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post #1 of 12 Old 07-18-2011, 9:38 AM Thread Starter
 
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gear problem

I amnot forsure where to start but I have looked around and can't find an answer. When I am steady accelerating and shift to 2nd gear I can only go to 7k rpm. then it drops to nuetral. If I only 1/4 to 1/2 throttle I can go all the way to read line. Has anyone else had this problem or heard of this. it only happens in 2nd. what is the fix if you have had this or heard of it.
thanks
Joe
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post #2 of 12 Old 07-18-2011, 2:10 PM
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Re: gear problem

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Originally Posted by Joey B View Post
I amnot forsure where to start but I have looked around and can't find an answer. When I am steady accelerating and shift to 2nd gear I can only go to 7k rpm. then it drops to nuetral. If I only 1/4 to 1/2 throttle I can go all the way to read line. Has anyone else had this problem or heard of this. it only happens in 2nd. what is the fix if you have had this or heard of it.
thanks
Joe


Sounds like worn dogs.

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post #3 of 12 Old 07-18-2011, 8:53 PM
 
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Re: gear problem

Agreed.
Most bikes use a shifter drum as the "brain" of the gearbox system. This drum has like serpentine cuts in it that through pegs control the respective shifter forks.

For a variety of reasons on most bikes the setup goes awol in 2nd first and sorry to say there is no quick fix or cheap fix.

What i CAN tell you is that there are those that can run forever on a set of fork/pegs/drum...and there are those that will wear it to smithereens in no time flat.
To really take advantage of a straightcut box means that you have to be engine savy,at least to some degree,and the sorry truth is that most are not.

If and when you have this apart be aware that the tolerances for the pegs and cutouts in the drum are most likely less than you would think.



This is said drum for an FZR Yamaha that behaved in exactly the same manner you describe. Notice the amount of wear in the cutout? Most hondos look approx the same.
Another culprit that might amount to the same fault is a bent shiftfork,which is what this drum controls a set of...via said pegs which are hardtailed into each shifterfork...and then of course the "locks"(dogs) on the gears themselves.
The shiftforks move like plates that are grossly serrated with "teeth" and these plates hook up to the mating set on each gear as you move respective shiftfork.(aka Dogrings)

Anyways. The wear of the shifterdrum in the pic was enough to make said FZR throw second into "neutral"(which it in reality is not) at WOT.

Last edited by Racing; 07-18-2011 at 9:28 PM.
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post #4 of 12 Old 07-18-2011, 9:03 PM
 
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Re: gear problem

Btw.



This is the selector side of the drum above. This is what your shifter mechanism affects. It either rotates that star wheel in the pic up or down-dependant of how you use the gearlever.(Shifter lever axle goes into the hole -bottom left and then runs through the entire block out the left side of the engine/box http://www.102983.org/gallery/albums/userpics/10003/10%7E5.jpg )

...and....



Here are the two axles with their respective straightcut gears and the "shifterplates" with their "pegs". The axle end that protrudes out the block closest to us in the picture is what the clutch is bolted to btw,and at the upper left corner the other axle protrudes as well...and that is where we put our primary sprocket for the drivechain.

In contrast to most boxes for racecars a bike has the primary drive just by the clutch btw. Just for sake of comparsion

Last edited by Racing; 07-18-2011 at 9:38 PM.
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post #5 of 12 Old 07-18-2011, 9:08 PM
 
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Re: gear problem

..and finaly...



These are the fabled shifter forks. I hope this pic gives you an idea of how the drum moves the forks via those pegs that are basicaly nailed into them. Forks are often aluminium while the pegs themselves are normaly steel. As you can see by the pic the two axles are installed atop of the forks on this bike.

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post #6 of 12 Old 07-18-2011, 9:25 PM
 
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Re: gear problem

Speaking of which,when you inspect dogs on gears as well as plates be rather anal about it. The dogs should look rather square no matter how you turn m so to say and whats more..gears or plates that show pitting is up for replacement. The "corner" of each dog should be reasonably sharp. Not knife edge sharp,but "dull" sharp for lack of better explanation.Rounded either means recutting,if ample material is still there,or into the bin and replace with fresh pts. If particular pts are surface hardened ONLY...that rules recutting out if you dont have a hardening company around.(Which might be a good idea anyways if racing is your game)
When you inspect both the gears and shifter dogrings try to have in mind how they work together to get a better idea of which standard so to say to strive for.

