LCGB Forums

Hi everybody

Newbie here - just finished building LI 150 with an Engine that had been totally rebuilt by somebody else!

Problem is that when running there is a noise coming from chaincase side as if something was catching - i have checked kickstart shaft (genuine Scootopia) no marks and shimmed correctly and sits on ramp in OK position.
I was wondering if gearbox shimming could be area of concern and if there was anyway I can check before starting to strip down and checking measurements ,. (pulling clutch in makes no difference)

Noise does seem to increase proportionally as you twist throttle but not 100% constant if you can understand that ???

any suggestions or help please before I start to strip her down would be greatly appreciated - THANKS

Your kickstart shaft may be catching on the teeth of the first gear.You say that pulling the clutch lever in makes no difference,does the sound go away once the clutch lever is pulled in and the scooter is put in gear.If so it could be what I suggest.

Hi - just tried it and yes when gear is engaged with clutch pulled in the noise disappears - can you tell me how to rectify please? thanks you spotted problem straight away !

Thanks for prompt response - my engine has the GP style ramp (inside main casing) and i assemble side case and turn kickstart shaft until pin rises on ramp but it still seems to catch first gear -the noise only goes when i hold clutch and select a gear as I guess that stops gears spinning, as soon as I release clutch the noise returns.
Tried kickstart off when running and noise is still there - tried replacing kickstart in different position - still NG - even tried different kickstart shaft
1- scootopia
2 sil

Exactly the same noise still there - any more ideas chaps ??

Is your front sprocket bolt correctly tightened down. Make sure the castled top is correctly tightened down onto the tube. Also check no marks on the chain case side where the front sprocket is located. Not always obvious that it’s tightened correctly.

If the noise disappears with clutch pulled in & gears engaged, then the problem is most likely within the gearbox area.

My suspicions would be:

something is catching on the first gear or the inner clutch top plate (typically the kickstart) or;

the gears are noisy through too much clearance, a mismatch of gears or a broken tooth/teeth.

Strip down seems inevitable & I would suggest that you have a new, really thick chain case gasket & a selection of gearbox shims to hand as that may be all that it takes to cure it.

Warkton Tornado No.1 wrote:If the noise disappears with clutch pulled in & gears engaged, then the problem is most likely within the gearbox area.

My suspicions would be:

something is catching on the first gear or the inner clutch top plate (typically the kickstart) or;

the gears are noisy through too much clearance, a mismatch of gears or a broken tooth/teeth.

Strip down seems inevitable & I would suggest that you have a new, really thick chain case gasket & a selection of gearbox shims to hand as that may be all that it takes to cure it.

When you take the chain case off, have a really good look for signs of rubbing. As already suggested, the inside of the kick start shaft can rub on the clutch top plate. It is possible to 'relieve' the shaft in this area but don't go mad and as WT suggests, a thicker case gasket might be enough.

Warkton Tornado No.1 wrote:If the noise disappears with clutch pulled in & gears engaged, then the problem is most likely within the gearbox area.

My suspicions would be:

something is catching on the first gear or the inner clutch top plate (typically the kickstart) or;

the gears are noisy through too much clearance, a mismatch of gears or a broken tooth/teeth.

Strip down seems inevitable & I would suggest that you have a new, really thick chain case gasket & a selection of gearbox shims to hand as that may be all that it takes to cure it.

Hi As you suspected - checked gear shim clearance and its 0.8mm when I believe max should only be 0.3mm so i guess this is moving and catching kickstart shaft ? - does that sound likely to you and I guess gears stop spinning when you pull clutch and select gear? - do i need to take engine out or can it be done insitu ?

Thanks

Alan

harps2 wrote:

Warkton Tornado No.1 wrote:If the noise disappears with clutch pulled in & gears engaged, then the problem is most likely within the gearbox area.

My suspicions would be:

something is catching on the first gear or the inner clutch top plate (typically the kickstart) or;

the gears are noisy through too much clearance, a mismatch of gears or a broken tooth/teeth.

Strip down seems inevitable & I would suggest that you have a new, really thick chain case gasket & a selection of gearbox shims to hand as that may be all that it takes to cure it.

Hi As you suspected - checked gear shim clearance and its 0.8mm when I believe max should only be 0.3mm so i guess this is moving and catching kickstart shaft ? - does that sound likely to you and I guess gears stop spinning when you pull clutch and select gear? - do i need to take engine out or can it be done insitu ?

Thanks

Alan

The excess running clearance of the gears on the lay-shaft wouldn't be enough in itself to cause them to rub on anything that they shouldn't.

