no compression 96 850 NA

waynej · Post by **waynej** » 27 May 2012, 17:44

Just took a trip of about 200 miles. Exhaust seemed a little loud. When we were near town and stopped for a light the engine was shaking badly. Acceleration was slow with lots of exhaust noise. Checked compression the next day. All were 180 dry except #2 which was 0 !
Does anyone have any ideas?

Post by **jimmy57** » 27 May 2012, 19:29

Burnt exhaust valve tops the list.

waynej · Post by **waynej** » 27 May 2012, 19:37

That's what I was afraid of. What caused that and how can I prevent it in the future. I have put a couple hundred thousand miles + on Volvos and never had anything that serious before.

waynej · Post by **waynej** » 28 May 2012, 11:55

Another question- will a 93 head fit on a 96. I have a 93 850 parts car and would like to have the VVIS on my 96 for improved performance and mileage. I understand I have to make my own control system for the VVIS but I don know if the early head is compatible with the later block. Thanks for any help you can give.

Post by **erikv11** » 28 May 2012, 12:26

Burned exhaust valves are common on these engines as they get up near 200k. The valve stem seals get hard and inflexible, and leak. Oil gets hot, burns the valve.

The 93 head will fit the same, I sold my 98 head to someone with a 93, and it is doing great on that engine. He mostly wanted it to get rid of the VVIS though! Anyway, you will have to swap over the intake manifold too for the VVIS. If you do swap in the 93 head, be sure to replace the valve stem seals first. Victor Reinz or OEM (do some searches), or they won't last long.

You can drive it on 4 cylinders for a while, just be sure to unplug the #2 injector so it doesn't dump raw fuel to the cat.

waynej · Post by **waynej** » 28 May 2012, 15:01

Thanks Erikv11, The 850 only has 136k but I was running with a plugged cat for a while and didn't know it. I suspect that's the cause even though it didn't show up until a year later. The exhaust manifolds look different where they connect to the exhaust pipe. Will the 96 manifold fit on the 93 head?

Post by **erikv11** » 28 May 2012, 16:44

It should fit yea, although exhaust manifold on a 93 I don't have specific experience with. But I have never heard of it being an issue and the replacement part # listing is the same for all 850s, 93-97 e.g. link at eEuroparts.

Is the actual flange or mating surface different, or maybe the flex pipe just looks a little different? For example, the mesh sometimes falls off, but the actual flex is underneath it.

I am assuming we are talking non-turbos here. Turbo changes the game for exhaust.

Post by **rspi** » 28 May 2012, 16:48

I use to fear burnt valves and did some research on the causes. Here's what I came up with:

1. Improper back pressure from the exhaust. This causes the valves not to seat correctly.
2. Running lean. Improper detonation causes the valves not to seat right.
3. Carbon build up from improper fuel mixture. I believe it's from people running 87 octane in cars that are made to run 91+
4. Valve crack or chip from any of the 3 problems mentioned above. Also, if some buildup or something comes loose it can get stuck in a valve and chip it.

When a valve doesn't seat right it builds up heat and makes it more prone to overheating and damage.

There is a slim chance that you have a slipped sleave on your piston or a hole in your piston. This is usually caused by knock or a messes up spark plug, like if it's broken. The best way to test a cylinder wall is to wet that cylinder with a little oil. If the number climbs it's likely the piston sleeve. But the sudden drop and no pressure usually points to a burnt valve.

http://www.dietersmotorsports.com/Compr ... wntest.htm

http://www.wcengineering.com/articles/leakdown.html

What kind of oil do you run?

Post by **erikv11** » 28 May 2012, 17:12

Great post, those are all good general causes for burning a valve. This is how the common occurrence on the 850/x70 relates to that list: The oil dripping on the back of the exhaust valve burns and causes carbon buildup. Those seals are an achilles heel of these engines. So at least according to the local indy mechanic here who has seen a lot of them, it is usually bad valve stem seals.

And I am reminded of a related story about the running lean. The mechanic also told me about an 850 that burned an exhaust valve, the owner DIY'ed it, then it burned again in the same cylinder! That's when the engine showed up at the mechanic. He quickly determined one partially clogged injector, on the offending cylinder.

waynej · Post by **waynej** » 28 May 2012, 18:37

Thanks guys, Am ordering gasket set, oils separator, 960 throttle plate etc. on the holiday sale @ eEuroparts. The VVIS gives a lot better low end performance and the 960 throttle improves low end response and overall performance.