Indeed.
A proper front drum will put you over the bars and IME a really good one is no worse than a disk brake, they're just massively heavier and have problems with heat, etc.
Nice Triumph
I’ve been using an 8” single leading shoe brake for years. It’s good enough on the road, if you can set it up so the leading shoe does the work.
Totally useless for racing: repeatedly charging at corners and braking hard makes it heat up and no longer work.
Lutin wrote: ↑Thu Aug 06, 2020 9:49 am
I'm sure that I've a copy of an article from Classic Bike magazine on sorting oil leaks from Triumph pushrod tubes. I'll have look now.
Thanks (have responded to your pm). Always good to have more information- one of the key things is the squish measured between the head and barrel (with gasket and pushrod oil seals etc all in place). Ideally you're looking for 30-40 thou, any more and you run the risk of bowing the head, any less and the push rod tube O rings wont compress enough to seal- there are different thickness O rings and seals available to achieve the required squish, but a dry run on the bench last night gave me 35 thou . I'm pretty sure my pushrod leak is in fact the tappet block which is pressure fed on the exhaust side- certainly the O rings inside were hard, brittle and squared off. I'm hopeful the new O rings fitted last night will be the cure
Well apart from the viton top seal and rubber lower one. And the alloy head with cast iron barrel ... and the steel pushrod tubes... and the silicone square section rings the tubes sit on... yep all the same...
I get where you’re coming from but getting the right relationship between all the components when cold is the correct starting point- as I say 30-40 thou is ideal but it would probably be ok at 50 or 20. The point being that there needs to be a sufficient amount of clearance before clamping down for the seals to compress enough before the head starts to bow over the top of the tubes (if that makes sense)
I've just nipped to the garage and thought I'd test the tightness of the pushrod caps, one came off in my hand and on closer inspection the rod has a slight bend to it. New set of Norman Hyde pushrods is en-route and should be here tomorrow
Makes perfect sense, I understand, but (in my ignorance) it seems like a strange design.
In my (limited) experience there is quite a lot of expansion in a bike engine when it gets hot, so it seems like a strange design to have it relying on such tolerances if unequal expansion is any sort of issue.
I think it pretty much characterises the British motorcycle industry, which basically was to keep developing the same basic engine to the point problems creep in. The Bonnie engine is broadly very similar to the 1938 Speed Twin, except it grew from 500cc to 750, went from iron head to ally etc but so a classic case of over development of a product
Yeah I think that's what I was getting at, they probably thought they were being innovative, but they created a problem that didn't need to be there.
Mind you, that seems to characterise the whole of industry now, not just old British bikes, it seems that everyone wants innovation for the sake of innovation because they think it signifies extra value for money. I'm amazed that the bike industry isn't touting AI and Blockchain like everyone else.
I think it was more hubris and a lack of desire to invest than anything else. For years British twins were the best motorcycles in the world and they didn't see that ever changing so 50 year old (and sometimes older) tooling was still used to churn out 50 year old designs because they knew best... I find the whole British bike industry story really interesting and really depressing in equal measure- on the one hand you had out of touch management and on the other resentful workers trying to compete with superior Japanese machines with zero investment and a genuine belief that "Jap crap" wouldnt be around for long
Well apart from the viton top seal and rubber lower one. And the alloy head with cast iron barrel ... and the steel pushrod tubes... and the silicone square section rings the tubes sit on... yep all the same...
I get where you’re coming from but getting the right relationship between all the components when cold is the correct starting point- as I say 30-40 thou is ideal but it would probably be ok at 50 or 20. The point being that there needs to be a sufficient amount of clearance before clamping down for the seals to compress enough before the head starts to bow over the top of the tubes (if that makes sense)
Makes perfect sense, I understand, but (in my ignorance) it seems like a strange design.
In my (limited) experience there is quite a lot of expansion in a bike engine when it gets hot, so it seems like a strange design to have it relying on such tolerances if unequal expansion is any sort of issue.
The rubbers filling the gaps are supposed to allow for expansion and differential expansion of materials, but they don’t really seem to.
You’d be ill-advised to be snobbish about using sealant.
You can block off the oil feed to the exhaust tappets.
To update the thread replacing the tappet block oil seals seems to have done the trick; 250 oil tight miles so far. I’ll need to retorque the head (which involves removing the tank and head steady as well as regapping the tappets) but for now all’s good
Yeah I think that's what I was getting at, they probably thought they were being innovative, but they created a problem that didn't need to be there.
Mind you, that seems to characterise the whole of industry now, not just old British bikes, it seems that everyone wants innovation for the sake of innovation because they think it signifies extra value for money. I'm amazed that the bike industry isn't touting AI and Blockchain like everyone else.
I think it was more hubris and a lack of desire to invest than anything else. For years British twins were the best motorcycles in the world and they didn't see that ever changing so 50 year old (and sometimes older) tooling was still used to churn out 50 year old designs because they knew best... I find the whole British bike industry story really interesting and really depressing in equal measure- on the one hand you had out of touch management and on the other resentful workers trying to compete with superior Japanese machines with zero investment and a genuine belief that "Jap crap" wouldnt be around for long
The story of the rebirth of "new" Triumph is based around exactly that. John Bloor tells the story of how he discovered the correspondence between the UK and Japan and how arrogant and patronising the Brit management was about inviting them in "because they'll never compete with us, who do they think they are" and how that led to the rebirth of the Jap bike industry. He also compares his experiences of writing to the big four when he first decided that Triumph was going to live again "Further your letter of 1948* and our subsequent hospitality I wonder if you'd like to return the favour?" and how, unsurprisingly, all but one declined. (It was Kawasaki that said "yes, come on over")
Supermofo wrote: ↑Wed Sep 09, 2020 10:48 am
I often think of getting a bike from the year I was born (1977) didn't realise Bonnies fitted the bill!
If you're feeling particularly patriotic you could consider the T140J Silver Jubilee (built to commemorate The Queen's 25 years on the throne in 1977). Basically Bonnie with a blue seat, a silver paint job and quick detach chrome on the engine covers
