Author Topic: CB750 Racing (Read 32724 times)

JohnN · « **Reply #125 on:** May 27, 2015, 04:30:07 PM »

Alan:
I'm glad you enjoyed it! I followed you around the back section and you had good lines through 7 & 8 and had good speed going up the hill into blind turn 9. Unfortunately I think you will find that the left side case will have to go away soon; hope you're not to attached to that electric starter! Maybe you can machine some parts to keep the starter and reduce width?
John

Haybus · « **Reply #126 on:** May 27, 2015, 04:56:38 PM »

I just need to wean myself off the chicken lever and go faster.

John, you removed the starter for weight or because it isn't compatible with your narrow alternator? What are my options here? Remove the alternator or buy a mini external like yours. Can I remove the alternator and keep the starter by machining a carrier plate for the starter gear? I'm out of town this week so I don't have a chance to dig into it. Figured I might have a peek this weekend.

Alan

JohnN · « **Reply #127 on:** May 27, 2015, 05:06:13 PM »

I removed it for cornering clearance. The modifications I have seen don't have a provision for retaining the starter drive gear, so you may have to invent something! A CR750 cover also loses the drive gear, so I opted to go with the CycleX exposed alternator. It fits within my fairing like the original CR part.

gschuld · « **Reply #128 on:** May 27, 2015, 07:50:40 PM »

I was wondering a bit about cornering clearance and at what point that alternator cover starts becoming a real limiting factor. Regarding the electric starter, Rob (Voxonda) is running a unique arrangement where he mounts his alternator over his front sprocket and runs a short belt from a small pull mounted outboard of the front sprocket. This separates his alternator from the crank completely. So if you wanted to use that system you could retain a factory starter and just shorten the factory cover to basically what the cr750 covers looked like.

There would be no charging at idle, but it probably isn't such a big deal for a road racer.

George

turboguzzi · « **Reply #129 on:** May 30, 2015, 05:12:37 AM »

george, plenty of us run total loss ignition off the battey, no charging, not a problem at all in a 20-25 min race..... Voxonda's bike is an endurance racer that needs to run lights and for a long time.
you seem to be looking for more work to do rather than less

in al my race bikes that will never see the street again i removed the whole alternator and just run a thin protective cover.
that said, if bike is setup right in temrs of suspension height, youll have to be going pretty fast already to drag the alternator.

voxonda · « **Reply #130 on:** May 30, 2015, 07:15:24 AM »

TG,

Dragging a alternator on the 750 is not that hard at all. Take in consideration that the 750 is a lot wider than a 500 four. Even when I lifted the bike 2,5 cm use longer shocks (+30mm) the oem alternator bottom out and believe me the suspension is set up like it should be, even if a bit on the hard(er) side. And even now with the alternator narrowed by 50 m/m the hump to protect the crank touched the ground. I know that I have two more than average riders, one multiple dutch champ and winner of several 24 hr races and international podiums in the late 70's.

PS. have no pic taken at the most demanding corners.

Cheers Rob

turboguzzi · « **Reply #131 on:** May 30, 2015, 08:30:16 AM »

"I know that I have two more than average riders, one multiple dutch champ and winner of several 24 hr races and international podiums in the late 70's."

that's what i meant by pretty fast Rob

our friend george is hitting the track for the first time.... so let's say that if he'll be dragging it it will be a sort of badge of honor!

Haybus · « **Reply #132 on:** May 30, 2015, 09:12:42 AM »

I too am guilty of "looking for more work to do rather than less" I've been looking at narrow alternator solutions, or belt drive solutions in an effort to keep my starter and charging system. I do like the starter, but I watch John fire his bike with a single kick, remove the kick start arm, and off he goes. So maybe simple is best. Longest I would ever run this bike is 20 minutes or so, with 1-2 hours between track use, on a normal race weekend. I have a jump battery to top up the bike battery between on track times. So maybe total loss is my best approach. It's certainly the easiest solution. Any issues simply loosing the alternator?

Alan

voxonda · « **Reply #133 on:** May 30, 2015, 09:46:45 AM »

Quote from: turboguzzi on May 30, 2015, 08:30:16 AM

"I know that I have two more than average riders, one multiple dutch champ and winner of several 24 hr races and international podiums in the late 70's."

that's what i meant by pretty fast Rob

our friend george is hitting the track for the first time.... so let's say that if he'll be dragging it it will be a sort of badge of honor!

So true.

