I've noticed a few things here lately.

[dieseltech]

Firstly, hello everyone, Its been almost 3 years since i have been active on this board, had a bad accident where a lift with a car on it fell on me, but im back, almost as good as new, we had to sell most all my 30+ vw's audis etc, because the shop i was working at had no insurance. anyway, enough of that.

I have noticed a few things when some of you rebuild your cylinder heads or get them resurfaced, what is this Dots on the prechambers from peening. I know its to hold them in, but its absolutely unnecessary, once the head is bolted on, the chambers are held in place from the head gasket, if they "fall" out like i have seen mentioned on here, you got bigger problems, secondly.
    When you get a head resurfaced, the prechambers are to be removed, and head cut, then fly cut the prechamber holes to proper depth, and reinstall prechambers, they are suppose to protrude slightly from the head. you never resurface the face of the prechamber, you Can touch them up to true them but resurfacing them causes the metal to be too thin in spots, that caused hot spots and cracking, possibly a chunk of metal falling off into engine.

i noticed in a few posts here that they machined right over the chambers, never removed them, you can see by the marks left from the machining process weather it was done properly. i spent most of my life in a machine shop, it just bothers me to see these things goin on.

thats about it, i hope all is well
happy vdubbin, hopefully i will own another, right now i own a $200 volvo 240, hey its all i could afford, and they are tough as nails.
chris

[arb]

Wow, I thought New York was a haven for lawyers !!! Would have thought 800-call-sam would have gotten you millions !!

Glad you're back.

[flapjack]

same thing happened to a buddy of mine. Wrecked his shoulder.
He didn't get any money either.   What can you do if the boss is broke?

[fatmobile]

I've always surfaced the heads with the prechambers in.
 You are saying they are not supposed to be surfaced because they get too thin?,..
 but touching them up to true them doesn't make them thinner?
 Often a surfacing is just a touchup.
 
 So surface the head and leave them sticking up?
 I think the headgasket would have a problem sealing over the edge of the step that would be left.
 
 I think the peens help,..
can't think of a way they would hurt and
 it doesn't take much time or money to do so being necessary is a moot point.

 Good topic.
 I've heard both ways and taking them out to surface the head always sounded anal,... especially if they are just going to surface them to the right height seperately and reinstall them anyway.

[Rabbit TD]

I've always surfaced the heads with the prechambers in.
 You are saying they are not supposed to be surfaced because they get too thin?,..
 but touching them up to true them doesn't make them thinner?
 Often a surfacing is just a touchup.
 
 So surface the head and leave them sticking up?
 I think the headgasket would have a problem sealing over the edge of the step that would be left.
 
 I think the peens help,..
can't think of a way they would hurt and
 it doesn't take much time or money to do so being necessary is a moot point.

 Good topic.
 I've heard both ways and taking them out to surface the head always sounded anal,... especially if they are just going to surface them to the right height seperately and reinstall them anyway.

I'm not a machinist but from what I have read lots of machinists won't mill the head with them in the head  because they can sometimes pop out during the process and mess up their cutter.  I've had 3 done over the years and these guys never gave it a thought and it never happened to mine.  But knowing this now if it was my milling machine I would probably want them out too.

[jtanguay]

sounds to me like a do it right vs cut corners debate  :lol:

if the head is severely warped, and you're milling the head to get it straight, then yea the swirl chambers should be removed.  for a light skimming to smooth it out, i think it might be ok.  i wonder how thick the swirl chambers are on the bottom?  from a pic i've seen they seem to be large enough. maybe removing a slight amount of material weakens them just enough to crack down the road, under certain conditions?

i bet getting it milled properly would add considerably to the machine shop bill.  probably why not many people get it done the way it was intended, if it was ever intended at all.

[dieseltech]

no insurance and the owner of the shop is,,, well i dont wanna sue him, it would cause problems in the family, we'll leave it at that.
now.
the prechambers are harder metal than the aluminium head, it will cause flaws in the cutting process, not enough to worry about but i am a perfectionist when it comes to machine work,  secondly the factory manual says they are supposed to protrude out a few ten thousands of an inch, because steel what the chambers are made of does not expand as much as the aluminium head, so when the head expands from heat, and the steel insert expands far less, at operating temp, the chamber is flush with the head, when you cut it with the head,  at temp it is now sunk into the head, those Germans spend a lot of time perfecting and overbuilding things, well most of the time.  peening wont hurt, but now that bump of metal that squishes up from around the peen is going to be a hot spot, the chambers are designed to move around in the head during expansion and contracting, that's why the head gasket has metal around the chamber area, not fibre. the the chamber has a surface to ride against, there is no possible way for them to fall out unless the head is removed from block, and if they fall out then, you have a seriously warped head, your supposed to warm the head and chill the chamber to make removal and installation easier now here is a lil science, a thinner piece of steel will heat up faster when heat applied, a thicker piece will take much longer with the same heat source to get to same temp, when you resurface the prechamber, it is making it thinner, the prechamber is where the most heat is generated as its where the injector sprays fuel into, the prechambers tend to crack at the exit hole in bottom from heat, when you take a layer of metal off, it makes the cracking much worse because it heats up red to white hot faster, all that concentrated heat will eventually cause it to crack just like exhaust manifolds on certain cars crack from heat and being too thin,,  don't believe me, look at yours after 75,000 miles if they been cut, you'll see the cracks especially if your running extra boost and fuel, now touching them up is usually accomplished by using either 2000 grit paper or valve lapping compound on a certified flat table and in a circular motion, rubbing by hand till the surface is flat, this takes off way less than resurfacing,  hope this helps
im not trying to point fingers, we all learn from everybody, i am just giving some education, that all

