Shift Drum/Star Setup? Begging for Help. :(

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Well-Known Member
Aug 12, 2009
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Hi all.

Quick question. Long explanation.

Is there a certain way the shift drum assembly must be put in during trans assembly?

I busted the cases on my yx160, have since updated to the new reinforced case and bearing and updated gearset.

I bolt it all back together and for the life of me i cant get it to shift right. Ive pulled motor back down about 4 times now.... 3 gaskets later.... and quadruple checked that i have every washer, shim, circlip etc all EXACTLY where they should be. Which they are. According to memory and $hitty exploded parts diagrams.

All shaft heights are correct before clutch goes on. Clutch is setup correct. I did get that stupid 3 pronged washer in the wrong spot first time round. But got that sussed now. Its not the clutch causing any dramas.

Ok so bottom line is, main shaft and counter shaft are in and shimmed up correctly.
Clutch is all in correctly.
Everything spins nicely, gears all mesh squarely.

But i dont know how the shift drum is supposed to be set. i was told to make sure its turned anti-clockwise all the way BEFORE mating it with the gears and dropping it in the case. I was also told to make sure the shift star had the rounded point set at5 o'clock... except my shift star isnt a star, the whole thing is kinda round. Not damaged, but round rather than a star shape like ive seen before

It all spins, and i spin whilst turning the shift star to "change thru the gears" it all seems ok but its a bit hard to spin squarely with the other case off. SO i bolt the clutch cover back on and then use the gearlever to shift whilst spinning flywheel by hand.... Hard to go thru gears or gets kinda stuck. Hard to explain.

Anyway, im getting really sick of splitting cases, replacing gaskets, and pulling all this $hit apart, does anyone have a idea on how it should go back in (shift drum and star)

AND how many turns does the bolt on the other side of the shift drum ( the one thats under the rubber grommet on your flywheel side) have to be out from flush.
Ive tried it all the way in, all the way out, 1 turn out, 2 turns out etc. But i just cant find the sweet spot. If its say 3 turns out it will shift 1-2 no worries but bottom out( bolt hit case) going to 3rd. so if i go out another 1/2 to full turn 2-3-4 will be ok, but n-1 will be near impossible.. so f**king frustrating...

Hope someone kinda gets the idea im talking about.

So after that long-winded essay, can anyone point me in the right direction to..

* How exactly the shift drum must go back in. (clockwise, anti, halfway etc)
* How many turns from flush should the bolt be on the other side?
*Or if no-one knows the answer here is there anyone in Adelaide i can take this engine
and a fistful of dollars to and say
'Please Fix" :)

Thanking you all in advance to help a brother get back out on his MotoVert.
Bike has spent more time in bits, than with me in the saddle. :(
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sly1300, i'm booked out all week and next weekend, however i may have some free spanner time next week... bit hard to diagnose over the keyboard, but have split the odd gearbox now and then, might be able to help somewhere... almost sounds like something is "bent" in the case, selector or both..
East50's also offer a bit of mechanic support.... but not many places will touch a motor that has been split, and i'm pretty sure Brian from East50's isnt a huge fan of playing with said motors...
I've split and reassembled a lot of these engines. I've never paid any attention to the orientation of the shift drum on assembly. It should go back together and work fine in any position. And that bolt under the rubber plug should be tight.

Maybe one shift fork has been rotated 360deg on the drum? That may put it out of whack. Might not even be possible though... I have one in the garage, I'll check.
Now mate ... I'm typing this info and trying think while my eyes are sore and my neck is aching so if it sounds a bit all over the place you'll know why ...

The reason why they've told you to rotate the drum fully anti-clockwise is to get the shift drum and gears set to the neutral position when you install it and the gear shafts into the clutch side case ... That will prevent the dogs from fouling on the sides of gears and holding things out of alignment ... All you have to do is THINK about how things work to sort problems out ...

IE ... When you push the shift lever down to downshift ... the selector fork catches on a pin on the shift drum and pushes it down ... that causes the drum to rotate counter clock wise ... and vice versa when you upshift ... Neutral is right at the bottom on a 4 up tranny so the drum will be rotated as far as it can go anti-clockwise when the tranny is in neutral ...

