revtothelimit - motorbike forum

Mr. Dazzle wrote: Sun Jan 10, 2021 4:04 pm

Yorick wrote: Sun Jan 10, 2021 4:01 pm Yeah, have you ever seen a 2 stroke triple ?

No I haven't.

Skub wrote: Sun Jan 10, 2021 4:12 pm

Mr. Dazzle wrote: Sun Jan 10, 2021 4:04 pm

Yorick wrote: Sun Jan 10, 2021 4:01 pm Yeah, have you ever seen a 2 stroke triple ?

No I haven't.

Technically not even true, it was just a house sized diesel one that I saw

A 180 degree two stroke is only balanced if the components in each half weigh the same, they're quite a bit out on production Yamahas, including TZs, especially the crank webs.

And just for interest, race RG500s vibrate when they're running rich, but don't when they're just right or lean.

Le_Fromage_Grande wrote: Sun Jan 10, 2021 4:20 pm And just for interest, race RG500s vibrate when they're running rich, but don't when they're just right or lean.

That'll be the smoothness (or rather, lack of) at work.

Smoothness issues are caused by the power strokes not being evenly spaced or equally sized. Smoothness really is effected by the strokes of the engine, whereas balance is just the reciprocating masses. The latter should be the major source of vibes, if everything is working correctly.

It's the same reason engines with unbalanced carbs are vibey - the engine is constantly speeding up and slowing down slightly as each piston produced slightly more/less power than the average.

Makes sense, RG500s are in effect two 180 degree twin engines running on a common clutch and gear box.

They're actually 4 separate singles geared together if you want to be pedantic, each cylinder has it's own crank.

Le_Fromage_Grande wrote: Sun Jan 10, 2021 4:20 pm A 180 degree two stroke is only balanced if the components in each half weigh the same, they're quite a bit out on production Yamahas, including TZs, especially the crank webs.

And just for interest, race RG500s vibrate when they're running rich, but don't when they're just right or lean.

A well built TZ twin has no balance problems. I had my LC cranks blueprinted and ran perfectly.

mangocrazy wrote: Sun Jan 10, 2021 3:51 pm Balance is not just about reciprocating mass and how it's distributed, but also about firing cycles.

Serious vibration is not about firing cycles.

Mr. Dazzle wrote: Sun Jan 10, 2021 3:48 pm Explain how being 2 or 4 strokes effects that

Affects.

Yorick wrote: Sun Jan 10, 2021 3:57 pmFFS, I give up.

If you give up, you won’t learn anything.

JackyJoll wrote: Sun Jan 10, 2021 5:54 pm

mangocrazy wrote: Sun Jan 10, 2021 3:51 pm Balance is not just about reciprocating mass and how it's distributed, but also about firing cycles.

Serious vibration is not about firing cycles.

I never said it was. Re-read my comment.

Biggest improvement in "smoothness" I ever got was on a 1340cc A series in a Mini. I had the crank, pistons and Flywheel balanced (and flywheel lightened). When built, It was running a single 1 3/4 SU Carb rather than the previous Webers (which were fuckers to balance), The Difference was like chalk and cheese, it would rev through to 7k RPM really enthusiastically.

mangocrazy wrote: Sun Jan 10, 2021 6:02 pm

JackyJoll wrote: Sun Jan 10, 2021 5:54 pm

mangocrazy wrote: Sun Jan 10, 2021 3:51 pm Balance is not just about reciprocating mass and how it's distributed, but also about firing cycles.

Serious vibration is not about firing cycles.

I never said it was. Re-read my comment.

I never said you said it was.

Serious vibration is what matters though.

G.P wrote: Sun Jan 10, 2021 6:04 pm Biggest improvement in "smoothness" I ever got was on a 1340cc A series in a Mini. I had the crank, pistons and Flywheel balanced (and flywheel lightened). When built, It was running a single 1 3/4 SU Carb rather than the previous Webers (which were fuckers to balance), The Difference was like chalk and cheese, it would rev through to 7k RPM really enthusiastically.

Agreed. I owned a YPVS-based 'special' in the 90s and had the engine tuned (for the road) and the crank balanced by Gerry Pell. I couldn't believe the improvement when I got it back. It was turbine-smooth and had proper mid-range grunt.

G.P wrote: Sun Jan 10, 2021 6:04 pm Biggest improvement in "smoothness" I ever got was on a 1340cc A series in a Mini. I had the crank, pistons and Flywheel balanced (and flywheel lightened). When built, It was running a single 1 3/4 SU Carb rather than the previous Webers (which were fuckers to balance), The Difference was like chalk and cheese, it would rev through to 7k RPM really enthusiastically.

The only significant vibration on a normally-timed four should be from a torque “jerk” when the pistons all change direction and a vertical effect caused by TDC being a more sudden change of piston direction than BDC.

Mr Dazzle knows about more complicated shit than that, but I’ve survived in ignorance this long.

Trouble was, BMC or BL built your original engine with the moving parts all randomly different in weight, because they didn’t give a shit.

The stroke on an RD350 is 54mm, on a classic Triumph 650 it's 82mm. The Triumph also has a bigger bore (72mm against 64mm).

For the same revs the Triumph piston has to travel nearly twice as far as the RDs and hence has much higher accelerations (and thus forces) involved. Said piston is almost certainly a lot heavier too. I've not seen an RD piston but it'd have a job to match the bean cans Triumph fit, even allowing for the 2T aspect!

From that you can see a big part of why a Triumph rattles your fillings out and the Yamaha doesn't! Before you even consider the 180' vs 360' aspect.

Let's not bicker and argue about who killed who, but if to ride a cafe racer you need to fold long socks over the tops of your boots?

Chicks dig seamen’s hose.

We found loads of those socks, cotton scarves etc. when sorting my FiLs estate.

I've still got his Champion Rivetts jacket upstairs, kts the right size for me too. Might even wear it on the Bonnie. Just like this.

Taipan wrote: Sun Jan 10, 2021 1:16 pm Always think I love the sound of Ducatis, but then I hear old Brit bikes...

Nice road too. I'm actually thinking of moving to Aberdeenshire.

Gimlet wrote: Sun Jan 10, 2021 7:22 pm Nice road too. I'm actually thinking of moving to Aberdeenshire.

That was filmed on the one day of good weather they have a decade.