Summary - compression & leakdown results (need some interpretation/diagnosis help) - PeachParts Mercedes-Benz Forum

rgnprof · #1 12-30-2006, 01:46 PM

This has been an ongoing process for me and I have two fairly recent threads covering some of my issues (excessive smoking - Clouds of white smoke (I mean clouds!)) and head replacement questions (Does cylinder head and cam towers have to match?.

I think I finally did a compression and leakdown test correctly this morning - car at operating temp, WOT, etc.). Results for the compression test are as follows after removing all plugs and cranking the engine a few times to clear out the cylinders:

Cyl 1 - 150 psi
Cyl 2 - 140 psi
Cyl 3 - 150 psi
Cyl 4 - 120 psi (first test), 130 psi (second test)
Cyl 5 - 150 psi
Cyl 6 - 150 psi

I used a Milton Cylinder Leakage tester (picture below). Used 100 psi to pressurize each cylinder, each cylinder at TDC on compression and all cylinders showed 20% or less than 20% leakage (see picture), except for cylinder 4 which was right around 40% (start of the yellow, moderate range). No coolant bubbles, no leaky exhaust valves or intake valves (except maybe for cylinder 4 where I heard a little leaking in the rear carb - so I'm thinking maybe a valve needs adjusting). All hissing noise is heard from the oil dipstick tube and the oil filler in the valve cover for all cylinders, which according to the leakdown tester instructions is normal - it just depends on how much leakage is evident.

According to my manuals, normal compression is between 142 and 156 psi, with 120 psi being the minimum and 22 psi the maximum variation between cylinders.

My initial reaction is that these readings don't explain my smoking problem - and these numbers are not that bad. Cylinder 4 is a problem (a wet compression test raised compression from 130 to 150 psi, but it did not affect the cylinder leakdown test results). Am I correct in this assumption?

I really don't know what is going on now, but as I mentioned in an earlier thread I have a seriously leaking intake manifold and it seems that when I spray carb cleaner in the leak - with the car idling- it affects the smoke from the tailpipe. Is there any way that this leak could be contributing to my smoke?

Any help would be appreciated - I have been in the process of buying a new head, camshaft and towers and was thinking of pulling the head, but I'm not so sure I need to do that now???

Ryan

t walgamuth · #2 12-30-2006, 11:10 PM

only intelligent thing i can think to say is that according to a friend who used to build and race funny cars, oil can seal a leaky valve as well as bad rings.

i am not sure why it is smoking so much.

for starters i would adjust the valves.

does it have a diaphram fuel pump? mechanical?

i have a vague memory of leaking fuel pump diaphrams causing oil consumption, but that may have been on my 53 caddy which had a combination fuel and vacuum pump.

are you runninng clean gasoline?

tom w

rgnprof · #3 12-31-2006, 09:45 AM

I'm not sure it's oil burning now... would fuel smoke like this?

Can a leak around the intake manifold cause excessive smoke like this?

I am going to start with replacing this intake/exhaust manifold gasket.

What do I need to be aware of as I pull the intake/exhasust manifolds from the head? Will I need to loosen anything other than the bolts/studs themselves and just pull it to the side?

Ryan

ctaylor738 · #4 12-31-2006, 10:32 AM

I think that you have a worn-out head, maybe with some warping and possibly/probably a head gasket problem. I think your smoke is coming from worn guides and possibly the head gasket. Your low readings on #4 are probably a burned valve. The block seems OK as you got less than a 20% boost from the wet test.

You may well have a vacuum leak, but fixing that is not going to affect the smoking.

IMO, you should remove the intake manifold, but do it as part of the head replacement. Once you get the intake/exhaust off, you are most of the way to getting the head off. While you are doing that, have your machine shop rebuild the new head. Take a good look at the cam sprocket and the other gears that come out and make sure that they are not pointed. Maybe even spring for a new chain and tensioner.

Good luck!

t walgamuth · #5 12-31-2006, 01:02 PM

fuel smoke will be black.

tom w

300SDog · #6 01-01-2007, 11:06 AM

Universal Truth: all m180, m130 and m110 inline 6 cyl engines need valve and head work at about 125-150k miles. My last inline 6 was twincam 280SEL w116. It had 189k miles and ran like a bat out of hell. Previous owner did a valve job at 145k miles. Also owned an m110 280/8, did a valve job on it and replaced the timing chain at 125k...... Then drove the car up to 289,000 miles. The engine was running strong at that point but the body rusted to smitherines.

General rules on mandatory head work include replacing all guides and seals, burnt sodium filled exh valves cannot be reground but must be replaced, and remove as little metal as possible from the cyl head surface or better yet none at all unless it's warped. Intake valves rarely need replacement and can be gently lapped to reseat em. The entire operation should cost less then $500 in parts and machine shop costs, pulling the head yourself. Deffinitely a bargain and money well spent.

And never replace the rings on the MB inline 6 or you will end up with piston slap. Your compression test readings sound pretty good to me (except for #4). And how many miles did you say were on the car?