Topic: CB750 AHRMA Sportsman 750 Racer

[scottly]

With heat, the clutch cover is expanding away from the pressure plate, also. My best guess is there is not enough range of lateral travel to allow for temperature changes; have you tried to measure it yet? Factors involved include adjustment at the clutch cover, adjustment in the cable, and play/ratio of the hand lever.

[slikwilli420]

With heat, the clutch cover is expanding away from the pressure plate, also. My best guess is there is not enough range of lateral travel to allow for temperature changes; have you tried to measure it yet? Factors involved include adjustment at the clutch cover, adjustment in the cable, and play/ratio of the hand lever.

Ok, I'll buy all that. But why am I the only person that's ever had this issue? Im not making more power or riding harder than others who have raced these bikes. No one has a solve because no one has ever heard of this problem.

[bear]

With heat, the clutch cover is expanding away from the pressure plate, also. My best guess is there is not enough range of lateral travel to allow for temperature changes; have you tried to measure it yet? Factors involved include adjustment at the clutch cover, adjustment in the cable, and play/ratio of the hand lever.

Ok, I'll buy all that. But why am I the only person that's ever had this issue? Im not making more power or riding harder than others who have raced these bikes. No one has a solve because no one has ever heard of this problem.

No your not the only person that's had this issue.

[slikwilli420]

With heat, the clutch cover is expanding away from the pressure plate, also. My best guess is there is not enough range of lateral travel to allow for temperature changes; have you tried to measure it yet? Factors involved include adjustment at the clutch cover, adjustment in the cable, and play/ratio of the hand lever.

Ok, I'll buy all that. But why am I the only person that's ever had this issue? Im not making more power or riding harder than others who have raced these bikes. No one has a solve because no one has ever heard of this problem.

No your not the only person that's had this issue.

Feeling like I am since no one has a fix. Im pulling the rest of the clutch out tonight. Kenny at Cycle X thought it could be related the the clutch basket/washer/clip. Im going to go through each part and make sure they are all correct relative to early vs late parts. Still baffling that it was fine all year then boom, issue. Now it won't go away. I hope its not something deeper in the engine. Its getting a full tear down after Barber but that doesn't much help me now.

[bear]

There's no sense in me repeating myself so I'll just offer this.
Running around in circles waving your hands in the air listening to six of us at the same time is not going to achieve anything.
Be a bit methodical, it is a clutch issue so don't go off in a tangent.

I am not a mechanic, I am not an engineer, I have had the same issue on a number of occasions.
But the underlying problem was not the same. Only the symptom.

If I was confronted with this issue now, I would replace the fibers and steels. (preferably with OEM)
Replace the springs with good HD units.
And double check that actuation components have not been mix and matched.

Then I would make sure that I ran the clutch in before I tried to race with it.

I would adjust as per the book before and after the run in.
I would avoid any adjustment while the motor is hot.

But as I said earlier you tread your own path.
 
 

[slikwilli420]

There's no sense in me repeating myself so I'll just offer this.
Running around in circles waving your hands in the air listening to six of us at the same time is not going to achieve anything.
Be a bit methodical, it is a clutch issue so don't go off in a tangent.

I am not a mechanic, I am not an engineer, I have had the same issue on a number of occasions.
But the underlying problem was not the same. Only the symptom.

If I was confronted with this issue now, I would replace the fibers and steels. (preferably with OEM)
Replace the springs with good HD units.
And double check that actuation components have not been mix and matched.

Then I would make sure that I ran the clutch in before I tried to race with it.

I would adjust as per the book before and after the run in.
I would avoid any adjustment while the motor is hot.

But as I said earlier you tread your own path.

Not waving my hands at all. I appreciate the feedback from everyone who has taken the time to respond. I have replaced the fibers and steels with known good units (twice, and the original was new steels and fibers as well), including the springs (though have never gone the HD spring route, top of the list now). The actuator parts are the same ones that have been on the whole time, and do not have any excessive wear or looseness between them. I will keep pulling this thing apart and examining the pieces until something sticks out as the culprit.

