Question regarding compression height of stock pistons...

[Reidler]

Hey everyone, It's been a long time since I have posted on here but it's nice to be back amongst all the smart people who are on this forum.
So my question is this, what is the stock compression height of the 1.9 TDI ALH piston? Can't seem to find that info anywhere.
Thanks in advance...

 

[Mongler98]

I dont know the direct answere but I know it depends on the MLS gasket hole selection that was installed from the factory.

 

[Vince Waldon]

No two engines are alike, which is why the head gaskets come in three different thicknesses:

1.55mm/1.63mm/1.71mm

SOP is to carefully measure the piston protrusion of all 4 pistons and then size the gasket according to the tallest piston.

 

[Reidler]

OK, thanks for your replies, let me clarify what I'm looking for here. Compression height of a piston is defined as the distance from the top of the piston to the center of the wrist pin hole. I realize that the thickness of the gasket can change and how that all works, but the main reason I'm looking for this particular dimension is because I'm in the process of building up an ALH and when I order new pistons I want to be sure that the they are available with a compression height that will allow me to deck my block. If I find a set of pistons that suit my purposes but don't allow for that I won't be able to use them. I'm planning on running pretty high combustion chamber pressures so I want to make sure I start with a decked block to minimize the chance of head gasket failure down the road.

 

[adamss24]

Stay with stock CR ratio and use pd150 pistons, they take insane amount of boost before trowing the toys out of the pram !

 

[Reidler]

Stay with stock CR ratio and use pd150 pistons, they take insane amount of boost before trowing the toys out of the pram !

Thanks for your reply, but the problem with stock pistons is they don't allow me to deck the block. Thus my question. If I knew what the stock piston compression height was I could compare pistons that will allow for it. The block I have has over 600K on it. In My opinion that's a good thing because it's a well seasoned block and probably not going to change much more than it has already. Therefore with a fresh fly cut of the deck and boring the holes out I should have a good block to build from.

 

[powermandan]

You are honestly mad, wanting to deck the block for the sake of it.

I doubt your going to find any pistons that are going to fit the bill.

You could offset grind your rod journal to the second repair stage to shorten your stroke. Most people do it to increase stroke. But I guess you could do it the other way.

Or you could have a small amount taken off the top of the piston to bring it into spec with the head gasket. You would also need the valve pockets dropped the same amount . Presumable it will be around 0.2mm

 

[Mongler98]

If you have to deck the block.... find a better block!
If you insist on it then go get a strocker crank and use the OEM length H rods and have the pistons milled
This is easily a $7k problem
Just to deck the block requires about 8 shop hours of measuring, balancing, adjusting, milling. Not to mention about a grand of materials and the deck job is no small task. It must be aligned via journals. Whatever you got quoted for a normal 4 banger block deck job... double it!
You think you can just order parts and make them fit with thoughts and prayers? This isnt facebook where anything is possible! I'm very sorry to tell you that your dreams may be crushed but it's a normal price for a machine shop to do a proper job on a build with these.... 5 grand just in blueprinting and machining.
Imo have darkside build you what you want. It will last longer!

 

[Reidler]

Actually there are pistons available for that very purpose, but the ones I have come across are billet pistons. That's ok, and I may have to end up using those, but for now I'm hoping to use forged pistons from the get go. I know everyone on here says it's not necessary, and they may be right, but if down the road I want to run nitrous or propane or some other radical top end configuration to get a ton more horsepower out of it I want to know that the bottom end will handle it without issue.
I guess what I'll have to do is contact the piston manufacturer and get the dimensions from them. Simple question that I thought someone could answer for me but it appears not.
Anyway, thanks for your input I do appreciate it all.

 

[adamss24]

The reason why not many aftermarket piston options are available is because stock pistons are very, very good and long lasting as well ! I have seen a few cracked pistons due to poor spraying injectors or high EGT but generally factory pistons do stay in one piece even in high boost applications ! As many advised beforehand, many ingredients on your list are supporting mods and not required at your desired power level but if you have the means and really keen then go for it ! Its not fun repairing an engine 3 times a month when things go wrong just because one didn't want to spend a few quid on some random parts... Please, please prove us wrong and build a monster...

 

[Reidler]

The reason why not many aftermarket piston options are available is because stock pistons are very, very good and long lasting as well ! I have seen a few cracked pistons due to poor spraying injectors or high EGT but generally factory pistons do stay in one piece even in high boost applications ! As many advised beforehand, many ingredients on your list are supporting mods and not required at your desired power level but if you have the means and really keen then go for it ! Its not fun repairing an engine 3 times a month when things go wrong just because one didn't want to spend a few quid on some random parts... Please, please prove us wrong and build a monster...