A shift star simply holds the drum in a fixed position after a shift has been made ... When you push the shift lever , the dogs get pulled out of one gear and pushed into the slots of another ... As that happens the shift forks rub on the sides of the dog ring groove ... Once the dogs are seated in the selected gear ... you want the selector fork to pull back slightly so that it rides lightly in the centre of the dog ring groove without rubbing on the sides ... otherwise it would rapidly wear thin ... That's WHY you have a detent spring and shift star ... you make the shift ... then the gear is supposed to "float" on the shaft with no side loading or anything rubbing ... IF you've ever dropped the bike on the shifter side ... chances are that you've bent something and that causes the shift forks to rub on the sides of the grooves ... A tranny that has bent shift forks will go into some gears really easy but be hard to get into others ... and it can jump out of gear a lot ... Unless everything is floating freely after finding it's own happy spot ... the tranny will feel notchy and hard to shift ...

After reassembling a tranny , it WILL be hard to shift gears unless you are holding the countershaft AND the mainshaft and wiggling them because the ends of the dogs can hit the flat spots in between each locator slot on the corresponding gear ... When you only turn one shaft ... the dogs can sit or push on those spots in between the slots of the gear you're trying to select causing the gear to rotate at the same speed as the dog gear and cause the dogs to fail to pop into the holes ...

That bolt on the end of the drum that you're talking about would HAVE to be tightened to stop the drum from being pushed sideways when the dogs hit the sides of selected gears ... You want the shift drum to be held firmly in position so that only the forks and dog slider gears move when it gets rotated as you shift gears ... Having the drum retainer bolt loose is allowing it to walk sideways and defeating that purpose ...

Basically ... to assemble a tranny without any exploded views or shop manuals ... You start from the flywheel case side ... Make dead sure every single gear set is aligned and centred with it's opposing gear when engaged ... and that the shift forks also sit dead in the centre of the slider rings while the gear sets are precisely aligned ... Don't go off the clutch /primary drive side shaft ends being aligned ... it's what's inside the two cases that needs to be aligned with minimal end play/walk/float or whatever you like to call it ... The clutch itself needs to have its own play ... that's WHY XR's have a floating clutch that's only held on by a circlip ... and the countershaft sprocket also floats on the countershaft ... 4 strokes have strong torque ... torque flexes things ...

Forget what you've seen inside a two smoke tranny ... They wouldn't last 2 seconds behind a 4 stroke as Yamaha discovered when they first mated a YZF road bike cylinder to a YZ250 tranny ... Same peak HP but gears , clutch and rear wheel hub went BAAAANNNG from the torque ... Even the 2 smoke frame broke ...
I just checked and I think it can be assembled with one fork rotated around a full turn, which will put the wrong fork in the wrong gear slot. Double check that its all good. You should be able to assemble both shafts and the shift drum in the left side of the case and rotate it all to confirm operation before final assembly.
hmm sounds kinda strange.
iv never had any trouble putting gearsets in or shift drums....iv never had to line anything up long as all the shift forks are in the correct location it should just work....

and that bolt your referring to under the rubber gets down up tight, but the shift drum must protrude thru the case a little(like 20thou or so ) or else you are locking the drum to the case...
if its not protruding thru then you have a shim in the wrong place.
and with that bolt left loose you are allowing the drum to walk out into the clutch which also allows the gears to miss align....
Have you ever had to reassemble a tranny from the exploded view stage ... ? ... Or have you simply only ever reinstalled undisturbed gear sets ? ...

I have a special 5 speed close ratio PK Racing 5 speed tranny for the 4 speed model XR75's and it was in pieces for years ... I went to several big Jap bike shops with it to ask the "mechanics" if they could show me which way around the gears go and where the washers and shims go ... Not one single professional knew or wanted to help ... They said they only know what is shown in exploded views in factory manuals ... so they had no clue with an aftermarket tranny ...

I went home and sat there until I worked it all out and understood that everything needs to be aligned precisely for the tranny to function smoothly ... A gear around the wrong way will give false neutrals ...

I HAVE encountered a shift drum that was tight in the RHS case ... I had to wet dry sand the drum bore in the case to get the drum to rotate smoothly ... And I'm talking about genuine Honda cases ...

I'm not 100% sure but I think Sly1300 has had to fit an entirely new and different (modified) RHS side case with a different countershaft , needle roller bearing and gears ... not just pulled his stock engine apart and reassembled it ... So my post was geared with that scenario in mind ...

