Can the port holes on a wobbler be made bigger to aid alignment?

[student123]

I'm attempting to novice build a small (allegedly) easy build wobbler, the brassy babe:

http://www.davegoodfellow.com/plans.pdf

the latest problem is doubts about location of the port holes
the instructions suggest stick a pin in the cylinder block port hol , scribe an arc on the frame & loctate the frame port hols that way

That’s what I did & carried on with the build. Looking again at it , if feels theres too much room for error
atempts to repeat the scribe process leaves varying results.
also theres play in the screw that hold the cylinder to the frame, so I cant see how the port hols would consistently align.
these small port holes look like little room for error.

heres a pic:

in the pic theres a scribe mark that doesn’t hit the holes - unreliable(?) , other scribe marks have hit them.


One solution might be to make all the port holes bigger - my question is can I do that ? Or will it make things worse
If yes, any suggestions as to how big should I make them?

At this stage it looks like I have to rebuild the cylinder block, piston & crankshaft anyway.
If I have to remake the frame…common sense tells me to chuck this project & move on, theres just a stubborn bit of me wants to finish it. If I can keep the frame by making the port holes bigger, possibly I'll stick with it.

 

[gbritnell]

There is a little room for error. As long as the ports from the cylinder overlap the ports on the base it will run. It might not run well but it will run.
It would help if you told us what type of equipment you were working with, that way maybe we could give you some better suggestions.
One thing I might comment on is the surface of the base that you have your ports drilled into will need to be much smoother to get the engine to work. You will need a perfectly smooth surface with the pivot screw at right angles to that surface.
gbritnell

 

[student123]

It would help if you told us what type of equipment you were working with, that way maybe we could give you some better suggestions.

A Taig lathe with milling vice attachement, a cheap & cheerful Chinese made bench drill press. Also a cheap Chinese made compressor recently acquired.

Since I posted I've been down in my shop. I decided the solution was to re-orient the input/output holes to run in line as continuations with the port vents on the frame. They should be check-able that way. Littlemachineshop do a wobbler that way.

Unfortunately I snapped 2 drill bits in the vent holes, so the frame is now for the scrap box.

Thanks for the reply,

Mike

 

[steamboatmodel]

Mike,
When I was first starting we were not allowed to chuck our mistakes in the garbage, we had to mount it on a wall in the shop with explanations as to what we had done wrong and how to fix it when you made the next one. You also had to put a couple of bucks in a tin, the proceeds went to a class party.
Regards,
Gerald.

 

[robwilk]

How about giving Elmer's Wobbler a try. I did it as my second project and found it fairly easy using the drilling jig in the plans.

 

[student123]

Rob,
Thanks for the suggestion, I skim read one of Elmers (#25?). Current thinking is a modified version of the little machine shop beginners engine.

Gerald,
You could have paid for a brilliant party if I'd been working there!
I've been loggin the errors/lessons, so if I ever get to the end I might post them on the wall marked "Mistakes, Blunders & boo boos".

Mike

 

[Cedge]

Mike
Since I suck at most things math related, I've learned to cheat, sometimes outrageously so. Thje last time i made a "wobbler" I need to find the location of the ports, but couldn't follow the math based formula t6o find the damned things. What I did will probably make poor old Marv Klotz cry in his afternoon cocktail....(grin)

I mounted the cylinder to the crank and the valve body..... after fitting a piece of pencil lead in the two cylinder ports. I then turned the flywheel a few times. When disassembled, the pencil lead had created two nice clean arcs. I then drilled the 4 ports to coincide with the ends of the arcs.... outside edge of hole to the very edge of the mark. Perfectly placed were the holes and my head didn't hurt....LOL.

Steve
Not real educated, but can sometimes be bloody smart.....LOL

 

[mklotz]

Sigh.

 

[Cedge]

(giggle)

Steve

 

[bearcar1]

You're my kinda guy Steve, (and not in *that* way either ) :big: If I can find a mechanical means of locating or setting something up I'll use it every time over doing the cyphers and such. Although I have on occasion used the formulas that Marv has so generously supplied for us "too stupid to add 1+1 folks" like me. :-X

BC1
Jim

 

[Julian]

Who needs maths. I use a ruler and a pen or scribe. Two lines that cross at the pivot and meet the crank pin when set at 4 and 8 o'clock works for me.

No offence student123 but the old saying of "measure twice cut once" is worth remembering. Through many cock-ups I have learnt this the hard way. Your port holes are, i agree, out but they also are not on the same radius. In my experience so far they need to be reasonably accurate to work but more accurate to work well. Also their size is fairly important for the timing of the engine.

Surface needs to be very smooth to work. Both my latest engines ("scrap engines" in pics and video section are very smooth but still leak air. Brasso or toothpaste to bed them in with.

Julian