shimming a 155z

[eagle]

Hi folks!

I just wanted to know whats your experience with shimming the 155z to reduce the axial end play of its shafts?
It seems to be a bit controversal, I read proper shimming should give a litte less wear/more durability but on the same time this kinda engines seem to need quite a bit of play too?
I'm also putting a 177ccm kit on, so it might matter even more.

I'm currently rebuilding my 155z (old/non-"HO") and got proper shims in all kind of diameters and thicknesses (0.1/0.2/0.3/0.5/1/1.5mm).

I started with putting them just on top of the sprocket/clip/shim/.. stacks but when I shimmed the shift drum also I had troubles with the drum jamming because of being shifted to much in the opposite direction primary and secondary sprocket stacks were.

Currently shift drum's fine, secondary gear side is fine, just on the primary in 4th gear the fork pushes the two sprockets on the top/right to much against the already installed shims and bearing/engine case so the drum jammes and dont fully angage 4th gear.
Now i also need to bring the whole primary stack more to the top/right, I just havent got 12mm shims at hand yet.

Play should be between 0.1-0.2mm with the two cases tightened together/compressed gasket.

As soon as I get the 12mm shims I'll finetune the primary too and reassemble the whole engine again. I'm just wondering if this nasty shimming procedure (had the case split about 15 times during the try and error shim placement procedure so far) is worth the effort or if those chinese engines won't even appreciate the work maybe even making things worse because they might need that much of a play?
Play before was somewhat between 0.5 and 1mm depending on shaft.

thanks

 

[zwebx]

i would say you want to get rid of most of the slop on load bearing things on the gearbox.. but still leave a little bit of play for heat and whatnot.. i probably only fix play if it was excessive though

 

[eagle]

Well... I studied precision engeneering... so "excessive" play can mean 5/1000mm ^^

I got proper shims and everything now and was able to actually measure play to give you a better idea.
(dial gauge mounted via a magnetic stand on the oilpump).

Fitted were:
-Crankshaft
-primary drive sprocket stack
-secondary drive sprocket stack
-(kickstart shaft)

The cases were closed and bolts tightened with 10Nm on each bolt.
Play:
shift drum: 1/10mm
primary: 2/10mm
secondary: 2/10mm

tolerance: +0 / -2/100mm

Everythings fine now, gears shift tru smoothly. I'm just wandering if I should reduce play on primary and secondary even more? I could reduce it by about another 1/10mm. I'm just not sure I should.
Currently I can feel the shafts knocking into its extreme positions when moving the shafts by hand, when adding another 1/10mm shim on each I still see movement on the dial indicator but its hard to feel its extreme positions. there is no defined stop anymore, it feels a bit more vague... more like the bearings inner rings moving from side to side then flat faces touching each other.
So I got measurable play thats harder to feel and I'm not sure if I should reduce play to this level (~1/10mm play) or leave it as it is now... (~2/10mm play)

 

[K.Jansson]

do you know how much the material will expand with the heat?

 

[eagle]

do you know how much the material will expand with the heat?

I have no idea. But since the case will also warm up and since that aluminium alloy will expand more for sure than the steel sprockets/washers/shims/etc (assumed theyre heated the same amount) play might even increase between the two inner/gearbox casings.
On the other hand those sprockets might get a good bit warmer than the casings because of friction.

 

[zwebx]

0.2 sounds like the magic number i reckon, not loose enough to smash gears yet not tight enough to crack the cases when hot (i would say)

 

[zwebx]

even daytonas manual does not say what tolerances (http://www.dhz.com.au/assets/brochures/EN-15.pdf) or maybe i missed it

 

[eagle]

I wouldn't expect daytona to put this kinda information in their manuals.
2/10mm means 0.2mm play, I'm not sure it was just a typo but there's quite a lot difference between 0.02mm and 0.2mm play ^^


here's a pic of the gauge setup

But I guess I'll leave it as it is now, it feels safer. I'm no engine expert tho...

 

[DHZ_XR8cing]

The main thing that should be shimmed in the shift drum more so then the gear shafts.
I have had a box that shimmed out nice. Turn the gear shaft half a turn an was close to zero tolerance.
I would not shim them out to much. With the low quality materials used in these engines it would be risky to run them too tight.
Don't be too fussy with it. The box will be ok with a 177 on it it. Its the bigger 190+ builds where its more critical.
If you bolt the cases together without the centre gasket how much play is there?
Have you tried bolting the engine together. measure the play. Split the difference and shim both sides of the shaft??

