it was parted out by then and the engine is the 1124 that I pronounced DOA. It has a welded and warped case and junk cylinder and 3 good 72mm pistons,
   He got ALS and passed a few years ago, I wish I had spent more time and asked more questions. I rode one of his former stock bikes to an ALS benefit and his kids came out to take pictures of it. 

[dragracer]

My old Honda guru Tom told me that he twisted the end off of his crankshaft running a stock flywheel,  that's where I got the lightened flywheel info.
  Tom told me once his bike ran .02 off the national class record, NHRA asked him to decide if he was willing to tear down if he went below it. I have that bike, but it was parted out by then and the engine is the 1124 that I pronounced DOA. It has a welded and warped case and junk cylinder and 3 good 72mm pistons,
   He got ALS and passed a few years ago, I wish I had spent more time and asked more questions. I rode one of his former stock bikes to an ALS benefit and his kids came out to take pictures of it. 

The end of the crank on my F3 broke off because i left the rotor on it. I was only kick starting it so i never replaced the crank. Its still in the bike after being broken over  25 years ago. 💪

[Don R]

  That makes two that I've heard of.
   For the actual street bike, I wanted a lightened rotor to go with the Hondamatic alternator since I have it anyway.
  The other bike will run the magneto and no charging system but won't need to go any distance. I'll run an LED parking lamp in the headlight to keep it legal for daytime riding. The turbo might need a fuel pump though, that's a catch. The big mikuni might flow enough by gravity.

[HondaMan]

I broached the 1/8 mile topic once with my former employer (they had a company-sponsored dragster or two), mentioning a CB750 they had in the back room (it ended up on the cover of my book, years later...). I asked them what it might take to make that 750 shine in that distance and they all laughed and said the same thing: "More cubes. Cubes rule the 1/8 mile."

[scottly]

My old Honda guru Tom told me that he twisted the end off of his crankshaft running a stock flywheel,  that's where I got the lightened flywheel info.

The only times I've heard of that happening were using the early rotor with the thick flange, not the later rotors. The flange added about 1.25 pounds compared to a late rotor, and as I noted on the other thread, my K1 rotor had no balancing done to it.
Regarding the lightened cyclex rotor you mentioned, it will not provide as much power as stock, as material was removed on the inside, where it helps conduct the magnetic flux from the field coil to the rotor poll pieces. Notice how I only removed material on the outer edge of the rotor, and just a short bevel on the hub. Actually, I probably should have just left the hub alone, as any weight that close to the center has much less flywheel effect than farther away from the center.
   

[Tracksnblades1]

g
  That makes two that I've heard of.
   For the actual street bike, I wanted a lightened rotor to go with the Hondamatic alternator since I have it anyway.
  The other bike will run the magneto and no charging system but won't need to go any distance. I'll run an LED parking lamp in the headlight to keep it legal for daytime riding. The turbo might need a fuel pump though, that's a catch. The big mikuni might flow enough by gravity.

The local guy here when using RC Engineering big bore kits always had us remove the flywheel flange (Scotty’s pic) on an old LaBlonde  and rebalance afterwards. I only remember the 12.5 kits snapping the flywheel side off. Savage engine braking clutch in or out….and most cams in 12.5 motors went past 10k like it wasn’t there…

Most here ran 16/48 with 130/90/ 16 hog wheels. Inch or two longer swingarms. Lowering block on the rear shocks, handlebar set backs so you could drop the tubes until the side winder dragged (DRUG for our round here improper dialect).
12.5s rode on the street had oil coolers. Mandel bent steel lines for behind the Honda down tubes, and plug welded wet down tubes for custom chopper frames…Drag only or bar to bar had none…

I personally think the 16 front is too small of a circle for a 530 5/8 pitch chain to bend around. They’re noisy and the chain doesn’t last as long compared to a 17/18, But 18 is getting close if you’re running a cheap/junk chain..the 76f OEM sprocket is a very robust looking compared to an aftermarket 16 or 18…The hog wheel is a gear reduction its self and a lot of stock fresh motors would carry the front just with the throttle in first and early in 2nd with a stock length swing arm, especially the short k arm..

