Classic Triumph Bonneville

[Mr. Dazzle]

Yeah old engine thing.

Modern engines have much better combustion chamber design! Not to mention knock sensors.

On this engine the three common CRs are 7.5, 9 and 11 to one. 9 is standard on a T120R cause its the sporty one which takes 4 star, 11 would be for high performance running 5 star.

[JackyJoll]

Once the head is on, you can measure the compression ratio, if you care that much.

[Mr. Dazzle]

Not a huge amount I can do about it.

Well that's not true, I van change the base and head gaskets. But I don't even know how much power I'll get, so.....

I think I'll try and figure out what cams it's got while I'm in here though. I can't actually see the part numbers but by putting the degree wheel on the crank I can see when they open/shut and try and get a rough measurement of peak lift.

[JackyJoll]

Once the head’s on it won’t be hard to see if the timings at 20 thou checking clearance match the E3134 figures.

The cam lift is easiest measured at the followers, before you put the pushrod tubes on.

[Mr. Dazzle]

My plan was to put the jugs back on, then whip of the covers at put the timing disc on crank. Should be a piece o' piss to find TDC when the head's off, then I can just find out what the BTDC and ATDCs are on the cams. Just put it in fourth gear, turn the back wheel and watch to see when the followers move.

Lift I was just gonna get a rough measurement for at the followers using a steel rule, I'm expecting the duration is the easier thing to track down.

[JackyJoll]

Yeah old engine thing.

Modern engines have much better combustion chamber design! Not to mention knock sensors.

As Henry Ford said about one of his early projects: “It was air-cooled, which really meant it was not cooled.”

[JackyJoll]

My plan was to put the jugs back on, then whip of the covers at put the timing disc on crank. Should be a piece o' piss to find TDC when the head's off, then I can just find out what the BTDC and ATDCs are on the cams. Just put it in fourth gear, turn the back wheel and watch to see when the followers move.

Lift I was just gonna get a rough measurement for at the followers using a steel rule, I'm expecting the duration is the easier thing to track down.

The degrees where lift just starts won’t match any published figures, because there’s a setting clearance. For Triumph’s own cams it’s 20 thou.

[Mr. Dazzle]

Ah right, so that's why it's better to do it by watching the rockers.

[JackyJoll]

I found (haven’t had to do it many times) it easy to set the valve clearances to 20 thou and turn the crankshaft slowly while rattling the rocker up and down, feeling for the clearance to close up to zero.

Re 20 thou clearance: if you have 24 tpi (UNF) threads on the adjusters, half a turn is 21 thou. If you have 26 tpi (BSC) threads, then half a turn is 19 thou.

If I’ve got that wrong, you can tell me seeing as you be an engineer.

[Mr. Dazzle]

Since I'm waiting for my pistons now I decided to do a job i was in 2 minds about....re-dressing the cam follower faces. Apparently its good practice to clean them up with a very fine grit stone and fortunately I've got just the kiddy...

Before.



After some careful polishing with 1000 then 4000 grit whetstone....really see the difference right. Despite appearances they were always mirror smooth.

[KungFooBob]

Are they not surfaced hardened?

Like Honda RFVC followers

[Mr. Dazzle]

They are...you can see the surface is a different material stuck on. Stellite I believe.

I cleaned em with a super hard whetstone I bought for doing knives. Took about an hour to do all four.

[JackyJoll]

It’s a stellite pad silver soldered onto the steel foot. The stellite is hard all the way through. It’s thick enough that they can be ground to a different radius.

[JackyJoll]

My sad story about grinding the followers is the machinist didn’t see the crack on one until after he’d done £5 worth of grinding.

[Mr. Dazzle]

These ones have a couple of tiny chips out of them, but they're on the corners and I can't see how it would really matter. Seems like it should be well away from where the cam runs on it.

[Le_Fromage_Grande]

You're not going to be doing mega miles on it or racing it so I wouldn't worry about it, you'll take it apart after a summer of riding it just to see how it's going inside - it's what classic bike owners so

[JackyJoll]

These ones have a couple of tiny chips out of them, but they're on the corners and I can't see how it would really matter. Seems like it should be well away from where the cam runs on it.

If you buy new ones, there’s a risk they won’t be as good as the old ones.

[Mr. Dazzle]

All the stuff on here has lasted 50 years after all...

[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.

[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 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

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