Author Topic: Repairing a high quality model marine engine  (Read 62483 times)

bogstandard

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Re: Repairing a high quality model marine engine
« Reply #25 on: April 21, 2009, 04:46:35 PM »
The saga continues.

When I got back to the engine this morning, the studs were in there rock solid. If ever they need to be replaced, a couple of nuts on the stud, and then warm the stud up to cherry red, give it a few seconds, and it will be able to be screwed out. The heat will transfer down the stud and break down the threadlock joint.
The excess jointing goo was cleaned from around the bases of the studs.
I used two thick gaskets as they will withstand handling better than the thin ones for what we are doing, the joints will all be made correctly on final assembly. I am just getting all the mechanical bits done first. The first shim was followed by the steam chest, then the cover. The bores look scored in this shot, but they aren't. I put a bit of detergent oil down the bores to remove the last remnants of gunge, what you are seeing is the dirty oil being streaked up the bore.




Then two washers were put on each stud, followed by a nut. Everything was tightened down.




Excess length on the studs was then ground off, and the studs were filed down flush to the top of the nuts. One of the washers was removed from under each nut and then reassembled.
The cloth was there just to protect the engine from grinding dust and metal swarf. We don't want that muck going up and down in the bores.




So this is what it looks like now it is finished. About one thread protrusion from each nut, and everything looking nice and neat.
The gaskets will now be a lot more stable and blow resistant because of this work.




So next I turned my attention to just around the corner, the steam inlet manifold.
I was going to fit studs on here as well, but because they would make disassembly more difficult, I decided to use hex head screws instead of the slotted ones that were in there. They will allow more pressure to be put on the gaskets.
This brings me to this shot. I made a few more 5 thou gaskets for the flanges this time. They do look rather rough, that is because they were difficult to cut around on the bench, so they were left slightly oversized and will be trimmed up when held in their final positions.




So after cutting four screws to the correct length, the manifold was assembled onto the engine and the gaskets trimmed up to match. So that brings me to the end of the top end refurb until final assembly. So off to the next bit.




This is the steam control valve, that controls the entry of steam to the engine, giving basic speed control. It is this coupled with the reversing linkage that makes the engine go backwards and forwards at whatever speed you want the engine to run at.
Now there is a major problem with this bit. At some time in the past, the o-ring has worn (it has a flat on one side) and allowed steam to come out where the handle is. I tried today to remove the handle, and it won't budge. So it looks like someone came across the same problem about the handle, and thought that putting a shim in the bottom of the chamber would cure the problem by pushing the drum harder onto the o-ring. Unfortunately, that wasn't the case. What it did was force the drum to rub on the bottom of the flange, and because it seems the drum is made of bronze, it has worn the bottom of the brass flange. I noticed that when turning the handle, it got very stiff in places, whereas it should move freely in a full 360 degree sweep.

This is where I got to today.



So I have made a decision to repair this unit, I will have another go at getting the handle off, but don't hold out much hope. I might just cut the shaft just below the handle. By doing that, and making up a replacement flange to cure the damage, plus a different type of handle, I can cure the problem about changing the o-ring forever. That will then be a five minute job.


Bogs
« Last Edit: April 21, 2009, 05:03:35 PM by bogstandard »

Offline sbwhart

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Re: Repairing a high quality model marine engine
« Reply #26 on: April 22, 2009, 03:21:11 AM »
Nicly done John  :clap:  :clap:  :clap:

I like the little tip putting two washers under the nut cutting the stud off flush then taking one washer away, I've strugled in the past getting studs all the same length, that way will make it easy  to get a nice neat finish    :thumbup:

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Offline John-Som

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Re: Repairing a high quality model marine engine
« Reply #27 on: April 23, 2009, 02:54:06 AM »
One supplier in the UK for PTFE sheeting is
https://www.directplasticsonline.co.uk
the thinnest sheet they do is .250mm - should be OK for small engine gaskets.

JohnS
start-model-engineering.co.uk - a friendly place for model engineering beginners

bogstandard

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Re: Repairing a high quality model marine engine
« Reply #28 on: April 23, 2009, 03:55:59 AM »
Very good link John, many thanks.

It is now in my ever growing favourites list.

John

Offline Darren

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Re: Repairing a high quality model marine engine
« Reply #29 on: April 23, 2009, 04:07:06 AM »
I buy my plastics from them...good company all round  :thumbup:
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bogstandard

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Re: Repairing a high quality model marine engine
« Reply #30 on: April 23, 2009, 05:37:18 PM »
To carry on from the last post. Yesterday I got the valve apart and ordered the o-rings.