Roger that! I have seen videos of PD engines putting out around 400HP (dyno'd) with pretty much stock bottom ends (PD150 block), so this would just be icing on the cake. Plus it gives me something to brag about when people ask what's been done to it, lol. I'm going to persue the forged pistons somewhat but if it becomes a wild goose chase to get them then I'll go with billet and have them coated. Time will tell.

 

[jmodge]

Actually there are pistons available for that very purpose, but the ones I have come across are billet pistons. That's ok, and I may have to end up using those, but for now I'm hoping to use forged pistons from the get go. I know everyone on here says it's not necessary, and they may be right, but if down the road I want to run nitrous or propane or some other radical top end configuration to get a ton more horsepower out of it I want to know that the bottom end will handle it without issue.
I guess what I'll have to do is contact the piston manufacturer and get the dimensions from them. Simple question that I thought someone could answer for me but it appears not.
Anyway, thanks for your input I do appreciate it all.

Forged pistons have a higher expansion rate than cast, so they have to be set at a looser tolerance. Cast is a better choice for a diesel, which run hot and are set at a tight tolerance due to high compression.

 

[Mongler98]

Imo for the $ spent... have darkside build it for you. It will last much longer!

 

[Reidler]

Imo for the $ spent... have darkside build it for you. It will last much longer!

Why? what will they do that I can't?

 

[oilhammer]

... well they could probably answer your question, or more importantly, inform you as to why you are not asking the right question in the first place.

I understand the dimension you are asking for, but I am not really sure as to the whole machining the block thing. I do know you will be almost certainly better served getting one of the pistons already available, widely known and used, for a lower CR. Sometimes reinventing the wheel isn't worth the effort.

FWIW, I have never bothered to measure that dimension, but I have never had to either. I do not know how much you can safely remove from the top of a [stock] piston either, but I know people have successfully done so.

 

[Mongler98]

Have you blue printed an engine before? That's what they can do that you can not.
Do you have a grand worth of tools to blueprint the block? Buying a cheap bore gauge and calipers is not good enough. Harbor frieght torque wrenches are not good enough. So on and so forth.
You can get a engine build done but it will not last if you either are doing performance or going for uber longevity like a TDI can do.
If you want a ton of HP that will last 30k before needing a rebuild... then save the $ and do it yourself.
Want a ton of power that will also get easily into the 200k realm with out batting an eye and with carefully maintaining it can still get you 300 to 350hp build that will see 300k miles.
It's all about what you want.

 

[1854sailor]

Have you blue printed an engine before? That's what they can do that you can not.
Do you have a grand worth of tools to blueprint the block? Buying a cheap bore gauge and calipers is not good enough. Harbor frieght torque wrenches are not good enough. So on and so forth.
You can get a engine build done but it will not last if you either are doing performance or going for uber longevity like a TDI can do.
If you want a ton of HP that will last 30k before needing a rebuild... then save the $ and do it yourself.
Want a ton of power that will also get easily into the 200k realm with out batting an eye and with carefully maintaining it can still get you 300 to 350hp build that will see 300k miles.
It's all about what you want.

Do they even have Harbor Freight in Canada?? The OP sounds like he knows what he wants and arguing about isn't going to change his mind...

 

[adamss24]

Do they even have Harbor Freight in Canada?? The OP sounds like he knows what he wants and arguing about isn't going to change his mind...

Sorry for being skeptical but internet is filled with project cars with many thousand bhp that never materialized or never ran ! I mentioned using off the shelf parts, they are easy to source in case of a mishap and its less headache to fit if needs arise ! Project cars and engines never run right for months and replicating custom work is the hardest part from a mechanical point of view ! I do not entirely agree with Mongler about blueprinting the engine but he is got a point- Darkside has been doing it for ages so they know really well what works and what not ! If i was to do a build from ground up i would rather get my wallet out and let someone experienced to do the build and take all the blame, however i was never loaded so i had to spend double what it costed me in R&D !

To the OP, get a pd150 bottom end, injectors of your choice, a big ass turbo and worry about mapping all the ingredients in the recipe ! Bulletproofing the bottom end is good however when it breaks too often you will learn to drive the car with mechanical simpathy and anticipate many, many near miss failures !
The fun is in the build- i know very well that- but you do learn to enjoy when it works well....

 

[turbocharged798]

OP get yourself Nural +0.5mm ASV pistons. These have a shorter height for block decking. You will have to bore the cylinder to get them to fit though.