Forks in turn should look unison in angles. Ie;if one "leg" of a given fork points another direction than the other-replacement time. Also check freeplay for each dogring with the entire enchilada installed(Ie;drum,forks,axles..the whole nine yrds). As such the amount of freeplay on each side of each dogring should be REASONABLY the same. This is a rather surefire way of knowing that your shifterforks are not bent.

Only times you dont right off the bat replace stuff worn when inside a box like this is of course with rare or scarse parts/bikes. Then..it comes down to what machining abilitys youve got around to make it all work again.
After all...if youve seen one...like in the pics above...and have had it explained...youve seen em all.

Last edited by Racing; 07-18-2011 at 9:41 PM.
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post #7 of 12 Old 07-19-2011, 1:16 AM
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Re: gear problem

Quote:
Originally Posted by Racing View Post
..and finaly...
These are the fabled shifter forks. I hope this pic gives you an idea of how the drum moves the forks via those pegs that are basicaly nailed into them. Forks are often aluminium while the pegs themselves are normaly steel. As you can see by the pic the two axles are installed atop of the forks on this bike.

The forks are steel, I've never seen aluminium forks in even the smallest engines.

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post #8 of 12 Old 07-19-2011, 2:14 AM
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Re: gear problem

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Originally Posted by Racing View Post
Agreed.
Most bikes use a shifter drum as the "brain" of the gearbox system. This drum has like serpentine cuts in it that through pegs control the respective shifter forks.
Nice explanation, and the photos help too.
The shift lever turns the shift drum which is cammed (your "serpentine" grooves). The shift forks control the three slider gears and are driven left and right by the turning of the shift drum cam grooves. The slider gears have dogs or slots in the sides of them which engage the dogs or slots in the adjacent fixed gears. Being a "constant mesh" transmission, all the gears are meshed together and spinning all the time - even in neutral.
The wear points in the transmission are the points of the grooves in the drum, width of the shift forks, bending the shift forks, wearing the points off the dogs and slots, and wearing an angle into the dogs and slots.
Other things can wear due to poor lubrication or mechanical failure.

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Originally Posted by Racing View Post
For a variety of reasons on most bikes the setup goes awol in 2nd first and sorry to say there is no quick fix or cheap fix.
Second gear wears the fastest due to the very wide ratio and being the most changed gear. Unless you ride everywhere in first you will shift to second every time the bike is ridden. I almost never get into fifth or sixth gears on my bikes, even the 250's.

Quote:
Originally Posted by Racing View Post
What i CAN tell you is that there are those that can run forever on a set of fork/pegs/drum...and there are those that will wear it to smithereens in no time flat.
To really take advantage of a straightcut box means that you have to be engine savy,at least to some degree,and the sorry truth is that most are not.
I'm not sure what you mean by a straight-cut box but I absolutely agree, not taking the time to learn to shift gears smoothly and cleanly is going to cost you money eventually. And playing tunes up and down the transmission is one of the true joys of motorcycle riding for me :-)

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Originally Posted by Racing View Post
If and when you have this apart be aware that the tolerances for the pegs and cutouts in the drum are most likely less than you would think.
Other than badly neglected engines I can't recall seeing any significant wear in the shuft drum grooves. Wear will usually become most obvious by the points of the drum being rounded off, usually due to old and dirty oil. The photo is the shift drum from an '86 GPZ250R engine I'm building at the moment for a project. The entire transmission is like new although the engine itself grenaded a bigend, crank, rod, piston, cylinder block, crankcase and head.

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Originally Posted by Racing View Post
This is said drum for an FZR Yamaha that behaved in exactly the same manner you describe. Notice the amount of wear in the cutout? Most hondos look approx the same.
I would probably regard that as damage rather than normal wear.

Quote:
Originally Posted by Racing View Post
Another culprit that might amount to the same fault is a bent shiftfork,which is what this drum controls a set of...via said pegs which are hardtailed into each shifterfork...and then of course the "locks"(dogs) on the gears themselves.
Yes, trying to force gears together can bend the forks and wear them away in the groove of the gear. Both of these will reduce the amount of throw on the gear and cause the dogs and slots to wear rapidly as they bounce off each other. As the contact edges wear, the dogs and slots develop a slope so that the harder you load up the gear the more force is exerted trying to push them apart. Since the only thing holding the slider gear in place is the pin in the groove of the shift drum, the point of the cam gets worn away. The wear in your FZR picture clearly shows that the shift fork was so worn that the pin wasn't even reaching the top of the cam slope before the gear dogs were engaging. The wear you see is the slider gear trying to bounce back from the fixed gear. Undercutting the dogs and slots puts an opposite slope on them so that loading the transmission actually pulls the two gears together tighter.