[754]

If its heating and slipping, increase adjuster clearance.
 When I installed my 78 F motor, I had clutch clearance wrong, bike warms up, it slips.
 Increased clearance , problem solved.. ( my supposed memory,  made me adjust it too tight. )

[slikwilli420]

If its heating and slipping, increase adjuster clearance.
 When I installed my 78 F motor, I had clutch clearance wrong, bike warms up, it slips.
 Increased clearance , problem solved.. ( my supposed memory,  made me adjust it too tight. )

Not slipping Frank, the lever is getting loose. It gets so loose that I have a hard time shifting once it gets to the end of the race.

[754]

 Spin your starwheel free play adjuster at lever, during the race. .
 Whatever it takes to get thru..
 What kind of lever, a dogleg may have less travel.. mod lever for more travel.

[Tintop]

My understanding is the only thing not stock (steels/plates/springs aside) is the clutch cover you machined,and the billet lifter plate.  Have you checked these against stock pieces for changes, could there be flexing as it gets hotter in a race, causing the adjustment change? 

[scottly]

Yeah, Bear. Matt, measure the damn amount of lateral travel in the lifter mechanism. At least it's something that can be measured easily. If it's too little, the problem may be at the hand lever end. I had a problem with my bike that turned out to be a worn pivot hole in the K1 lever, plus a worn pivot bolt. There was 1 inch of free-play at the end of the hand lever before the cable started to move.

[slikwilli420]

My understanding is the only thing not stock (steels/plates/springs aside) is the clutch cover you machined,and the billet lifter plate.  Have you checked these against stock pieces for changes, could there be flexing as it gets hotter in a race, causing the adjustment change?

Clutch cover only had the bungs for the cover removed and kicker hole plugged. The billet lifter  plate needs to be looked at.

Yeah, Bear. Matt, measure the damn amount of lateral travel in the lifter mechanism. At least it's something that can be measured easily. If it's too little, the problem may be at the hand lever end. I had a problem with my bike that turned out to be a worn pivot hole in the K1 lever, plus a worn pivot bolt. There was 1 inch of free-play at the end of the hand lever before the cable started to move.

Movement on the actuator arm is about 60 thousandths. I pulled the clutch apart and noticed about 25 thousandths of lateral play on the bigger shaft that the clutch basket rides on. That seems like a lot of movement. Kenny is looking at parts in the shop to see if he can replicate that movement. Hopefully not missing something deeper in the trans.

[bwaller]

I always find a little extra play at the lever after a race, normal me thinks.

Just throwing this out there.....if there are only a couple modified parts from stock, replace them with stock for a race to see if there's a difference.

I've made a bunch of changes with primary drive and clutches and yes there are teething issues.  Hang in there, you'll get it sorted.

[slikwilli420]

Back from Little Tally, the second to last race of the 2019 season, with only the big show at Barber to go. I am solidly in 2nd place in points so feeling pretty damn good any way the next month goes.

Tally was the bro trip my brother and I had been planning all season. Burning fuel at an alarming rate (about 9.5mpg towing the trailer) we stopped a total of 14 times for gas in a 1550 mile journey. But we still had time to hit a favorite brewery of ours in Nashville on Thursday night. Arriving a little before dark, we got all set up and headed to bed.

Friday came nice an early and we were up and through tech in no time (1 tech all weekend now instead of 1 each day). He was practice group 2 and I was 3. He has been fighting ignition issues all year related to the battery and is now on a self-generating PVL system, which ran flawlessly all weekend.

I was hopeful of the new clutch fixing my woes but as the weekend wore on, the clutch loosening continued, though I never did miss a shift because of it. I have a Pro Taper Profile clutch perch on the way to try, so I can adjust on the fly via a large thumb wheel. I found that getting the bike hot in a scrub lap right before the race allowed me to pull a bit more free play out and I was good through the race. That is a bandaid and not something I wan to continue, but I only need to make it through Barber before the engine comes down to every nut and bolt for a look over.

Practice sessions on Friday delivered lap times below my race times of last year, which makes me quite happy, and of course there is always more to be had during the race.

