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PostPosted: Sun 28 Jun 2015 18:56 pm 
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Location: Dayton, Ohio USA
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This is my first post so if I'm in the wrong place please let me know! I just started my first Airfix kit, the Four Stroke Engine, and immediately ran into what seems to be a considerable problem. The first assembly phase is cleaning up and assembling the crank shaft and piston. The crank shaft has two counterweights and each has a shaft and bearing. The con rod shaft connects the two counterweights. One weight has a square section shaft which mates with a square hole broached in the shaft of the other weight to align them squarely. This is to ensure that the main bearings are perfectly coaxial and align properly with the crankcase journals.

The counterweight with the square shaft section seems to be correct, but in my kit the other weight, with the square hole, has the hole rotated slightly, about 7 or 8 degrees. When I join them, consequently, the counterweight lobes are twisted axially and the crankcase bearings are out of line, so that they can't be inserted into the crankcase. There appears to be no damage or other mischief that I can see. They just seem to be made wrong.

Am I doing something wrong here? I can correct this problem with some cutting and gluing, but would rather do it right. Thanks for any advice you can offer!


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PostPosted: Sun 28 Jun 2015 20:39 pm 
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It would be good if you could introduce yourself here 8-)
We don't know how long you've been modelling, whether you have any expertise on the subject and we wouldn't want to insult your intelligence :sofa:

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PostPosted: Sun 28 Jun 2015 22:08 pm 
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Hi uheckjk

:welcome: to ATF. I have this kit but haven't built it yet so I had a look at the parts this evening. My kit matches yours, the two counterweights are offset by a few degrees which as you say puts the bearings out of line and makes the assembly of the crankcase impossible. This is either an error in the tooling or something that happened in the moulding process.

You could just cut the square bar and rotate it slightly before glueing. Alternatively, assemble and glue parts 5,6,7 and 8 and set aside to dry. Next fit the piston rod between them applying a little glue only to the square shaft. Before the glue has set very, very gently twist the two counterweights so that they line up correctly. This will twist the square shaft a little but if you are careful won't snap it.

Hope that helps.

Enjoy your build.

Colin


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PostPosted: Sun 28 Jun 2015 22:11 pm 
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I have built this and can attest that you sometimes need to really study the instructions to ensure everything is lined up correctly. However, without the instructions in front of me, I'm no help. Perhaps if you took a look at some completed examples here

viewtopic.php?f=33&t=36051&hilit=four+stroke+engine

it might help. If there is a problem, it happened after a significant production run as all these kits function correctly.


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PostPosted: Mon 29 Jun 2015 03:29 am 
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Joined: Sun 28 Jun 2015 01:56 am
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Location: Dayton, Ohio USA
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Colin's reply has assured me that I'm not seeing things the wrong way. I like the idea of cutting off the square portion of the shaft then assembling the unit, including the cut off piece, making sure to apply cement to all the several indexing points of which there are several. I will have to clamp the whole into a set of vee blocks to assure proper alignment but that presents no problems. Colin's second suggestion, of partially softening the square shaft then torsioning it into alignment until the cement dries gives me some pause. It's far too likely to twist or warp parts you didn't intend to when doing that.

I believe that this problem originated at Airfix, and Colin's reply seems to support this. I can fix the problem in this case by myself but I'm wondering if Airfix would care to know about it or would really not really care. Is it worth letting them know?

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PostPosted: Mon 29 Jun 2015 22:26 pm 
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Hi John

An email to Airfix would normally be the right thing to do but whether anything comes of it who knows. If the tooling is damaged it might cost a lot of money to fix and the kit isn't a big seller. It was one of many sold off at a massive discount in the UK as part of the Black Friday sale which is when I got mine. At the same time I bought the Maudslay's Paddle Steamer Engine at a major retail store for half price and it is still offered at similar discount on the Airfix website. If the problem is down to a production problem at the factory, the factory is thousands of miles away from Margate and I doubt anyone there will worry much.

Colin


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PostPosted: Mon 11 Jan 2016 18:41 pm 
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Sorry I realise I'm late in the response, but I can only say mine went together ok and all the parts work ok, I've seen a few other builds but not heard of this problem, I wonder if it's a one off, maybe you could get some replacement parts from airfix to check for warpage or something.


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