Now to get back to a rather bad problem that I had notice before. I started this yesterday but didn't really feel up to it. But I did think I had found my 7BA tap. But when I really checked it out, it wasn't, so this is where having friends locally comes into it's own. A quick call to Stew and the required tap was on my workbench, ready for doing the job today. Thanks Stew.

So this is the problem, and one of the main reasons I think that this engine was finished off by an amateur who knew nothing about how this type of engine works.

If you look at this pic, it shows the problem. When the steam slide is in the back position, all is well, and the nut is prevented from turning by the bottom of the slot it is sitting in pressing against one of it's faces. The problem starts when the slide goes into it's normal operating position, pushed forwards by steam pressure and forcing it against the port face, ready to do it's job. There is enough gap between the slot bottom and the nut face to allow the nut to do full revolutions around the screw, so allowing the critical timing to lose position. You can spend hours fine tuning the engine timing, only to have it all undone in a matter of minutes when the engine is running. If you look at the drawing, you can easily see that even if the slide is very loose, there is no way that the correct shaped nut can rotate and allow the timing to move. I can only assume that a bit of Loctite was used on the nut after timing setting, but that is a long time burnt away, if it was there in the first place.




So yesterday, I modified the slot in both slides, and cut a piece of brass down until it was a smooth sliding fit in the slots.




Holes were drilled in the required offset positions along the length of the bar. Should have been 2.05mm, but 2mm will do fine, so that is what they got.




Then onto the tapping stand. Not having the correct width parallels, the way I easily got it level in the vice was pop the part onto the table, turn the vice upside down over it, and tightened  up the jaws. Once the right way up, they are seen to be spot on along the whole length. All holes were tapped in a matter of seconds.




After a date with the bandsaw and mill, the nuts were to the right size, and as you can see in this pic, there is no way that the nut can rotate. This is a standard method that is used on slides on this type of engine.




The other block, ready to go in the engine, with a few spares for the customer. Another job out of the way, now onto the previous one.




I ended up cutting the stuck handle off, I couldn't risk damaging the very finely lapped spool.
Once it was off, I could see what damage had been done, and measure up the o-ring. They came today, so I can carry on with the job now. Looking at it now it is apart, I think it has been like this from the very beginning. As it looks like the o-ring seating has been cut too deep, so it wasn't sealing properly from the start, so a shim was put in there to get it to compress enough to stop the leak. If I am careful, I might be able to skim off the inside of the flange to get the seating to the correct depth, then take the same amount from under the flange face to put everything back to original. That will save me having to make a complete new flange, and everything that it involves.



So now we are on the downwards slope, just this job to do, plus a few parts to make from the drawings that are missing from the reversing linkage, and I will be ready to start the build up.

Bogs

Offline Darren

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Re: Repairing a high quality model marine engine
« Reply #31 on: April 23, 2009, 06:15:13 PM »
It's the size that gets me, these parts are so small.

I'm not sure I could see them never mind machine them  :bow:
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

bogstandard

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Re: Repairing a high quality model marine engine
« Reply #32 on: April 23, 2009, 06:27:53 PM »
Darren,

These are large compared to some bits I have to make for steam engines. It is all in the mind. As long as you can hold it rigid enough, you should be able to machine it.
Not used on these bits as they are fairly large, but I have a 1" micro sized grinding vice that holds the small bits and then that is mounted into the normal vice.

http://www.arceurotrade.co.uk/Catalogue/Workholding/Machine-Vices

The smallest one in the first lot.

John

Offline Darren

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Re: Repairing a high quality model marine engine
« Reply #33 on: April 23, 2009, 06:30:24 PM »
I nearly fell off me chair laughin....9mm opening, jaw 25mm width.... :lol:

Sorry, I'll go to the back of the class...... :hammer:
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

Offline Bernd

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Re: Repairing a high quality model marine engine
« Reply #34 on: April 23, 2009, 07:16:12 PM »
Bogs,

This is going to be a bit  :offtopic: but I followed the link you gave. Very nice place to get tooling and the like.

But what interested me was link to the location via google map. I looked around using the satelite veiwing. Can't believe how those houses are packed in there like sardines in a can. I can now understand why you chaps that live in cities have such small shops. I can also see why it takes you  so long to get somewhere. Don't seem to be any direct routes to were you want to go.

