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Zero compression in cyl.5?[850/1994] posted by Tony D. on
Saturday, 20 October 2001, at 4:00 p.m.
My 1994 850 Turbo wagon was just diagnosed by Volvo with a bad intake valve on cyl.5. They said that the valve could be bent. When they took off the timing belt cover they noticed that the intake gear (top right one)was out (ahead) by 5 teeth. They had no explanation for this, none. That really bothered me. Well the car does start and can be driven, it just feels and runs very rough, especially at idle. Imagine running only 4 of the cylinders rather than all five. I have a friend working on it now, we took off the intake manifold so far and the right intake valve in cyl.5 was all black. The rest, including the left IV in cyl.5 all looked the same, pretty clean and normal.
But what I need to know is:
1.- what caused this to happen?
2.- what should I look at doing to prevent this from happening again? (one friend suggested the timing tensioner)
I should also add that there were no warnings. No funny engine noises or error codes. The car did smeel a little rich though and maybe lacked a little power. I was driving home from work on the highway and noticed the engine shaking at a 100km/hr. When I came to a stop at the end of the offramp the car was displaying the symptoms as mentioned above. The car also had new plugs, wires, cap and rotor as well as a relatively recent oil change.
--Tony D
Re: Zero compression in cyl.5?[850/1994] posted by Norman on
Saturday, 20 October 2001, at 8:36 p.m.
I'd find the jumping belt idea questionable unless it wasn't installed right to begin with by whoever last changed your T-belt but then you'ld notice a power loss too. I have heard where cars with manual trannys where the customer parks the car on hills, in gear can cause the belt tensioners to fail but I've never seen it myself.
Get the cyl head off and see if it's just a burned (not bent) valve as I've seen burned valves in 850 engines before. The cause of burned valves is usually either poor quality engine oil, lack of changes, and/or low speed, low rpm driving where the valve lifters don't turn in their bores as they should thus causing them to stick.
If it turns out to be a burned valve, I'd suggest using synthetic oil to prevent future problems. If the valve is bent (and only one would be very unusual) caused by a t-belt that did jump, then by all means replace the belt tensioner too. Any time one replaces a t-belt, one is suppose to check the t-belts tension first to know what condition the tensioner is in. If there's oil leaking from it, replace it always.