Featured Back To The Forum...with A New Mountain Cub

Hey hey. Glad to be back to the forum. My first thread was 'potential new Triumph owner' where I made some friends and ended up getting my first Triumph. Which by the way is still going strong. After starting my love affair with old Triumphs, I finally acquired two more! A 71' Bonneville and a 66' Mountain Cub which I'm just getting started on!

They both need plenty of work but on the Cub I did a compression test and the needle barely moved. Tried two testers and my thumb...nothing. So, I proceeded to pull the engine and took it apart to see what lied within.

What I found was a seemingly fresh rebuild. New piston, rings, fresh hone, valves didn't leak at all so of course I was like what have I done?!

I've never been inside a Triumph motor so now I need some help. My thought was maybe the rings although new were stuck until I pulled the barrel. I doubt it though. I didn't adjust the valves before dismantle as the compression was so low I didn't think it would matter.

What's everyone's advice? Anxious to hear some feedback! I'll get some pictures uploaded soon!

 

Probably no compression due to the timing being out. A valve open when it should be shut.
Other than that, it'll be that bloke on the guitar

Nice little thing, are really popular now, keep us posted on progress.

 

So you're referring to cam timing? Get at that and see if the dots align? Like I said, never been inside a Triumph motor. Super exciting stuff

 

Yes, there's two pushrods in the tube on the side of the engine. These are pushed up and let down down by the lifters running on the camshaft.
The pushrods push the rockers onto the valves which then open and close at the right time to allow fuel mixture in and then the exhaust gases out.
Sorry if you already know all above
If the engine isn't timed correctly then the valves do not open and shut correctly.
The right side of the engine is the timing side. Check your workshop manual. This will show you how to time the camshaft correctly.
Here's one online if you don't have one

https://www.manualslib.com/manual/1001952/Triumph-1964-Tiger-Cub-T15.html

Always exciting getting a proper Triumph. Enjoy

 

Here's the bit you are looking for

 

Cool, looks like I'll be going deeper into the motor as I only have the outer cover off. I have a Haynes manual but it kinda sucks lol. To be clear we're talking strictly cam gear timing & pushrods not related at all to ignition timing yeah?

 

The Haynes manual is for entertainment and a general guide only. You need a parts catalogue for spares (find your engine year)

https://partsbooks.britishonly.com/#200Single

And, as I advise everyone who buys a Trumpet, unless you absolutely KNOW that the engine rebuild included the sludge trap being cleaned, you really should get in there and make sure it's clean.
In a Cub it is located in the timing side crankshaft half. It is under the slotted plug shown here



Keep going with the engine and get it totally apart. Why not, it's fun, you learn and it'll be fully yours when it's done.

Oh, and yes, sorry. The ignition timing isn't the issue. Crack on

 

Top dead center, timing marks aligned. What the hell. Put back together and now it comes apart again cuz it won't shift right, feels like I have a neutral and 1 other gear. I guess I'm learning.

 

Basically I'm trying to get it together enough to recheck compression, then I'll source some things and maybe a barrel/head as I have broken fins.

The jug will not go down all the way and it was absolute hell to get off in the first place. Any tips? Got super frustrated and had to walk away before I screwed something up. It'll slide down to that lip and then stay real stuck.

 

Stunning little bike! Welcome back

 

That’s going to be a great little machine once you’ve fixed it, I know nothing about these little cubs but I’m thinking the tolerance between the barrel and case will be tight and it looks as though it’s not very clean, I’d pull the barrel off given the mating face a meticulous clean and try again, as I said I’ve never worked on one of these so the above should be regarded as a guess!

 

Thanks Mark I'll take a the help I can get!

 

These sort of issues can be really frustrating, you don’t know the history of the engine so anything could have been done to it previously, I don’t know if you have any technical measuring gear but if checking for damage and cleaning doesn’t help then I’d measure the OD of the barrel and ID of the case to check for roundness and to find out if logically they should fit together, a local machine shop should be able to help if you don’t have OD and ID micrometers or the like.
It was together so we know it goes in, but if it’s an interference fit I’d have thought that’s wrong, I’d expect a few thou clearance on such components, anyway good luck.

 

I cleaned everything up and still no fit. There's no way it'll go in the cases unless it's hammered in which I will not do. I'm going to take it to a friend with more measuring tools and if needed he can probably take a touch off the skirt.

 

Sounds good, it could be that it’s had a replacement barrel that’s right on the top limit of it’s manufacturing tolerances and the case is right on the bottom manufacturing tolerance, anyway your friend should be able to fix it if so

 

That will be a cracking bike when you get it sorted.
Regarding the problem you have about getting the barrel (jug) back into the cases, Are you sure that you haven't missed something?? The barrel was fitted to the cases when you had the bike first and obviously it therefore should go back. I would be very wary about taking anything off the skirt until you have checked, checked and checked again.
First question is how easy was it to get the barrel off when you dismantled it?
It should need a similar amount of force to go back on.

Best of luck!!

 

It took a massive amount of work to get it off, which is how the fin was originally broke I'm sure. I'm guessing the previous owner forced it on, in fact I'm not guessing I'm sure of it. I don't know what else to check, it just plain won't go into the cases without excessive force.

 

That puts a different light on the matter, if it took a great deal of force to get it apart then there is something wrong and a light skim off the skirt should ease things.

A very good reference book as a new 'Cub' owner is 'The Tiger Cub Bible' by Mike Estell - not very cheap but well worth getting a secondhand copy if you can find one.

 

These Mountain Cubs are quite sought after.
It seems as though the PO really didn't know what he was about, it happens as we are all learning all of the time. Looks like the engine has been worked on due to the gasket surfaces being clean, engine clean etc etc.
I assume you know some history.
I refer the honorable gentleman to my previous answer the engine really could do with being rebuilt from the flywheels up. With everything being checked as you go.
The barrel may not be fitting due to a bent bolt/stud rather than anything wrong with the cases or the barrel. You'll probably go for a new barrel anyway.
Triumphs are simple souls, are easy to work on. And, as I've found out, easy to break as well.
No real force should be used anywhere, especially near alloy casings.

Don't worry about compression, if there was anything seriously wrong you would have spotted it by now - broken rings, head gasket, dropped valve etc.
Go for the rebuild and check all the available information you can, as @Samsgrandad has suggested above, on these really quite rare and special little machines.

Most of all, enjoy it, learn from it. There's no rush.
I don't mean to sound bossy or what's that other really long word....erm..dunno.
Just trying to help. Honest. cross my heart and all that

 

Much appreciated the kind words Iron. Couldn't agree more, aside from my first Triumph (69' Bonneville) this is the most important bike I own so great care will be taken!