 

[Reidler]

OP get yourself Nural +0.5mm ASV pistons. These have a shorter height for block decking. You will have to bore the cylinder to get them to fit though.

Thanks for the reply, those are the ones I am aware of, was just hoping to get the same thing in a forged version.

It's amazing how people put words in your mouth and assume how you are going to build things or that you are going to screw things up without even knowing who you are or what your experience is. I'm not even going to address the things that were said. I started this thread with a simple question that no one seems to know the answer for. I've learned not to argue with comments like that because it usually ends up in a battle or a dead end. I'm well aware of the capabilities of some shops and also my own capabilities. Thanks for those of you who offered up helpful comments. It is appreciated.

 

[turbocharged798]

The problem we seem to have an influx of people who have no idea what the hell they are talking about and are armchair mechanics. Somehow they love to keep posting blatant wrong/dangerous information which is really bad as it misleads people.Its basically destroying which once was a very good site.

Anyway the Nural .5mm are shorter, I have used them in the past and even after a block decking I still end up with a one hole gasket. I believe you should be able to go on their site and find exact numbers. Ideally you should deck enough off the block to put you in a 2 hole range. I have just guess in the past and it worked out for me but I don't think that is the right way.

 

[MEgearhead]

I was looking up the comp. height of BHW pistons a while ago and found that the Kolbenschmidt 40409600 replacement for 038 107 065 HF, HL, KK, KM on the BHW BHW BMM BMP lists a 45.8 CH.

The Kolbenschmidt 94427700 replacement for 028 107 065 BC, BS, and 038 107 065 AA on the ALH and many others also lists a 45.8 mm CH.

This is info off the internet and worth exactly what you paid for it. Possibly good for preliminary parts availability research but you will want to verify before committing on anything.

Piston with rings and pin - 94427700 KOLBENSCHMIDT

Piston with rings and pin - 94427700 KOLBENSCHMIDT - 038107065AA, 028107065BS, 028107065BC

www.kmotorshop.com

 

[Fix_Until_Broke]

Reidler - I don't have the measurement you're asking for directly, but have been down this road somewhat.

Feel free to read the whole thread, but at the end of Page 5 you'll see why I believe it's a good idea to have the block and head decked when replacing the head gasket - particularly when expecting high cylinder pressures.

Where to stop?

I guess it's too late now, but I thought I would see someone suggest to bore and stroke to 2.1 liters to get more power from 1000-2000? I've been dreaming about putting together a 2.1 ALH with an increased compression ratio and big heavy flywheel. Big IP, BIG injectors, extra-short duration...

forums.tdiclub.com

I was not there when the block was decked (see page 7-8 I think) and I'm suspect that they didn't do a great job so you can read about the fun it was dealing with all that in subsequent pages.

I think (don't know) that the OEM cast pistons have a steel support cast in around the rings. While forged pistons -may- (or may not) be stronger, my understanding is that they won't live hundreds of thousands of miles like an OEM piston would. Depending on your goals, this might be a deciding factor for you.

If I stumble across the picture/dimension you're looking for, I'll share, but it should be the same as the OEM pistons you removed.

This rebuild has ~185k miles on it...

 

[Reidler]

Thanks for the replies, I'll do some reading.
As for the forged pistons, I've heard good and bad about them. The biggest thing I have heard is that they tend to slap when they are cold due to the fact that they expand more than a billet piston . This may not be an issue on a gasser that heats up rather quickly at idle, but as we all know TDI's just don't heat up unless they are driven. From what I've heard the slap does not damage anything, it's just annoying... Anyway, still doing research...! Thanks again for the positive replies, much appreciated.

 

[adamss24]

No need for forged pistons if ARL pistons can take over 350bhp without much bother…keep egt low and get large nozzles so you don’t have crazy PCP and you’ll be just fine !

 

[Reidler]

No need for forged pistons if ARL pistons can take over 350bhp without much bother…keep egt low and get large nozzles so you don’t have crazy PCP and you’ll be just fine !

Yes I think that's what I'll end up doing. Finding forged pistons is one thing, then finding someone that has stock is yet another issue. Main reason for forged was just to have the higher heat handling ability.

 

[Mongler98]

Yes I think that's what I'll end up doing. Finding forged pistons is one thing, then finding someone that has stock is yet another issue. Main reason for forged was just to have the higher heat handling ability.

Is that an issue you might have? Proper ceramic top coat can do a big difference with that issue. Typically heat issues are only related to the temp of the hot side of the turbo as it's the hottest part