Classic Triumph Bonneville

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Le_Fromage_Grande
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Re: Classic Triumph Bonneville

Post by Le_Fromage_Grande »

There's always a risk that new parts aren't as good as the originals, with old Kawasakis a lot of so called race parts aren't as good as the Kawasaki OEM parts and also cost more.
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Mr. Dazzle
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Re: Classic Triumph Bonneville

Post by Mr. Dazzle »

Yeah I can see how that might be. Oddly enough, I'm deeply familiar with the relative quality of OEM parts and aftermarket :D Hell, alot of the time I AM the aftermarket!

I've no plans to replace the tappets. In fact the only bits I've replaced are either things I have no choice in (valves for example) or bits where there's a clear reason to do so, e.g.. upgraded rocker spindles with better oiling. Even then I can consider if the new pattern part is likely to be OK or not based on how complicated and heavily loaded it is - again something I've quite a bit of background in :D

I'm replacing the pistons too of course, but they're not OEM anyway 'cause they're +40s.
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Re: Classic Triumph Bonneville

Post by Mr. Dazzle »

My new pistons arrived today, ahead of schedule. Spot the difference....

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Aside from the obvious crown shape, the new ones have different pins (smaller ID, presumably to make them stronger), chrome plated rings and more 'meat' around the pin holes inside. The new ones also have a vertical groove by the pin hole, not sure what that's about.

They weren't kidding when they said "new old stock", they came in the original packaging complete with the instructions and new clips.

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Unfortunately the pins are stuck solid in the pistons. They're supposed to be a easy finger tight fit, but the instructions do say that they might get stuck due to oil coagulation in storage. I'm currently say watching them simmer very gently in hot water....

I now have to gap another set of rings.
Le_Fromage_Grande
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Re: Classic Triumph Bonneville

Post by Le_Fromage_Grande »

The vertical groove is for getting the circlips out.
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Re: Classic Triumph Bonneville

Post by Mr. Dazzle »

Yeah I just twigged that :D

Hot water worked a treat, the pins just slid out. The 11:1s are also 'superfinished' on the pin holes (that's a real thing BTW). Dunno if you can see it here, the 11s are on the right. The hole is mirror smooth on them but just simple machining on the standards.

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I did another one of those jobs I'm not sure is strictly necessary but since I'm here: Knocked all the very sharp edges off the valve pockets with 4000 grit wet and dry then polished everything with Autosol before a thorough wash in very hot soapy water.

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Re: Classic Triumph Bonneville

Post by cheb »

There's something amusingly ridiculous about really high domed pistons. A high quality work around I suppose.
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Re: Classic Triumph Bonneville

Post by Le_Fromage_Grande »

Sharp edges promote detonation, so removing them can't be a bad thing
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Re: Classic Triumph Bonneville

Post by Mr. Dazzle »

The instructions claim they're "ready for competition use"...I can only assume that what passed for ready in 1973 was different to today. The edges were borderline sharp enough to cut your finger!
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Re: Classic Triumph Bonneville

Post by ogri »

Mr. Dazzle wrote: Sun Jun 20, 2021 8:49 pm The instructions claim they're "ready for competition use"...I can only assume that what passed for ready in 1973 was different to today. The edges were borderline sharp enough to cut your finger!
Probably less problems with detonation in those days unles you used aviation fuel etc?
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Re: Classic Triumph Bonneville

Post by Le_Fromage_Grande »

Ready for competition use is marketing, but to be fair to whoever made them not much was known about what caused detonation in the early 70s, nobody uses high domed pistons in modern race engines, that went out in the 1980s, now it's shallow smooth domed combustion chambers and nearly flat pistons.
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Re: Classic Triumph Bonneville

Post by Mr. Dazzle »

No one has used a domed combustion chamber in a performance engine for few decades at least, its pent roof now. Goes back to supermofo's point about how his modern bike can run 12 or 13 to 1 when I'm worrying about 11. The chamber shape is a big part of that.

