Paranoid about dropping a prechamber

[jackbombay]

Hmmm... 

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

  The head I removed with 3 or 4 precups loose was a factory non-rebuilt head.

[Kudagra]

As Emir from Office Space said... "Up your azz with the Resurrection"

Bringing this one back..just in case something new has been thought of about a 30 year old engine.

SO...Whats wrong with machining a hole in the precup and tapping inside the head and just cranking on a retaining bolt that doesnt protrude into the cylinder.

Down side of course is Bolt would have to be something interesting like titanium and a pain in the butt to surface flat..and would probably just screw up the swirl action in the cup.

Screw in cups would have to be indexed and also a pain to get correct...and even then there is no guarantee that it still wont rattle loose.

I WISH there was some way to machine in a ring retainer groove into head and precup to install...but then pieces of this or the head would disintegrate with the violent environment inside the cylinder.

Another idea would be to drill and tap the EDGE of the prechamber on the deck surface..Half on the chamber half on the head and screw in (or press in) retaining bolts. Then again the violent environment of the combustion chamber will toast this.

Gaaa...There has to be a way. Im so paranoid about this I cant make the leap of faith to assemble this engine. I was researching (google is god) and found that Benz uses a Precup retainer.. unfortunately these go in from the top side. Fubar.

Any more ideas??

[R.O.R-2.0]

why so touchy about them? its not like every VW diesel on the face of the planet is going to drop precups. and they cant come out whole. they gotta fallout of the head in pieces.

i think you guys worry too much. throw the motor together and run it. thats whats been done to every VW diesel on the face of the planet..

[rodpaslow]

I'm going to put in my 2 cents - I have owned 8 of these diesels - 4 1.5 NA, 2 1.6 N/A, 2 1.6TD's.  1 was professionally done by VW's and the rest done myself.  At no time was the head not gone over throughly.  I even had 1 where the compression ring broke and was rattling around 1 cylinder as I had partially melted a piston (1.5 engine).  I'm on my 8th  (1.6TD) and have spent god knows how much on the car and engine.  Myself - I like knowing what goes in and what condition they are in.  I've never had the problem of a prechamber coming loose.  An now with steel head gaskets, I think this is not an issue.  However, the head MUST be in good shape and gone over with a fine tooth comb - prechambers, bore they fit into, any wear issue seen from it possibly previously been loose, bores must be spotless - no sign of any misshaps previously....

[RabbitJockey]

i still just don't see how they can fall out unless there is some other issue.  even if them tapping around slowly wore their bore deeper and wider before they would even fall out, there would be all kinds of crazy noises.  i've seen plenty of pictures where they were melted or cracked and pieces have fallen in, and i've seen them cracked in person, but i never saw one just fall in for no reason

[Kudagra]

Ok...trust those that know...they do fall out. I dont want to do a bunch of work and have it crap out on me. I like to over build and eliminate any possible weak spots. Thats why just about all the wiring going to the front of the car is all relayed and the rest of the wiring has been re-strung with a few gauges larger wire..that was fun. I want a reliable problem free car for when the Zombie Apocalypse happens.

So..yes..I want a retainer.

[RabbitJockey]

they did use a scirocco to escape in dawn of the dead...

[Kudagra]

Eureka!

So I'm pulling apart a junk mech head (ate the cam..too bad since there are NO cracks between the valves) and I've noticed the mech pre cups are a hair larger in just about all measurements.  Now I'm not sure why other then mech and hyd. Both German heads. Both 068 103 373. Mech has a 53 after where as the hyd has 65.
Now on to what I see...looking at a precup you will notice a groove cut into it between the combustion surface and the pre cup body. Its about 6mm from the deck surface. A set screw could be drilled into the head and tightened into this groove there by locking it in place. Sure it wouldn't be 100% end all fix...but its atleast something for piece of mind. My other idea was gleaned from rebuilding hydraulic cylinders. Some caps use a curved metal strip that, in this case if one small enough could be found, could be inserted to curve around the precup giving it almost 360 locking. A diagional hole would have to be machined in just the correct place. Problem with that is a steel strip would probably just gouge into the aluminum of the head.
Both of these fixes bypass the problem of violent atmospheres or screwing up the swirl.
At this point I'm leaning towards the set screw for simplicitys sake.
I COULD have some precups cnc'd from Inconel with a slightly sharper groove.

Maybe I could machine a 16v head to accept Benz precups. :-P

[rallydiesel]

Or as was mentioned, build a tdi/mtdi.

[Kudagra]

How about no. Diesels are a premium. Since I'm looking at 700-2000 for just a DONOR...and I have 3 of these engines that's not a viable option.
Its not like I'm talking about having a new iron head machined. I'm looking for a way for everyone to improve on these engines and take out any worries one might have.
I used to deal with 2.3 fords. The bottom ends are actually pretty beefy..the weak point is the slider cam..that can be fixed by installing a later Roller cam from a ranger. If I could figure out how to do that on one of ours id do that as well.

[gldgti]

I get your point about reliability, but in reliability, its all about statistics.

There must have been millions upon millions of IDI vw diesels manufactured in the world, and I am certian that as a percentage, the precup falling out of the head is a miniscule issue. Its no suprise that we've got a few examples on this forum - because here is where all of the 'statistical anomolies' live - the people who tune the engine to make 3 times the factory rated power output, people who  (in some cases) do fairly average rebuilds, and people who have owned many of these engines and done LOTS of miles - lets face it, you arent likely to become a VW diesel addict if you only do 5000 miles/year.

Add to that that just coming on the internet to a car forum and reading about people horrific experiences in itself causes undue worry - think about how many things you might never have considered an issue until you read someones horror story about a crank pulley, and all of a sudden you can find a wobble where there isnt one, if you look hard enough.

Paranoia wont get you a bulletproof engine - common sense is more likely to. Add to that a bit of dosh and some genuine know-how, and your well on your way.

[vanbcguy]

I think some of the precup incidents on here also stem from people running merc nozzles rather than any problem with the heads/precups themselves.  Oh there was also the guy who was running CNG as a supplemental fuel I think...  None of those cases are typical of most engines though...  I totally get what you're talking about with wanting to avoid failure at all costs, but don't forget how close the precups are to the water jacket in there.  Would suck to create a problem...

[bajacalal]

In the automotive world, failures tend to happen in clusters and involve a specific part weakness, like that problem you mentioned with the Ford "pinto engines" and the non-roller cam or the killer dowel pin on a Cummins 6BT. The problem will become notorious among the group of people who own that specific engine and people will take steps to prevent it. Since precup loss is something that has hardly come up before in this group of people who, as mentioned, have a lot of experience and millions of collective miles with these engines, I don't think it's an issue.

Since it was mentioned, I would love to build a mech-TDI engine at some point, maybe retire my IDI to a Samurai conversion... Aside from the power increase without a loss of efficiency, here the TDIs have a fairly large following whereas old VW IDI diesels are like one in a million engines. They used to be everywhere on the roads but it appears they pushed them all into a hole somewhere... I'd love to find where it is...

[R.O.R-2.0]

if we had all had pre cups fall out, i would say its a bit of an issue, but since ~1% of the users here have had cups fall out, im just not going to worry about it. ive never had one break up and fall out..

[levi20AE]

I just got a head that I had rebuilt with new valves, guides, seals, keepers, and buckets.  The cups protrude slightly so I'll be taking it back tomorrow to have that remedied but the most concerning issue is that one of the cups comes out of the head freely.  What is the proper way to repair this? I have heard of knurling the cup and press them into the head. Is this the right way?