VWDiesel.net The IDI, TDI, and mTDI source.
Engine Specific Info and Questions => IDI Engine => Topic started by: GTD0023 on October 13, 2008, 09:25:38 am
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I send my 1.9 TD head to the workshop to flatten. But when i got it back i was surprised to see how much material they removed.
They removed so much that now the valves are on the same height as the bottom of the head. i know they used to be a little inward.
So the question is: will this head still work?
I know my CR will be higher, but how bad is going to be?
Will my performance drop?
will i be able to push 20-25 psi??
Any help is very much appreciated.
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Honestly as far as i'm concerned and what we were told at VW no diesel head can be shaved. If they took that much off then i wouidn't use it. The compression will be way too high and there'll be a good chance that the inserts will fall out and ruin the rest of the motor.
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o oh :( . I don't wanna take any chances and risk further damage.
I've spend too much money on this.
Does anyone have any experience with this situation?
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Honestly as far as i'm concerned and what we were told at VW no diesel head can be shaved. If they took that much off then i wouidn't use it. The compression will be way too high and there'll be a good chance that the inserts will fall out and ruin the rest of the motor.
Well not exactly.
It wont change the compression but it they removed that much material there is a possibility of valve contact I think. I mean there isn't suppose to be an issue with that unless there is a failure of some sort but higher RPMs may be a problem.
Caveman brings up another point on the precups, the surface that actually holds them in is part of the upper shoulder (looking at the head upside down) if that area is shaved to thin the surface area holding the chamber in is reduced quite a bit.
I suppose you could peen the precup in so it wouldn't fall out but I still think there may be a higher RPM valve piston clearance issue. Is it a solid lifter head or Hyd?
Can you post up a pic?
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get a 3 notch gasket on there.shaving the head wont change compression,because your piston protrusion is still the same.The heads are flat to begin with.The valve relief is the gasket itself.As long as the valves dont go below the contact surface.
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i will post a pic later after work.
it is a hyd lifter head.
zukgod1 said:
I suppose you could peen the precup in so it wouldn't fall out but I still think there may be a higher RPM valve piston clearance issue
how do you "peen" the precups ?
It is a 1.9 so 5.5-6.0k is as high as it would probably go. is that still too high?
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I wouldnt peen them myself.Id have a shop do it.
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get a 3 notch gasket on there.shaving the head wont change compression,because your piston protrusion is still the same.The heads are flat to begin with.The valve relief is the gasket itself.As long as the valves dont go below the contact surface.
A thicker head gasket may screw up cold starts. Gasket tickness makes very little difference in the compression ratio, but VW saw fit to give us three options to maintain something. And I suspect its squish band which deals with piston cooling, and swirl chamber effectiness.
If they took that much off, i suspect the swirl chamber covers are really thin. And thats a recipe for disaster, if one of those falls appart.
Here's a head for $100.00: http://www.vwdiesel.net/phpBB/viewtopic.php?t=16815
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I wouldnt peen them myself.Id have a shop do it.
Why not?
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I wouldnt want to take a chance hitting my head with a drift.
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I wouldnt want to take a chance hitting my head with a drift.
Oh come on!!
Done in the correct places it's fine and very easy to do.
Here is a pic of one.
Mine is peened much more than this for reference.
(http://i13.photobucket.com/albums/a269/libbybapa/IMAG0098-1.jpg)
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i will post a pic later after work.
it is a hyd lifter head.
zukgod1 said:
I suppose you could peen the precup in so it wouldn't fall out but I still think there may be a higher RPM valve piston clearance issue
how do you "peen" the precups ?
It is a 1.9 so 5.5-6.0k is as high as it would probably go. is that still too high?
Here ya go.
I still want to see a pic of your head though, we need to get a scale of how much they actually removed.
(http://i13.photobucket.com/albums/a269/libbybapa/IMAG0098-1.jpg)
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I had to take a few thou off of my head (block too), but they machined the valve seats also so it was about the same in the end. Did they tell you how much they shaved off? You may be able to regrind the seats and valves to get you back to spec.
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I had to take a few thou off of my head (block too), but they machined the valve seats also so it was about the same in the end. Did they tell you how much they shaved off? You may be able to regrind the seats and valves to get you back to spec.
They shaved the valve seats?????? :shock:
did they also remove material off the valve stem?
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Yes, they re-ground the seats to clean up some pitting, re-ground the valves and took some material off the stems to get the valve adj in spec (with room to shim either way).
Had a complete valve job done with new guides also of course.
As I mentioned in some earlier posts, I should have just bought a new head, but the place that did this one is a reputable shop and this is what he said he would do if it were his. It's off now, and all seems good. These heads are getting hard to find in rebuildable shape, this was the 3rd I brought them untill they were willing to work with it.
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why peen only around the "front of the prechamber?why not all the way round?
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why peen only around the "front of the prechamber?why not all the way round?
