Valve stems, 8mm vs. 7mm

[Benjamis]

Seems at least a few people talk like 7mm valves are better. Is that the case, and if so, why? Just because you can install a fatter valve guide?

 

[Steve Addy]

It's because early cylinder heads used valves with 8mm stems and later cylinder heads used 7mm valve stems.

I don't know when the changeover took place but IIRC Oil Hammer knows. Seems to me it's not when they switched from 1Z to AHU, but I could be wrong.

Steve

 

[Lug_Nut]

The smaller diameter stem allows a wider stem seal. The seal's flex (same valve stroke) can be better tolerated over a 'longer' distance from seal outer edge to stem. Longer lasting seal, less seal wear.
The valve, seal and upper spring seat change took place (on the engine assembly line) at engine 770 001 going to 7 mm. The lower spring seat was then changed at engine 800 001.
The "1Z" in the 1997 B4 Passat is using the AHU engine despite the sticker in the trunk. Since the 8 mm valves are not available and 8 mm seals are not available, there isn't any reason to not transform a 1996 B4 1Z head into an AHU head with the better 7 mm seals as were used in the 1997 B4 with its "1Z".

 

[Steve Addy]

The smaller diameter stem allows a wider stem seal. The seal's flex (same valve stroke) can be better tolerated over a 'longer' distance from seal outer edge to stem. Longer lasting seal, less seal wear.
The valve, seal and upper spring seat change took place (on the engine assembly line) at engine 770 001 going to 7 mm. The lower spring seat was then changed at engine 800 001.
The "1Z" in the 1997 B4 Passat is using the AHU engine despite the sticker in the trunk. Since the 8 mm valves are not available and 8 mm seals are not available, there isn't any reason to not transform a 1996 B4 1Z head into an AHU head with the better 7 mm seals as were used in the 1997 B4 with its "1Z".

I prefer to go by what the block says...

Steve

 

[volksguy]

ID Parts Has The 8mm Valve Seals
Valve Stem Seal Set 8mm (B4)(A3 1Z)
OEM Number: 026109675

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• Be the first to review this product

$4.95

 

[GTiTDi]

7mm valves are also lighter, which has a multitude of benefits

 

[oilhammer]

The 8mm valve guide seal is a commonly used on many VAG gasoline SOHC inline engines, they are widely available.

But the 8mm stem valves, both intake and exhaust, are specific to JUST those early TDIs. The later 7mm ones are also used on a bunch of other engines (including the ALH) so even though you can easily get the seals, if you are doing a valve job you may as well just go to the newer stuff anyway.

 

[Lug_Nut]

I prefer to go by what the block says...

Steve

The sticker (probably long gone by now) on the cam sprocket cover has the engine code and engine build serial number.
It's the complete assembly, not the block casting, that determines if the assembly is "1Z" or "AHU".

 

[oilhammer]

My '98 Jetta had 1Z on its build tag in the trunk, and AHU on the tag on the engine.

I honestly think that it was an engine that got "caught" late in the transition from two to three letter identification convention around that same time. Because the rest of them changed when the platform changed. The one that started it was the VR6, which right from the beginning got a three letter code, AAA, which may have been the very first one ???

 

[turbodieseldyke]

I think it's more because they were built in mexico, where the local language has no words for "attention to detail", whereas German has 48.

 

[oilhammer]

And yet the Puebla plant is VAG's most awarded assembly plant on the planet, including the Wolfsburg plant.

The Puebla plant enjoys an almost entirely Spanish-speaking workforce, that are paid well above average, and jobs there are very sought after.

The Wolfsburg plant has, since its start, been a soup of all kinds of refugees and languages, and has struggled to maintain a consistent workforce and is easily not paying the local equivalency of "above average".

Some really good books out there regarding Volkswagen's history around the world. If more people availed themselves of that, they'd ditch the notion that "other-than-German" assembled cars are somehow inferior.

Puebla has been assembling Volkswagens since long before Audi designed the first water-cooled engine for Volkswagen.

Anecdotal:

I've purchased five Volkswagens brand new. Three Puebla cars, one Wolfsburg, one Emden. The Puebla cars all were flawless. Both the German cars had several build quality issues. When I PDI'd them new, the Puebla cars were rarely ever a concern.

 

[turbodieseldyke]

The Wolfsburg plant has, since its start, been a soup of all kinds of refugees and languages, and has struggled to maintain a consistent workforce and is easily not paying the local equivalency of "above average".

That I believe. It's why "Made in USA" means nothing anymore, except that there's no overseas cargo shipping in the cost.

Still, printing "1Z" on a million stickers when the installed engine says "AHU", and nobody noticed it? Or someone noticed it, reported it, and they still kept printing 1Z on the stickers? Lame.

 

[Matt-98AHU]

And yet the Puebla plant is VAG's most awarded assembly plant on the planet, including the Wolfsburg plant.

The Puebla plant enjoys an almost entirely Spanish-speaking workforce, that are paid well above average, and jobs there are very sought after.

The Wolfsburg plant has, since its start, been a soup of all kinds of refugees and languages, and has struggled to maintain a consistent workforce and is easily not paying the local equivalency of "above average".

Some really good books out there regarding Volkswagen's history around the world. If more people availed themselves of that, they'd ditch the notion that "other-than-German" assembled cars are somehow inferior.

Puebla has been assembling Volkswagens since long before Audi designed the first water-cooled engine for Volkswagen.

Anecdotal:

I've purchased five Volkswagens brand new. Three Puebla cars, one Wolfsburg, one Emden. The Puebla cars all were flawless. Both the German cars had several build quality issues. When I PDI'd them new, the Puebla cars were rarely ever a concern.

Yeah, never really had a concern over Puebla cars personally.

What I do have concerns with are the turds coming out of Chattanooga recently, though... Water leaks galore and all kinds of other dumb assembly-related problems. Dealer technicians have lost all faith in VW's ability to make a quality car. And, despite a large exodus of experienced technicians already due to VW's terrible practices, they're still kicking back warranty claims and making the dealer (and sometimes by relation, the technician) eat the warranty work. Then they wonder why so many dealer techs decide to leave for greener pastures

 

[oilhammer]

I won't ever go back to a dealer. Lexus wasn't awful, but was starting to get worse once the GR V6s hit, which was 2006.

 

[Benjamis]

7mm valves are also lighter, which has a multitude of benefits

I could guess why but would you care to elaborate?

 

[Benjamis]

So 7mm valves would use different keepers than 8mm valves correct? So would they also need different retainers? The springs and lifters are the same correct?

 

[Lug_Nut]

The B4 Passat TDIs came from Europe, Emden Belgium I believe.
The A3 TDI sedans from Puebla Mexico had German assembled engines.

The valve keepers for 8mm valves are 113 109 651A
The keepers for the 7mm valves are 021 109 651
There is no cam follower part number change for the AAZ, 1Z and AHU associated with the valve change.
Answers to retainers / seats and springs are in post #3.

B.T.W.: The ABA, 2.0, also had a valve change from 8mm (up to engine 807 036) to 7mm (807 037 and onward) yet was still an “ABA”. This engine did have a cam follower change at that valve transition to the same follower as had been used in the diesel AAZ, 1Z and AHU.