I think you’ll find a modern tire that can hook the high rpm shock load of a standard weight crank and fly wheel clutch dump.
I would definitely balance the flywheel and crank whether you go heavy or light…I’m sure you’ve already experimented tuning the launch before with heavy and light flywheels. Small front sprocket moves the torque to the chain. So have a good one…😁

[dragracer]

I've been thinking for several years about freshening up a bone stock 736cc engine and dropping it into my F3 chassis. Of course it would require a set of rejetted stock carbs and I'd be using my current sidewinder.. I'm curious to find out what  numbers i can get out of this setup in the 1/4 mile versus my built 1030cce gine.

[dusterdude]

Do it!!!!!!

Sent from my SM-G973U1 using Tapatalk

[HondaMan]

While we're mentioning alternator rotors, I have an off-topic question: does anyone know where I could get a CB550 flywheel balanced?

[PeWe]

The end of the crank on my F3 broke off because i left the rotor on it. I was only kick starting it so i never replaced the crank. Its still in the bike after being broken over  25 years ago.

-Did that happen at take off?

I can imagine a heavy sudden load when let go of the clutch at rather high rpm.

[dragracer]

The end of the crank on my F3 broke off because i left the rotor on it. I was only kick starting it so i never replaced the crank. Its still in the bike after being broken over  25 years ago.

-Did that happen at take off?

I can imagine a heavy sudden load when let go of the clutch at rather high rpm.

I was testing it on the road near my house. When i pulled back in the yard i noticed oil on my shoes. The cover was cracked so i pulled it off and the rotor dropped on the ground with the end of the crank still bolted in. I'm not exactly certain when it broke on that short ride.

[scottly]

That does sound odd, Frank. How did you plug the oil galley in the end of the broken off crank?

[dragracer]

That does sound odd, Frank. How did you plug the oil galley in the end of the broken off crank?

There was no stator inside the cover. Only the rotor was there bolted to the crank. At the time i  used a grinder to clean up the jagged edge but didn't give any thought to plugging the galley back then. Its been that way for over 25 years with no visible oil starvation problems anywhere. Thats not to say something isn't suffering and could show up when i tear it down this time. Maybe I've simply been lucky for 2 and a half decades.

[Don R]

  I don't recall seeing an oil flow chart but there isn't usually a lot of oil in the dyno. I do recall someone drilling an 030" hole in the crankcase oil plug to spray oil onto the starter clutch and gear.
  There is the oil seal on the starter gear, one of my bikes that ran a lightened flywheel with no starter retained the hub of the starter gear, I presume for the oil seal but that's the only one I've seen that bothered with it.

[dragracer]

  I don't recall seeing an oil flow chart but there isn't usually a lot of oil in the dyno. I do recall someone drilling an 030" hole in the crankcase oil plug to spray oil onto the starter clutch and gear.
  There is the oil seal on the starter gear, one of my bikes that ran a lightened flywheel with no starter retained the hub of the starter gear, I presume for the oil seal but that's the only one I've seen that bothered with it.

I wonder how much of a pressure drop is happening without the hole being restricted.  I could be subjecting  it to a 25 year slow death.

[Don R]

 I honestly hadn't noticed the oil hole in that end of the crank, it makes me wonder when the starter gear is left off, what happens? 
 I have two cut down flywheels for no starter, one was on a crank in a motor and it still has a cut down starter hub remaining, although it floats back and forth in a gap between the case and the flywheel it does cover the oil hole.

[scottly]

The oil hole in the center of the crank intersects a galley from the main journal, which has one end of the drilled hole sealed with a steel ball. If the steel ball is missing, bad stuff happens: ask Jerry. Normally, the hole through the center of the crank is sealed with the bolt that holds the alternator rotor on. I don't know if the hole is as big as the main galley. The cross-drilled hole that feeds the starter gear is about 3mm, but has a 1mm restrictor jet, so the loose fitting starter gear has no effect on oil pressure. The oil seal merely directs the oil out towards the side of the case, and away from the spinning starter clutch.     

[scottly]

Regarding the CX lightened rotor, notice how much material has been removed from the inside. This is where the field coil magnetizes both sides (north and south poles) of the rotor, and the increased gaps reduce that coupling, reducing charging system output.