Because the gasket seals around the back part. The area peened in this pic is open to the combustion chamber, doesn't touch anything.
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You had your head shaved but you didn't do a valve job ? (Regrinding the valve seats and valve faces - a 3 angle being better than single angle) I would take the time to do this too. If you pull the valves and the seats and faces look very good, maybe just "lap" the valves - that is polish them with lapping compound to give the best seals possible.
Your compression ratio will absolutely change if you change the chamber in the head. It is a common misconception that it will not by shaving the head alone. Doing a valve job w/o shaving the head, or changing the thickness of the head gasket will also change the ratio.
How much ? That all depends on how much you changed any given part. Maybe you went from 23.11:1 to 23.37:1 ;-) Maybe much more. Compression ratio by definition is the ratio of total volume in the cylinder (valves closed) including prechamber / squash area, etc - at bottom dead center VS. the same at top dead center. Here is a good calculator that takes into account all the variable.
http://www.csgnetwork.com/compcalc.html
When you "blue print" an engine for aviation / racing, many builders will actually measure the CC of fluid the chambers hold (as well as intake / exhaust runners) on each cylinder to be sure each has the same compression ration and therefore the same theoretical HP.
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WOW !! I was just playing with the numbers in the calulator - I moved the example's combustion chamber to 45 cc to get the CR in our range - 22.7:1 - then I added 1 mm of head gasket thickness ( .039") and the compression dropped to 18.4:1 !!!
So, changing the gasket / shaving the head has a real effect, depending on how much you change things.
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WOW !! I was just playing with the numbers in the calulator - I moved the example's combustion chamber to 45 cc to get the CR in our range - 22.7:1 - then I added 1 mm of head gasket thickness ( .039") and the compression dropped to 18.4:1 !!!
So, changing the gasket / shaving the head has a real effect, depending on how much you change things.
This misinformation needs to stop!
Shaving the head on these engines DOES NOT change the CR.
The entire combustion area is in the gasket and pre cup.
Please PLEASE stop post up mis information...
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WOW !! I was just playing with the numbers in the calulator - I moved the example's combustion chamber to 45 cc to get the CR in our range - 22.7:1 - then I added 1 mm of head gasket thickness ( .039") and the compression dropped to 18.4:1 !!!
So, changing the gasket / shaving the head has a real effect, depending on how much you change things.
This misinformation needs to stop!
Shaving the head on these engines DOES NOT change the CR.
The entire combustion area is in the gasket and pre cup.
Please PLEASE stop post up mis information...
This would imply there is absolutely zero space between the valves, head, prechamber and the piston. If there is space, it is part of the compression ratio calulation, even if it is 1 mm or 1 micron.
I am sorry you feel it is mis-information. Can you point someone to engineering data that would show there is 100% contact between the piston and everything on the head ? Or that this is mis-information ? As the calulator can show you, the amount it changes depends on how much change there is.
http://www.answers.com/topic/compression-ratio
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That post wasn't directed exactly towards you even though I quoted you, it was more of a point to be made regarding this issue. That being said.
The amount of space between the piston and valves is so minuscule there is no reason to figure it in.
What I'm getting at is we seem to be telling people that milling the head changes the CR and in reality it does but not enough by any standards to be discussing it or to be bringing up the physics behind it or thinking it will change the way the car runs and this is what you are portraying.
Your comments are misleading people in regards to these engine.
You reasoning may be accurate but in this matter your going way overboard.
These are not gas engine that get the CR drastically altered when the head is milled, the CR is figured by the HG and the Precup.
If you want to start a thread discussing CR please do so I'm sure it will be interesting.
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Yes Andrew is absolutely correct !
arb i think your getting confused between gasser and diesel C.R. your formula will work on gassers but does not work the same with diesels !
there was a paper floating around about it! i don't have it anymore! it's on my other lab top that don't work! maybe somebody might still have it and re-post it
Duane
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You are absolutely correct - the formula for that site is not correct for our diesel - the concept is. The squash area under the valves is certainly made smaller by milling.
Look at the area of the squash area - its what ? About 25% - 30% of the bore ? That means in the example I gave for 1 mm milling would be only 25% - 30 % of the change in compression the formula gave - so instead of going from 22.7:1 - to 18.4:1, it would be more like 21.6:1 - still a reduction, but I can see your point it is not huge as it would be on an open chamber as in a gas engine.
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The difference due to the shaving would be SO negligible it's ludacris. Just so long as the vaves dont hit the pistons? triple check the timing?
I've been a tooth out before by accident and thankfully they didn't mash.
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So what is the accepted limit in shaving these heads? I know some say none, but many of us have with no problems. I agree that it's a must to grind the seats/valves to negate the head shave (a new valve job is worthwhile anyway), isn't there only like 10 thou piston to valve clearance stock? going closer seems scarey, and provides even less margin of safety in the event timing is off.