Topic: CB750 AHRMA Sportsman 750 Racer

[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

[gschuld]

Yes that is a bummer.  And you were 98% done for the year with very little trouble😏

Let’s hope for damage limited to the obvious.

George

[Jerry Rxman Griffin aka MuthaF'er]

Well you sounded great on SATURDAY...….. plan on finding extensive carnage ie $$$. Good luck.

[turboguzzi]

Sorry to see that its a pretty big kaboom...
we are all eagerly waiting for that striptease show were all will be revealed

in these postmortems, not always easy to determine cause and effect,

recently had a piston in a DR350 loose two little chunks of crown/ring land, exposing the top ring to combustion and causing a light seize but still got home. have no idea how the two pieces got out without causing any damage...

new piston is in, bike runs great but still does my head not knowing why it happened.
check the valve relief area, it can be weak, sometimes can trigger a crack and then all goes belly up

[Rocketman]

Oh man!  That stinks!  Hope you find some good news when you tear it down.

[Old Scrambler]

Note that for the lash-cap to come off, the valve-to-rocker clearance has to be very wide..............is the collet-keeper still in place?

[slikwilli420]

Note that for the lash-cap to come off, the valve-to-rocker clearance has to be very wide..............is the collet-keeper still in place?

Keepers in place but with the valve bent the spring is partially compressed increasing the lash allowing the cap to come out. More pictures and info once I'm back at my computer.

[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.

Gonna have to rethink that response.

[gschuld]

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.

Gonna have to rethink that response.

😂

[RAFster122s]

Mike, you think the head may be a big paperweight? I hope not...

[slikwilli420]

Well, as it turns out, the damage is extensive and severe. I need to have the head assessed by Mike but it may not be worth saving if the cost to do so is the same or higher than having a new head done. I am considering going back to stock valve stem diameters, but will discuss with Mike before making the decision. I really don't know the cause yet, but did find that the Cappellini cam chain tensioner was completely destroyed, and likely over a very long time. I have to wonder if a piece got somewhere on the top end and caused the exhaust valve to seize which then caused the holed piston, which then caused the broken intake valve. Not much more to say at this point, pictures are worth far more than 1000 words.

[turboguzzi]

sorry to see this... will not be easy to determine what caused what.... If i get it right, cam chain was not broken and i also dont see any valve-pisotn  touching signs on the  neighbor hole
So i think you can rule out the capellini idler blame
But surely the steel pieces missing from it must have been sloshing around in the oil...

try to look under a magnify glass in the break points of the valve stems. if it was a clean break, then they should be bright. if it was a crack there that developed over time, then you'd see an "darker" part  in the break area. im totally against thin stems. I measured marginal improvement in flow but surely weaker and with a rocker arm that puts side loads on it less well supported by the guide (less bearing area). Maybe acceptable in dohcs that push the valves straight, not in our sohcs.
Check your other valves for play in guide. might be that valve was already loose in it, hitting seat out of concentricity creating bending forces where you see the break in the stem.

[slikwilli420]

sorry to see this... will not be easy to determine what caused what.... If i get it right, cam chain was not broken and i also dont see any valve-pisotn  touching signs on the  neighbor hole
So i think you can rule out the capellini idler blame
But surely the steel pieces missing from it must have been sloshing around in the oil...

try to look under a magnify glass in the break points of the valve stems. if it was a clean break, then they should be bright. if it was a crack there that developed over time, then you'd see an "darker" part  in the break area. im totally against thin stems. I measured marginal improvement in flow but surely weaker and with a rocker arm that puts side loads on it less well supported by the guide (less bearing area). Maybe acceptable in dohcs that push the valves straight, not in our sohcs.
Check your other valves for play in guide. might be that valve was already loose in it, hitting seat out of concentricity creating bending forces where you see the break in the stem.

The lack of favor of thinner stems keeps coming up with a number of racers in AHRMA talking about bikes eating 5mm stem valves and having to use stock diameter stems to combat this. The strength of a stock stem has to be significant compared to a 5mm unit, given the same material and manufacturing specs. Id gladly swap some flow for much higher reliability in this department. Its going to be tough making this right and preparing for next seasons run at a championship but I will do my best. When Mike gets the head he can check the other stems but I am definitely leaning toward stock stems in the oversize for the intake.