Another Paddleducks build log

[spuddevans]

A little update on this.

I discovered what is almost certainly the cause of the escaping air. In efforts to trace any problems I took the top section and hooked up air to one inlet at a time. I found that one piston valve leaked more than the other, but both piston valves leaked. I dismantled one of the valves and measured the "piston" part of the valve, and it was 5.82mm. The bore was reamed to 6mm.

No wonder there was a lot of air escaping.

When I made the piston valves originally I made them out of some 6mm stainless rod, or so I thought. I measured the piece of 6mm rod I used and found it to be 5.9mm.

So this afternoon I remade one piston valve from 8mm steel and turned it down to fit snugly in the bore. After re-assembling the valve assembly to the cylinder and the whole top section to the bottom section, I then hooked up the air to just the newly made valve and turned on the compressor.

Virtually no leaking air and the engine tried to turn over. There is still some binding in the conrod/crankshaft area that prevents the engine from spinning freely. I think that I'll have to shave a little off a boss on the crankshaft bearing blocks to give a little extra clearance, and I have to remake the other piston valve too.


Tim

[sbwhart]

Hi Tim

Your at the stage where you really start to learn about your engine, what's needed now is a nice methodical approach to tease out the problems, as you have been, and you'll soon get a runner for sure.


Keep at it

Stew

[spuddevans]

Thanks Stew, aint that the truth. When I started to assemble all the bits together, I had to go back over the plans in order to find out what went where, it had been so long since I started it I had forgotten

Now that I've had it apart a couple of times, and back together too, I am getting to know it a bit better.

At first I was going to go at it with all guns blazing, kinda like "right, lets re-make everything at one time and then try again" sorta attitude. But then calmness and reason set in and I realised the truth of what you said, work at the problem methodically. So I removed the part that I thought was the issue ( the reversing/speed control valve ) and applied air direct to one piston valve/cylinder at a time, and that was where I found the one of the problems with the escaping air.

So now I can re-make the other piston valve ( which, by the way, leaked worse than the one I just remade ) and sort out the binding con-rods and then try running it again.

So, step by step it is, I am learning that with these little engines, it only takes parts to be a fraction off the size that they need to be in order for things to either bind up or be too loose a fit. All part of the learning process.


Tim

[kvom]

This was tricky for me to get running as yoyu probably remember.  The main problems I had were (in no particular order)

1) Binding in the crankshaft parts.  I disassembled the bottom completely and lined up the bearing blocks with a length of drill rod, then tightened down gently so that the rod would still turn fairly freely.  Then I could assemble the crank components again.

2) Binding in the guides.  I basically got it running with only one guide rod per cylinder.

3) Getting the timing precisely right.

[spuddevans]

Yea, I remember you had some issues Kvom. So far the guides are fairly smooth and free, (oops, shouldnt have said that, they'll probably be stuck tight when I get back into the workshop )

On mine the crankwebs are binding with the con-rods once each rotation. They are only slightly binding, so I think I will just shave off a few 0.01mm's from the bearing blocks to allow the webs to be widened by a tad.

Tim

[NickG]

Tim,

you will get there - it's easy to forget things like clearances when your making these models. Model engineering drawings are never toleranced so parts have to be 'fitted' together with the correct allowances - this project will certainly help you do that in the future.

Nick

[kvom]

the crankwebs are binding with the con-rods once each rotation

That sounds to me as if the journals and shafts are not precisely parallel.  If you do want more clearance between the webs it might be better/easier to narrow the conrod ends.

[spuddevans]

That sounds to me as if the journals and shafts are not precisely parallel.  If you do want more clearance between the webs it might be better/easier to narrow the conrod ends.

Ding ding ding ding ding!!! We have a winner!!!!!!!!!!!

When fiddling with it today I noticed just that the crankshaft/webs/shafts/ect were not totally in line.

After making a new piston valve ( for the other valve ) and re-assembling everything, re-timing it all and making sure that everything was in line, and ( tempting fate ) I also reattached the fw/rev speed control valve and hooked up the air.

