1Z vs AHU engine

What exactly is the difference between the AHU and the 1Z engines? The reason I ask is that I have a 97 Passat with what may be a bad engine (lots of bluish black smoke) and would like to look into a donor long-block or entire engine to replace it. I may have access to one from a 98 Jetta TDI. My understanding is that the Passat's had the 1Z engine and the later Jettas in the U.S. had the AHU. I will check to make sure the engine is indeed an AHU, but assuming that it is, are there any differences that would make this swap not work?
Thanks for the help.
Ken

Same engine just different code . All US spec A3 TDIs ( 96 - early 99 ) will work in your Passat .

There were 3 different turbos used across the line . 4 different intakes & EGR coolers , but all are interchangable on the 1.9 L 1Z - AHU block .

Before you go to the trouble replacing the engine check the cylinder bore . Many of the early 1Zs had undersized pistons , there was a shortage of parts at the time of assembly . I have replaced the pistons on a couple of 1Z engine that had the wrong size pistons installed at the factory .

Hmmmmm.
I have the same question...
Because the engine that is in MY '96 Variant, seems to have an oil ring break or a seal go bad, there is a lot of light blue smoke at start up but once it warms...it is OK.Could it be also a bad valve? Seems to "pop" a little at start up .
Disconnecting the CCV tube to the intake tube while engine running, will give a LOT of blow-by, I think way too much IMHO .

Personally, I would really entertain an AHU engine because of the higher capacity for HP. to get down the road , like close to 170ish HP/240TQ .
(in case a "Gasser" wants to show me a thing or two , actually to change the final drive ratio{5th gear MOD} for longer in between fill ups ).

Or maybe change the pistons, rings, seals, bearings...BUT then it would be a new engine and still ~125HP/185TQ .

PS. I forgot to add that the AHU's pistons are lighter and that the breathing is better.

B4 Variant w/285K and "a couple of MODS".

Thanks.
That was going to be my next question - or more broadly, why am I likely getting blue smoke? Valves or Rings? I'll check compression, but will that tell me anything? If I understand you, though, you're saying it might simply be that the original pistons are undersized?! What the?! I hate to even contemplate the incompetence of V.W. if that is true...

ken.fresno-tdi said:

Thanks.
That was going to be my next question - or more broadly, why am I likely getting blue smoke? Valves or Rings? I'll check compression, but will that tell me anything? If I understand you, though, you're saying it might simply be that the original pistons are undersized?! What the?! I hate to even contemplate the incompetence of V.W. if that is true...

Click to expand...

Yes the out of spec pistons were used ( one manufacturer made the blocks and several manufacturers made the pistons ) . And no this isn't uncommon in the auto industry .

VWAG isn't the only one that does this , I've seen Mitsubishi/Chrysler engines so far out of spec new!!!! I was amazed they even ran .

New Rings & Valve seals ( rings $25 - $40 & seals $10 - $20 ) and you should be fine . Just make sure you replace all the stretch bolts ( rod & head $50 - $70 for both ) . And measure piston protrusion to assure that you have the correct head gasket ($40 - $60) .

With you doing the labor you chould be able to get it back up & running for less than $300 .

Hey ken glad to see another Fresno TDI member! good luck with the passat.

If you are replacing the rings for the few dollars extra pick up "Total Seal".
They have a 2nd ring that essentially has no gap. www.totalseal.com



robert

Thanks for all the replies. I'm still wondering if I can first just check to see if it is the valve seals that are bad - I read somewhere on the forum that blue smoke was often due to those, not the rings. I assume that if I take the head off there is a way to check either/both the valve seals and the rings - a leakdown test?

ken.fresno-tdi said:

Thanks for all the replies. I'm still wondering if I can first just check to see if it is the valve seals that are bad - I read somewhere on the forum that blue smoke was often due to those, not the rings. I assume that if I take the head off there is a way to check either/both the valve seals and the rings - a leak down test?

Click to expand...

You can change them just remove each of the valve keepers only while that piston Is At Top Dead Center so the valves don't fall out .

I've done it several times on these . You will need to buy the valve spring compressor & valve seal removal tool & the valve seal installer tool - the Mushroom tool it looks like a mushroom . I bought them a few years back , If memory serves it was less than $ 200 for all the required tools .

Thanks for that info. I've never done much at all on TDI heads, so that is indeed good to know. It seems worthwhile, given how much less work, just to try changing the seals first since it doesn't require complete engine removal, and since they probably need to be changed anyway, even if I later need to change the rings.

Is the 'mushroom' tool a specific TDI tool or a generic valve seal installer tool? For that matter, are all the valve tools generic or specific to TDIs?

My rings were shot in my 1Z. That and the valve guides. Check this video of my old car out. Because it's angelfire the hyperlink probably won't work. If that's the case, right click on it, copy link location, open a new window and paste it in.
Cheers, and good luck!
-BB

ken.fresno-tdi said:

Thanks for that info. I've never done much at all on TDI heads, so that is indeed good to know. It seems worthwhile, given how much less work, just to try changing the seals first since it doesn't require complete engine removal, and since they probably need to be changed anyway, even if I later need to change the rings.

Is the 'mushroom' tool a specific TDI tool or a generic valve seal installer tool? For that matter, are all the valve tools generic or specific to TDIs?

Click to expand...

VW/Audi/Volvo diesel specific tools as I used my tools on a 2.0 L IDI TD head last week . The same ones I used on my 1Z TDI 6 years ago . Metal Nerd or Zelenda should have want you need . I think I bought mine from Zelenda .

If you do a little digging on here, you'll find a homemade contraption to depress the springs to release the keepers. My OEM VAG compressor that worked on a gasser 8v won't work on a tdi. I just couldnt get the angle of the dangle correct on most springs using the VAG system.

thanks - I'll look around... if anyone knows what ninedee is referring to I'm open to search hints !