My first race on Saturday was my bump class into Formula Vintage. Bike classes include Sportsman 750, Formula 500, Formula 750, Vintage Superbike Heavyweight, and some fast 2 stroke machines. I was running with a more modern RZ350 and a guy on a CB900F, both of which are AHRMA champions multiple times over. I thought I pulled out a 3rd on Saturday but the guy in 1st was so far ahead we never saw him. Apparently an ex-pro and a Schwantz racing school instructor. Go figure.

My class, sadly, only included me both days, so all I had to do was not f*ck up and I would get my 1000 points per win. And I did just that, working more on technique than all out racing and feeling good about it. That fact was the biggest reason I bumped classes, so I didnt drive 1500 miles with no one to race.

The awards ceremony on Saturday was my brother's first wood and was pretty pumped. It was awesome to be there to share that moment with him.

Sunday came and it was a near facsimile of the Saturday session, though slightly more bearable heat wise, but still running right around 95 all day long. I placed 4th in Formula Vintage again, 1st in S750 (duh) and my brother grabbed another 3rd.

Beer + bikes = happiness:


Your boy in his new Honda hat:


Nice right side shot of my at speed, which I have so few of:


Its the wood that makes it good:




A laundry list of items to take care of before Barber sits in front of me, including going back to my Conti 3CR tires, engine maintenance and a few other items.

22 days...

[dragracer]

Now that's what I call an outstanding weekend.  Spending time with your brother is priceless and placing for both of you is an added bonus. I'm working on a bike right now for my older brother to race so we can spend a little more time hanging out together.  Nothing like family unity when you combine it with our passion for racing.

[gschuld]

Now that's what I call an outstanding weekend.  Spending time with your brother is priceless and placing for both of you is an added bonus. I'm working on a bike right now for my older brother to race so we can spend a little more time hanging out together.  Nothing like family unity when you combine it with our passion for racing.

That’s great Matt.  Good to bond with family, even better when doing an activity you both enjoy.

George

[RAFster122s]

Great news on a great weekend racing. Hope the trip to Barber and the racing goes well for you.
David

[MRieck]

Yes......good luck at Barber.

[slikwilli420]

Thanks guys! Im really looking forward to the new race surface and all the fun Barber has to offer.

Yes......good luck at Barber.

Thanks Mike. The head will be coming your way for a look over just to make sure its good for another couple years of racing duty. Hopefully you can pencil me in during the offseason.

[MRieck]

Thanks guys! Im really looking forward to the new race surface and all the fun Barber has to offer.

Yes......good luck at Barber.

Thanks Mike. The head will be coming your way for a look over just to make sure its good for another couple years of racing duty. Hopefully you can pencil me in during the offseason.

I look forward to it.

[CBJoe]

Hey Matt...nice meeting you (though briefly) how were your overall results at Barber?  Jerry, Dennis and I were cheering you along one of the turns Saturday

[slikwilli420]

Welcome back race fans! The 2019 season is officially closed out and the results are in! I finished 2nd place in points in the Sportsman 750 class. I ran 12 races this year, visiting Roebling, NOLA, Road America, Gingerman, Talladega and Barber in the process. It has been a great 2019 and of course I am already prepping for the start of the 2020 race season, a short 5 months away.

Barber was a great time and always brings out the best in every rider and every machine, and this year was no different. I practiced Thursday so I had time to enjoy the swap meet on Friday but had enough time on track to feel really good about my prospects. It turns out that I had rear shock springs twice as stiff as was needed (they had apparently been built with side by side springs) and after lunch on Thursday, I got swapped to the correct 2.2kg springs from the original 4.5kg springs by Matt at Race Tech. He is a really stand up guy and helped get the rear dialed in. The last 2 sessions of the day were on new springs and the bike certainly felt more compliant and did a nice job of soaking up the bumps (though on the fresh tarmac, they were few and far between).

I was race 16 of 18 both days, so there wasnt much to do but wait around. Still having some clutch issues, I made a move to get the bike good and hot, then tune the clutch so there was less to worry about during the race. It seemed to work well both days, with only hints of clutch issues rather than fighting it every lap. That will hopefully all be corrected during my full tear down which starts very soon.

