Author Topic: Zero...zilch....no compression (Read 4056 times)

e30rookie · « **on:** February 06, 2011, 10:11:34 PM »

I've got an M42 that went dead while driving down the highway. No noise, no smoke...just shut off. The car cranks but sounds like it's spinning freely...like there is no compression. Put 2 different compression testers on it and it shows zero compression. How is this possible? I pulled the valve cover off..cams look good, timing chain looks fine. Cranked it over using a large wrench and at TDC, the cams and crank appear to be timed correctly. Even if they were off by a tooth, I would still expect some compression somewhere in the cranking cycle.

Other interesting notes. I took out all the plugs. I used my air compressor to pressurize cylinder 1. When pressurized, the air came back out of the spark plug hole for cylinder 3. Seems pretty strange to me.

Car has fuel and spark, but with zero compression....well...the internal combustion just won't fly.

I'm baffled..Any thoughts or ideas would be greatly appreciated.

DesktopDave · « **Reply #1 on:** February 06, 2011, 11:04:20 PM »

That'd happen if your valves are bent. They now cannot seal after they kissed the pistons, so air will freely flow around the intake manifold. Pressurized air from cyl #1 will flow out the bent valve, through the manifold, into #3's bent valve and then out the plug bore.

A tooth off should make no difference to compression. I think you're going to have to pull the head to really see what's going on.

e30rookie · « **Reply #2 on:** February 07, 2011, 10:54:47 PM »

I pulled the head tonight....all intake valves bent, and 8 exhaust valves. Car appeared to be timed correctly...who knows what happened. It's going up for sale..or getting parted out...

Warsteiner · « **Reply #3 on:** February 08, 2011, 06:54:08 AM »

e30rookie,

The most common way to bend intake/exhaust valves is an over rev on a mis-shift, and another way to bend valves is to have your timing chain let go. Are you SURE that your chain is 100% intact and not broken, such as missing a link?? That would account for your " The car cranks but sounds like it's spinning freely..." If you spun the motor with a breaker bar and socket on the crank bolt, did the cam gears and chain spin with your movement of the socket?

Just a thought...

Cheers,
~Ralph

DesktopDave · « **Reply #4 on:** February 08, 2011, 08:55:01 AM »

Sorry to hear about the valves. It's a well-known problem with the engine. Used heads or whole motors aren't that expensive. I'm guessing that you have an e30...the e36 motor is very similar. You'll have to swap your intake manifold and a few other parts over. I see nice e36 M42's going for $300-400 every once in a while. I've seen whole running low-mileage cars go for well under $1000. The M42 just doesn't get a lot of love.

Rebuilding a head with all-new valves would be pricey though. Post your location, maybe a board member will be interested or can help out with parts.

rjcaptsean · « **Reply #5 on:** February 08, 2011, 11:07:22 AM »

I can tell you that pressure testing, machining, replacement of 2 exhaust valves, and machining of the front cover will run you about $400 here in Roseville. If you have that many bent valves, that head is probably toast.

e30rookie · « **Reply #6 on:** February 08, 2011, 09:15:24 PM »

The car is going to be parted out. I bought it cheap with the motor issue...so I'm just going to recover the costs, and send the rest to the yard...I listed the car whole on R3V. I hate to throw away a nice non sunroof E30, but I need to get the money out of it.

romkasponka · « **Reply #7 on:** February 09, 2011, 03:41:23 AM »

Quote from: e30rookie;101271

The car is going to be parted out. I bought it cheap with the motor issue...so I'm just going to recover the costs, and send the rest to the yard...I listed the car whole on R3V. I hate to throw away a nice non sunroof E30, but I need to get the money out of it.

Replace whole motor from E36 318is M42...