Quote:
Originally Posted by Racing View Post
The shiftforks move like plates that are grossly serrated with "teeth" and these plates hook up to the mating set on each gear as you move respective shiftfork.(aka Dogrings)
Anyways. The wear of the shifterdrum in the pic was enough to make said FZR throw second into "neutral"(which it in reality is not) at WOT.
Attached Thumbnails
Shift_Drum_Cams.jpg‎  

"I won't forget that ride for a while. Maybe you're right. Living fast might be worth the final crash. Maybe that's the secret you fliers know." - Flight of the Intruder
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post #9 of 12 Old 07-19-2011, 2:23 AM
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Re: gear problem

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Originally Posted by Racing View Post
Speaking of which,when you inspect dogs on gears as well as plates be rather anal about it. The dogs should look rather square no matter how you turn m so to say and whats more..gears or plates that show pitting is up for replacement. The "corner" of each dog should be reasonably sharp. Not knife edge sharp,but "dull" sharp for lack of better explanation.Rounded either means recutting,if ample material is still there,or into the bin and replace with fresh pts. If particular pts are surface hardened ONLY...that rules recutting out if you dont have a hardening company around.(Which might be a good idea anyways if racing is your game)
When you inspect both the gears and shifter dogrings try to have in mind how they work together to get a better idea of which standard so to say to strive for.
Absolutely. Any pitting of the hardening must be replaced as it will rapidly deteriorate and spread metal through the engine. This is important on camshaft lobes, rockers and lifter buckets as well.

Quote:
Originally Posted by Racing View Post
Forks in turn should look unison in angles. Ie;if one "leg" of a given fork points another direction than the other-replacement time. Also check freeplay for each dogring with the entire enchilada installed(Ie;drum,forks,axles..the whole nine yrds). As such the amount of freeplay on each side of each dogring should be REASONABLY the same. This is a rather surefire way of knowing that your shifterforks are not bent.

It's also important that the forks are perpendicular to the shaft. If the forks are bent to one side then when it pushes the slider gear along the shaft the dogs will engage the slots too early, before the fork has mounted the cam groove and can lock the gear in place. When pushing the slider gear the other way the dogs and slots will only just strike each other without actually engaging causing wear and damage.
If you have the transmission apart, it's never a bad idea to replace the shift forks - especially on an engine that must be split to do so.

"I won't forget that ride for a while. Maybe you're right. Living fast might be worth the final crash. Maybe that's the secret you fliers know." - Flight of the Intruder
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post #10 of 12 Old 07-19-2011, 7:07 AM
 
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Re: gear problem

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The forks are steel, I've never seen aluminium forks in even the smallest engines.
If were talking bikes yes. If were talking gearboxes in general no.
In fact to the point where many older syncromesh boxes even use brassforks to move the sliders within.
Please dont frown on aluminium for diehard use. These days there are aluminiums,like for instance Alumec,that will outclass good ol Titianium grade 5 on many counts. Both from strength and longevity aspects. But i guess youre aware of that.
I make these...


...for the Mercedes Cosworth/former DTM circus these days. Alumec indeed,and the point is that they hold up better over time that the equivalent Titanium. Asea/ABB had the material developed by Uddeholm at one point for use in their robot arms. Us motorsport foos "discovered" the material too and these days we even cut conrods from it.(In fact there are sets in use even in your neck of the woods ). Making shifter forks from it though.. ..would be VERY expensive as it by weight is approx 10 times more than regular 7075T651.(Up here former European dragrace champ Anders Karling even made engine blocks out of the stuff-he was sponsored by Uddeholm tho...*LOL*)

Btw. The wear on the shifterdrum in the pic above of mine even has a name. Its called the "Yamaha sickness" around here.
From what i gather,as ive replaced a drum or two,manily as a function of what you describe coupled with riders that wouldnt experience a feel for metal,which is essential when shifting without a clutch,if the box so fell on them.

Learning to shift a straight cut(as opposed to helical cut) dog box clutchless is an artform if you ask me. One that is seldome taught im sorry to say.

Last edited by Racing; 07-19-2011 at 7:36 AM.
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post #11 of 12 Old 07-19-2011, 10:54 AM
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Re: gear problem

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If were talking bikes yes. If were talking gearboxes in general no.
In fact to the point where many older syncromesh boxes even use brassforks to move the sliders within.
I've never seen a constant mesh car box that uses forks, I'm sure they exist though. Since this is a thread about his bike and it is a bike forum I assumed we're talking bikes. Specifically though, you posted pics of steel forks while stating they're aluminium.

