Volkswagen Passat Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter #1
I've been pouring through the search engine for awhile looking for an answer and I've come up empty.

I'm trying to find out if AHA and ATQ 30V V6 heads are interchangeable. Beyond that, I'm also trying to find out if the driver and passenger sides differ.

From what I can tell, the castings are identical; the only thing that differs is the cam chain adjuster stepper motor position.

Can anyone straighten me out on this?

Beyond that, I'm working on a 2001 2.8 30v 4Motion Passat. It was a bank repo that I'm putting back together. When I got it, it had a nasty driver side rattle but was otherwise smooth. I pulled the valve cover and it was obviously a cam chain tensioner; so bad that the plastic guide was gone. The cam chain did /not/ appear to have skipped any links.

So now I'm at the point where the engine is in the service position and put back just enough to run a compression test. The passenger side is at 170 or so, and the drivers side is coming in around 100 per cylinder consistently.

I'm not sure what to do; if I bent valves, I'd expect to see much lower compression than 100 psi, and not so much consistently lower on one whole bank compared to the other. I'm /certain/ I replaced the tensioner with everything back in alignment perfectly.

What's going on? Could this be a side effect of an 'empty' cam chain tensioner that isn't pumped up at all? I've barely got the engine back together to just crank it over; I can't start it and run it.

Sorry for the long winded post (and my first here no less!)

Cheers!

-jeff
 

·
Registered
Joined
·
3,203 Posts
If the cam chain tensioner is bad, that may lead to valve timing that is off, leading to low compression. Make sure the cams are in the proper location when the pump is at TDC. There is a notch in each cam on the tensioner end that aligns with a mark on the bearing cap at TDC. If the engine is back together, it can be run for a minute or two without coolant to build oil pressure to tighten the tensioner. Just do not run it until it heats up. Getting oil pressure should take only a few seconds.

Also, while you are in the service position, think about changing the timing belt, timing belt tensioner/roller, idler roller, water pump, thermostat.
 

·
Registered
Joined
·
4,817 Posts
Remove the fuel pump relay (and spark plugs) before running the starter motor long enough to get the oil pressure near normal.

My bet is the timing on the replaced head is off (difference could be in the cam and or cam belt pulley). If this is the case, the cam sprockets may be slightly different between AHA & ATQ engines. Check the position of the cam sprocket keyway (relative to the permieter teeth) with a machinists square. As little as ~2 degrees difference in the TDC indexing between AHA & ATQ sprockets would be enough to give you a ~70psi lower observed comression value.
 

·
Registered
Joined
·
3,203 Posts
There are no keyways on the cam sprockets for the timing belts, at least on the AHA. When you pop the cam sprocket loose, they freewheel. Put the cam bar tool on the ears of the cam plates to get the cams in TDC position, pop the sprockets loose with a puller, then re-tension the timing belt. Following this, re-tighen the bolts on the timing belt gears. This should make every thing properly in time.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #5
Sorry, I wasn't too terribly clear in my first post.

Here's another try--I'll fill in the gaps as best I can.

1) The motor is a 2.8 ATQ.

2) They are the original heads.

3) I replaced only the driver's side cam tensioner.

4) The motor has 151,000 miles on it.

The cam tensioner I replaced was bad--and I mean bad. Both the bottom and top runners were gone; only the metal pads were left. There are slight dragging marks on the bottom of the head where the chain would periodically come in contact with the head.

I'm doing this without the cam alignment bar and without the tdc bolt; I'm just rotating things to TDC on the balancer and aligning the belt driven cam mark with the arrow on the bearing shell.

This afternoon I got home, rotated the engine by hand a few times until the balancer was at tdc and looked at the exhaust cam--it looked very slightly off --by possibly a tooth. That said, I adjusted that cam back a tooth on the sprocket and reran the compression test and now everything is up to around 140 PSI but the other bank is still at 170+.

All of this is about figuring out if I have a motor really worth fixing up--go out and buy the cam bar and tdc bolt and do the water pump, timing belt, all the tensioners, thermostat, etc. Possibly replace the cam chain that rode on the damaged tensioner? It's a very beefy chain; it looks to me like it has alot of life left, but for all I know it could be stretched out of spec.

What do you think? The car is otherwise nice, but needs some bodywork, etc. I bought it to fix up for my girlfriend for $1600 US. So far I've got $200 into it for a used cam chain tensioner--and that was just to figure out if I should go deeper into the motor?

What do you think? Start buying parts for the timing belt (and related parts) change or part it out?

jeff
 

·
Registered
Joined
·
3,203 Posts
1) fix the engine. At most it will cost you $600 to rebuild both heads. (I did both mine for that with bent valves)

2) Update your profile so people can see where you are located. There may be someone close by that has a cam bar and pin that you can borrow. I have loaned mine in the past.

3) Try squirting some oil in the cylinders as seals for leaky rings as a possible troubleshooting.

4) The cam bar will make sure the heads are properly aligned, so you can verify if the timing marks are in the appropriate areas on the heads with the valve covers off. If the valve covers are off, the notches in the cams should be visible and the arrows on the cam bearing caps should be pointing toward those notches at TDC.
 

·
Registered
Joined
·
3,203 Posts
If you are not going to use the cam bar/pin to make sure everything is at TDC, then I used a mirror to look into the hole to make sure the crankshaft is at TDC by viewing the centering hole in the crank through the port behind the alternator.

Then, make sure the notches on the cams line up like this:



That will make sure both heads and the crank are in alignment.
 

·
In reverse, but chained to a tree.
Joined
·
13,906 Posts
I can become a party to the conversation?
not unless you can contribute a proper question about the topic, or have sane/reasonable and on-topic input.


now then. about the AHA heads on the ATQ engine.

here's what i know for fact from my fact books. they have the same bore, same stroke, same valves, same compression specs (10.9 ) and everything else in the books is the same when it comes to he basic info. from what i've seen in pictures here (the guy that was selling parts in classifieds a while back) they look identical and seem to have the same galleys for oil and coolant and everything.

i do not know the oem cam profiles. (and differnces between the two)
i do not know the cam chain tensioner differences.

all my info comes straight from the books, so as long as those bently publications are dead on, so am i.

i have heard that you cannot run an atq properly with aha heads (from Pz) from a very well informed source, but from what i've been reading up, i'm strongly led the other way.
the only way to sort out for sure if it works or not is to slap it on and see what happens. i would more than love to know. you really have no idea.


hope this helped you out a bit.
if you can find a set of good AHA heads around that require no machine work (good mating surfaces and no sludge/rust) get em and pop em on. always worth the trial and error to see!

so long as you don't run the engine for more than 1 minute, i'd say you don't even really need to put coolant in it as the waterpump bearing is selaed, and you won't get anywhere near operating temperature for the engine. but within that one minute, you will have more than enough idea based on the performance if it's going to fly or die.

and if it does work, i will not make fun of you for the pun of "AHA!" but join in the punny conversation as well. :lol:

in hinesight, i forgot to address your compression issue.
i had a similar issue going on with my car so i thought
go run your car around for a bit, then do it again. could be the car adjusting the timing of the valves by screwing with the cct or something...

other than that, bad valves, or you lost a head gasket.
OR, on an off case, the mechanism that flings the oil up into that side of the engine could be another issue as well.

from what i've seen on mitsubishi motors they have a seperate rail that comes off the main and runs down the 4 cyls to a nozzle that shoots oil up into the cylinder, if you have an issue where the oil is disabled from travelng up into that half of the engine, goodbye cylinder wall crosshatch, hello low-compression glaze!
 
1 - 8 of 8 Posts
Top