Oscillating engine port holes 'moon phases'

[student123]

On an ongioing novice build of the littlemachineshop oscillating engine

http://littlemachineshop.com/Projects/OscillatingEngine.php

I have a Taig lathe & a cheap & cheerful drill press & a cheap & not-so-cheerful airbrush compressor.


My first attempted build, was abandoned , one of several problems being the port holes not properly aligned.

http://www.homemodelenginemachinist.com/index.php?topic=9657.0

Have completed assembly of a second engine:

I've put compressd air on , no movement.

This new engine ,after measuring several times & using a tin template I've again managed to not get the vent holes fully aligned
Best way I can describe it is , lookin thru the holes in the upright uou can see 'moon phase' shapes
heres a pic

the black bits are where port vents do go thru to the cylinder

Julian mentioned in my earlier post timing in this context but not sure what it means (google for timing & engines brings up IC engine stuff)

What now … can I just make the holes in the upright bigger?

Mike

 

[itowbig]

move it to where u see half moon holes and drill right there just a little just to get the are though

 

[student123]

Itow - thanks for the super quick reply!

An alternative has occured to me - the holes in the upright are part threaded - well one is ) the cylinder vent hole is not - could I just make the vent hole in the cylinder bigger instead?

Mike

 

[Deanofid]

Mike, you could plug the bad holes with round stock and drill them again in the proper orientation.
Make a couple of plugs the same size, or .001" over size for the holes, coat them with Loctite, and
tap them into place. Wait overnight for the Loctite to cure, and drill the new holes.

To make it a little easier, make the plugs a little long so they are easy to handle, and after they are
set in the holes, remove the excess. I would do that from the side shown in your 2nd picture, so you
don't mess up the mating surface for the cylinder.

The engine in the first picture looks quite nice!

Dean

 

[student123]

The engine in the first picture looks quite nice!

Dean thanks!

I think I can see a possible problem now with making the upright holes bigger - with larger holes air aganst the cylinder wall pushing the cyl away from the upright. Plug & redrill then...

<drinks tea & ponders...>

There is a hybrid alternative where I drill 4.5mm , tap 5mm for the holes in the upright, on a 'nothing to lose' - plugging the holes later if that dont work?
Or is that wasting time on a horse that aint gonna jump the fence?

<cranks brain while attempting thinking...>

OK. decided. straight for the plug & redrill.


Mike