Flat surface

[Gordon]

I am building the Webster engine and the valve body calls for the alum pieces to fit together with no gasket. I have tried to get a good fit but I still have air leaks. I can get the engine to run by putting a teflon gasket between the pieces but it soon melts. Standard high temp gasket does not work either. How do I get the pieces to fit together with enough precision to eliminate leaks? I have tried using a flat diamond hone and other sharpening stone but they soon are not flat enough.

 

[AlanHaisley]

If the surfaces to be flattened are external, you could try fine wet/dry paper on a sheet of plate glass. Use wet with something like kerosine which will tend to hold the paper on the flat surface as well as float off the residue.
Also be concerned when bolting the two parts together. Try to match the torque on all the bolts and tighten them in stages. Tighten opposites and go slow.
Don't forget to wash the parts carefully after sanding.
Alan

 

[starbolin]

My guess as to your problem is too much abrasive on your lap. If the work floats on the abrasive it is no longer following a flat surface. Too mush abrasive cuts slowly and poorly. Less abrasive cuts faster. Only enough abrasive to finely rub across the lap is necessary. Less is more.

How are you measuring flat? You can't manufacture flat unless you can measure flat.

High temp grease will probably work as a gasket just as well as anything else, assuming you are anywhere close to flat. For vacuum work, even after careful polishing, a touch of glycerine was added to the joint to seal up troublesome leaks. A temporary fix, of course.

 

[lensman57]

I am building the Webster engine and the valve body calls for the alum pieces to fit together with no gasket. I have tried to get a good fit but I still have air leaks. I can get the engine to run by putting a teflon gasket between the pieces but it soon melts. Standard high temp gasket does not work either. How do I get the pieces to fit together with enough precision to eliminate leaks? I have tried using a flat diamond hone and other sharpening stone but they soon are not flat enough.

Hi,

I have built the Webster engine on a little Taig lathe and even a smaller Taig mill which to this date refuses to be trammed properly. The aluminium valve blocks seal together without the use of gasket material. I milled them using 1/4" TILAN coated end mill but for once I listened to some old words of wisdom, the step over distance between the cuts were less than 1/4 of the end mill diameter and the depth of cut was about 0.008". The surfaces were truly flat and smooth with no sign of "steps" in the cuts, I then lapped them on 1500 grit wet and dry paper as suggested in the other posts. The sealing of the valves in the guides are however, a totally different matter that I have not resolved as yet. Perhaps you could use some copper shimming in between the surfaces and see what happenes, I know that you can get these in about 0.05 mm thickness or 2 thou in the old money, from specialist art and craft shops.

Best of luck and regards,

A.G

 

[Gordon]

I have lapped the pieces together with 400 grit lapping compound which got me much better results but I still had leakage so compression was too low for reliable starting. I finally put the pieces together with a thin film of RTV and I now have sufficient compression.

 

[mcostello]

Lensman 57- Any more old words of wisdom to share? Inquiring minds want to know?

 

[kvom]

You might try RTV hi-temp silicone

 

[hammer2100]

Loctite make a product that works better than RTV it's #510 Flange sealent works at higher pressure. Will fill gaps up to .010".

 

[lensman57]

Lensman 57- Any more old words of wisdom to share? Inquiring minds want to know?

Hi Man,

Many around but I only remember them when the questions are asked. just having a bad memory I guess.

Regards,

A.G

 

[lee9966]

For a flat surface I have been using a granite (or maybe marble?) gloss floor tile 12" x 12" . I figure if when seeing reflections in it there is no distortion it must be pretty flat.

Lee

 

[Brian Rupnow]

I could never get them to seal either. I used a gasket between all bolted surfaces and I 've never had a problem with the gaskets burning.