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Originally Posted by Racing View Post
Please dont frown on aluminium for diehard use. These days there are aluminiums,like for instance Alumec,that will outclass good ol Titianium grade 5 on many counts. Both from strength and longevity aspects. But i guess youre aware of that.
I make these...
Absolutely. There's almost nowhere on a bike that titanium is better than aluminium or steel. The main one is the exhaust system athough that isn't really related to its strength at all. On a different point, have you had anything to do with carbon conrods? I have seen them a few years back but they don't seem to have progressed much?

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Originally Posted by Racing View Post
...for the Mercedes Cosworth/former DTM circus these days. Alumec indeed,and the point is that they hold up better over time that the equivalent Titanium. Asea/ABB had the material developed by Uddeholm at one point for use in their robot arms. Us motorsport foos "discovered" the material too and these days we even cut conrods from it.(In fact there are sets in use even in your neck of the woods ). Making shifter forks from it though.. ..would be VERY expensive as it by weight is approx 10 times more than regular 7075T651.(Up here former European dragrace champ Anders Karling even made engine blocks out of the stuff-he was sponsored by Uddeholm tho...*LOL*)
I have seen lots of aluminium rods and they're way better bang-for-buck than titanium. Both have too limited a fatigue life for general engine use though, although I have heard of a few road cars running aluminium rods for very long periods with no trouble. Wasn't it Mercedes that did a car engine with a billet titanium crankshaft some years ago?

Quote:
Originally Posted by Racing View Post
Btw. The wear on the shifterdrum in the pic above of mine even has a name. Its called the "Yamaha sickness" around here.
From what i gather,as ive replaced a drum or two,manily as a function of what you describe coupled with riders that wouldnt experience a feel for metal,which is essential when shifting without a clutch,if the box so fell on them.

Learning to shift a straight cut(as opposed to helical cut) dog box clutchless is an artform if you ask me. One that is seldome taught im sorry to say.
I learned the trick many years ago with the BW gearboxes in Ford Falcons, Cortinas and Escorts.

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post #12 of 12 Old 07-19-2011, 3:07 PM
 
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Re: gear problem

Agreed.
Reason fpr using brass or aluminium forks is one of noice and feel. As you state a car sets different parameters than a bike does. Hence why brass as well as aluminium is/was used.

Nah. In practice ive never run into carbon fibre conrods. Weve made stuff from it tho,like intake stacks and what have you not and many of the single seaters since the early 90s use monos made from it. The latter tho being WAY more advanced than laying CF down for intake stacks or whatever as them chassis are normaly baked under temperature and vaccum conditions. Mainly in England to this day.

Conrods tho have been mainly TiAl or steel of various kinds. Up here we preferable use conrods by local manufacturers as this country is VERY spoiled as far as speciality steels and aluminium.(For instance stuff by Stefan Verdi-as in AutoVerdi)
Indeed aluminium conrods can be had very light seing their physical proportions. Alumec tho put the "normal" reasoning for aluminium rods to shame due to the materials,being aluminium,remarkable cyclic life. Have in mind that pure Titanium is very rarely used but instead it is almost always an alloy of some sorts. TiAl for instance,which has been used like forever. Further,most of the titanium is US made making is pointlessly expensive to us over here...and as in our opinion Alumec will superseed and exceed titanium...titanium gets kind of moot for most apps on our behalf.
Alumec when put through industrial anodizing to approx 20my will show a hardness along the lines of HRC65.... Tough material to say the least,and that means that you can in fact use anodized Alumec as cutting material in a lathe in a pinch.

Yes. Mercedes racing development has mainly been a function of their involvment in DTM.(Deutsche Touring Meistershaft-Ie;German touring car championship)-and THESE days formula 1. DTM has been known to be more expensive to the manufacturers than formula 1 on occasions,so to claim that Mercedes et al has blown redicolous amounts of money on various racing enterprises is to be diplomatic about it. Titanium cranks...nah..through good friend Ingemar Persson whos a semi works crewchief within DTM since ages i know for a fact that theyve even played around with polymer cranks from time to another. As the saying goes...in racing only the rich will survive ...
To put numbers to it..when Merc developed the rear end for the "valver" back in the 80s that ran them along the lines of 1 BILLION deutsch marks. In short a s-load of money,and that for the rear end alone.
Before DTM became silouette cars in -94 almost anything in sight on the "stockblock" cars was titanium et al. It became completely silly with active suspension aso aso.
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