Author Topic: Cylinder mods  (Read 293 times)

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Saluki42

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Cylinder mods
« on: 29 October, 2020, 12:32:38 »
Hi as it possible to convert cast iron A7 cylinders to A10 by just boring out to 70mm or is the overall height wrong
Chris

idie

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Re: Cylinder mods
« Reply #1 on: 29 October, 2020, 12:58:01 »
I believe the cylinder block will just take the over boring. The A7 cylinder is one fin shorter then the A10. The A10 pistons will need to be used but the gudgeon pin is bigger so the small end bush will need to be bored out. You can't use the A10 rods as they are longer and will bring the pistons up to high. Like every thing in life it is doable  if your throw enough time and money on it. Easy option is a new crank barrel and head. You can use the A7 rocker box.

DAVE BRADY

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Re: Cylinder mods
« Reply #2 on: 29 October, 2020, 13:33:14 »
Hi,

It would be an interesting project to open up the A7 barrels but keep the A7 stroke.  I think you would end up with a 560cc almost square engine.

Dave.

idie

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Re: Cylinder mods
« Reply #3 on: 29 October, 2020, 14:42:39 »
A friend of mine is doing just that. He has bored out the barrels. His next job is making up new small end bushes.

Speedy

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Re: Cylinder mods
« Reply #4 on: 01 November, 2020, 12:48:21 »
Hello all
I have  herd of this before,  and I believe that  triumph pistons have been  used, the gudjon pin is higher up the piston nearer to the crown.

DAVE BRADY

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Re: Cylinder mods
« Reply #5 on: 01 November, 2020, 14:59:36 »
Hi,

A bit of a sideways step but I sold some knackered big bore barrels to a chap in Sweden.  His idea was to cut off the top 12mm to 15mm and attach it to another set of barrels and line the resulting cylinders.  Then use longer rods to alter the rod/crank ratio.   I think the idea is to alter the angle between the rod and the big end to crank centre line so that the rod stays as close to vertical as possible.  Thus the optimal efficiency of 90 for mechanical advantage is kept to as close as possible during the power and compression strokes.
Any experts out there so clarify this?

Dave.

JulianS

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Re: Cylinder mods
« Reply #6 on: 01 November, 2020, 15:13:01 »
Are you thinking about the "desaxe" arrangement?

Lots on the internet.

DAVE BRADY

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Re: Cylinder mods
« Reply #7 on: 01 November, 2020, 16:04:13 »
Hi Julian,

I do not recognise 'desaxe' as a term but there is a lot on the internet about the con rod ratio.  My conclusion was a lot of work for not too much gain especially for a road engine.  As I am not an engineer I can only guess that this concept was used a lot in steam engines and possibly the Panther 650 single.

Dave.

ps. Just had look at the desaxe design and I think the idea is similar in that the power stroke pushes down to be at 90 when piston speed is at its highest thus delivering maximum force.  There will be a compromise when the cylinder is directly above the centre line of the crank so the longer the con rod the closer it will be to the desaxe position - I think.
« Last Edit: 01 November, 2020, 16:12:41 by DAVE BRADY »

Calum

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Re: Cylinder mods
« Reply #8 on: 02 November, 2020, 09:58:26 »
In the steam world it is more of a problem as the pistons are dual acting - it's called the obliquity of the connecting rod. The longer the rod is the lesser the effect. Basically when the crankpin is at 90 degrees the piston is not at half its travel. So on a forward stroke the piston 'lags' behind the valves a bit but on a backwards stroke the piston leads the valves slightly, affecting the valve events.

Obviously you get the same effects on the valve rods but the throw of the eccentrics is so small compared to the length of the rods the effect is very small.

On a single acting piston such as in an internal combustion engine surely the error is constant for every power stroke and the inlet and exhaust valves are adjusted accordingly to compensate?
« Last Edit: 02 November, 2020, 10:08:35 by Calum »

DAVE BRADY

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Re: Cylinder mods
« Reply #9 on: 02 November, 2020, 13:11:04 »
Hi,

If I remember correctly the articles that I have read relate to big competition engines were they will be looking for marginal gains in power and reliability. 

Dave.

Just read this - it helps a bit.

https://www.enginebuildermag.com/2016/08/understanding-rod-ratios/
« Last Edit: 02 November, 2020, 13:27:47 by DAVE BRADY »

Calum

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Re: Cylinder mods
« Reply #10 on: 02 November, 2020, 14:09:08 »
Hi,

If I remember correctly the articles that I have read relate to big competition engines were they will be looking for marginal gains in power and reliability. 

Dave.

Just read this - it helps a bit.

https://www.enginebuildermag.com/2016/08/understanding-rod-ratios/

Interesting stuff. I guess you must have to have everything else dialled in to its absolutely optimum setting before you start messing with rod ratios and seeing benefits? By that point you're probably comparing thread count of your underwear and wondering where more weight savings can be made  ;D

Certainly in the steam world rod length affects the valve events in such a way to make that the biggest consideration as far as I can tell. Not many of the effects mentioned in that article are applicable to steam engines really, so whilst the con rod length is fairly important it is for very different reasons! Also it's not so easy to change the rod length on a loco to find out ;D

Funnily enough whilst replying to this thread I am currently machining some cylinder liners, but at around 26" stroke and 18" bore they may be a cylinder mod too far!!
« Last Edit: 02 November, 2020, 14:16:35 by Calum »

DAVE BRADY

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Re: Cylinder mods
« Reply #11 on: 02 November, 2020, 15:40:46 »
Hi Calum,

Definitely better just to read about it I think.   What are you working on? 

Dave.

Calum

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Re: Cylinder mods
« Reply #12 on: 03 November, 2020, 15:27:02 »
It's an LMS 3F 'Jinty' we have in for overhaul.

DAVE BRADY

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Re: Cylinder mods
« Reply #13 on: 03 November, 2020, 16:16:12 »
Hi,

Am I right in assuming that it is train/loco?

Dave.

chaz

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Re: Cylinder mods
« Reply #14 on: 03 November, 2020, 17:15:22 »
It's an LMS 3F 'Jinty' we have in for overhaul.

if we were in the old factory, we could do the brake system for you also steam valve and other bits . nowadays its just Ally billet stuff.