Kick Start Return spring

[Chris Exelby]

After a layup over winter the Silk amazingly kicked into life after only 7 vigorous and enthusiastic attempts. Unfortunately the kick start flopped down wards and refused to return. The spring has broken in two. Can anyone help me identify the replacement part? Also any help with the installation process would be gratefully received.

[hendred]

If you type "Spring" into search box you should find a topic on fitting kick start return spring. It is a fiddly job but got there in the end.  I believe the spring is from a three speed Scott, look in Scottparts as there two types, see which one matches your broken spring.

https://www.scottparts.co.uk/product-category/scott-motorcycle-parts/scott-kickstart-and-gearbox/page/3/

Hope this helps.

[Chris Exelby]

That's great, part ordered, thankyou!

[hendred]

Out of interest, which spring did you order?  Can't remember whether it is the tight or loose spring - may need to get one in the future!

Thanks

[Chris Exelby]

I ordered the one that looked like the one I had removed - the tight one. Experience of the Silk so far is that it may not be the correct part, just one that fitted! I will let you know

[hendred]

Thanks for posting the picture.  I should have kept my old spring for reference.  Hope you don't have too much trouble fitting it.  It is a bit of a challenge at times working out where the parts come from.

[Chris Exelby]

Spring fitted quite easily and remembering that the kick start return action was always quite sloppy decided to Pre-load the spring by rotating the housing an extra third. Now much better and should hold it in place when out on the run as it had a tendency to slip down. But this has shown a new fault. Kicking down beyond about half way the kickstart shaft tightens up and the kickstart remains pointing down, requiring a push back to overcome the stiffness to return it to the normal upright position. So that’s not much good.
It’s not the spring fouling on the housing by being ‘nipped’ as loosening the bolts has no impact. It’s something inside the gearbox that’s causing the problem. My guess is that tightening up the spring to make it more usable has caused the shaft to twist and foul inside the gearbox perhaps due to to worn bearing or thrust washer.
To check this out if I remove all the bolts that hold the gearbox side plate will all the internals fall out? Or will be able to service the kickstart shaft? Data on the gearbox seems hard to find.

[hendred]

One step forward, one back.  Have you tried reducing the spring pre-load by turning the housing back one third? I have just checked my kickstart and there isn't much spring tension when the crank is upright.  The greater the pre-load the more coil bound the spring will become on using the kickstart. With the kickstart mechanism off the bike does the crank move freely and return ok? A thought on the kickstart spring - if there are any sharp/rough edges on the spring it could bind when the spring is wound up.  
 
The Silk gearbox is based on the Velocette gearbox as used in Venoms, etc. laid on its side. If you don't have access to a Velocette manual there are several sources on the web such as this one

https://dunhackin.com/index.php/velocette-documents/mac-manuals/mac-service-guide-1965/118-the-gearbox

It is for the light weight MAC gearbox but the principals are the same, the main difference is the cam plate is at the front of the box and on a Venom it is at the back of the box (on a Silk it is at the top).  To remove the end cover take off the triangular plate in front of the kickstart crank housing and remove the circlip from the end of the mainshaft.  Then remove all the caphead screws round the edge of the cover.  The end cover should then pull off leaving the gears, etc. in place.  The two rods which the selector forks slide on may come out with the cover. Not a problem, just hold the selector forks in engagement with the camplate and slide the rods back in.  

The outboard end of the layshaft runs in a bearing in the kickstart mechanism gear.  The layshaft runs "backwards" and will try to turn the kickstart crank.  On early bikes the bearing is a bronze bush and on later ones a needle roller bearing.  Several of us have found the cage cracked on the needle roller bearing.  It is worth replacing it if you are in the gearbox.  The spec for the bearing is in the bearing list on the Technical Data / Downloads page.  They are readily available from Simply Bearings and are very cheap.  I use the best quality ones, the difference in price is minimal.

If you type "layshaft bearing" in the search box you should find several threads on gearbox and kickstart bearings
 
Hope this helps.


   

[Chris Exelby]

Thanks, this is incredibly helpful! I tried all ways of relieving the pressure on the shaft and it was clear that the greater the tightness of the spring the more the level of stiffness in the crank return. The kickstart shaft runs free without the spring, but there is substantial movement about the axis so something inside is not supporting it adequately. So it seems correct that the stiffness is due to the spring putting a twist on the shaft that it causing it to bind. With the instructions you have provided on the gearbox I will quickly find out the cause.
I will advise, many thanks!