The clearance to aim for is actually only 0.003" (three thousands of an inch) & it really is worth the effort to get close to that, but definitely no less.

(I keep about two dozen various shims engraved with their sizes & kept in size order so that it makes the process of checking a little less hassle)

You can check clearance with the engine in situ, but I always remove the cluster ("Christmas tree") whilst checking nowadays as it's easier to remove the end plate on & off, then on & off & repeat (Yawn!) until the best shimming is obtained. In other words, the check is only of the loose gears & the cluster being in place is a hindrance whilst that is carried out.

(Do try & obtain 'proper' M7 hardened nuts & spring-washers if you can. Mind you, I don't know who sells them these days)

Once achieved, the cluster with gears can be refitted & that may be enough to quieten down the gearbox.

You will, of course, have checked there hasn't been anything rubbing (shiny internal kick start lever face/swarf in oil) on the clutch top pressure plate, which is such a common problem if the ones I've seen in my lifetime are anything to go by! It's very rare to strip an engine & find one that hasn't rubbed.

I hope that I have helped & not confused you

Warkton Tornado No.1 wrote:

harps2 wrote:

Warkton Tornado No.1 wrote:If the noise disappears with clutch pulled in & gears engaged, then the problem is most likely within the gearbox area.

My suspicions would be:

something is catching on the first gear or the inner clutch top plate (typically the kickstart) or;

the gears are noisy through too much clearance, a mismatch of gears or a broken tooth/teeth.

Strip down seems inevitable & I would suggest that you have a new, really thick chain case gasket & a selection of gearbox shims to hand as that may be all that it takes to cure it.

Hi As you suspected - checked gear shim clearance and its 0.8mm when I believe max should only be 0.3mm so i guess this is moving and catching kickstart shaft ? - does that sound likely to you and I guess gears stop spinning when you pull clutch and select gear? - do i need to take engine out or can it be done insitu ?

Thanks

Alan

The excess running clearance of the gears on the lay-shaft wouldn't be enough in itself to cause them to rub on anything that they shouldn't.

The clearance to aim for is actually only 0.003" (three thousands of an inch) & it really is worth the effort to get close to that, but definitely no less.

(I keep about two dozen various shims engraved with their sizes & kept in size order so that it makes the process of checking a little less hassle)

You can check clearance with the engine in situ, but I always remove the cluster ("Christmas tree") whilst checking nowadays as it's easier to remove the end plate on & off, then on & off & repeat (Yawn!) until the best shimming is obtained. In other words, the check is only of the loose gears & the cluster being in place is a hindrance whilst that is carried out.

(Do try & obtain 'proper' M7 hardened nuts & spring-washers if you can. Mind you, I don't know who sells them these days)

Once achieved, the cluster with gears can be refitted & that may be enough to quieten down the gearbox.

You will, of course, have checked there hasn't been anything rubbing (shiny internal kick start lever face/swarf in oil) on the clutch top pressure plate, which is such a common problem if the ones I've seen in my lifetime are anything to go by! It's very rare to strip an engine & find one that hasn't rubbed.

I hope that I have helped & not confused you

Well that's puzzled me a bit actually because the noise disappears instantly & completely when you pull the clutch AND SELECT GEAR and returns when you release clutch (in or out of gear) - its definitely something catching by the sound of the noise - ie rotational noise (if you know what i mean by that) - clearance already done on kickstart shaft and actually tried two different shafts and no change to noise.

Do you know which parts stop rotating when clutch pulled and gear selected (sorry i don't) as I believe that will be the source of noise...............

thanks for the advice to date by the way

Hi, I believe (& I'm sure others will correct me if I'm wrong ) but with engine running & obviously the scooter in neutral, once the clutch lever is pulled in this pushes the clutch arm shaft on the chain case which in turn pushes down on the clutch bell which engages & "catches" the clutch spider, the clutch spider is bolted to the gear cluster,so as this action takes place it stops the cluster from turning & the loose cogs as they are meshed together as one unit,all that remains spinning then is the crown wheel as it's still free to run & is still being pulled round by the front sprocket which links the two via the chain as the engine ticks over. I have tried to explain it as best I can & I believe how it all roughly works & I hope you can follow what I've written but I'm sure an adult will be along shortly to explain it properly

al pushpak wrote:Hi, I believe (& I'm sure others will correct me if I'm wrong ) but with engine running & obviously the scooter in neutral, once the clutch lever is pulled in this pushes the clutch arm shaft on the chain case which in turn pushes down on the clutch bell which engages & "catches" the clutch spider, the clutch spider is bolted to the gear cluster,so as this action takes place it stops the cluster from turning & the loose cogs as they are meshed together as one unit,all that remains spinning then is the crown wheel as it's still free to run & is still being pulled round by the front sprocket which links the two via the chain as the engine ticks over. I have tried to explain it as best I can & I believe how it all roughly works & I hope you can follow what I've written but I'm sure an adult will be along shortly to explain it properly

Not trying to be cheeky but Sounds very precise for me but too many words - Question - Do you know which parts stop rotating when clutch pulled and gear selected ?

