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Hello, can I measure the stroke of a crank by measuring how far the piston goes down the bore from tdc? I have a inline a series engine Im about to sell and I was told it was a 1430/1460 Can't remember which so I figured id double check it before I sell it.

Cheers

Head on or off?

Yes head is off, sorry I neglected to mention that! I have a long dial gauge and was just going to measure it with that!? In my head that makes sense!

That should do it, or a good steel rule. Measure the piston down the bore at tdc and the repeat with it at bdc or simply measure the next bore.

then it's bore dia x.5 x squared x pi x stroke x 4 = capacity

Being used to mathematical formula on a daily basis:



Which means for an A-series engine (4 cylinders):



In both formula, the Greek letter is called pi, which is valued 3.1415...

Filling in the Bore and Stroke values in cm gives you the capacity in cc. This gives the numbers that we all know for the standard engine sizes 848cc, 970cc, 997cc, 998cc, 1071cc, 1098cc, 1275cc. These numbers are actually rounded as they are in reality closer to: 849.4cc, 970.5cc, 995.2cc, 998.4cc, 1070.1cc, 1097.2cc and 1274.9cc respectively (presuming that the bore & stroke values in my books are correct).

You can measure it with a ruler

1430 is 73.5 bore and 84 stroke

1460 is 73.5 bore and 86 stroke

If it,s 1460 I have someone who would be very interested in it

Cheers chaps, i'l let you know 251eng

I use this equation 3.14 x (piston size) x (piston size) x stroke= cc

For example to get 1460cc

3.14 x 73.5 x 73.5 x 86= 1458823.6 = 1459 cc (1460)

Err, nup that formula doesn't work. By chance it gives you the right answer, but only for that size of piston.

It needs to be pi times the piston radius squared (you've used diameter) times the stroke, but that's only for 1 cylinder and you want it for 4

So

3.14 X 36.75 x 36.75 x 86 x 4 = 1458823.59

divide by 1000 to fix the units = 1459

With a bit more precision to pi it works out closer to 1460.

Tim

on 'another forum' i was recently amused to see a 'youth' claim that his engine was a '1355 innit' because it was plus 20.

his mathamatical reasoning was that you added the 4 x +20 to the original engine size, so 1275 + (4x20) = 1355....


god knows what he would do if it was stroked!

guru_1071 wrote:on 'another forum' i was recently amused to see a 'youth' claim that his engine was a '1355 innit' because it was plus 20.

his mathamatical reasoning was that you added the 4 x +20 to the original engine size, so 1275 + (4x20) = 1355....


god knows what he would do if it was stroked!

Excellent

Vegard wrote:

guru_1071 wrote:on 'another forum' i was recently amused to see a 'youth' claim that his engine was a '1355 innit' because it was plus 20.

his mathamatical reasoning was that you added the 4 x +20 to the original engine size, so 1275 + (4x20) = 1355....


god knows what he would do if it was stroked!

Excellent

if you throw undersize bearings into the mix you would probably end up with a 2 litre

Tim wrote:Err, nup that formula doesn't work. By chance it gives you the right answer, but only for that size of piston.

It needs to be pi times the piston radius squared (you've used diameter) times the stroke, but that's only for 1 cylinder and you want it for 4

As indicated in my post, the formula's are equivalent for a 4-cylinder engine. As you will agree Radius = 0.5 x Bore (to complete things Bore = Diameter ≈ Piston Size). Squaring the Radius is then equivalent to 0.5 x Bore x 0.5 x Bore = 0.25 x Bore x Bore. The 0.25 disappears against the 4 of the cylinder count.

Sorry, I'm just a nerd sometimes

My apologies, you're correct. As a professional nerd I'm embarrassed that I'd never noticed that.

But just so that I can be more correct, your formula starts to get messy for anything with a different number of cylinders.

Tim

obviously using the squaring of the bore works exactly the same as the std formula on a mini engine. But it fails a bit on a 6 or 8 and is not really much use on a 28 cylinder radial aircraft engine.

god knows what he would do if it was stroked!

I imagine it would certainly involve a hard on

mk1 wrote:god knows what he would do if it was stroked!

I imagine it would certainly involve a hard on

What are you saying Mark, that it gets harder the more its stroked?

Mine certainly does

Blimey maths was never my forte!

My education went as far as "the wheels on the bus went round and round" then i discovered minis......

I have a 13 year old son who would understand those workings I will get the lego out and get him to show me

Tim wrote:Err, nup that formula doesn't work. By chance it gives you the right answer, but only for that size of piston.

It needs to be pi times the piston radius squared (you've used diameter) times the stroke, but that's only for 1 cylinder and you want it for 4

So

3.14 X 36.75 x 36.75 x 86 x 4 = 1458823.59

divide by 1000 to fix the units = 1459

With a bit more precision to pi it works out closer to 1460.

Tim

How does my equation come to prety much the same answer though? Haha! granted if I got it wrong I got it wrong! But it's funny it pretty much works?!

Also, iv measured the stroke at 83.6 which I came to 1418cc.. thought it sounded odd to me!
what does that stroke give in cc with the correct equation?

I've provisionally sold the engine and told him what Cc I came too. So I would like to know for definite what it is!