chris

[dieseltech]

i usually charge about 350 to 450 depending on how bad the head is and weather i had to heat and press the head straight,  pressure checking is 50,  but i also cut the valves and seats when i resurface, that way the correct amount of clearance is still there,  there are allot of guys out there interested in the money, yea the head will work, but how long? and the customer will be back, "cause it must have been a bad gasket," or " i got a great deal on the head for 149.99 to cut it"  i refuse to do that, my customers know its done right or you go to somebody else,  you pay for what you get, most head rebuilding company's on the internet sell butchered up junk, although topline solid lifter heads are ok for every day cheap head, the hydro, well thats annother story
 

chris

[Turbinepowered]

i bet getting it milled properly would add considerably to the machine shop bill.  probably why not many people get it done the way it was intended, if it was ever intended at all.

All the Bentley manuals I've read do rather explicitly say you aren't to mill diesel heads, so I doubt they ever intended them to be trued or resurfaced 'in the field' so to speak.

[dieseltech]

i bet getting it milled properly would add considerably to the machine shop bill.  probably why not many people get it done the way it was intended, if it was ever intended at all.

All the Bentley manuals I've read do rather explicitly say you aren't to mill diesel heads, so I doubt they ever intended them to be trued or resurfaced 'in the field' so to speak.

bently manuals are not the same manuals the dealers use, i have the original white cover engine. trans manual, trans auto, body and sub frame, electrical body, electrical power train, etc in separate 3 ring binders, in that book it has the head rebuilding procedures, you ever read in the bently book "this item to be serviced by qualified persons or shop"  i have seen that many times in the bently, i got pissed and bought the dealers "out dated" manuals, much much way way better, you can rebuild everything in the car with the vw manuals,

chris

here is a link to show that they exist http://cgi.ebay.com/ebaymotors/VW-Six-Speed-Automatic-Transmission-Self-Study-Manual_W0QQcmdZViewItemQQ_trksidZp3286Q2em20Q2el1116QQitemZ110094853406QQptZMotorsQ5fManualsQ5fLiterature#ebayphotohosting

[clbanman]

I think it is also unlikely that the Bentley was written with say a 450,000 km car in mind.  My owners manual says that the trans lube never needs to be changed.  I have 495,000 kms, and you can bet that I have a different viewpoint.  Similar thing with items like "lubed for life" ball joints.  They don't mean a life of 400,000+ kms.  So some things that they say shouldn't be done or don't need to be done may not apply to the type of service life some of us are putting our cars through.

[dieseltech]

the term "lifetime" means for the life of the warranty period, so in other words, if your car has a 36,000 mile warranty, that lifetime trans fluid is good for that 36,000, it should be changed soon there after,  

about the scan, i am not able to scan at the moment, i dont even have a printer! and im using $10 month dial up on a pentium II 350mhz machine with win98, i still have not recovered financially from my miss hap,  i can give the specs though if you would like?

chris

[Rabbit TD]

i usually charge about 350 to 450 depending on how bad the head is and weather i had to heat and press the head straight,  pressure checking is 50,  but i also cut the valves and seats when i resurface, that way the correct amount of clearance is still there,  there are allot of guys out there interested in the money, yea the head will work, but how long? and the customer will be back, "cause it must have been a bad gasket," or " i got a great deal on the head for 149.99 to cut it"  i refuse to do that, my customers know its done right or you go to somebody else,  you pay for what you get, most head rebuilding company's on the internet sell butchered up junk, although topline solid lifter heads are ok for every day cheap head, the hydro, well thats annother story
 

chris

Well that makes me feel a little better, I just bought a mechanical Top-Line head.  Like you said, you don't know what you're getting anywhere anymore from what I've seen from TV's to T/D's :lol:

[fatmobile]

Thanks for the info on why they should be sticking out above the head surface, and the source for your info.
 I have seen prechambers sticking up proud of the surface. It didn't look like the head gasket would seal properly around it.
 
jtanguay,

if the head is severely warped, and you're milling the head to get it straight, then yea the swirl chambers should be removed. for a light skimming to smooth it out,

 That should never happen.
  Surfacing a head that is severly warped would cause the cam to rock in the saddles.
 It should be bent straight first,.. then the cam journals line bored
 ,... then lightly skimmed if it needs it.

[Rabbit TD]

Thanks for the info on why they should be sticking out above the head surface, and the source for your info.
 I have seen prechambers sticking up proud of the surface. It didn't look like the head gasket would seal properly around it.
 
jtanguay,

if the head is severely warped, and you're milling the head to get it straight, then yea the swirl chambers should be removed. for a light skimming to smooth it out,

 That should never happen.
  Surfacing a head that is severly warped would cause the cam to rock in the saddles.
 It should be bent straight first,.. then the cam journals line bored
 ,... then lightly skimmed if it needs it.

So then a person should be able to tell if a head is warped pretty bad by the fact that if the cam doesnt spin freely when the head is off the car and dissaembled then is that correct, I know a straight edge should be used too though.  But if it does spin freely then how is it possible to cause problems if it is surfaced or milled to straighten it as long as you don't go past the valve to piston clearance point.  The actual combustion chamber area is in the pre-cup area anyway isn't it ?  I never could understand why they don't recomend it and I've had 3 done so far but they told me they only took off about .003 just to make sure it was flat and clean it up.