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Tiger Cub Modified Gearbox Cover


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  • 2 weeks later...

Today's Progress: (Just in case anyone is still interested!)

I managed to source a metric oil seal ID 22, OD 28, W 4. (Thanks for making me look again Oldas:))  So I ordered 2 off. 

I made a 1:1 paper template and placed on the kick start spigot, it will just fit. (see photo)

If necessary, I will get a blob of ally weld put on the end of the flat but I'm not too bothered if the seal OD just breaks through.  I will need  to buy a cheap boring head for my mill or get a 28mm cutter to modify the housing to accept the seal.

I fitted the Ally end cap I made to my modified design cam bush which all looks o.k.  The cover is a light press fit over the bush and I may loctite it in place if I need to remove it to open out the bush on final assembly.

I couldn't resist a little go with my polishing wheel.  I think it looks o.k.

My next job after the kick start spring and oil seal arrives will be to check this part of the assembly to see if I can design and make some form of cover.

As the 22mm oil seal ID is 0.23mm smaller than 7/8", I will need to check how freely it turns on the kick start spindle.  As it isn't constantly rotating, I can't see this being a problem as I can always make the seal ID a bit bigger if necessary.

Armac case progress 3.JPG


14/01/18 progress.

The selector rod and kick start return spring arrived.  This let me check the repair bush I fitted to the gearbox case for the selector rod and fit the kick start spring to see how much room I have for a cap.

Unfortunately my kick start shaft oil seal didn't turn up but the boring bar for my mill did!  I can probably get an oil seal from a local bearing company.

I have attached photos of my progress.  I would love to know if this is the same design of kick start cap that other people fit as I have never seen one 'in the flesh'.

I'm also still trying to decide if I should counter bore the fixing holes slightly for aesthetic reasons.  I guess I'll also need to get some shorter 2BA bolts to hold the new cover on.


Armac case progress 4 140118.JPG

Armac case progress 5 140118.JPG

Armac case progress 6 140118.JPG

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I managed to obtain the 22 ID x 28 OD x 4 W oil seal from a local supplier (£2.50) and tried it on my spare kick shaft spindle.  It looks like it will be fine especially with a bit of 'O' ring grease on the shaft.

Next job will decide if I need to add a bit of weld.  If not I will machine a Diameter 28 x 4 deep recess into the case to fit the seal.  All set up and ready to go.


kickstart oil seal 1.jpg

kickstart oil seal 2.jpg

kickstart oil seal.jpg

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I machined and fitted the kick shaft oil seal last night.  The recess is 28mm od x 4mm deep and just broke through the housing where the flat is (as anticipated).

I'm not too fussed as I will put a smear of sealant in the recess on final assembly.

I will also be fitting the double lip seal with the spring facing outwards as I think there is more chance of water entering the gearbox through the kick shaft spindle than oil coming out.  If you want to fit the seal the other way around, I would recommend you machine the recess 5mm deep to allow the seal lip to clear the outer step on the shaft.

Photos below.

I hope this helps someone else.


kickstart oil seal fitted.jpg

kickstart oil seal recess.jpg

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O.k, I removed the existing gearbox side plate from my Armac Cub over the weekend ready to fit the modified one. 

Unfortunately the cam came out with the cover instead of staying in the engine case!  I didn't notice until it was too late as I have a blind camshaft bush fitted.  The cam followers then dropped down along with the push rods.  I have no idea how I'm going to put it all back together without lifting the head.  I do have an access hatch to locate the top of the push rods but I may bite the bullet and take the engine out.  Any advice on this would be appreciated :-)

I did notice my blind camshaft bush was a slightly loose fit in the cover which was causing a small engine oil leak.  I also had signs of gearbox oil weeping around my Armac clutch lightener (I have now made a replacement 'O' ring to cure this).  I also had some oil coming down the kick start spindle. My new oil seal should also cure this.  Hopefully I will have an oil tight Cub engine at the end of all this!

The other thing | noticed was just how thick my standard (Halfords classic) motor oil gets when cold.  I'm seriously thinking about using a multi grade oil (10/50) in the gearbox and going for a fully synthetic (PJ1?) in the engine now that it is run in and I'm running a Honda 220cc piston with decent seals.  The oil that came out looks like treacle!