Bernd
Route of the Black Diamonds

Offline Darren

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Re: Repairing a high quality model marine engine
« Reply #35 on: April 23, 2009, 07:21:20 PM »
Thats exactly why I live where I do  :ddb:

Google LL41 ...
« Last Edit: April 23, 2009, 07:28:11 PM by Darren »
You will find it a distinct help… if you know and look as if you know what you are doing. (IRS training manual)

bogstandard

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Re: Repairing a high quality model marine engine
« Reply #36 on: April 23, 2009, 07:30:48 PM »
Darren,

Laughable or not, sometimes that is the only way to hold really small parts in the mill or on the grinder, big vices for big things and sometimes small but little vices for small or tiny.


Bernd,

I told you ages ago about how cramped we were, and showed you how tightly packed the houses are.

I am not too bad, as I did have a reasonably sized garden until the shop went in.

Like Darren, if you look for CW1 3RQ you should be able to find my shop in the rear garden, from aerial photos, it shows up as a large white rectangle.

Bogs

Offline Bernd

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Re: Repairing a high quality model marine engine
« Reply #37 on: April 23, 2009, 07:41:50 PM »
Thats exactly why I live where I do  :ddb:

Google LL41 ...

I found one Darren, Tanygrisiau, Blaenau Ffestiniog, Gwynedd, LL41, it's right next to the Ffestiniog Railway.   :lol: :lol:

Regards,
Bernd
Route of the Black Diamonds

Offline Bernd

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Re: Repairing a high quality model marine engine
« Reply #38 on: April 23, 2009, 07:48:18 PM »
Boy Bogs, you are cramped in there. I thought the houses over here in the housing tract were jammed together, you guys are even closer.

No more "space" jokes from me. Honest, unless of course..... :wack:....... no never mind.   

Bernd
Route of the Black Diamonds

Offline Darren

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Re: Repairing a high quality model marine engine
« Reply #39 on: April 23, 2009, 07:49:38 PM »
Those little steam engines are a marvel, old quarry engines.

Have to wonder if they are large models or little real ones. They are stunning though. They pass right by my house.

Peeps come from all over the world to see them. They have been extending the track (putting it back) over the last few years. Now you can travel for many miles on them through stunning scenery where no roads go.

I must take a trip one day, never have...yet..
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bogstandard

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Re: Repairing a high quality model marine engine
« Reply #40 on: April 24, 2009, 06:18:49 PM »
Now to get this steam control valved fixed. I have decided to try the fix I mentioned in the last post, and if it won't work, only a few minutes will be lost.

The first job was to clean up the end where I had to hacksaw the lever off.




This is the first part of the fix, skim 0.015" (0.4mm) off the end of the internal spigot. This is also where the o-ring fits into, so that will allow the ring to sit further out and push against the spool face to form a seal.




The same amount was taken off the flange face. By doing this, the spigot will still sit in the same position, but the ring will be deeper in the bore, so allowing the makeshift fix of a shim under the spool to be redundant.




Now you can see what has happened. The o-ring is holding the spool away from the flange which the spool was previously rubbing against.




When assembled completely, this gap here will be closed, forcing the ring against the spool and forming a steam tight joint.




So to final assembly of the valve. A dollop of good quality steam oil was put into the bottom of the chamber.
Because this valve is using very fine tolerances to work, I won't fit gaskets, so each joint face was painted with Hylomar jointing compound, and the valve was assembled. The spool now runs between the bottom face of the chamber and the o-ring, as it should do, instead of between the shim and the spigot face.
I checked the turning pressure and it was spot on, a nice constant drag as it was rotated. So it looks like the fix has definitely worked.




Seeing as I hacked the operating lever off the valve, I had better make another.
A bit of scrap stock was selected for the job.




A few minutes on the mill had the makings of a handle. If you can just see the scribings on the blued up bar, I have drawn up what I want it to look like, to put it into the same operating area as the old one.
Because the engine will be radio controlled, there will be holes drilled into the arm that match the standard centre and hole pitches of a servo control arm (the black bit). This will make setting up a lot easier.




After a bit of manual cutting out on the mill, the handle is finished. The handle can be mounted in any position so that it suits the operator how he wants the way for the valve to work.
Now if the valve starts to leak steam after the o-ring is worn out, take off the handle, remove four small screws and the ring can be changed. Because of the way Hylomar works, it should be able to be reassembled without changing the gasket cement, because it never sets. So five minutes at the most to change the ring



I now have to make some missing parts, so I will make those as per the plans, but because it will be radio controlled, I have to design a friction slip joint for the reverse operating lever. That will be a bit of trial and error, but it shouldn't take too long, I have ideas in my head already.

Bogs

Offline John Stevenson

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Re: Repairing a high quality model marine engine
« Reply #41 on: April 24, 2009, 06:45:44 PM »
John,
have you seen these quick clamps ?

http://www.arceurotrade.co.uk/Catalogue/New-Products/Vices-and-Clamps

two up from the bottom. No real defined use but different uses for different people.