I say "no one".....the yanks still make 2v hemi engines and put them in fast cars, coz of course they do. :D

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Re: Classic Triumph Bonneville

Post by Le_Fromage_Grande »

I'm guessing that what I called a shallow some is actually called a pent.
I have one of the last domed performance motorcycle engines, my 1983 Kawasaki engine has combustion chambers like bath tubs, Suzuki and Honda had gone to 16 valve pent chambers in 1979.
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Re: Classic Triumph Bonneville

Post by Mr. Dazzle »

The key thing with a pent roof is that it's a triangular top rather than a hemisphere. To be fair that's as much about getting the 4 valves in as it is anything else. With a 4v head it's hugely easier to get the valves and cams in if the valves are 'square' to each other in a straight line. Imagine the difficulty in actuating two valves which are not on a common axis - possible, but a ball ache.

It also means the spark plug is in the centre rather than hugely offset to one side like it is me auld Trumpet.

As you say, modern pistons tend to be flat topped, but the shape of the chamber roof means you can still squeeze it down to high compression ratios even with flat pistons. My (diesel) car runs 17:1 and has so called 'omega pistons' which are flat topped with a cutout in them...

Things have come a long way in 50 years!

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Re: Classic Triumph Bonneville

Post by Rockburner »

Mr. Dazzle wrote: Mon Jun 21, 2021 9:02 am The key thing with a pent roof is that it's a triangular top rather than a hemisphere. To be fair that's as much about getting the 4 valves in as it is anything else. With a 4v head it's hugely easier to get the valves and cams in if the valves are 'square' to each other in a straight line. Imagine the difficulty in actuating two valves which are not on a common axis - possible, but a ball ache.
IIRC Rudge had a 'radial' 4-valve head race bike pre war. I think it was pretty fast for the time.
Mr. Dazzle wrote: Mon Jun 21, 2021 9:02 am
As you say, modern pistons tend to be flat topped, but the shape of the chamber roof means you can still squeeze it down to high compression ratios even with flat pistons. My (diesel) car runs 17:1 and has so called 'omega pistons' which are flat topped with a cutout in them...

Things have come a long way in 50 years!

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Isn't that very similar to a 'Heron' head? Where the valves open 'into' the head of the piston?
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Re: Classic Triumph Bonneville

Post by Mr. Dazzle »

'Radial' 4v heads are definitely a thing, it's just much much easier to make engines where the valves are in a nice straight line!

I think in my car it's about the way the gases move about and swirl in the chamber. Doubly so when you consider it's a direct injection engine with a complicated multi-stage injection. Modern diesel engines might have 5 or 6 steps to the actual injection event, it's not just sprayed in.

It's called an omega piston 'cause that's the shape of the cross section.

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Re: Classic Triumph Bonneville

Post by KungFooBob »

Honda made Radial Four Valve engines, you can spot them because they have RFVC written on the side :)
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Re: Classic Triumph Bonneville

Post by Mr. Dazzle »

KungFooBob wrote: Mon Jun 21, 2021 9:46 am Honda made Radial Four Valve engines, you can spot them because they have RFVC written on the side :)
Indeed...then you end up having overhead cams and rockers! Not so bad on a single, but imagine doing it on a V4 for example - possible, but cost adds up pretty quick.

It's also not too bad fitting everything in on an SOHC engine with a bunch of rockers on a single, but it gets tight on multis.

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Re: Classic Triumph Bonneville

Post by Rockburner »

Mr. Dazzle wrote: Mon Jun 21, 2021 9:42 am 'Radial' 4v heads are definitely a thing, it's just much much easier to make engines where the valves are in a nice straight line!

I think in my car it's about the way the gases move about and swirl in the chamber. Doubly so when you consider it's a direct injection engine with a complicated multi-stage injection. Modern diesel engines might have 5 or 6 steps to the actual injection event, it's not just sprayed in.
Is it injection into the combustion chamber itself? Or into the manifold?
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Re: Classic Triumph Bonneville

Post by Mr. Dazzle »

Straight into the chamber, the injector is where the spark plug is in a petrol car. That's why modern diesels have crazy high fuel pressure (~2000 bar), so you spray it in at really really high pressure and get fine atomisation and very fine control.

It's all getting a bit blurred now when you consider the use of multi stage injection, turbulent jet ignition, gasoline direct injection, HCCI etc. etc.

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Re: Classic Triumph Bonneville

Post by Le_Fromage_Grande »

Mr. Dazzle wrote: Mon Jun 21, 2021 9:52 am
It's also not too bad fitting everything in on an SOHC engine with a bunch of rockers on a single, but it gets tight on multis.
Would it ever, the valve gear is wider than the piston on most Honda RFVC engines
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