In that case you HAVE to check for misalignments and machining variations ...
yeah i have assembled moto gearbox's that have been sitting in parts for years also...
and i understand what you are talking about....

and i have actually had to repair gearbox's that have been assembled wrong too...

yeah he did say he had to do a RHS case change and used the upgraded version...and only changing 1 case side can be problematic sometimes as cases are machined as pairs and by only replacing one case you can run into the problem of misaligned bearing journals and base gasket surfaces...but you gotta do what ya gotta do with these engines...

another thing too is that in some of these china box's they dont always have the same shims or same size shims...
so im not sure if an exploded view of the box is going to proof useful except for the gear layout.

one other thing just occured to me.....

is Sly1300 changing only the counter shaft gearset or both? if both then disregard the next bit..
reason i ask is because there could be a ratio difference with the gearset he got with the case....

this case upgrade comes with full gearset and drum OORacing - performance monkey bike, pit bike, madass, zoomer, dirt bike components - YX150/160 needle roller gearbox conversion kit (Powered by CubeCart)

dhz sell on the countershaft gearset with the case upgrade DHZ Mini Moto - Dirtmax YX 160cc 150cc Engine Bottom End Upgrade Kit
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I'd say you've hit the jackpot sean01 ... OORacing most likely replaces the lot because they've had problems replacing just the countershaft and gears ... Sly1300 sounds like he knows what he's doing ... he's more than likely put it all together properly yet he's STILL having problems ...

And you're dead right ... centre cases should only be machined whilst assembled as a pair and sold as a matching set ... just as car engine blocks and conrods are ... You can't swap bearing caps without re machining them (closing and honing them) no matter how well they've been originally machined ...

The same thing applies to bike engine cases ... you're taking a risk hoping everything is precisely aligned ...

Each gear shaft needs to be shimmed to suit the inner width of the cases ... and that distance is also affected by the thickness of the centre case gasket ...
wow. a big THANKYOU to all for such lengthy and informative replies.
Very, very much appreciated guys!

Seems i think ive found the problem.
I did get the updated case AND gearset from Brian@ East 50's (& for a good price too thx mate :) )

I was putting everything back together correctly after pulling down and redoing about 10 times.. seriously...

Everything would spin and engage thru the gears beautifully with the new side case OFF.
I went to dummy fit the new side case and it wouldnt fit.
New countershaft needle bearing wouldnt fit in its spot in the new case.
Neither did the gearbox bearing. Both casts were just a tad too tight, a light wet sand and wash the case down and i gently tapped the bearings into place. All good.

Oh also the crank bearing was a reeeal snug fit, gentle tap on the case with a rubber mallet to get it to seat square.

Case sitting flush, recheck everything spins, changes gear etc
Sweet as...... or so i thought

Id run a light silicon film and whack on a fresh gasket and press the case on. Yup everything still spins. Cool.
Put bolts in finger tight then go round in opppsite corners (like you do car wheel nuts) and nip them up.
Tight, but not bullshit tight. Have smoke, let silicon+gasket settle for 5-10.
Put all the rest of the crap back in, gearshift selector arm, kickstart cog, counter cog, oil pump, clutch etc.
Clutch cover goes back on. All good, install engine in vert... Did i mention i now hate cradle frames and the way the bloody peg mount balances whilst ur trying to wedge a 160 in the frame.. grrrgot about 3mm clearance from frame to breather... really need 2 people to make this job easier.
PROTIP: Take sidestand off pegmount, makes it soo much easier to balance on cradle mount whilst trying to get engine in

Engine in, lever goes on. Check to see how it feels shifting with foot... Nothing.. Jammed up good. Go to spin drive sprocket.. Jammed also.

Have another cig, open can of JD
Remove engine (again)
Pull it all apart again, not clutch or anything above case causing jam... pull down further.
Crack 8mm nuts holding new case to other case, loosen off a bit... drive sprocket spins..
Nip the bolts back up, drive sprocket jams.. FUUUUUUU

Shit casting by the chinamen. Basically, as the cases are squeezed together, the gearbox shaft is being
squished together. If that makes sense. Too many or too thicker shims. Casting is a little thicker, and near impossible to get the dremel out and rub back EXACTLY the width i need.
Basically what Cactus has said in above post. Spot on. God damn it.

