Pre combustors (new manufacturing)

[jackbombay]

JB weld is rated to 600*F. I would not use it for the precup...

[Jet A]

I have built a mazda rotary for aircraft use (never made it to the plane though)...i have seen the jb used in the intake as a guide, but not in the reference u used.

In that case it sounds like it would only be heated to roughly 250 degress F.  This is no wear near the 1400- 1800 degrees F that the precup see. I have no idea what these actually see, but i am betting its higher than the egt.

I like a slight interference, and peen them in place. They are not going to fall out when the head is seated. part of the cup rests on the block, its not all free hanging over the chamber.

[jimfoo]

They don't have to fall out, only get loose enough to start hitting the piston. Ask me how I know. :cry:

[Jet A]

They don't have to fall out, only get loose enough to start hitting the piston. Ask me how I know. :cry:

After reading through several of the threads on here....i have come across many of your posts that have that last sentence in there. Sounds like you have a lot of life experiances on these motors!!  

[jackbombay]

They don't have to fall out, only get loose enough to start hitting the piston. Ask me how I know. :cry:

  I have such a head/block in my yard too. :-/

[gigaz2]

I have the opportunity to get one like that real cheap, might get it and try to stick the renault precups in there

[gigaz2]

it is in the vw design

take a look at these Renault:





EDIT: just realised that as they are much bigger theres less chance that they fall into the cylinder as the VW ones do.

I got the opportunity to get a Renault head apart so:







these are the second design from the above drawings, they come with two sizes 37,5mm and 37,7mm if I remember correctly

BTW, these came from my 1.6D 55hp Express van, 240K km, the head looks new, no cracks, honing marks on cylinders :O and I can still see the markings on the piston tops, they look new!
but it has 11mm bolts.. so the block is cracked in about 20 places:(

[arb]

Actually ended up doing 2 in 4140 and 4 in 304ss. they are gunna be my test pieces. Once i get the hole correctly in place, i am going to have them cast in stellite...which is a chromium cobalt alloy. Havent got a firm price on casting, but sounds like approx $20 per piece

stellite ? I haven't seen that ancient metal for years. $20 each would be a very very good price. Cobalt being a strategic metal ( you can't make a jet engine without it and there are few places in the world to get it)

If you are looking at super alloys, look for something like HMS-1011, Inonel, or a similar Ni-Cr-Co alloy. The nickel and chrome are the bulk ( Ni 70% - 80%, Cr 10% - 15%, Co 5% - 7% as I recall when I was melting then for testing)