Race time on Saturday was really exciting with everyone getting ready to finish strong for the season. I was on the front row based on points, and got my typical slow start, and by T1 was near the back of the field but once I get going, the Honda 750 power started to shine strong. I was able to make my way up to a battle between two strong guys, one on a Yamaha XS and another on a Triumph triple, both very fast. As I was working on the Triumph I was passed by the XS and now had 2 guys to make it through to get on the podium. I eventually made a few choiceful passes and locked in my 3rd place, though both finished only a couple seconds behind me. Nothing like knowing you are being hunted to make times drop! 1:52 lap times in practice (about 4 seconds faster than race times last year) made way for times in the 1:50 range.

The clear skies of Saturday left to allow the first rain on the new track to come our way. We dealt with rain for most of the evening and it resulted in some slick conditions for the first half of Sunday. My race, being later in the day allowed lots of rubber to be laid down and made for some very sticky track conditions, perfect for going fast!

Race time on Sunday was similar to Saturday, with a few warm up laps to get the clutch hot and adjusted. I had a far better start on Sunday and found myself mid field as we exited T1, mixing it up with the Motard guys that were in our wave. I need to be more aggressive with my passing as I felt I lost time trying to get around some of those guys. I was half way through the race in a solid 3rd place when going through T2 I heard the most awful bolts in a tin can noise and chose (wisely) to pull off the track and get out of the way. As it turned out the #2 place racer had pulled off with a mechanical so I was actually in 2nd! Oh well, that's the race game. I have not been inside but I suspect it was a tappet adjuster nut that came loose as I head the same noise after a quick fire up in the pits. Hopefully it didn't do too much damage inside there but we will have to wait and see.

The drive home was uneventful but I have started formulating all my thoughts and tasks on what to get done before next season.

The list:
Head checked over by Mike Rieck
Install new primary chain tensioner
Install new trans, primary gear and clutch hub
Revise breather for engine so I can remove the carb bowls without removing the breather lines
Mount new seat
New magneto ignition, then I can ditch the battery and extra wiring
Paint bodywork
New front brake rotor (found a few cracks between holes after Barber)
One piece front rotor carrier
100 other little things I can't remember right now

Waiting for the 2020 schedule to come out then the official countdown begins!

[turboguzzi]

Good to hear you finished 2019 all in one piece, even if bike not quite so , congrats!
Needles to say, a loose tappet nut is something that shouldn't happen... ditto for your clutch issues. so go find the root case before jumping on other improvements. having no DNFs is more important than any 0.1 sec you shave through upgrades.

[slikwilli420]

Well, the last race of the season brought a DNF, caused by what I thought was a loose tappet and a nut bouncing around the valve train. How wrong I was!!

I began pulling the bike down and after pulling the carbs went to plug each intake with a paper towel to keep crap out, 1 looks good, 2 looks good, 3 looks good, 4 looks... holy sh*t what is that!!

I found a HANDFUL of aluminum chunks, some as big as a dime, just sitting in the intake boot. I scraped all of that out and onto a rag, pulled the exhaust and emptied that out, only to find a smaller handful of smaller pieces had made their way into the collector.

I pulled the tapped caps and did find that the exhaust lash cap was sitting next to the valve spring and the tappet was quite loose because of it, but the keepers on the valve looked intact and still seated in the retainer. The exhaust valve is completely destroyed as seen through the exhaust spigot.

The carnage:








No telling how bad it will be until the head comes off but Im guessing the chamber is peppered with the remnants of my piston, which is now fully ventilated on the top of the crown. Thinking at a minimum new piston, exhaust valve (possibly intake too), combustion chamber damage to be welded and smoothed, and possibly cylinder damage that may be too great to fix, necessitating a new sleeve or simply a new block bored to spec.

I will be pulling the engine tomorrow night and should have the head off for more carnage pics.

[RAFster122s]

Oh man, that is awful!  Sorry to see this happened. Hope it isn’t too extensive andglad it was not the cam.
David