Not sure if you forgot about gear being selected as noise is still there when clutch pulled in when in neutral so I think the gear selection is the key to the noise............. -

Hi, no probs, now I've read it back it was a little long winded basically the job of the clutch is similar to that of a brake, to stop things moving, in a lambretta engine (& most other engines) the clutch stops the gear cluster & loose cogs from spinning, this will happen whether a gear is selected or not whenever the clutch is pulled in, it "neutralises the gears" ie stops them moving/spinning, so basically if I'm correct the gear cogs are spinning until the clutch is engaged, hope that explains it a bit better

al pushpak wrote:Hi, no probs, now I've read it back it was a little long winded basically the job of the clutch is similar to that of a brake, to stop things moving, in a lambretta engine (& most other engines) the clutch stops the gear cluster & loose cogs from spinning, this will happen whether a gear is selected or not whenever the clutch is pulled in, it "neutralises the gears" ie stops them moving/spinning, so basically if I'm correct the gear cogs are spinning until the clutch is engaged, hope that explains it a bit better

It does thanks very much, but that means if the clutch stops the gear cluster & loose cogs from spinning whether a gear is selected or not then this is not where the catching noise is coming from - only when i select a gear does the noise stop !

Hi, I had similar experience to what your describing a few weeks ago, except my noise was more of a clunk, clunk, clunk sound like the cogs were rattling against each other, I , like you, checked everything, gearbox shimmed correctly,chain tension,no excessive crown wheel rock etc, & like your symptoms the noise dissapeared when the clutch was pulled in, i fitted a different gearbox in the end & the noise was no longer there, if you have a spare box it might be worth a try? I'm afraid anything like this is a process of elimination good luck

no spare unfortunately - anybody else got an idea as to what it is ???

Question - Do you know which parts stop rotating when clutch pulled and gear selected ?

I think with the clutch pulled, the only tings rotating would be the chain and front and rear sprocket (clutch basket) all else should be stationary. However, when you select a gear, there will be some load on the chain as there is bound to be some drag via the clutch. That could cause some noise as the chain tightens and rubs on the tensioners.....just beer induced hypotosizing

coaster wrote:I think with the clutch pulled, the only tings rotating would be the chain and front and rear sprocket (clutch basket) all else should be stationary. However, when you select a gear, there will be some load on the chain as there is bound to be some drag via the clutch. That could cause some noise as the chain tightens and rubs on the tensioners.....just beer induced hypotosizing

No sorry coaster - noise stops completely when gear is selected - so i don't want to know what is rotating more what has stopped rotating when gear selected but clutch pulled in???


Question still remains - Do you know which parts stop rotating when clutch pulled and gear selected ?

The whole gearbox stops spinning when you pull the clutch in (if the clutch is working correctly) so it's most likely either the kickstart piston teeth on 1st or the gear selector slightly kissing 1st or 2nd while in neutral.

If you have a GP ramp and it's the kickstart teeth then AF Rayspeed have a solution in a larger diameter pin for the kickstart piston which will pull the teeth back another 0.5mm (but try shimming your kickstart shaft again first).

If it's the gear selector then you'll most likely hear the same noise pushing the scooter along with the engine off in neutral. If it clicks like that then something is wrong in the gearbox and it needs dealing with.

Sticky wrote:The whole gearbox stops spinning when you pull the clutch in (if the clutch is working correctly) so it's most likely either the kickstart piston teeth on 1st or the gear selector slightly kissing 1st or 2nd while in neutral.

If you have a GP ramp and it's the kickstart teeth then AF Rayspeed have a solution in a larger diameter pin for the kickstart piston which will pull the teeth back another 0.5mm (but try shimming your kickstart shaft again first).

If it's the gear selector then you'll most likely hear the same noise pushing the scooter along with the engine off in neutral. If it clicks like that then something is wrong in the gearbox and it needs dealing with.

Hi Sticky - the strange thing is that the noise is still there just pulling the clutch in - it only disappears when you select a gear - does that make sense? Alan