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Valve Timing

Bolton Marine Triple Expansion Engine

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Dick Castle16/12/2018 16:09:36
1 forum posts

Having just completed the build of the Bolton Engine I am in some doubt as to whether the valve timing is correct. Due to a lack of exact information on the drawings I guessed a setting of the valves starting to open at 10 degrees after TDC? The engine is not self starting but runs very nicely at 150 RPM on air or steam. Before I strip the engine for painting I would like to have some confirmation as to whether my settings can be improved?

I would be pleased to hear of the experiences of another builder.

Regards Dick Castle

JasonB16/12/2018 19:03:12
18139 forum posts
1997 photos
1 articles

If running on air then with the crank at TDC the high point of the eccentric wants to lead by about 90degrees plus 10degrees so 100 degrees ahead total. If on steam you want about 30 degrees of lead so 120degrees total.

So for air with crank at 12o'clock high point of eccentric wants to be at 20 past 3 and with steam at 4o'clock. for teh opposite direction then 8.40 for air or 8 o'clock for steam

Which of the Bolton engins is it?



Edited By JasonB on 16/12/2018 19:06:18

Paul Relf-Davies21/12/2018 14:36:31
74 forum posts
1 photos

As a follow-up question to the reply above...

When the crank is at TDC & the inlet valve set at (for example on steam) to 120 deg of advance, should the valve be:

  1. just opening/about to open...?
  2. fully open...?

And following on from this, should be exhaust valve be 180 degree ahead/behind the inlet valve (and open for the same length of time)?



JasonB21/12/2018 16:02:04
18139 forum posts
1997 photos
1 articles

1 & 2 really depend on how much lap the valve has, on an engine with little or no lap the inlet port will be uncovered earlier than on an engine with a lot of lap. Generally it will have just opened.

Once I have checked that I get equal movement each way I don't bother looking at the valve again, just go by the eccentric angle.

I just noticed in the title that it's the Bolton triple, you can set that up much the same as the Stuart which is detailed here

Paul Relf-Davies23/12/2018 12:41:56
74 forum posts
1 photos
Thanks Jason,

I'm currently designing/making my first valved engine. So far, I have made the eccentric, conn-rod, piston-valve piston (blank) and drilled the ports for the inlet and exhaust.

At this point, I'm trying to work out how to machine the piston valve so that it exposes the inlet and exhaust ports in the correct in relation to themselves.

My initial assumption would be to have zero overlap , with one port starting to open as soon the other is fully closed, fully open 180deg apart.

This is for a very small engine (8mm bore, 16mm stroke...Mamodish) and the eccentric is fully adjustable.

TBH, I'm just playing around, trying to work out how to build this engine from 1st principals, both in terms of the engineering principals and the manufacturing techniques.



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