Old Scrambler · « **Reply #134 on:** May 30, 2015, 10:21:25 AM »

Lost the dyno............kept the starter. We did not cut the end of the crank..........so dyno can be installed if needed. No problems with on-board battery for the ignition...........we use a separate battery to jump the starter. Some of the newer lithium jump-start units will also run the starter.......and charge your cell-phone

voxonda · « **Reply #135 on:** May 30, 2015, 11:22:01 AM »

Yes, a bit like mine. No cut of crank, made a collar with both ends o-rings to cloe the oil hole from the crank.

gschuld · « **Reply #136 on:** May 30, 2015, 04:15:25 PM »

Quote from: turboguzzi on May 30, 2015, 08:30:16 AM

our friend george is hitting the track for the first time.... so let's say that if he'll be dragging it it will be a sort of badge of honor!

Oh for sure. Assuming, of course, I don't drag it hard enough to unload the tires and low side it in a tight turn.

I just like to think ahead, and learn as much as I can. That's a lot of the fun for me anyhow.

George

Haybus · « **Reply #137 on:** May 30, 2015, 08:05:13 PM »

Excellent pictures guys. Really appreciate those.

Rob, does the collar with the O-rings make that a dry enclosure, and if so do you still run a cover? Maybe just to protect the crank end? I'm assuming that was the cover with the ground off end in the first picture, but wasn't sure if that was another bike.

Dennis, what retains your starter ring gear with the alternator removed? Maybe just a simple spacer? Would you happen to have a picture with the cover removed? I'm sure it will be clear once I pull the alternator off.

I'm not really in a hurry to fix the alternator issue, just kind of planning like George says. My frame slider sticks out quite a bit so I can get some decent additional clearance that might get me through another round before I get brave enough to start dragging other stuff. Looks like my pegs, shifter and pan need a little attention about the same time at the alternator cover.

My wife asked if I was going to tear my bike apart after every race weekend. Apparently so

Alan

johno · « **Reply #138 on:** May 30, 2015, 10:52:31 PM »

The area is a wet area and needs to be sealed off somehow, ie a complete cover over the whole area including crank or if the crank protrudes through the cover it needs a seal to stop oil coming past the crank, the crank has a hole in that lets the high oil presssure lube the starter bush on the big starter gear so if no starter gear run you need something to block off the oil pressure hole, Rob used the alloy sleeve with o rings , I used two seal surface reclaimers, one was to block the oil hole the other was to put more pressure on the seal in the side cover, as per pic,
cheers johno

voxonda · « **Reply #139 on:** May 31, 2015, 02:10:32 AM »

Quote from: Haybus on May 30, 2015, 08:05:13 PM

Excellent pictures guys. Really appreciate those.

Rob, does the collar with the O-rings make that a dry enclosure, and if so do you still run a cover? Maybe just to protect the crank end? I'm assuming that was the cover with the ground off end in the first picture, but wasn't sure if that was another bike.

........................................................................

Alan

Hi Alan, yes the o-rings seal it off perfect;y but it is still a wet area like Johno says. In the early days we sometimes welded the lower casing shut and ran without cover. But even an innocent slide could destroy the cranks so for years now I run with cover s an extra protection. And imo it looks better too.

Cheers rob

Old Scrambler · « **Reply #140 on:** May 31, 2015, 05:56:17 AM »

The starter gear is held by a retainer...........we use a starter motor from a CB900C. The alloy 'cover' was made to protect the pigtail and smooth the rotation 'air' inside of the outer cover.

bwaller · « **Reply #141 on:** May 31, 2015, 07:56:13 AM »

Before I cut the crank stub off I made a similar cover. Eventually I made a piece out of Delrin to slide over the alloy tube covering the stub. In a left side crash that cover can still be damaged and contact the crank...or worse. The delrin is hard enough to tap and install with screws from the inside of the cover and certainly is tough to prevent get-off damage there. I couldn't find a picture but I'll look later.

Haybus · « **Reply #142 on:** June 06, 2015, 10:00:13 PM »

Finally had some free time to tidy up the alternator. Made a sleeve with O-rings either side of the cross hole in the shaft, and an O-ring on the bolt end. I think the oil flow is safely stopped up. 3/8" plate for a cover with a bolt on shaft cover. The cover has and O-ring that goes into the bore in the plate and the bolt holes are blind. Don't think it will leak either. Weighed all the parts when I was done and I took off around 18 pounds. Weighed the bike right before tear down and it weighed a portly 460 pounds with half tank gas and full of oil. Next up I'm going to trim my belly pan, again, to get a little more clearance. After that I think the exhaust will be dragging, but I don't think I'll get that far over by the end of this season.

