Valve Timing

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Valve Timing

This topic has 5 replies, 3 voices, and was last updated 23 December 2018 at 12:41 by Paul Relf-Davies.

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16 December 2018 at 16:09 #385982
Dick Castle
Participant
@dickcastle
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
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16 December 2018 at 16:09 #3354
Dick Castle
Participant
@dickcastle
Bolton Marine Triple Expansion Engine
16 December 2018 at 19:03 #386002
JasonB
Moderator
@jasonb
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
21 December 2018 at 14:36 #386853
Paul Relf-Davies
Participant
@paulrelf-davies37806
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)?

cheers

Paul
21 December 2018 at 16:02 #386874
JasonB
Moderator
@jasonb
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
23 December 2018 at 12:41 #387272
Paul Relf-Davies
Participant
@paulrelf-davies37806
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.

Cheers

Paul
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