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Old 31-07-19, 02:13
greasychebacca greasychebacca is offline
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Location: Vancouver, CA
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T4 Post Icon 2.4 AAB Piston Protrusion Measurements

Hey T4 Community,

Thanks for reading. I know its long but I would rather have too much information than come in missing important pieces.

I am in the process of rebuilding my 2.4 AAB diesel engine out of a ’93 Eurovan (in Canada here). The pistons are in (and torqued) and I am trying to measure deck protrusion before fitting the appropriate head gasket. However, being that this is my first rebuild and first time using a dial gauge/indicator to measure piston protrusion, I am in need of assistance.

Here is some brief background for context:
Original engine is a ’93 2.4 AAB but I had to scrap the block and replaced it with a ’97 AAB block. I’m still using the original crank and conrods from the ’93 though (inspected and balanced). I had the block mating surface decked and the cylinders bored and honed at a local shop. New oversized (80.010) Kolbenschmidt pistons and rings installed.


Ok, so as per the VW Service Repair Manual, I am using the following as a guideline for which head gasket (based on notches) to fit:
- Up to 0.86 mm = 1 notch
- 0.87 mm – 0.90 mm = 2 notches
- Above 0.90 mm = 3 notches

The values I got for piston protrusion are as follows. I took 4 measurements ( 2’oclock, 4’oclock, 8’oclock and 10’oclock) from each piston and referenced it against the deck height:

1. 0.699 mm | 0.686 mm | 0.711 mm | 0.711 mm AVG 0.702 mm
2. 0.668 mm | 0.762 mm | 0.683 mm | 0.724 mm AVG 0.709 mm
3. 0.706 mm | 0.724 mm | 0.757 mm | 0.757 mm AVG 0.736 mm
4. 0.739 mm | 0.706 mm | 0.742 mm | 0.686 mm AVG 0.718 mm
5. 0.533 mm | 0.648 mm | 0.610 mm | 0.691 mm AVG 0.621 mm

I am surprised that all of the readings are as low as they are, especially considering the block was resurfaced. But, I am ESPECIALLLY concerned about the piston 5 readings.
Any thoughts? Could it be a bent rod? I want to do the build right and will take the time I have to in order to do so.

Thanks in advance for your help.
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  #2  
Old 31-07-19, 10:41
hybrid800's Avatar
hybrid800 hybrid800 is offline
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Location: Ammanford, Wales
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Default Re: 2.4 AAB Piston Protrusion Measurements

Quote:
Originally Posted by greasychebacca View Post
Hey T4 Community,

Thanks for reading. I know its long but I would rather have too much information than come in missing important pieces.

I am in the process of rebuilding my 2.4 AAB diesel engine out of a ’93 Eurovan (in Canada here). The pistons are in (and torqued) and I am trying to measure deck protrusion before fitting the appropriate head gasket. However, being that this is my first rebuild and first time using a dial gauge/indicator to measure piston protrusion, I am in need of assistance.

Here is some brief background for context:
Original engine is a ’93 2.4 AAB but I had to scrap the block and replaced it with a ’97 AAB block. I’m still using the original crank and conrods from the ’93 though (inspected and balanced). I had the block mating surface decked and the cylinders bored and honed at a local shop. New oversized (80.010) Kolbenschmidt pistons and rings installed.


Ok, so as per the VW Service Repair Manual, I am using the following as a guideline for which head gasket (based on notches) to fit:
- Up to 0.86 mm = 1 notch
- 0.87 mm – 0.90 mm = 2 notches
- Above 0.90 mm = 3 notches

The values I got for piston protrusion are as follows. I took 4 measurements ( 2’oclock, 4’oclock, 8’oclock and 10’oclock) from each piston and referenced it against the deck height:

1. 0.699 mm | 0.686 mm | 0.711 mm | 0.711 mm AVG 0.702 mm
2. 0.668 mm | 0.762 mm | 0.683 mm | 0.724 mm AVG 0.709 mm
3. 0.706 mm | 0.724 mm | 0.757 mm | 0.757 mm AVG 0.736 mm
4. 0.739 mm | 0.706 mm | 0.742 mm | 0.686 mm AVG 0.718 mm
5. 0.533 mm | 0.648 mm | 0.610 mm | 0.691 mm AVG 0.621 mm

I am surprised that all of the readings are as low as they are, especially considering the block was resurfaced. But, I am ESPECIALLLY concerned about the piston 5 readings.
Any thoughts? Could it be a bent rod? I want to do the build right and will take the time I have to in order to do so.

Thanks in advance for your help.
before you panic about the protrusions,
whats the tolerences for the components? conrod C-C length, piston hight, bearing clearance crank main / bigend & conrod 'little-end' / wristpin) & even the crankpin grind offset can affect totals (also, how accurate was the deck-face skim? can get taper in such with a mill thats too short )

is it possible that you have the bad luck to assemble 'short' components togther to make number 5

Rich.
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Old 01-08-19, 04:34
greasychebacca greasychebacca is offline
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Join Date: Jun 2017
Location: Vancouver, CA
Posts: 33
Default Re: 2.4 AAB Piston Protrusion Measurements

Hey Rich,



Thanks for the message. It sounds like I should start looking into those component tolerances. I'm also working to get a straight edge so I can check the deck-face for taper. Thanks for that thought.


I'm also going to get a deck-bridge and use that with my dial indicator to re-measure the protrusions. As I was using a magnetic stand with the adjustable arms, I'm hoping another round of measurements with a different mounting tool will illuminate if user error is contributing to the situation.


I guess it is possible that I had some bad luck and assembled "short" components together, for sure. My next question would be if I get the same measurements, should I be concerned about putting the cylinder head on? Like, could I just go ahead and be fine with a compression ratio that is off for cylinder 5?


Cheers,

Will
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Old 01-08-19, 09:25
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hybrid800 hybrid800 is offline
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Join Date: May 2013
Location: Ammanford, Wales
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Default Re: 2.4 AAB Piston Protrusion Measurements

Quote:
Originally Posted by greasychebacca View Post
could I just go ahead and be fine with a compression ratio that is off for cylinder 5?
that's working on the assumption that everything else in the world is perfect? theoretical compression is one thing, actual (with a pressure-guage) will be diferent as will the cylinders port effenecy (got access to a flow-bench?), injector & pump pressures / delivery volume etc

from a quick look at the hight diferences, 0.1mm is 0.0039" (yep, I work in Imperial at home & metric in work - throwback to my apprentaceship 30 years ago in a machine-shop with older lathes, mills & even micrometers! so all drawings had to be converted ), doubt that would alter the compression on a diesel engine by enough to cause issues

personally, I'd run it as you've got issues getting replacements or used spares where you live
although, over here spares are common (plenty of dead vw's ) I have a dead 2.4D engine outside my shed that was removed from a mates t4 and replaced with a 1.9tdi conversion - more power, better economy, cruise control & cheaper maintanance


anyway, once you have it built, installed & running you'll not worry about any possible imballance, just enjoy the 5-cylinder soundtrack


Rich.
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