 

[eagle]

Alright, thanks for the answer.
Shift drum is fine. Its got 0.1mm play but since its only bolted to one side of the case this was easy.

I had problems with those knobs on the side of the sprockets to be pushed to hard against the side of the sprockets with the slots before holes and knobs aligned and engaged.
If shimmed to much on a particular side of the assembly the fork pushed those sprockets to hard or too early against each other, making engagement less smooth.

Yeah, you may be right... I just tried to make this rebuild as clean as possible. Having gears jumping out after some time seems to be a common problem on these china engines. I tried my best to avoid that as long as I can. And who knows if I might get a bigger bore and new head somewhen ;-)

If I leave out the gasket theres no play left at all in prim and sec shaft. But thats no surprise since that centre gasket has at least 0.5mm thickness.

I haven't tried this but the smoothest results so far where with the primary shaft slightly offset to the drum. (0.6mm shims underneath the drum, 0.3mm shims underneath the prim (0.6 ontop), in this particular case), secondary seems not to be that fussy with shifting it to either side. And I doublechecked with engine diagrams, every shim, clip, washer,... is at its right place.

 

[eagle]

Current status: As I continued engine assembly (clutch side almost complete) I had the drum stuck once again... So I took everything apart again and now I'm starting to do things a bit more methodic.
I'm not sure of the outcoming, I'm doing this also to learn something and since I found no proper guide for shimming anywhere else this might be of interest to others.
"Fortunately" I currently got the time for such experiments because of a knee injury...


First things first: the shift drum:
I found the shift forks and especially the pins that ride in the grooves quite loose.
I drilled and tapped the hole that held the bolt securing clip so I could use a M4 set screw (ISO 4027 / DIN 914) to hold the pin in place and replaced the rather short pins with longer ones (haven't got the standard code at hand, but its the kind of hardened pin with rounded off faces, not chamfered).
The used pins are 6 diameter by 10mm lenght. No Problem on the primary fork, but on the secondary I needed to grin off the protruding portion of the pin to clear the sprocket.

The Drum itself had about 0.7mm axial play when inserted and tightened down with that "neutral switch washer".
I used a lathe to machine 0.6mm off its face.
It has now got about 0.08mm of play left.
I've now got the benefit to be able to shift the drum with adding shims from as close to the ignition case side as possible to anywhere further away (closer to the clutch side). Also by adding shims I can increase its play in 0.1mm amounts.
(ID 6mm shim between "neutral switch washer" and drum to shift the drum more to clutch side/increase play, and ID 15mm shim between drum and ignition side gearbox case to decrease play)

I then assembled the gearbox (with crankshaft and center gasket, without kickstart shaft) and measured the axial play of primary (closer to crank) and secondary (where the chains sprocket goes onto) shafts. M6 case bolts tightened down with 10Nm (I wouldn't recommend exceeding this torque on aluminium cast alloys)
I had about 0.6mm play on primary, and about 0.75mm play on secondary.


From here I'll do my testing.
First test included putting ~0.4mm of shims between primary stack and clutch case side, and ~0.6mm of shims between secondary stack and clutch case side.
This resulted in about 0.15mm play on primary, and about 0.1mm play on secondary.
(of course there's some measuring error and those shims also got tolerances)

I then put that drum location arm back on so the drum snaps into its positions as under riding circumstances.

I used a phillips screwdriver to turn the drum (of corse without unscrewing the bolt that holds those pins and plate) because of getting a better feeling of what the drum is doing, shifting through the gears while turning primary shaft counterclockwise (seen from the clutch side).

I will repeat this test with different shim locations and thicknesses but this inniate test gave rather amazing results... not a single jam so far. And I really tried hard to get this drum to stuck (varying turning speed of primary shaft, variing drum twisting speed and torque). Even when I felt a slight resistance in the drum (because of dogs and slots not having alignet yet) it would snap into position/gear after another half turn or so of the primary. Previously such circumstances created jams, causing the drum to get stuck once in a while (especially if you forced the drum with the screwdriver). However, currently it seems to snap into gears pretty smoothly.

As said I'll try shims in different locations and combinations too, and I'll also check if I can reproduce this current condition.

Please note that the engine isn't fully reassembled and ridden yet, and also note that the specefications and toleranced these engines are made to very likely won't allow you to use the exactly same shims in the exactly same spots as I do to get the same results.

I'd still appreciate input from more experienced riders/mechanics on the subject.

 

[zwebx]

you did it fine, aslong as there is a little play in the load shafts and as tight as you can get the selection drum with catching all gears you did good

aslong as its not so tight that its forcing the bearings to the side it will be fine