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Old Aug 26, 2011, 09:54 PM
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Here is some pics of my RJL made replica Forster .99 engine:























I am going to have to make a spacer or something for the drive washer as it rubs up against the points,timer unit and housing. As is the engine likely won't work as the timer unit rubs against the drive washer. Now it is possible that after the engine has been run a while, that the crankshaft might protrude slightly more aleviating the problem. But I won't know until I actually run the engine.
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Old Aug 26, 2011, 09:58 PM
Time for me to Fly...
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Very nice Earl.... It's a good thing for you that you saw that post before I did or you'd be looking at pictures of my Forester 99 instead of it being the other way around.

It sure is a beauty. You gonna fly it or display it?
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Old Aug 26, 2011, 10:17 PM
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Fly it of course.

Thanks
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Old Aug 27, 2011, 03:01 AM
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Originally Posted by earlwb View Post
Fly it of course.

Thanks
Personally I would make an entirely new drive washer so the needed distance ring is integral. Should'nt mr Linsalato have noticed this ? I do have an original 99 and I wonder if these RJL castings are "old stock" ?
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Old Aug 27, 2011, 07:31 AM
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Personally I would make an entirely new drive washer so the needed distance ring is integral. Should'nt mr Linsalato have noticed this ? I do have an original 99 and I wonder if these RJL castings are "old stock" ?
Yeah I was thinking long those same lines too. I am surprised they didn't notice that when they were making the engines in the first place. But then maybe they did and didn't care. Maybe the original Forster engines had that same flaw, I don't know. I agree making a new drive washer is very likely the way to go. I need to practice on my "D" hole making skills for the center hole anyway. I also think the drive washer needs a little knurling or grooving or teeth to help hold the prop with too. That drive washer just seems so flimsy for that purpose too.

I think they had the original molds for these engines, so they could cast up new parts. When MECOA buys a engine brand, they also get all of the tooling, dies, molds and whatever parts are still leftover too.
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Old Aug 27, 2011, 07:39 AM
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If you don't have a knurling tool, a disk of stick on sandpaper works well.
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Old Aug 27, 2011, 07:56 AM
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Originally Posted by earlwb View Post
Yeah I was thinking long those same lines too. I am surprised they didn't notice that when they were making the engines in the first place. But then maybe they did and didn't care. Maybe the original Forster engines had that same flaw, I don't know. I agree making a new drive washer is very likely the way to go. I need to practice on my "D" hole making skills for the center hole anyway. I also think the drive washer needs a little knurling or grooving or teeth to help hold the prop with too. That drive washer just seems so flimsy for that purpose too.

I think they had the original molds for these engines, so they could cast up new parts. When MECOA buys a engine brand, they also get all of the tooling, dies, molds and whatever parts are still leftover too.
I did have a look at my engine and it is very very close, not sure where it is exactly resting on. I would use a Dremel bit first and then go on hand filing,
tedious but not really difficult. By the way, does your engine have two piston rings ?
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Old Aug 27, 2011, 02:43 PM
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Yes it does have two piston rings on it.
The drive washer rests on a very small raised edge on the crankshaft. They have a brass points cam slipped over that part on the crank. Since the drive washer is fairly thin, I can see the outer edge bending or bowing back into the timer unit. I think if the drive washer is made more thick and the outer edge recessed slightly then it ought to not wind up touching and dragging on the timer unit. Plus it allows more metal in the center part to resist bending and deforming there in the center. You can see in a couple of the pics above where the timer unit is shown where there is that small more thick section in the crankshaft forming a small narrow shoulder. But that small shoulder there raises some concern with me. MECOA's parts list shows the drive washer and prop washer being different with different prices too, but they look the same to me though. I don't see any obvious differences between the two washers on my engine.

The other thought was to use both washers as drive washers and make another washer as a prop washer too. Both drive washers have a D cut for the center hole in them.

But then maybe this all works OK like that. I haven't looked at or ran Forster engines before, so it is new to me. Thus maybe that is all normal and they work fine like that.
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Old Aug 27, 2011, 03:37 PM
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Out of curiosity, just how do you make a "D" hole? I would be interested in trying it myself.
DrZook
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Old Aug 27, 2011, 03:38 PM
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I ran across pics of this Forster 99 engine and it had a cool special intake venturi with a simple throttle built in. That does give one some ideas about it.

Now then this thread here http://www.rcgroups.com/forums/showthread.php?t=1085999
had a post where Jack Hiner showed a Forster 99 with a RC carb adapter on it too. It looks like they made a exhaust restrictor for the engine too.


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Old Aug 27, 2011, 03:53 PM
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Out of curiosity, just how do you make a "D" hole? I would be interested in trying it myself.
DrZook
Well for me it is an exersize in patience mostly. The classic approach is to use a broach, these look like a tapered long D shaped file. You use them in a press to force feed through the hole. But having a broach made is quite expensive though.

The other method is to use a lathe mill with a rotary table and a cutting tool to nibble away at the metal bit by bit until you get it machined out to the shape you are wanting.
Model engine News has a nice article on making square holes, but the same method applies to D holes too.
http://modelenginenews.org/techniques/sq_hole.html

Now one can also use a set of jeweler's files too. You drill the largest hole you dare to drill in the metal, then hand file the D shape into the hole. Then mount the object in a mandrel so you can use a lathe to make it round and centered based on the D hole in it. Just take your time and pay attention to the detail and take slow patient swipes with the files so the hole comes out as a almost snug fit.

It is easy to make the mandrel as you can use a length of round bar stock, where you lathe the end down to the round size for the D and then file or machine in the notch. You can either thread the end for a spacer and a nut or use a bolt or screw where you drill and tap out the center for it. Then you can mount the D shaped drive washer or whatever onto the mandrel, chuck it up in a lathe mill or drill press, to make it round and centered so it doesn't wobble.

Anyway, that is how I have done it. That way if the D hole or square hole or other shape is off center, it is easy to use a lathe to make it look round and centered when you are finished. I have used a drill press to hold a mandrel before to manually use a large file to round off and center a washer too. Just be careful, it is dangerous if the tool gets caught in something.
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Old Aug 27, 2011, 04:32 PM
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Earl, thanks much for the explanation. Not sure if I need to do this, but now I know how!
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Old Aug 27, 2011, 11:01 PM
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You are welcome. I got to thinking about it and one could make their own broaches too.
Here is the Wikipedia article on it http://en.wikipedia.org/wiki/Broachi...etalworking%29
Anyway, one could likely use a decent steel and after machining it, they could harden it and it would work well for a limited number of parts. But then if you are only making one or two items it probably isn't worth the effort though.
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Old Aug 28, 2011, 02:56 AM
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Broaching

These are some broaches as mentionned by earl. The whole length of the blade is tapered, is inserted into a standard bought or turned to appropiate size counterpart and then slowly pressed in resulting, in this case, of a nice slot. I use this when making an excentric propellor drive plate for my ignition conversions on an engine that does not have a conical end on the crankshaft.
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Old Aug 28, 2011, 03:02 PM
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I've made drive washers by turning one out on the lathe then boring the hole to correct size, then making a little crescent shaped piece like a woodruff key and silver brazed it into place. A bit of touch up with a file and you can hardy tell it's two pieces.
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