Author Topic: How NOT to make a model engine  (Read 12187 times)

bogstandard

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How NOT to make a model engine
« on: June 23, 2009, 04:02:03 AM »
This was sent to me recently, and I have only just started on the refurb of it. The customer said that he had made it, and it just would not run.

It was supposed to be a Stuart Turner twin oscillator.

http://www.stuartmodels.com/inprod_det.cfm/section/casting/mod_id/89

As soon as I stripped it down, I recognised the age old problem.
Because it would not run (caused by the ports in the main blocks being the wrong size and also in the wrong position) he did what normal people who do not know better do. He stuck the crankshaft in an electric drill and let it run for an hour, just to free it up? :bang: :bang:




Because the porting was in the wrong position, when he turned it over, instead of having a nice open to air running, it was building up pressure inside the cylinders, and putting heavy forces on the engine as it was being turned over. So effectively he has worn the engine out before it would even run by itself.

It isn't a major issue for me, everything can easily be rescued, in fact in the top right, I have already started on a new crank. But for the newbie, this engine would have to be scrapped.

Bogs

Offline John Stevenson

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Re: How NOT to make a model engine
« Reply #1 on: June 23, 2009, 04:10:39 AM »
Crank main bearing hole looks badly worn John, either that or the screen want's cleaning again.  :med:
John Stevenson

bogstandard

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Re: How NOT to make a model engine
« Reply #2 on: June 23, 2009, 07:06:45 AM »
John, shame on you, didn't you read my post, these are stupendous ST castings you are talking about here.

I have already cleaned it up as much as I can John, it has been reamed out to 4mm and the new crank is a perfect fit. It is because of the crap fantastic Stuart Turner, always perfect castings. The hole is in the correct position, it looks non central because the great ST castings are done like that to give them a hand made look ----- by blind chimpanzees.
:lol:

John

Online John Hill

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Re: How NOT to make a model engine
« Reply #3 on: June 23, 2009, 07:20:03 AM »
Quote from: Mr Bog Standard
How NOT to make a model engine

You had me worried for a moment there John,  I thought you had sneaked a peek at my next project! :lol:
From the den of The Artful Bodger

Offline NickG

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Re: How NOT to make a model engine
« Reply #4 on: June 23, 2009, 07:26:00 AM »
Oh dear! How are you going to break all of this news to him gently?!  :lol:
Location: County Durham (North East England)

bogstandard

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Re: How NOT to make a model engine
« Reply #5 on: June 23, 2009, 08:40:57 AM »
Surely you aren't that bad John.

Nick,

News has already been broken, and he has admitted to everything, and I am about to make him a happy chappie by putting it right for him.
It is a very easy job if you know what you are doing. Unfortunately for him, he doesn't.

This sort of thing is a very common occurance, when people in the know tell newbies that they should start off with a casting set. I think personally, people who do that should be castrated, and have to pay the poor newbie the cost of the castings. They would think twice about it before recommending it again.

To me, it is always better to start with barstock, at least then you can obtain a datum very easily, and work from there. Castings invariably have no fixed datums, and can be almost any shape, so as soon as a newbie does his first cut, the project is doomed to failure. Some do get away with it, but a great many more are put off model engineering for life, because they had a complete failure on their first attempt.

John


Offline NickG

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Re: How NOT to make a model engine
« Reply #6 on: June 23, 2009, 10:00:59 AM »
John,

I found this out to my cost when I was a teenager, and it nearly put me off, but several years out to reflect on what I'd done wrong (well, university really!) and steering well clear of castings renewed my passion for the hobby!

Hopefully the chap will learn from his mistakes and embark on a more suitable beginners project.

Nick
Location: County Durham (North East England)

Offline SPiN Racing

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Re: How NOT to make a model engine
« Reply #7 on: June 23, 2009, 08:18:15 PM »
To me, it is always better to start with barstock, at least then you can obtain a datum very easily, and work from there. Castings invariably have no fixed datums, and can be almost any shape, so as soon as a newbie does his first cut, the project is doomed to failure. Some do get away with it, but a great many more are put off model engineering for life, because they had a complete failure on their first attempt.

I remember being a tiny bit more noob than I already am.. and asking that specific question for one of my first posts here.. Someone was making a cokebottle or something from a casting.. and my question was... Where do you start? I mean.. if the casting is all rough and there is no machined starting point.. do you simply guess?  And I gather the answer is YES. You make an educated guess as to where you start, based on the information of what you will be achieving in the end. If you know what you are doing you can think 40 steps down the road.. and where you need to end up.. not just on that one cut.

I had originally thought of making an engine from a casting.. but as time progressed.. thats very very very very low on my desire list. I even picked up 4 drops from the metal heaven I go to. 2.5" diameter .75" wide disks of surgical stainless.  :D Look like they will be perfect for some flywheels..  :proj:

Now to get myself one of those damn rotary tables.... and a dividing head table thing... and some sort of chuck for them.. and a 4 jaw for them..  :thumbup:
SPiN Racing

Offline Bernd

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Re: How NOT to make a model engine
« Reply #8 on: June 23, 2009, 09:18:03 PM »
Someone was making a cokebottle or something from a casting.. and my question was... Where do you start? I mean.. if the casting is all rough and there is no machined starting point.. do you simply guess?  And I gather the answer is YES. You make an educated guess as to where you start, based on the information of what you will be achieving in the end. If you know what you are doing you can think 40 steps down the road.. and where you need to end up.. not just on that one cut.

Scott,

That was me. I put it back to collect some more dust. I was going to machine the main frame for it but decided it was to difficult for me to do that right now. Even with the encouragement of John (Bogs). I don't want to mess it up as I believe they don't make them with bronze castings any more.

I've taken to the non casting method to make my steam engine for now. Need to get a bit more experince under the belt. Perhaps one day I'll get back to it. I have casting for building a 1 1/2" Shay locomotive so need to practice more before getting into milling and turning of cast parts.

Bernd
You can't fix "STUPID".

Offline rleete

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Re: How NOT to make a model engine
« Reply #9 on: June 23, 2009, 09:43:17 PM »
Uh, Bernd, actually it was me (although you participated in the discussion).  http://madmodder.net/index.php?topic=543.msg2329#msg2329  Just after my visit, I think.  You showed me what you'd done, but we were both confused as to the frame part.  I even used your website pic to show what we were talking about.  You are still ahead of where I am.

I still don't have the guts to try it yet.  Castings are scary when you've had to remake each part three times.  No second chances without spending money on a new one.

Fixed the neighbor kid's bike tonight.  I may not be known for my machining skills, but even the little kids know who to come to for mechanic service!
Creating scrap, one part at a time

Offline Bernd

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Re: How NOT to make a model engine
« Reply #10 on: June 24, 2009, 11:26:07 AM »
Roger,

I stand corrected, you did start the thread. I knew I had posted some pics in there somewhere of what I had started.

Ok guys Roger is the one that had the question.  :)

Bernd
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Offline rleete

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Re: How NOT to make a model engine
« Reply #11 on: June 24, 2009, 11:46:19 AM »
I admit to being more ignorant?
Creating scrap, one part at a time

bogstandard

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Re: How NOT to make a model engine
« Reply #12 on: July 13, 2009, 12:38:47 AM »
This post is now being carried on here.

http://madmodder.net/index.php?topic=1370.0


John