jc1113

I just did my timing belt tensioner water pump ect. While I was doing it I replace the valve cover and cam tensioner and cam seals. The exhaust camshaft broke after about a thousand miles or so on the drivers side. After I took the valve covers off three of the journals were loose in the middle. I don't know what happened I torqued these bolts down and double checked them before assembly. When I was driving I was accelerating on an entrance ramp I don't recall it making any loud noise or anything but the radio was on it just lost power but I was in the middle of nowhere so I had to drive it about 30 miles it would only run about 50 and only half of the motor was running. Do the valves bend for sure when this happens? Is my head ruined? There was some scoring on the journal cap but not bad. All of the valves look like they went to a closed position when the cam broke. Looking back I should not have driven the car so far the check engine light was flashing and coding for cam sensor.


Follow up:

This is a follow up on this post for any one who might be interested. I ordered the inspection camera as stated before, took the spark plugs out the valves appeared to seated. There was none of the carbon buildup gone like the valves impacted on the pistons in any of the cylinders. After this I took a chance on just buying a camshaft instead of the head. I put everything back together and turned the motor over and the car cranked and was running. It was making skipping noise so I thought they were bent. I let everything sit for the weekend thinking I was about to have to remove the motor. I gave everything another look and found that the combi vavle was not seated all the way the metal line that bolts to the bottom hole of the combi valve had got in between the combi and the cylinder head which was causing an exhaust leak fixed that and now everything is running fine no skip motor sounds and runs good I must have got lucky.

jc1113

For anyone that has to remove the camshafts and reinstall them, I recommend putting a small amount of blue locktite on cap bolts. I torqued them down and rechecked them and they vibrated loose on the exhast cam for some reason on one side. Better safe than sorry.

SloopJohnB@mac.com

There are bent valves IMNSHO.

Update: And it's not so humble although it was clearly wrong in this circumstance since the OP claimed the issue was resolved with simply replacing the broken camshaft (and eventually the reseating the kombi valve).

N_Jay

Not too such about the Audi engines, but broken/bent camshafts are usually caused by uneven tightening of the bearings.
You need to work them down slowly and evenly because the valves that are opening put uneven forces on the lobes.
Pulling one cap tight (Even a little) when another is loose bends/stresses the shaft.

CRuby

Yeah, I'd say bent valves would definitely occur on all valves downstream of the exhaust cam crack. There is more torque load in the exhaust cam, since it not only activates the exhaust valves, but also all the intake valves via tensioner & cam chain. But it's not the torque load that cracked the shaft. As NJAY said, the crack likely occurred due to mis-assy or the loosening of the center bearing caps. The loose bearings let the cam flex & bend while rotating, eventually resulting in a fatigue crack failure.

jcman

I've seen camshafts crack because of a slipped belt = major loss of timing, the pistons slammed the valves so hard the impact translated into the camshaft but our engines usually just bend valves.

SloopJohnB@mac.com

If the fracture is a helical one at about 45degrees, the failure is almost certainly torsional. A straight planar fracture, OTOH, is a bending fracture. You can google pics of various types of fatigue fracture, generally the arcs' concave side will point toward a fracture initiation point. An improperly torqued or loosened bearing cap can cause a bent shaft that either cracks immediately (planar) or with the constant flexing initiates a helical fracture.

jc1113

I ordered an inspection camera so i can see if the valves are bent and not seated properly. You guys may be right but I just want to be sure before ordering a head instead of just a camshaft. If I do have to remove the head, does the engine have to be removed? Can it be done in the car? It is the one on the passenger side. There is more access on that side but the bolts on the bottom side of the exhaust manifold look really difficult to get to.

jcman

Generally you would be better off replacing the head and it can be done with the engine in the car, the problem with replacing a camshaft is the bearing cap's wear may not be even and you don't know the status of your existing one yet from what I've gathered.
BTW what engine is this?

the_duke

I just did valve covers on my 2.7t and that was a pain in the ***. Although not nearly as bad as my 4.2 in the A8. I can't imagine getting the exhaust manifold/turbo loose while the engine is still in the car. Seems like it would just be easier to drop the motor.