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Problem setting up stationary engine.

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Brian John25/04/2014 05:48:39
1456 forum posts
579 photos

I am building the 3BIM stationary engine by PM research ; this is my first attempt at building a steam engine. I thought I had set everything up correctly (including the valve) but I am still having problems setting the piston.

1. When it reaches TDC there is a loud clunk when turning by hand. There is also a lot of play in the crank at this point. At BDC, the change in direction is very smooth with no play in the crank. What do I need to do here ?

2. The nut that passes through the connecting rod into the crank also keeps coming loose. If anybody else has built this engine can you tell me if you had this problem too. I was thinking of putting some Loctite 222 on the nut to stop it coming loose but PM research have advised that Loctite should not be necessary.

Stewart Hart25/04/2014 06:40:46
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I'm not familiar with the design but it seems like your connecting rod is too long. Look for ways to shorten it a tad, you may have to screw it into the cross head a bit more, this also could be why the nut keeps coming lose from the constant nock.

Stew

JasonB25/04/2014 07:46:16
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As Stew says it sounds like the piston is hitting the cylinder end cover. I'm not sure if the conrod can be adjusted for length but you should be able to adjust it by turning the piston rod in the piston or cross head.

If the piston rod screws into the piston then the nut is simply a locknut and if done up tigth should remain so, you will need to hole the piston firmly as you tighten the nut - protect the edge of teh piston. If the rod just passes through the piston then the nut will be more likely to loosen. A dab of 222 won't do anyharm as its one that releases easily if you have it, if not a dab of paint or nail varnish will do.

J

FMES25/04/2014 07:47:00
606 forum posts
2 photos

Hi Brian,

You could also check that the index on the cylinder cover isn't too deep and hitting the piston at tdc, or that the piston itself isn't fractionally too thick (drawings aren't always right).

Lofty

Brian John25/04/2014 10:54:26
1456 forum posts
579 photos

1. No, the piston is not knocking against the piston cover ; I have not put the piston cover on yet so as I can see TDC.

2. Jason : the nut holding the piston rod to the piston is not coming loose ; that is not the problem. It is the nut passing through the connecting rod to the crank which works itself loose.

3. I wil try to screw the connecting rod further into the cross head but last time I did this it made it too short and it would not reach BDC.

FMES25/04/2014 11:50:11
606 forum posts
2 photos

Crosshead hitting the piston rod gland nut?

Brian John25/04/2014 13:08:37
1456 forum posts
579 photos

No, the crosshead is nowehere near the gland nut.

FMES25/04/2014 14:17:50
606 forum posts
2 photos

I should have added how about the crosshead hitting the end of the slide? it looks pretty close even on the works photo.

If its none of the above the other area to look at is the valve and linkage.

As this is a pre-made kit all the machining should be spot on, and the 'play' you refer to could be 'Ineffective crank angle' i.e when the crank turns but the piston doesn't move much (TDC /BDC).

Any chance you could do a bit of video showing the problem so that people could make a better guess as to what is going on?

Brian John25/04/2014 17:51:37
1456 forum posts
579 photos

The cross head is not hitting the end of the slide.

The valve is okay ; it still makes this clunking noise when the valve and the eccentric is disconnected from the axle.

I do not have a video camera so I cannot post a video of the problem.

Yes, the crank can be turned a few degrees forward and backwards at TDC with no movement of the piston. This is where the clunking noise occurrs. They have made hundreds, if not thousands of these engines, so I am a bit reluctant to blame the machining. The problem must be in how I have set up the connecting rod ie. I must not have centred the piston correctly.

Nick_G25/04/2014 19:16:41
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1808 forum posts
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Would it help others to advise if you took video with your phone. (does not have to be a good one) and posted it to Youtube.?

Nick

Neil Wyatt25/04/2014 21:19:04
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Turn the crosshead trough 180 degrees. If the clunk is now at BDC then both crankpin may be slightly out of line. At one centre this could stiffen things up, and at the other it would make it looser.

Unlikely but possible.

Neil

Brian John26/04/2014 05:07:07
1456 forum posts
579 photos

I have tried turning the crosshead over and it made no difference. The clunk is caused by too much play in the crank/connecting rod area at TDC ; that is all I can think of and I have no idea how to remedy this. There is also quite a bit of play (but not as much) at BDC but no clunk noise. I switched cranks with an unmade 7BIM engine I am also building but it did not help.