This time the "Ffffffffffffffffffffffsssssssssssssssssssssssssssssssss" was a little less and with a little encouragement it turned over a few times, by this time the little air-brush compressors tank had been depleted and the pressure dropped below 20psi and the engine stopped. By closing off the speed valve I was able to build up enough pressure to have a few more rotations.

I think that the speed control valve needs some attention, I think that is where I am losing most of my air, I haven't put an O-ring in there yet, so that will be the 1st attempt at a fix, then if that doesnt cure it I'll have to remake the spool.


Tim

[NickG]

Nice 1 Tim, nearly there 

[CrewCab]

Sounds like a bloomin' steep learning curve Tim, but well done for the methodical approach and sorting it ............. the old adage of "If it ain't broke, don't fix it" applies I'm sure .............. Good luck I'm sure it will be running as sweet as a nut in a day or two 

CC

[shred]

Before re-making the spool, try whipping up a temporary manifold from a bit of pipe and some soft solder (connect either both top or both bottom ports).  If you install that instead of the spool assembly the engine will run in only one direction, but you cut out a lot of the plumbing for debugging purposes.

[spuddevans]

That is a great idea Shred,

Before re-making the spool,

 

I spent yesterday afternoon remaking the spool, it was probably a needed action as when I examined the bore of the speed/direction valve I noticed that it was not truely round and parallel, so I mounted it up in the vice and took a skimming cut with a boring bar until the bore was properly cleaned up. Then I remade the spool, it turns out to be about 0.4mm bigger than the original one, but it fits better in the bore now.

When I re-assembled the spool into the valve but before remounting the valve onto the engine, I applied air to it to see if it would shut off properly ( the previous spool would leak like the titanic even when turned off ) and it did ( apart from a little hiss leaking from the joints, and that is because I have no gasketing at the moment ) so I think that the remake was needed ( or at least that is what I keep telling myself  )

It did turn over for a little while ( about 20 revolutions or so ) before stopping, so I think I need to spend some time on the timing of it.


( repeat with me ) We WILL get it working, we WILL get it working 


Tim

[NickG]

Not far off now Tim, does it turn over freely by hand now? There really shouldn't be any binding. Once you get this valve sorted that should be it keep at it, most engines have a period of trouble shooting esp relatively complex ones like this! 

[spuddevans]

Not far off now Tim, does it turn over freely by hand now? There really shouldn't be any binding. Once you get this valve sorted that should be it keep at it, most engines have a period of trouble shooting esp relatively complex ones like this! 

When I had the top and bottom of the engine seperated the bottom crank assembly was completely free. When assembled there is some friction coming from the crosshead guide rods, I have one in each pair or rods fastened slightly loosely in order to get it running in.

There is also a little friction coming from the piston valve and pistons, but it does turn over with fingers.

I havent had time yet to look at the timing, that will be the 1st thing I look at and try to get sorted.


Tim

[Brass_Machine]

I have faith Tim, you will get it running. I have no suggestions for trouble shooting as I haven't built one of these (yet!)

Eric

[spuddevans]

Thanks for the vote of confidence Eric I appreciate that.

I just had a little look at the timing, it was well out. That sorted there was still a lot of air escaping without doing anything so I removed the speed control valve assembly and attached the air supply to each of the 4 ports in turn.

This was to allow me to see just where the air-leakage was coming from. I found that there was some leakage from one piston valve, but it would turn the engine over a half turn or so. However, the other piston valve was leaking worse than the titanic, and wouldnt even attempt to turn the engine over.

This is rather frustrating, I had already remade the piston valve once ( well to be truthful I did remake both piston valves ) and I thought I had made, or remade, it to fit the bore.

So it looks like I have to remake the remade piston valve  or at worst it might have to be a remake of the piston valve housing 


Oh well, its all a learning process. I gave up for the moment as I started to get rather frustrated with it all, so me thinks I need to just leave it for today.


Tim

[NickG]

These piston valves sound quite difficult. I haven't seen the plans for this Tim but is there any way you can ream the valve bore and use a ground stock size for the valve?

Nick

[madjackghengis]

practice makes perfect better.