Alan

Haybus · « **Reply #143 on:** June 08, 2015, 08:50:54 PM »

Got the bike all buttoned up tonight and fired her up. Wow, she really revs freely now. Even had to lower the idle a bit. Fires right up with a quick stab of the kick starter. I'm very happy. Before I put oil back in I decided a little lean test was in order to see where I'm at. I checked it all over with a straight edge and chalk lines on the floor, but I just don't get the feel of how far over it really is. So I just couldn't resist. It's pretty cool to see it leaned over that far. I didn't end up trimming the pan yet and it's about 1/4" from touching in the picture. Front end it ratcheted down as far as I could get it. That's 48 degrees lean. Seems like a good number, no? I'm not saying I plan to be at 48 degrees all the time, just wondering if that's reasonable. Probably better if I learn to get off the bike more and keep her a bit more upright anyways. I've read that most modern sport bike rubber, like pilot powers, are only rated for 50 degrees on dry pavement. I can't imagine those Avons can take more than that? Doesn't seem like much though when you watch the telemetry on MotoGP bikes hitting 62, 63... But as said before, I'm no Mick Doohan, let alone Marc Marquez

.

Forgot to add the picture.

Alan

JohnN · « **Reply #144 on:** June 09, 2015, 05:38:08 AM »

Nice work Alan. Part of the reason I raised the rear so much was for cornering clearance; you may not have to raise as much with this modification.
John

teebee67 · « **Reply #145 on:** June 28, 2015, 12:58:00 PM »

Don't forget that ground clearance leaning the bike over in the garage will be a lot diferent than on track with rider's weight and cornering forces loading up the suspension.

turboguzzi · « **Reply #146 on:** June 28, 2015, 01:30:15 PM »

under the centrifugal loads suspension compresses easily to middle of the stroke.

so on top of the 45 degs lean you need to add a parallel offset of some 50 mm, just add a block of foam

second tip, no need to lean the bike and risk an hernia.... get a large plywood plank, press it against the wheels and tilt it

Haybus · « **Reply #147 on:** June 28, 2015, 10:21:58 PM »

She definitely revs a lot higher now. Makes for a bit different gear choices than what I was using previously in some corners. Saw the 9000 rpm shift light quite a bit, where I didn't before removing the alternator. My tach bounces a bit at the high rpm's though, so I'm not real sure how high she was going. Need to call speed hut and see what I can do to quiet down the signal from the Pamco ignition and calm down the tach a bit.

I left the whole right control switch with the start button in tact, but capped off the wires that used to go to the starter solenoid. My pit mate turned on the ignition switch and hit the start button and blew my fuse right before the first race on Sunday. I kicked and kicked, then he pushed me before I realized the fuse probably blew. Quickly swapped it out but I was too late to take a lap, had to go straight to grid. Then John has some problems right before the start, needing to get push started out of his grid position a couple times only to lock up his transmission about 50 feet past the start. I felt real bad seeing that happen. I hope you get it sorted out for the next round John.

The Lord Moon Pie (ex) bike made it's debut this weekend. That's a really cool machine that catches a lot of eyes with the very distinctive paint job. Needed a bit of sorting over the weekend, but she finally made some good laps during the second heat on Sunday.

Alan

Haybus · « **Reply #148 on:** July 16, 2015, 06:47:00 PM »

Been looking for a spare frame and motor for awhile now, but they just don't come along that often. Another 75 no title bike, and it was only 5 miles away. Might have to build it into a complete 2nd race bike, but do some motor work this time around. Those floor boards might be just the ticket for the track, with a little relocation of course

. And that seat!! Oh man that's going to be comfy on the straights, and super stylish too.

Alan

Haybus · « **Reply #149 on:** August 03, 2015, 08:37:13 PM »

Delayed update from last race. Ran really strong most of the Saturday practices, but started running rough on the last lap of the 2nd practice. My times were good (for me

), and I felt better than ever. Spent a good portion of the afternoon diagnosing a dying ignition. Was intermittently loosing 1 & 4. After a lot of rewiring/soldering I was about to give up and work the track on Sunday and John loaned me a spare, but questionable ignition. What the heck, worth a try. That John is a great guy!! Wired up the new ignition and fired her off at around 8:00 pm to a round of applause from the pit next door. Slept well knowing I should be able to race. But once I was able to run the bike in the pits she wouldn't rev past 5k. Ran in the races anyways, and I think I learned a little bit about carrying corner speed. It was rough not having the motor to rely on out of corners or on the straight, but was still super fun as always.

Sold the bike I bought recently to another racer friend who is stepping up from 250 to 750 next year. So I bought a pair of K and A motors to work on over the winter, both with 392 heads. Don't really care about the auto, but it was too cheap to pass up. Not planning on going crazy with this motor build as I like mid range power and reliability. So how much better are these heads than say the '75 head on my bike? Do they support more cam lift as is or do they still need port work to wake them up? Was planning on getting the 12.5:1 +1mm pistons, but maybe that's futile without a decent flowing head first? The springs in these heads are stronger, but are they strong enough or am I better off with race springs/beehives? That's the beginning of my questions.

Alan

News:

Author Topic: CB750 Racing (Read 32724 times)