I also tried shortening the piston rod by screwing it further into the cross head but there is little room to manoeuvre there. Only an adjustment of about 0.5 mm is possible and it did not remedy the problem. Any shorter and it will strike the bottom cylinder cover , any longer and it will strike the top cylinder cover.

FMES26/04/2014 07:08:23
606 forum posts
2 photos
Posted by Brian John on 26/04/2014 05:07:07:Any shorter and it will strike the bottom cylinder cover , any longer and it will strike the top cylinder cover.

That doesn't sound right Brian, there has to be a reasonable clearance at each end of the stroke to enable the ports to be uncovered, and even with a small engine like this I would have expected a mm or so.

The only other clue you give is that the crank pin (nut) keeps coming loose, that shouldn't happen unless the fit is way too tight ( and that wouldn't help with clunks ).

Brian John26/04/2014 09:57:16
1456 forum posts
579 photos

You are right, there is about 1mm of clearance at the end of each stroke. But no more than that, so there is not much room for further adjustments. I am certain that the problem is not with the piston anyway.

Tomorow I am going to try setting the valves and run it on air. I may as well see how bad the problem is when it is actually running.

Edited By Brian John on 26/04/2014 10:38:20

Ian S C26/04/2014 11:21:39
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7468 forum posts
230 photos

If it's not the big, or small end bearings, the clearance should be very small, are the main bearings similarly close fitting? The only other thing I can think of just now is the flywheel moving on the shaft, or perhaps the eccentric strap is a bit loose. Ian S C

Brian John26/04/2014 13:11:51
1456 forum posts
579 photos

Neither the flywheel or eccentric is yet connected. There is too much play in the connecting rod/crank area at TDC. At TDC I can wiggle the crank and connecting rod back and forward a few degrees with no movement of the crosshead or piston. I do not think that this is correct but to be honest I am not sure. The loud ''clunk'' at this point is definitely not right !.

 

 

Edited By Brian John on 26/04/2014 13:57:04

steamdave26/04/2014 19:28:42
462 forum posts
35 photos

Brian

I don't know where you are located, but is there a model engineering club or another engine builder anywhere near where you live? If so, why not take your engine along and let others see first hand what the problem is. Being able to see up close and dirty will be a lot easier to diagnose the fault than trying to describe things in writing.

Dave
The Emerald Isle

frank brown26/04/2014 20:19:26
436 forum posts
5 photos

If there is nothing touching that is visible, then it must be something that is not visible, like the piston ring is tight near the top of the bore,all the slack is taken up as the piston goes up to TDC, then as it goes over TDC the ring is pulled free and all the slack jumps in again leading to the clunk,

Frank

Brian John27/04/2014 05:15:46
1456 forum posts
579 photos

There are no model engineering clubs in my area. I have already checked this because I was hoping to get somebody to teach me how to use a lathe. It looks like youtube for now when it comes to the lathe !

UPDATE : I assembled the engine and tried to run it off a small air pump but it would not work. I suspected that this air pump was not quite strong enough so I tried my air compressor which I use for the airbrush : SUCCESS ! The engine runs like a top and there is no ''clunk'' noise when it runs so it looks like that free play at TDC is not affecting anything at all. It really seemed like a problem when turning things by hand.

The nut holding the connecting rod to the crank does work it self loose after a few minutes so some Loctite 222 will be required ; it should arrive in the mail on Monday. I might also put a drop on the nut holding the piston rod to the piston as I would not want that to come off while it was running !

I managed to get the engine to run at less than 5 PSI ; sometimes it will even start without touching the flywheel. I have not yet sealed the grub screws in the port holes with thread sealant (Loctite 567) as per the instructions. I can feel air coming out of there so that should improve things a lot when I do that.

Thanks for all the advice.

 

 

 

Edited By Brian John on 27/04/2014 05:18:34

Edited By Brian John on 27/04/2014 05:47:47

Brian John27/04/2014 05:51:31
1456 forum posts
579 photos

dscn0008.jpgdscn0005.jpg

dscn0004.jpg

I am making a proper plinth for this engine but this is what it looks like now. You can see the small pump I first tried in the background of photo 2. I think this pump only generates about 1 or 2 PSI but I think that once I seal the holes to the valve it may just have enough power to turn the engine over slowly.

Now I have to build a boiler !

 

 

Edited By Brian John on 27/04/2014 05:57:24

Edited By Brian John on 27/04/2014 06:00:53

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