2.8L V6 90CS - Interference?

Old 12-28-2006, 06:16 PM
Thread Starter
Join Date: Dec 2006
Posts: 1
Default 2.8L V6 90CS - Interference?


I am new to the Audi forums- As you can see from my sig, I do not personally own an Audi, but I've been a shadetree mechanic for almost 30 years and am helping out a buddy.

The timing belt on his 2.8L 12V 90CS shredded the other day. The Duratec engine in my Cougar is most definitely an interference motor- Meaning if one or both of my chains snapped, that'd be all she wrote for the motor. [/align][/align]A search here came up with J_ripper saying that all of the Audi V6s were interference motors. However, I am getting conflicting information from Google as far as whether or not the2.8L is interference. Some sites say yes, some sites don't say at all. Nothing associated with the timing belt was seized that I could see- tensioner, idler, and water pump spun fine, so we went ahead with the swap.

We got the replacement kit from Blaufergnugen, I installed it last night after fabricating a cam sprocket brace so that the cams were positioned properly. The timing belt was tensioned properly (90 degrees bendable at the midpoint between the cam and new water pump). All new idlers/tensioners. I spun the engine by hand about 6-8 times, and the marks that I'd made for myself lined up perfectly after spinning.

We fired the motor, and it was dead obvious that something was horribly wrong. I took a compression check, and it wasn't happy:

Cyl 1: 135psi
Cyl 2: 142psi
Cyl 3: 0 psi
Cyl 4: 0 psi
Cyl 5: 45 psi
Cyl 6: 0 psi

Huston, we have a problem. Ideas? If it's an interference motor, then it's obvious what happened. I can't help thinking I mis-timed the thing, but if that was the case, why are cylinders 1 & 2 fine???

Thanks in advance.[/align]
Old 12-28-2006, 07:41 PM
Join Date: Aug 2005
Location: Brooklyn, NY
Posts: 1,561
Default RE: 2.8L V6 90CS - Interference?

Yes, our engenes are interfeering.
the rapair would be taking the heads off, replacing valves, and doing valve job.
u can do upgrades as well, like lower compresion for supercharging. or port and polish, stuff like that.
Old 12-31-2006, 05:00 AM
2nd Gear
Join Date: Mar 2006
Location: Black Mountain, NC
Posts: 852
Default RE: 2.8L V6 90CS - Interference?

i vote interference and try to stick a led light in the cylinder and try if you can see some sighns of a valve hitting the cylinder
Old 09-27-2007, 01:36 PM
1st Gear
Join Date: Sep 2007
Posts: 9
Default RE: 2.8L V6 90CS - Interference?

Hi. I am volkswagen certified. You can use an air pressure test. I will not give all the details or instructions, but basically, blow air through the motor with it off, and listen for where it is leaking. Basically, take out the spark plugs, then stick just the tip of an air nozzle--for air testing--into the spark plug whole. Make sure it seals. Then, if you hear air coming from the intake, then that means the intake valve is open/leaking. If you hear it coming out of the exhaust system somewhere, then that means the exhaust valve is open/leaking. If you hear it from both, then they are both open/leaking. They should NOT both be open.

Another way. You should be able to turn the engine by hand with a wrench. If the pistons hit, you most likely will feal hard resistance to for the engine to move.

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