SNAIL

ami8i

Hello,

I got a pair of 9.5 pistons and want to increase compression ratio to 10.7 --> I have to machine off 1.0mm of the Visa cylinder.

First cylinder modification was no problem, looks very nice.

When we tried to find out a good position of the cylinder in the lathe we heard a 'cluck', sounded like a tool (wrench...) is hitting a metal part. My friend just turned on the three-jaw chuck slightly. We found nothing and continued.
When we did the last chip(?) the cylinder broke! 400rpm, 0,2mm (x-axis) and 0,08mm/U (z-axis) automatically (in)feed(?).

How could we clamp the cylinder so that it will not crack?

My ideaa is to turn a small (0.2...0.4mm thick, 4mm wide) Aluminium stripe around the base of the cylinder so that the slot/groove of the bottom O ring will be unstressed.

How do you machine a Visa cylinder?

Thanks
»Horst
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champy2k · Dropped Joined: 02 Jul 2007 Posts: 116 Location: uk

i use reverse jaws and clamp on the bore, use shim to protect the boreno probs, just take small cuts
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ami8i · Posted: Sat Jul 26, 2008 10:47 am Post subject:

Hello champy2k,
thank you for your experience.

I repeat in my own words to clearify:

1) Reverse jaws clamp the cylinder inside the bore.

Do you clamp it on the cylinder head side and machine bottom side?
I have to machine the cylinder head side of a Visa cylinder. --> clamp bottom side. I can't imagine how to do this because I can't clamp it in the thick material. The tube at bottom is too weak (as I head learned the hard way).

2)

dyanut · Posted: Sat Jul 26, 2008 3:12 pm Post subject:

Horst,
I guess Geoff may be recovering from setting fire to his underpants while welding a 2CV yesterday ( Surprised

) or just enjoying the sunshine we've got in the UK at present.
Anyways, that sentence should be easier for you to understand with the missing comma & space added... " use shim to protect the bore, no probs".
( Also, we use 'bore' to refer to the inner surface of the cylinder and I'd guess Geoff uses a strip of shim steel between the jaws and the cylinder bore to avoid any damage. Probably well worth checking with him which thickness of shim steel has worked best. )

hth, Ken.

jose of jura · Snailer Joined: 22 Jun 2007 Posts: 38

you can also attach the cylinder at the vertical and use milling machine, and to machine with a tool has to ream!

for attach the cylinder at the vertical it should be attached on a half casing.

be careful, the Nikasil coating is very hard has to machine! Wink

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ami8i · Posted: Sun Jul 27, 2008 1:28 am Post subject:

Hello Ken,
thank you very much for decoding Geoffs message. :)
Thank you bore is clar for me, shim was not, but I think it's just a sheet of metal (I guess Aluminium, because it's more friendly to Nicasil surface).
Yes, I'm very interested in Geoffs solution how he is able to get the jaw deep enough into the cylinder.

Hello jose of jura,
we have no access to a milling machine. Long time ago (technical shool) I learned to handle such a machine (but forgot all :) ).
I guess just very expensive milling/cutting heads have such a small radius which is at the step between O ring (oil) surface and vertical cylinder wall.

On lathe we paid attention not to touch this surface except at the height of removed material (1mm).

I would not been surprised if Nicasil were spalled off, but luckily no probs with Nicasil.

»Horst
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ami8i · Posted: Wed Jul 30, 2008 10:03 pm Post subject:

Hello,
yesterday we machined the second cylinder and both pistons.

The jaws of the lathe are awful because they're not really linear.
We made a shim (0.4mm, ~3mm) Copper metal to give the lathe just one position to fix. A GS piston with central hole was put into the top of the cylinder. One piston ring kept the worn pistion in position which was pressed slightly(!) by the cone at the right, moveabe body of a lathe.
After checking round running (just a few 1/100mm) we machined the O ring 'oil' surface and most of the cylinder 'gasket' surface. Always just 0,1mm chips.

Then we removed the cone, put the piston inside cylinder, moved the cone in position.
And now comes the special tool! I took a broomstick and adapted (quick&dirty) a pin as center mark. This tool was put from left side through turning axes of the lathe and prevent the psiton to loose the cone!
Was funny to do - but it worked.

Finally we machined the pistons. ~0.7...0.8mm deep and 1.0...1.5mm inside diamter. Piston falls down to the same position than before.
I will check clearance when mounting the new parts.

»Horst

PS:
'Now' I have to shorten the exhaust manifold by 2mm. This should be the chance to insert a vent/valve to connect and disconnect each exhaust pipe. Then we'll see the influence of the cross pipe (Streetdyno).
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