VWDiesel.net The IDI, TDI, and mTDI source.
Engine Specific Info and Questions => IDI Engine => Topic started by: Kudagra on May 23, 2010, 05:54:32 pm
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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?
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CHeck Kevin's thread in the FAQ
http://www.vwdiesel.net/forum/index.php?topic=24690.0 (http://www.vwdiesel.net/forum/index.php?topic=24690.0)
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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?
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Once your head has lifted far enough off the block for a cup to fall out, does it really matter?
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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...
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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.
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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. :)
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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.
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Can't we just put a couple of peen dimples in the head on both sides of the cup and call it a day?
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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.
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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.
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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.
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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 (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.
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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.
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Hmmm...
Anyone ever seen a pre-cup dislodge on a factory non-rebuilt head?
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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.
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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??
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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..
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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....
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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
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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.
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they did use a scirocco to escape in dawn of the dead...
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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
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Or as was mentioned, build a tdi/mtdi.
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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.
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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.
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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...
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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...
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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..
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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?
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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.
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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?
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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
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would definitely work to knurl it..
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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.
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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.
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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.
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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!
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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.
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hey, knurling wast my idea.... they always seem to stay right where they are supposed to be for me :-)
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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
(http://farm7.static.flickr.com/6063/6075307944_c2965c9aa3_b.jpg)
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That's cool haha
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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
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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.
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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.
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I think it was about 220 Grit.
I didn't have a floor sander roll to hand. The strength of the cloth of the floor stuff is such that I may have had a problem keeping it flat. Maybe there is some on a roll that is slightly less 'heavy duty'
I think I only had one join give me brief trouble, but it glued back with that spray adhesive.
I did it completely dry, and quite slowly, so I didn't have any heating issues.
It did amount to about 72 pulls, split up into 12 lifts to photograph and 24 raises to blow/brush swarf out. I think the bed was about an inch too short to completely avoid the head overlapping it's footprint, hence the lifting of the head to blow the 'filings' away.
I found the symmetry of the areas as they were being levelled quite fascinating...
I used new bolts for this event, but knowing the history of the bolts reused them last year. Not sure if I'll reuse them a third time; but I may run some tests on them next time ;DLooks 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.
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Very cool! How much was the warpage before you sanded it down?
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Very cool! How much was the warpage before you sanded it down?
Between 3 and 4 thou.
I think main issue was a sudden catestrophic gasket failure, possibly caused by corrosion of the metal band gasket edge. Top hose burst with a 6" slash. Exactly the same as on another Quantum, and neither installed by me.
If I need to do it again, the only changes, would be to be sure I counterweighted the manifolds more exactly, and aim to take off no more flesh than neccessary.
Believe you me, I became mesmerised with the symetrical patterns forming :o
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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.
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I agree you would have little chance of knurling a precup that way, but seriously you guys should try filing a precup with a file... it does work. I'm tired of hearing that "inconel" which is a general sales term used to classify a huge range of alloys, is "bloody hard" when the only thing most people know about it is that its harder than the aluminium head casting, which is "bloody soft"!
thats mega cool head sanding DIY btw.
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Hand filing will not help all to much.
It might help hold when peened, but thats about it.
Knurling is a forming operation that presses material into a knurling tool. The pressing causes the texture, and also bring up to diameter, usually upwards or .005 (depending on material/depth and type of knurl)
It's a bit touchy to do on a manual lathe on steel, let alone an exotic metal.
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Hand filing will not help all to much.
It might help hold when peened, but thats about it.
Knurling is a forming operation that presses material into a knurling tool. The pressing causes the texture, and also bring up to diameter, usually upwards or .005 (depending on material/depth and type of knurl)
It's a bit touchy to do on a manual lathe on steel, let alone an exotic metal.
oh, i totally believe you..
thats why i said on my post:
"it would work IF you could figure out how to do it"
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Here's my stab at a cure:
If your cups are loose, remove them, and then in 90 degree intervals file a bevel into the face edge. Tap the perimeter of the hole with a bodywork hammer to tighten hole slightly.
Reinsert cup, then with a suitable punch, push the head material slightly into the bevel. I guess you could do 3 or 5 etc, but, should you do too many and need to remove the cups for experimentation purposes such as ceramic coatings, it could make it too hard to remove them again...