JS.
John Stevenson

bogstandard

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Re: Repairing a high quality model marine engine
« Reply #42 on: April 25, 2009, 02:18:47 AM »
John,

I had seen those bits, but couldn't really make up my mind if I really needed any.
I suppose because they are so cheap, they are not worth making a copy of, so next time I order, I might get a couple, just in case I ever have a use for them. You never know, they just might turn out to be a tool you can't live without.

John

Offline Darren

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Re: Repairing a high quality model marine engine
« Reply #43 on: April 25, 2009, 05:52:37 AM »
They look very handy to have, I like the way this chap is using them to reference his center tool  :thumbup:

http://www.homemodelenginemachinist.com/index.php?topic=4294.30

I think a set will be going on the order list  :thumbup:
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Offline Brass_Machine

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Re: Repairing a high quality model marine engine
« Reply #44 on: April 25, 2009, 09:49:20 AM »
I love to see a craftsman at work. I believe your customer picked the right man for the job!

I do love to see posts like this. While it may seem to you that you are just doing simple tasks in a common rebuild/repair... the viewing collective are picking up many hints and tricks. Thanks John!


Eric
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Offline John Stevenson

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Re: Repairing a high quality model marine engine
« Reply #45 on: April 25, 2009, 09:57:18 AM »
I love to see a craftsman at work. I believe your customer picked the right man for the job!

I do love to see posts like this. While it may seem to you that you are just doing simple tasks in a common rebuild/repair... the viewing collective are picking up many hints and tricks. Thanks John!


Eric

Personally I think he's winging it, he should have been finished by 3:47 last Tuesday afternoon.

 :poke:

.

John Stevenson

bogstandard

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Re: Repairing a high quality model marine engine
« Reply #46 on: April 25, 2009, 01:12:42 PM »
Quote
Personally I think he's winging it, he should have been finished by 3:47 last Tuesday afternoon.

You're quite right John, I could have had it finished, but to tell you the truth, I am letting Bandit do it, but he isn't quite up on all the techniques just yet, so he is a slow worker. I am just taking credit for the job.

Until I can get crutches permantly fixed to the saddle of the lathe and the table on the mill, everything is going a little slow at the moment.

Bogs

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Re: Repairing a high quality model marine engine
« Reply #47 on: April 26, 2009, 08:13:20 AM »
Quote
but to tell you the truth, I am letting Bandit do it, but he isn't quite up on all the techniques just yet, so he is a slow worker.
  :thumbup:

You watch out he dosen't get too much swarf in his coat and paws John..... I'll be there next week to inspect the job he's doing first hand  :coffee:  (Cause I know what I'm looking at ehh!?!?!  ::)  :lol:)


That said, it all looks good to me :headbang:   As Eric said.... We're (the lowly newbies) all picking up little bits here and there and it's here in glorious technicolour if we ever need to refer back to it  :)


Take your time (I'm sure the owner is happy about the pace) and keep up the very good thread :beer:





Ralph.

I know what I know and need to know more!!!

bogstandard

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Re: Repairing a high quality model marine engine
« Reply #48 on: April 27, 2009, 04:56:48 PM »
I actually had to take a rest over the weekend, but I have got a little done today.

If you remember, I left the last post saying I had some parts to make that were missing from the engine. Basically all the bits above the rod need to be made, except the part in the very middle just above the rod. I have to design and make a friction device rather than a locking one. The design is done, so that will be made tomorrow.




The smaller the bits, it seems the longer they take to make. These have taken me most of the day, but I have been working ten minutes on, half hour off.




This shot is to give you some feeling of scale. These bits have yet to be cleaned up fully.
The little handle took a bit of figuring out, but as soon as I got the ball hand shaped to within 0.002" of a 3/16" sphere (slightly larger than shown on plan, remember friction joint, so needs to be a tiny bit larger) it worked out dead simple to finish off.




Medicos first thing, then member visitors in the afternoon, so I will have to get my a**e into gear if I am going to get the other bits done tomorrow.

Slow down Bogs
« Last Edit: April 27, 2009, 05:03:08 PM by bogstandard »

Offline Stilldrillin

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Re: Repairing a high quality model marine engine
« Reply #49 on: April 28, 2009, 02:09:53 AM »
Nothing to add.....

I`m sat here, just shaking me head......  ::)

Astonishment, admiration, respect.....  :headbang:

David D
David.

Still drilling holes... Sometimes, in the right place!

Still modifying bits of metal... Occasionally, making an improvement!