Paranoid about dropping a prechamber

[RabbitJockey]

they are actually supposed to stick out from the head a tiny bit because they are made from some inconel chromium metal (good ***)  anyways the aluminum of the head expands more than the inconel, so the cup should stick out just a tiny bit further.  also knurling is a good way to get they to stay in tight,  how ever i had a head that the prechambers came out of pretty easily, but it ran fine i probably drove it for 20kmiles, and its still running today 2-3 years later.

[92EcoDiesel Jetta]

Can you still buy pre cups? Anyone have a pic? Are they pressed in when replaced? I just had my head out for a head gasket job and none of the pre-cups were loose (182K miles) and AFAIK the head was never machined. When a head is machined due to warpage (which VW says is a no no btw), are the pre-cups removed first or machined in place? Maybe the small number of pre-cups that has "fallen out" (I really can't inagine how that can happen) has been machined?

[RabbitJockey]

they're supposed to be machined separately, but pretty much no shop knows this, i believe if there is less than .004" difference across the head, you should not resurface it because tightening the head bolts will straighten it enough to stop any issues.  also when u resurface a warped head, and then bolt it down this messes with the cam journals alignment.  most heads i have seen the chambers won't just fall out.  but on one of my old cars with an aftermarket head, i could simply blow compressed air into the whistle hole and they pop out.  the car ran fine... and still does

[R.O.R-2.0]

would definitely work to knurl it..

[monomer]

would definitely work to knurl it..

Every try to knurl inconel? - and if they're coated, you might messup the coating.


Why not divit/peen the hold inside the head with a punch? That'll create a tighter fit.



All that aside, i think it's a non-issue. It simply wont just fall out of the head. It'll have to fall out in pieces - and that failure is caused elsewhere.

[R.O.R-2.0]

idk if its actually possible, being that inconel is SUPER HARD, and work hardens also.. but if it could be done, it would solve problems.

i think the set screw idea that someone came up with would be the easiest to work.

[gldgti]

there are lots of types of inconel alloys, and some of them are not super hard at all. if anyone has a clue what inco they are made of it would give a clearer picture.

many inco alloys have good machinability, and its likely the prechambers are made of an 800 series, like 800H or 800HT, or even 801. These are all quite machinable alloys. (the 800 series inco's are for extended high temperature operation, with very good oxidation resistance and high temeprature creep strength. Also, the 800 series alloys appear a kind of darker colour, much like the new prechambers do.

[RadoTD]

I threw one of my old precups at the ground as hard as I could. Knocked a decent chunk of concrete out but no discernible scratching or gouging.
Mathematical/scientifical proof it's some tough stuff. Don't mess with science!

[monomer]

there are lots of types of inconel alloys, and some of them are not super hard at all. if anyone has a clue what inco they are made of it would give a clearer picture.

many inco alloys have good machinability, and its likely the prechambers are made of an 800 series, like 800H or 800HT, or even 801. These are all quite machinable alloys. (the 800 series inco's are for extended high temperature operation, with very good oxidation resistance and high temeprature creep strength. Also, the 800 series alloys appear a kind of darker colour, much like the new prechambers do.

So, say you can machine it.



You get your little shop lathe set up, and you have the prechamber in your hand.


You goto chuck it up....











.....and then you realize there's no way you could possibly hold it in the lathe tight enough to have the proper tooling pressure to knurl.

[gldgti]

hey, knurling wast my idea.... they always seem to stay right where they are supposed to be for me :-)

[RadoTD]

I invented a way of knurling without a lathe. Roll said device along the table putting lots of pressure down on your weighted object.

Licensing fee = honoring your next sip of beer to me

[rabbitman]

That's cool haha

[monomer]

Flawed.


The file is going to be softer then the inconel, and the weight required to press in the tooling to form the knurl (not cut/scratch) would be immense. Crude cold forming, no?


Props for the drawing, the engineering department at my previous employer could have used you. Much better then a dootle on a napkin (in crayon, even) I would normally get.


Peen them in if your worried, grease them and slap them in if your like most on here. Used THE PROPER injector/nozzle for your make of car (tested) and be on with your day.



.02

[Mark(The Miser)UK]

http://imageshack.us/g/222/tenthabradeka0.jpg/

Here's a few pictures of the various stages of my 'hand' abrading my head some 3 years ago. Done due to a head gasket failure.

Things to note are:
 
My use of carborundum paper on 3 layers of plate glass, padded with sheets of newspaper to compensate for any 'sag'

My use of a counter weight to offset the weight of the manifolds.

My leaving of the manifolds on to avoid pre/post abrading, warping of head, and flexing cam holders.

Each head pic denotes six traverses along the paper.

Every 3 slides, head lifted and filings brushed away. I found this neccessary, else build-up of inconel grit scoured the rest of the head.

Note symetrical abrading. Note part of head warping is from the inconel  twisting and sinking into the head.

Note the abrading took the ears off the ex manifold too.

No issues in 3 years.
Took head off last year to do the rering.
Reused bolts, as only torqued to 45 deg or less each time, as and when each bolt hit the plastic range.

[92EcoDiesel Jetta]

Looks like you did a nice job! I know silicon carbide paper is black. Is Carborundom red? You can get floor sander paper from a roll so you don't have to stagger 8.5 x 11 sheets and eliminate the edges. What grit paper did you use? I think the floor sander paper in fine is somewhere between 120 to 220 which is close to the finish you want on the head. Did you do it wet or dry? How many times did you re-use the head bolts?

http://imageshack.us/g/222/tenthabradeka0.jpg/

Here's a few pictures of the various stages of my 'hand' abrading my head some 3 years ago. Done due to a head gasket failure.

Things to note are:
 
My use of carborundum paper on 3 layers of plate glass, padded with sheets of newspaper to compensate for any 'sag'

My use of a counter weight to offset the weight of the manifolds.

My leaving of the manifolds on to avoid pre/post abrading, warping of head, and flexing cam holders.

Each head pic denotes six traverses along the paper.

Every 3 slides, head lifted and filings brushed away. I found this neccessary, else build-up of inconel grit scoured the rest of the head.

Note symetrical abrading. Note part of head warping is for the inconel to twist and sink into the head.

Note the abrading took the ears off the ex manifold too.

No issues in 3 years.
Took head off last year to do the rering.
Reused bolts, as only torqued to 45 deg or less each time, as and when each bolt hit the plastic range.