96 850 turbo Burnt valve or slipped timing belt ?

opelrick · Post by **opelrick** » 20 Apr 2014, 11:12

: Intake cam gear

: Exhaust cam gear

Was out bedding the the rear brake shoes after rebuilding the rear suspension (new links, arm mounts, brake calipers and rotors). The car sat in the garage for 6 months while I found time to complete the suspension work (might be relevant). I drove for about an hour at varying highway speeds before trying the brake bedding process (8 - 10 immediate "hard as you can" decelerations from high speed (55-60mph) to about 20mph with immediate reacceleration). After (actually during) this process while I was letting the brakes cool down by driving at 55mph for 5-10 min, I noticed a pronounced mis-fire and lack of power. I pulled over after ~ 10 min, definite ticking/missing. I was still ~45 min from home, drove home nursing the car, but still able to drive @ highway speeds, just rough running, especially ~ 2000rpm / 50-55mph. Was able to restart the car this AM without an issue, misfire still there (no I haven't pulled codes yet). I'm guessing a valve went (coolant level in overflow is at same approx level this AM as when started yesterday - doesn't rule out head gasket but that I'd mention it), but became fearful that the timing belt slipped. I pulled the front cover today and this is what I was greeted with. Any thoughts on how to interpret the marks on the cam gears (one mark that isn't visible on the intake is a "pencil" line that is inline with the cover notch, which might indicate things are still timed correctly from the previous owner's work; see image Intake cam gear v2)?

Post by **Ozark Lee** » 20 Apr 2014, 13:24

Those lines are not the timing marks so I would ignore them. The timing marks are the ones that are at around the 12:00 position on the exhaust cam and the one at around the 9:00 position on the intake cam. It is very rare for the engine to "jump" timing and the tensioner really needs to fail for it to do so. Other things can cause the timing system to fail but they don't just up and jump a tooth.

There are tons of things that can cause misfires and poor performance. Start by checking for codes.

If this all happened suddenly then make sure that one of the lines to the intercooler didn't come loose. From there check the usual stage zero stuff like spark plugs, distributor cap and rotor, etc.

...Lee

Post by **tryingbe** » 20 Apr 2014, 13:26

Use the factory notch on the gear.

http://volvoforums.com/forum/volvo-850- ... rbo-67561/

opelrick · Post by **opelrick** » 28 Apr 2014, 22:08

Confirmed what seems to be a burnt valve in cyl 3. Codes showed Cyl #3 misfire, have spark, 0 psi compression in cyl #3, other 4 cylinders all show ~ 155 psi dry / ~ 185 wet with cheap compression tester.

Post by **abscate** » 29 Apr 2014, 02:26

Ugh. Time for that head job.

Don't forget timing belt, roller, tensioner, water pump, cam seals

Post by **mecheng** » 29 Apr 2014, 07:44

How many miles do you have?
What octane fuel do you use? Original owner?