Clarkson 2" x 2" horizontal mill engine

[crueby]

Big th8ng to check is that the distance from the eccentrip strap up to the curved link bar is the same on both. If not, you'll  never get it to run evenly in both directions.

[Sanjay F]

Thanks Chris, I'll take a look; there must be some sort of tolerance/deviation which will still allow it to run both ways? I'd be happy if I could get to run at all in both directions atm! 

I'm going back to basics and checking the cylinder, piston and rod as the noise has increased progressively this evening, its been clunky from the day I got it and I've never quite figured out what's caused it. The bushes certainly made a diffrence but looks to be temporary

[Charles Lamont]

I would be inclined to treat the direction you have it running as the primary forward direction and set the valve and forward eccentric for that and leave it alone.  I think it must be possible to then adjust only the other eccentric to get reverse running, but because of the lifting link geometry it is likely to be a bit ragged at best. Ensuring there is a little clearance between the die block and the ends of the expansion link slot throughout the cycle will mean there is quite a lot of clearance in places. I suggest some temporary limit stops on the reversing screw, even if only some sticky tape. If it really won't run in reverse, I think the valve gear will need to be modified.

[Sanjay F]

Hi Charles

That's great advice  - I wondered about where the die block position and where the eccentric should engage. I'm interested in your statement 'If it really won't run in reverse, I think the valve gear will need to be modified'

I'll like to understand how the valve gear should/could be modified?

[Jasonb]

The amount of play in the previous work is not going to help and that is allowing  the expansion link move about too much. Take a look at the forked lever that the reversing screw nut fits in, the sid enearer the engine is moving a lot. The two should be screwed solidly together, these days we would make that as a solid part but it was easier to file the two halves to create the slot.

The lifting arm also looks way too long which just magnifies any play, if you look at the drawings it would appear much shorted and give a more vertical position to the lifting link if it were.

many of the parts are the same as used on the larger vertical, this one runs quite smoothly with no play. The only obvious change is to the screw and quadrant rather than screw and nut reverser.

<a href="https://www.youtube.com/watch?v=zueGtMsTLpk" target="_blank">http://www.youtube.com/watch?v=zueGtMsTLpk</a>

[Jasonb]

If you look at my Minnie you can see that the horizontal lifting arms barely move unlike yours. Also the lifting link is near vertical not right over at an angle.

The only downside to reducing the lever to what it looks like in the drawing would be that you have to wind the screw a bit more to raise and lower the expansion link enough to get the valve rod to line up with the eccentric rods.

<a href="https://www.youtube.com/watch?v=NyZCpQyTHjU" target="_blank">http://www.youtube.com/watch?v=NyZCpQyTHjU</a>

[Charles Lamont]

What Jason says. I would also refer you back to my posts #26 and #46. If the lifting arm on the weighshaft is longer than the drawing shows, that would definitely be the modification I would make. But slop reduction first. BTW, in the running video I think I also noticed the valve rod had some vertical movement, possibly caused by having the gear lifted too far. 

[Jasonb]

It's interesting comparing the GA with the part drawing. GA looks much more like the longer horizontal lifting arm that Sanjay has but the drawing for the actual part is much shorter compared to the vertical fork.

[internal_fire]

I think the forward and reverse eccentric rotational positions on the crank may be swapped.

The "forward" direction of the crank and flywheel would typically be anti-clockwise, as shown. This of course is due to the favorable force directions on the single-sided crosshead.

It is typical in horizontal Stephenson link designs (widely used in early locomotives) that the entire link assembly is in its lower position for forward rotation. This one shows the links in the upper position.

It is also typical that the radius arm "far end" is near the die block when operating in forward. (Locomotive designs typically place the connection to the curved link in the middle, not the end, but marine designs usually are similar to the Clarkson.)

I believe the motions are a bit smoother with less die block slip when the usual convention is followed.

I don't imagine that many mill engines were reversible, so it is not clear to me what the designer intended in this case.

Gene

[Charles Lamont]

Gene has a point. He brings us to the matter of 'open' and 'crossed' eccentric rods - a complication I have avoided so far, not least because it is something I have not studied and don't understand.

For a reversing stationary engine, forwards is normally with the top of the flywheel moving away from the cylinder, for the reason Gene gives.

Looking at the engine as shown in the GA above, the engine is at bottom dead centre. The upper anticlock (as seen) eccentic is connected to the upper end of the expansion link, and the lower to the lower. This is 'open rods' and is used in locomotives, we are told, because this arrangement increases the lead (makes the inlet earlier) as the valve gear is notched up for economical high-speed running.

If the upper eccentric (still viewed at BDC) were connected to the lower end of the expansion link, and vice-versa, the rods would be 'crossed'. This is a common arrangement for stationary and traction engines, and the lead decreases as the engine is notched up.

"Hmm, that's all very well," you ask, wearing a perplexed expression "but at top dead it's surely going to be the other way round and the open rods will be crossed, and crossed ones, open - so what's the difference?" I am afraid I haven't done that class either.

However, I agree with Gene that lowering the gear for forward running is what we would normally expect. Crossing the rods would do that for us, and I think it could be worth trying, but not until the lifting arm and link are sorted out. The valve would also need to be reset.

[Jasonb]

Looking at the general arrangement drawing I would say the original design has the forward eccentric going to the lower hole on the expansion link.

If we take it that the eccentric leads the crank pin by 90degrees plus 30degrees then you can see the throw of teh forward eccentric is towards the bottom and it'd rod goes to the lower hole on the link.

So the designer either intended the engine to run the other way or o have the link up in usual forward running.

I'm not sure if an unsupported trunk guide offers much more rigidity in one direction than another, different it it had a support down to the bed but it is only bolted to the cylinder end.

[Sanjay F]

Lot's to digest there but the first thing sounds like I need to remove the 'slop'. I noticed the valve rod jittering too. What is meant by the 'forward eccentric', are we talking about the one nearest when facing the engine with the flywheel on the right?

If 'forward' direction means the flywheel moving anticlockwise away from the cylinder, which eccentric be engaged, the one nearest or the one furthest away.

I'm confused, can either eccentric be connected to the top or the bottom of the expansion link, I didn't think this was possible as the eccentric rods have fork ends which face left or right?

[crueby]

The forks usually do have an offset, but you could put them to either end of the link by rotating on around. Important  thing is just that the slots line up so the link is in line and not angling off to the side. Depending  how well they were made and that the link is symmetric, that is! In the engine world the only standard is that there are very few standards, every designer and builder can have their own ideas, sometimes  driven by whats at hand.

[Charles Lamont]

You can define forwards how you like, but most commonly it is the top of the flywheel moving away from the cylinder. (As Gene pointed out, this convention probably arose because it results in a mainly downward force on the old type slipper crosshead.) I am deliberately not saying clockwise or anticlockwise because that would depend which side of an engine the flywheel happened to be mounted (also making the tacit assumption that you are looking at the engine from the flywheel side).

The forward eccentric is the one that is ahead of the crankpin when running forwards. (For an outside admission valve)

Yes, you should be able to swap the eccentric rods over to opposite ends of the expansion link, just by removing and replacing the pins. (But I agree with Jason: the GA drawing would be expected to show correctly which way they are meant to be.)

[Charles Lamont]

PS: A little more thought revealed to me that open eccentric rods produce a slightly greater valve travel in mid-gear than crossed rods would. Learn something every day.