Minnie

[David Bothwell 1Participant @davidbothwell1]

After a long (uphill) struggle with my part made Minnie I arrived at the stage where I tried to run it on air, I let the compressor build up a large tank of air and released this and turned the flywheel, The engine ran for a few revolutions then stopped. I removed the top cover of the valve chest and adjusted the the valve on the rod, after replacing the cover I tried again, although I was fairly sure that either end was exposing the passage to the cylinder, the engine still stopped after a few revolutions, any suggestion would be most gratefully acccepted!

[David Bothwell 1Participant @davidbothwell1]

runs but stops

[JasonBModerator @jasonb]

Where are you feeding the air into?

Does it turn over freely by hand?

[David Bothwell 1Participant @davidbothwell1]

Hello Jason! The engine turns over (very) freely, I have fed the air into the boiler from one of the sight glass inlets (back of the boiler) with the other (lower one blanked off.

[JasonBModerator @jasonb]

When it comes to a holt have you tried turning the flywheel by hand in both directions, if so is there a point where the flywheel tries to turn by itself as this woul point to a timing problem. Is it the same in fowards and reverse?

[David Bothwell 1Participant @davidbothwell1]

The con rod tries move when the ar is applied at front dead centre. never thought to move the flywheel when the engine stopped. I did remove the valve chest cover when the engine stopped first time and the inlet to the cylinder was covered i.e. unequal opening which I thought I had dealt with. I set the eccentrics as per the illustration in the Model Engineer construction articles and this seemed alright. Most frustrating as there is initial movement. I have had to leave it today as I was afraid of overheaiting the compresser!

[JasonBModerator @jasonb]

Does sound a bit like timing. Try what I said about moving teh flywheel and whichever direction it shows sogns of life then adjust teh eccentric a little and try again.

When in forwards the flywheel rotates "backwards" being a 4 shaft engine. Eg when looking from the flywheel side it should be going clockwise.

[Neil WyattModerator @neilwyatt]

It's always worth a sanity check to make sure the valve is just opening as the cylinder passes TDC. It probably won't run as smoothly on air as steam.

N.

[David Bothwell 1Participant @davidbothwell1]

thanks for the suggestions. I will give it another "go" in the morning and let you know.

[julian atkinsParticipant @julianatkins58923]

Hi David,

Assuming no further problems with your cylinder block etc,

Setting of valve gear ought to be approached methodically and carefully.

It must not be rushed, and may take quite a long time to get 'right'.

There is obviously something still seriously wrong. Exactly what, is impossible to predict or advise upon from the available information.

Suggest for a start you accurately establish the front dead centre (FDC) and back dead centre positions (BDC) and establish at what point the valve opens for each in fullgear.

Cheers,

Julian

[David Bothwell 1Participant @davidbothwell1]

Thanks for the responses, I have altered the eccentrics to match a couple of printed pictures (of working engines) but the effect has made things work. I will revert to the settings according to the build articles. I will take Julians advice on board when I return to the engine this afternoon. Just in passing there was no movement and quite a bit of resistance and absolutely no chance of rotation!

[JasonBModerator @jasonb]

Well at least it sounds like air is getting to the cylinder, just not when needed

[David Bothwell 1Participant @davidbothwell1]

Having spent another couple of hours adjusting things it has now become obvious (and probably VERY obvious to others) that the position of the eccentrics on the con rod is "critical" to gthe vlave events. On tghis basis I realised that I was not getting a correct opening of the valve, i.e. crankshaft at back dead centre but inlet to cylinder was covered. I have re-adjusted the eccentrics but not had any time to try the new settings.My thanks to each person who has replied and hopefully I may have the problem solved, but I will have to wait until the morning to try it out.

[Neil WyattModerator @neilwyatt]

Bear in mind it's Stevenson's valve gear (IIRC) make sure it is in full reverse or ahead gear as you set each eccentric. If the gear is well made each eccentric will operate independently at the extremes of travel. In between the valve motion is a blend between the two, making accurate setting nigh impossible.

Neil

[Brian AbbottParticipant @brianabbott67793]

There was an article not so long ago about setting the timing on a 1" minnie, not sure what the issue number was but sure you could search it, April 2016 i think.

[David Bothwell 1Participant @davidbothwell1]

thanks once again to repliers, will check fir timing article

[duncan webster 1Participant @duncanwebster1]

If it has loco links it can be the devil to set, as changing the fore gear eccentric alters back gear movement and so on. The best way is to fix the eccentrcs in their correct relationship to each other first, then proceed to set fore gear keeping the eccentrics in their same relative position, then see what happens in back gear. If the eccentric rod wants extending fit a shim between it and the strap, if it wants shortening either file a bit off , or fit the shim in the foregear assembvly , adjust the valve on the rod and try again.. There is some very good reading on google, search for 'Don Ashton vale gear'. as Juian says, it can be very long winded, and if you don't approach it logically even worse.

[JasonBModerator @jasonb]

Unfortunately the way the rods are fixed to the eccentric straps you can't shim of file anything off.

I took the valve chest cover off of mine and took a few pictures for you. Reach rod in full forwards (or as far as you can get it before links hit the boiler) This will have the expansion link in its lowest position. The forward eccentric is the one nearest the flywheel and this rod should be in the top hole of the expansion link therefore when in full forwards it should be inline with the valve rod. All comments are looking from the flywheel side and flywheel rotating clockwise.

Starting at Forward dead ctr eg crank pin at 9.00 o'clock the valve has just started to move towards the rear of the engine

By the time the crank has rotated clockwise to 10.00 o'clock the front port has started to be uncovered

at 12.30 the valve has moved as far back as it is going to and max port open

At 3.00 o'clock (back dead ctr)the valve has just started to moved forwards and is about to uncover the rear port

4.00 o'clock and port has started to open

And by 6.30 the max of the rear port is open, after this the valve will start moving forward as we get back to 9.00 o'clock

Well thats how mine is set up, seems to tick over OK on a bit of air

J

PS Sorry about the dust, you just can't get decent domestic staff these days!

[David Bothwell 1Participant @davidbothwell1]

Many thanks for the trouble all the people who have answered, and a special thanks for the pictures!!

[David Bothwell 1Participant @davidbothwell1]

I have had a couple of sessions with the Minnie and it became obvious I had the eccentric set in the wrong position (in relation to the crankshaft) I also thought there was too much of a rush of air through the exhaust and not enough pressure on the piston. So I have sweated a piece of thin brass on the base of the slide valve. This has improved things (I think) but I have not got the engine running as yet, but I am ever hopeful that Friday may prove the day! (with some adjustment to the valve rod. Thanks for participating, I should add that this engine has caused a lot of problems due to the boiler being constructed too long. I have folllowed the very good advice on extending the fixings to the motion plate to compensate for the movemnt needed to the hornplates. I am still not 100% sure the valve rod needed increasing in size as well? This is the existing problem. I assumed it needed to be longer?

[David Bothwell 1Participant @davidbothwell1]

Engine now running! My sincere thanks for all the assistance with this problem, they go especially to Jason B the pictures he posted were invaluable in sorting out the timing (eccentrics and relationship with the rest of the motion) I spent a while on dismantling the eccentris and associated parts and tweaking them which has paid off.

[JasonBModerator @jasonb]

I do like a happy ending

[Neil WyattModerator @neilwyatt]

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