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Not a fan of fully synthetic oil in Brit motors.

I'd put a high quality mineral 20/50 in the engine and whatever the Triumph Competition Dept recommended in the gearbox. EP90 ?

Oil in a trials bike is cheap enough, not a lot used and changed regularly.

By the way, I ran/owned a Meriden Triumph twin shop back in the UK for 15 years and have worked on British bikes for over 35 years.


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Thanks for your reply.  Point taken.  The gearbox uses standard engine oil and I am running a (dry) diaphragm clutch so I could probably get away with using modern 20/50 for both engine and gearbox.



Again, thanks.  I read the article with interest.  I managed to relocate the push rods as the engine was at TDC (without the valves lifting).  I removed a little access plate I put in the head when I built the engine originally and managed to locate the inlet push rod into the rocker shaft.  I was then able to hold both cam followers up and pop the camshaft back in!  I think being a side point engine probably also helped.

I have fitted my modified gearbox cover to check the end float on the main shaft.  (as photo)

I also removed the primary case outer cover to do this but I think I'm also going to have to remove the clutch diaphragm and basket to measure the end float accurately.

I also need to fit my spare kick start shaft oil seal on final assembly!

Oh well, at least it's progressing slowly :-)

armac side case trial.JPG

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I just thought I'd add a photo of the mod that saved the day when I accidently pulled my camshaft out. 

I take no credit for it as a local Tiger Cub Guru from Pluckley (thanks Henry!) told me what to do when I was rebuilding the cylinder head.

It obviously has a nice shiny ally plate that covers the access hole.

It may help somebody else.


head rebuild3 access hole 141117.jpg

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Probably my final post on this subject!

I have finished final assembly.  I learnt from my mistake and added an M5 c'sunk screw to the end of the camshaft end  cap so I can hold the cam in place next time I remove the side cover.

I also made a spacer bush for the gear change shaft to make it a little less vulnerable to being bent.  (It's still pretty tucked out of the way)

I think my original oil leaks were coming from a slightly loose blind cam bush and along the kick start shaft.  Both of these should be sorted now.  It should be easy to see where any oil is coming from now!

I have attached some photos of the finished item.  I'm still waiting for 3off 2BA cap heads to be delivered to fill the final fixing holes but you get a pretty good idea.  It has been more work than I anticipated but I have enjoyed doing it (most of the time!).

Do I like it?  To be honest I'm not sure, but it's growing on me :-)  I hope this has been of help and interest to other people who like to muck about with these strangely addictive trials bikes in their sheds!  If you do something similar, let me know how you get on.




Armac case progress 9.JPG

Armac case progress 10.JPG

Armac case progress 11 finished.JPG

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Stanmet, thanks for your comments. Nice to know it’s helpful to someone. If you are fitting an outer cover with the kickstart seal I would recommend you get the end of the flat in the casting welded so your seal recess doesn’t break through. However, make sure you leave enough of a flat (or file a small recess) to get the selector pin back in the case. I would probably go 5mm deep on the bored hole too. 

It doesn’t matter so much on mine because the spring cover, spring retaining washer and kickstart hold my seal in place. 

I would still love to see what UPB do to modify their kickstart housing. 


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I also forgot to say, my Armac Cub is my ultimate 'state of the art' bike.  I also have this slightly more traditional Cub that I have just rebuilt to allow my Son to do some pre 65 trials with his dad :-)

This is another bike that I built from bits and pieces.  For example the oil tank in made from a piece of Class 465 train cable conduit, the oil filler plug is a used gearbox drain plug from a class 395 high speed train (all from the scrap bin at work).  I swapped a few cub wheel bits with Malcolm Simmons for  the back wheel out of his green Trials Francis Barnett (I kept it the green he painted it to remember a great guy)

I'm no expert rider but I do like modifying and making bits for these old bikes and then trying them out.  You can't really do this sort of stuff on a modern bike. 



old cub rebuilt 041217.JPG


Edited by brucey
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