Cheers, Chris

[Chris Exelby]

Ok. Removing the gearbox end plate was straightforward. The small circlip holding the layshaft into the bearing actually fell out as it was not engaged! The Sprag gear was a little worn, it seems ok as you can see in the photo but any advice appreciated.
The mating cog on the shaft also seems ok as you can see in the photo.
There was evidence of some rubbing on the gearbox end case (on the inside) where the sprag gear had caught. This gearbox is an earlier one (bike number 46, engine 48) and the bearing is bronze bush (not the later roller bearing) and when mated with the shaft there was play in the bearing as the result of lots of kickstart activity due to poor starting!
Hypothesis is that when the kickstart was tightened up to make it more usable, the additional torque on the shaft caused it to flex which led to contact between the sprag and the gearbox end plate. So to restore the action to that of a firm action I will replace the bronze bush.   I understand that the bronze bearing is a Caro bronze se46 and any help finding a source would be appreciated. Google would indicate its the same one as fitted to the gudgeon pin on the piston? Getting the old one out might be difficult and I might take it to a machine shop, recommendations welcomed! Based in Hungerford in Berkshire.

I have an MGB which I use for endurance rallying and also a Norton Commando 850, so I am used to belt and braces British engineering!

[hendred]

A couple of observations:

The kick start mechanism acts as the support for the layshaft outboard end bearing, there should be minimal radial movement of the assembly when fitted to the gearbox end cover.  If there is, something is wrong with the ballrace in the kick start cover and/or the bearing in the end cover.

Looking at the pictures of an engine/ gearbox rebuild on an earlier iteration of the Silk website the bronze bush should be a floating fit on the layshaft and the inside of the kick start shaft. It is a flanged bush in the rebuild pictures.

I think Caro bronze SE46 is a material specification not a particular bearing.

Try Clive Worrell for a replacement bush - he may have one.

I'm in Wantage so not far from you.  That makes four Silks in the area.  Hopefully Popham Mega Meet goes ahead this year, we managed to get three there one year.

[Chris Exelby]

Thanks Hendred, and I will let you know how it goes. I don't have an direct recent email for Clive so if you have chance to alert him to my problem I would be most grateful. I have reached out to him using using my old information.
I went on my Silk to Popham in August 2019 and I could not see any others. The Silk gathered quite a crowd and it was with relief and some cheers that she started on the 12th kick when leaving for home! Wantage is not far away and is on one of my regular ride out routes so it would be great to meet up at some point. Not sure how we go about publicising a meet on this website?

[Smokey_Paul]

Chris we did have a small gathering at Popham a few years ago and could maybe do so again inthe future if there is enough interest. I saw you leaving but couldn't catch up as I was walking from the Rotary stand.

I have a few standard springs left by the way if needed for reference or for sale if you are struggling as I think these were the last ones left I bought from Clive.
Let's see if he has some, I also speak to George who may have some thoughts.

[Smokey_Paul]

I have Phosphor bronze to make replacement bushes and also remember later engines had needle rollers so they can be viewed as a replacement if fit is good. Mind you they need changing quite often thus why I bought the phosphor bronze to make some good bushes.

[Chris Exelby]

Thanks Paul, in fact I have found a local guy who has a lathe and has accepted the challenge of making a sintered bronze bush. I hope to get the new part back in a day or so. I managed to communicate with Clive and he was really helpful on the bush material (Phosphor Bronze PBI) and clearances (0.001"). I picked up a box of Silk spares which included a spare kickstart shaft so I can try some alternate strategies. Is it worth updating the bush, or is it even possible, to update an earlier bronze assembly to needle roller?

Looking forward to perhaps meeting some fellow Silk owners at Popham this year, or anywhere local in Berkshire/Wiltshire/Hampshire. We can share battle stories.....  

[Chris Exelby]

Hi Paul,

Thank you for the offer of the bronze to make the bush. In fact my lathe owning friend is having trouble securing the correct bronze and so if you would be prepared to sell me enough to make one or even two (i have a spare kickstart shaft) I would be very grateful. I tried to contact you through the site email but it bounced. You can email me at [e-mail]

Many thanks,
Chris

[hendred]

Chris
I see Paul hasn't got back to you yet.  There is some phosphor bronze on EBay of the correct grade, it seems to come in 13 " lengths.  CC481K is the European equivalent of PB1.  An EBay search for "phosphor bronze PB1" or "phosphor bronze CC481K" should bring up the correct material.  Not cheap.  I looked at machining a Velocette gearbox bush to fit, unfortunately the internal diameter is to big for a Silk gearbox,  the external diameter could be turned down.

Hope this helps.

[Smokey_Paul]

Sorry all been a busy boy with a pile of Scott's yes all OK

Will email

[Smokey_Paul]

Have emailed send me your phone number
Also I have a funny feeling I have some new bushes somewhere....