So deciding NOT to attack the new case with the dremel ive then spent countless hours removing shims, swapping shims from old gearset (they are a poofteenth thinner on the old gearset than the new one) i thought i found a happy medium..
Making sure it doesnt "squish up" once case is tightened or is too sloppy once its all together.

So tonight engine is all back together, tight, and everything spins, shifts gear (still a tad notchy by hand but its a little different once bike is rolling)
Finish work, bolt engine back into Vert, hook up cooler n shit, cables blah blah. Feed it some oil, key off give her quite a few gentle turnovers to get the oil thru the engine, put plug back in, fuel on.

find tdc, and bugger me. 3rd kick and it starts.... and idles LOL. ( i did redo the valve clearances whilst the head was off, heaps easy!)

typical yx160 rattles and clunks but nothing out of the ordinary, let it warm up. one tiny drop of oil hits ground... damn it, i did restick that gasket dwon about 50 times.... no biggie lets go for a gentle test ride.

helmet and gloves, out the drive and down the road, very gentle thru the gears, slow down speed up a couple of times.. everything feels kinda ok.. round the block and back home.

oil leak is more of a weep, can be fixed later. readjust throttle cable and clutch cable, retighten rear spokes (is this a common thing on rx's?) and decide to go back out again,

same route but feed the power on a little more thru the back streets. still good. nothing rattling. as this point im feeling pretty proud with my handiwork and cant believe this thing is actuall running after id had it in a million pieces. Stop at a servo, fuel up. cruise home..

Get half a block from home slow down for a tight set of esses and gently shift from 4th to 3rd and into second... but it felt like it kinda grabbed into second.
half throttle lean left, lean right still half throttle. and bike jumps like ive accidently blipped the clutch?


shift to 3rd, everything fine. 4th fine. Cruise to a stop sign. Take off 1st, halfway round corner and it "grabs" going into 2nd again.. gentle throttle around corner and bike is jumping like im clutch kicking it/like the gear is slipping?
grab clutch hit 3rd accelerate. fine. 4th fine.. slow back down back to 3rd. back to second. feels fine cruising along half throttle in a straight line, gently feed power on. slip/grab/slip/grab. not happy.

1st, 3rd and fourth are all fine. can idle along or hold them W.O.T. not an issue. if im in second, no more than 1/3 throttle before it slips and jumps and bangs. and if im going around a right hander it doesnt matter if im coasting it does the jump/grab/slip/jump/bang/slip/jump thing.....

nurse bike home in 3rd & 4th. Not making the best noises.. Walk it part of the way home.
dump oil whilst its hot. magnetic drain plug has shavings on it.

I think ive just Grenaded a motor ive just spent a bit of coin on. And only ridden for like an hour.
And the 2 guys keen on my other bike for sale seem to have dropped off the face of the earth.

What a day.

I obviously left out a shim on second gear somewhere.... will pull motor out and tear it down and keep you all posted... and probably leave it out on the street for hard rubbish day..

Ive already ordered a new UPDATED yx160 from dhz..should be here in the next day or two.
so i shouldnt have this drama again now ive learnt to start from tdc and have done that igintion pickup mod to the old engine that did make a HUUGE difference to kickback.. rather than 8/10 kicks resulting in kickback it would only be about 1/10. cheaper than a decomp cam. :)

one question, the 160 i have at the moment is running the 155z top end
got it off the previous owner like that.
Is there any benefit from running the 155 top end on the 160, apart from cooler looking tappet and cam covers
or did previous owner just pinch the bigger 160 topend to go on his "stronger" 155 bottom end in his other bike? :(

Should i leave the new 160 as is, or slap the topend ive got onto it?

Thanks again guys. Thanks for listening. Had to get this shit off my chest.
hmmm. thats not nice....

going from wat you have said...the only shim that would of needed to be reduced is the one under the needle roller bearing(opposite side of the kick idler)

you can measure the thickness difference with a steel ruler and vernier calipers...(ruler across the center case mating surface and check the dept down to the bearing) do that on the old and new case...
i have noticed these gearboxs like alot of end float. so maybe it didnt have enough...

its hard to say what your next step is tho, as you have moved shims around between gears. hope you remember where they go, cause thats where they need to be...

any possibilities of pics when you pull split it again... maybe with the gearset in the case and without...

as for the 155z top end...are you referring to the both the barrel and head...or just the head...

the 155z head has longer valve covers and has different valve angles...they are spose to be better then the 150/160 head...


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