Paranoid about dropping a prechamber

[Kudagra]

I like stuff that locks in as opposed to press fit. Im really leary of assembling a engine with alot of money into a bottom end only to lose it all because a precup decides it wants to fall out. I know of one guy locally that rebuilt his engine only to lose it 200 miles later because of this.

2 things..

1. Ive heard that Turbo and NA precups different. I dont believe this but I figured Id ask. Is one bigger then the other? Length and diameter?

2. Any thoughts on drilling and tapping a tiny 2-3mm hole just below each glow plug, tapping it and installing a set screw?

[macka]

CHeck Kevin's thread in the FAQ

http://www.vwdiesel.net/forum/index.php?topic=24690.0

[Rabbit on Roids]

1.5 cups and 1.6 TD cups are dimensionally identical ive been told. any truth to that? and the n/a cups are bigger around?

[745 turbogreasel]

Once your head has lifted far enough off the block for a cup to fall out, does it really matter?

[bajacalal]

If you have a precup fall into the cylinder, you're doing it wrong.

They fit into a part of the cylinder head that is contacted by the engine block (with the head gasket in-between) and only partially protrude into the area on top of the cylinder bore. It's not physically possible for them to fall in once the head is installed. 

Once you have the head off and see how they sit, this will make more sense...

[Rabbit on Roids]

how do the pre chambers come far enough out of the head to fall in? just crack the face off them? cause if you set a cup at the top of a bore before you tap it in, they stick out over a quarter inch.. the only way i can see something going wrong is if it dropped the face of the cup.

[wolf_walker]

That's not fell out, that's got loose and beat apart from incorrect machining that VW says don't do in the first place.

[wolf_walker]

I don't recall ever feeling a pre-chamber being really tight going in or out of a head.  You'd think with thermal expansion and retraction and the godawful heat and stress it'd happen more often.  Guess VW (more or less) knew what they were doing.

[Syncroincity]

Can't we just put a couple of peen dimples in the head on both sides of the cup and call it a day?

[Kudagra]

Can't we just put a couple of peen dimples in the head on both sides of the cup and call it a day?

That is what was done on the guy in my example. Hes also a machinist at the local reputable VW machine shop. He peened them and it still ate his engine after 200 miles.

The cups get loose and then punch through the headgasket (just like..well...a hole punch) Needless to say..a hunk of inconel bouncing around in the cylinder tends to mess stuff up. Head, Block, pistons...all toast.

[wolf_walker]

There has to be a way to make them stay, the vast majority of them do for many hundreds of thousands of miles.  We just don't know what it is apparently.  Maybe they are just a tighter fit when the heads are young?  Aluminum deforms and all that.  Peening only snugs up the lip.

[alexgingles]

That's funny.. I saw mike's headgasket after that happened.. and yeah... where the pre-cups sit was eatin' away on the hg.

Can't we just put a couple of peen dimples in the head on both sides of the cup and call it a day?

That is what was done on the guy in my example. Hes also a machinist at the local reputable VW machine shop. He peened them and it still ate his engine after 200 miles.

The cups get loose and then punch through the headgasket (just like..well...a hole punch) Needless to say..a hunk of inconel bouncing around in the cylinder tends to mess stuff up. Head, Block, pistons...all toast.

[jackbombay]

Here's one, unfortunately the pics aren't still up.  They were gruesome.  Do some searching and you'll find others.

http://www.vwdiesel.net/forum/index.php?topic=14690.0

  I should have saved those pics for posterity's sake.

  But, the HG will fail before the precup falls into the engine, and the HG will fail only after the deck of the block is jacked, crumbs of block have fallen into the cylinder and score the wall of the cylinder and the Head will be totally jacked.

  That car was run too hard up a LARGE STEEP mountain pass, 2 times a day. 3 precups in the head was loose, the one that got the coolant last was the one tat was super loose and caused the HG to fail, the one next to it was a bit loose, the next one was just a little loose and the last one did not move.

[Patrick]

Somewhere on this site there's pictures of the destruction of a 1.6 td that happens when a precup comes out. I posted them a few years ago....... I'm using a different computer now, so I don't have access to the pictures or the link. I'll see if I can find them........  Enging was a volkswagen Canada factory rebuild too! I'll take more pictures if I get theh chance (still have the parts) But not today. Headed for VW Scully's show.

[wolf_walker]

Hmmm... 

Anyone ever seen a pre-cup dislodge on a factory non-rebuilt head?