I like that quote, may I borrow it from time to time Tim   

and ............. thanks for taking the time to do a complete write up, fine job so far and no doubt it will just get better 

CC

A couple of years ago, when my younger sister was suggesting I wasn't practicing my violin enough, I stated "practice makes perfect", and she retorted with "practice makes permanent, perfect practice makes perfect", and that shut me down immediately.  As she is a consumate player of the violin as a second instrument, and her first is the cello, which she is quite a performer on, I bowed my head, and accepted the admonishment.  Mad Jack

[spuddevans]

These piston valves sound quite difficult. I haven't seen the plans for this Tim but is there any way you can ream the valve bore and use a ground stock size for the valve?

Nick

When I originally made the valve bores I did ream them with a 6mm machine reamer. I dont have any 6mm ground bar-stock so I have to turn it down from 8mm stock.

This gives me an idea, I might try and rig up my dremel-clone as a kind of a heath-robinson toolpost grinder to finish to size on the remake. I dont know if it will work or not, but I guess it cant make any worse of a job that I have done so far

Once I get this engine running I am going to start on working on my machines and one of the projects I have planned is to make a proper toolpost grinder. ( one of the many projects to upgrade the mill and lathe )


Tim

[NickG]

Toolpost grinders look very handy indeed. As long as you can keep it still there's no reason the dremel shouldn't work with light cuts. Was just thinking you could buy some 6mm silver steel or something and it should be a really nice it in the reamed bore. I know it's nice to try and use what you already have though.

Nick

[kvom]

Do you have room to bore out to 8mm?  Then you could use the 8mm drill rod.

I lapped mine with toothpaste to get them to fit.

[spuddevans]

Toolpost grinders look very handy indeed. As long as you can keep it still there's no reason the dremel shouldn't work with light cuts. Was just thinking you could buy some 6mm silver steel or something and it should be a really nice it in the reamed bore. I know it's nice to try and use what you already have though.

Nick

I was thinking of attaching it to a QC toolholder in some sort of fashion.

I did have some 6mm silver steel, maybe the better thing to have a cleanup and maybe it'll show itself.

Do you have room to bore out to 8mm?  Then you could use the 8mm drill rod.

I lapped mine with toothpaste to get them to fit.

That is an option, there might just be room, the only thing is I only have a 6mm machine reamer, the other reamers I have are hand reamers, you know the kind that have a fairly long tapered section at the end, and so no use for a blind hole.

I wont be able to get out into the 'shop for a couple of days, so I will be giving the matter some more thought. At the moment I am thinking I will try to find out if I have any 6mm silver steel, if I have then I will remake the piston-valve out of that. If not I may make a heath-robinson toolpost grinder and work with the 8mm stock I have, and if that doesnt work I will investigate the bore in case that somehow it is not straight/parallel/true/tapered.

That's the plan anyway, it is good to have a plan, even if it doesnt get stuck to 


Tim

[madjackghengis]

Toolpost grinders look very handy indeed. As long as you can keep it still there's no reason the dremel shouldn't work with light cuts. Was just thinking you could buy some 6mm silver steel or something and it should be a really nice it in the reamed bore. I know it's nice to try and use what you already have though.

Nick

When I needed a tool post grinder to grind the valves of my tractor (53 Farmall Cub), I took a piece of inch and a half angle, about three inches long, welded a piece of half inch square hot rolled to the outside of the corner of the angle, with two welds, leaving a slot between the welds, used a large hose clamp to clamp an air die grinder in the angle, and held the square of steel in a quick change tool holder and held down the air lever while traversing my top slide at 45 degrees, grinding out the divots in the valve faces.  A dremel would fit the same way and not need the handle held down.  Mad Jack

[sbwhart]

Tim

The dremel may work at a push but you'll risk knackering its bearings, I'm led to understand that dremel bearing are not very good in that sort of application.

Stew

[Bluechip]

Tim, Mad Jack et al.

Stew is 100% right ...

Dremels DO NOT LIKE SIDE THRUST ...  

I knacked one like that, fortunately got it replaced under warranty, 2 weeks old  

Strangely enough, I believe I was once told the el cheapo Draper version is more robust in this respect. Cannot say by my own experience, never had a Draper. Gave the Dremel away .. found little real use for it.

Dave BC  



Dave BC