Stuart 7A Build

[jeff l]

nice save !

[b.lindsey]

Glad you could save it Warren, I am just catching up on your progress so far.

Bill

[bent]

Ouch.  But the fix looks good!

[warrenmaker]

Thanks guys,,

Now I have ANOTHER problem.

Going by the dimensions on the drawings the groove in the piston should be 13/16 in diamater, and the piston is 1" dia.

At 13/16" dia for the groove though,, the piston will not go in the cylinder with the O ring fitted. The OD of the ring fitted on the piston measures 1 and1/8".  That's like 3mm oversize.

 No wonder it wont go in. I tried the zip tie trick, I also have a healthy lead in chamfer on the bottom of the cylinder..  SO, in desperation I deepened the ring groove by 40 thou !!! 

I can now get the piston to slide into the bore with a bit of effort. But then it jambs tight. I can feel metal on metal, as if the piston is rubbing on the bore. It certainly is not a nice slide fit like I was expecting.

The bore is 2 though over size and the piston is a half though under,, so there should b perfect clearance.

I then attached the cylinder and piston rod to the cross head  in the standard, thinking that might help hold it all in alignment and square, but no go.... still grabs and binds like crazy... ANY THOUGHTS..

[Jasonb]

How much width did you allow on the groove so that the ring could be compressed?

Assuming a nominal 3/32" section ring which is actual 0.103". for a model piston you want a groove depth of 0.098" but the width needs to be 0.125"

If it is 1/8" nominal which your 3mm oversize suggests then they are actually 0.139" section and groove should be 0.132" deep x 0.188" wide.

Note groove depth is calculated from cylinder wall so you will want to be about 1 thou less

[warrenmaker]

thanks for the groove specs Jason.
Stuart must have changed O ring wall thickness without altering the drawing cause it was NEVER gonna go the way it was.

Just a bit more progress...

[warrenmaker]

I double sided taped the chest to the cylinder block.

Stuart decided to give me 5ba studs and nuts enstead of 7ba 

So the socket head cap screws will have to do for now on the cylinder cap...

[warrenmaker]

getting there

[warrenmaker]

came across this at boot sale.. 2nd hand but never used..  $150       

[warrenmaker]

Needs a palette to b useful... so here goes. I knew I had been saving this piece of Aluminium for something

[warrenmaker]

Hopefully it will look this in a few days....

[Jasonb]

As your hole pattern follows the 3 slots would tee nuts and studs not have been more versatile? That is all I use on mine.

[warrenmaker]

HA.... U got me AGAIN...       (I can't believe I didn't see that) 

OK smarty;    I'm gonna go and change the hole pattern so it actually sort of makes it worth having... 

[Jo]

I have patterns of drilled holes on a plate on the rotary bed of the BCA and I find them very good. There are tee slots underneath the plate but I have never felt the need to take the plate off 

Jo

[warrenmaker]

   Ummm... forgive my dumminess... but what exactly is a BCA..??