Compression Results- Help

[digitaldav]

I had my OMC Cobra 5.0 winterized. The motor oil was milky brown. So I checked comp. Any thoughts?<br /><br />Compression Results:<br />Engine was not warm & throttle was not wide open<br /><br />#1 = 135<br />#3 = 152<br />#5 = 135<br />#7 = 165<br /><br />#2 = 180<br />#4 = 165<br />#6 = 175<br />#8 = 182

 

[Walt T]

Re: Compression Results- Help

Those are ok.

 

[coupedeville]

Re: Compression Results- Help

Really? That's almost a 30% difference between the highest and lowest cylinders. That's a bigger spread than I'd like to see.

 

[digitaldav]

Re: Compression Results- Help

The reason I checked was I found my motor oil a milky brown color when I had my OMC Cobra 5.0 winterized. Any thoughts??

 

[sony2001]

Re: Compression Results- Help

It MIGHT be a problem needing a new head gasket.

 

[geriksen]

Re: Compression Results- Help

those compression readings are marginal. It's hard to really tell. they are not even enough, but we see engines with readings like that that run just great for years. My suggestion would be to change the oil at least twice, running the engine between changes and see of the water comes back. If it doesnt, there is no need to tear that engine apart. If it does, fellow who suggested a head gasket may be right.

 

[digitaldav]

Re: Compression Results- Help

Are these readings meaningless sincr it was just winterized? There was a lot of oil(fogging) that shot out of the cylinders while doing compression test. I did try to crank all the oil out of the cylinders before testing.

 

[Trent]

Re: Compression Results- Help

As Walt said, their ok....Would I tear down an engine with those readings? NO!! And that was what Walt was trying to say!<br /><br />Big spread yes. Run it again and get it up to temp and re-check. Compression readings vary. Trend is what your really looking for.<br /><br />Milky oil is a different subject. Check manafolds and risers.

 

[coupedeville]

Re: Compression Results- Help

Squirting a little oil in the cylinders is a great little trick to raise compression numbers in an engine with worn rings: It helps them seal better. So your real readings may even be lower than what you first saw.<br />But would that be enough to take it apart? Not for me. If it ain't broke...

 

[digitaldav]

Re: Compression Results- Help

Thanks for all of your encouragement.<br />Trent you mentioned to check the manifolds and risers because of the milky oil. How do you check these? Do I need to remove these and inspect or is there another way? If I need to remove will this destroy the winterization?

 

[geronimo]

Re: Compression Results- Help

milky oil means water in oil and pls check wether milky oil in valve covers only or as well in oil sump<br />i had similar problem and suggest you drain oil instantly , remove exh manifolds and risers and cheks these by putting water under pressure and covering outlet... if water shows up at exhaust holes you have to replace either the packings or the risers...<br />how old are the risers?

 

[digitaldav]

Re: Compression Results- Help

I have no idea how old the risers are. I bought a few months ago as a project boat. I am replacing the floor, but was not expecting to be working on motor!! A little more project than expected. I am not familiar with checking ex. manifolds and risers. Can you explain a little more on how to put under pressure or is there somewhere I can read up on this.

 

[geriksen]

Re: Compression Results- Help

It is not easy to check the manifolds without custom made plates to seal the gasket surfaces. Here is an easier way to do it. Run the engine, (you still need to change the oil twice to get that water out) then let it sit for several hours. Pull the spark plugs and crank the engine over. Look for water coming out of a spark plug hole ot two. If water squirts out not only do dyou know you have a leaking manifold, but you know which one it is. Your compression check is meaningless if the engine had storage oil in it. Like someone else said, the oil will artificially seal the rings. You have been getting good advice from everyone here. I suspect that there is nothing wrong with this engine. that is why I keep saying to change the oil until the water is gone (run it in between changes). If it doesn't come back, you can proceed on with your floor job.

 

[digitaldav]

Re: Compression Results- Help

geriksen,<br />If when I do what you say and I do have water coming out of a cylinder or two, could it also be a head gasket or worse a cracked block?

 

[geriksen]

Re: Compression Results- Help

could be, but generally a cracked block will put water in the valley not in the cylinder. Also if your head gasket is blown enough to fill a cylinder w/water it would be obvious on the compression check<br />the blown head gasket water also blows aout while it is running and quits when you turn the engine off. The exhaust manifold will empty itself into the cylinder after the engine is off. There is a degree of luck needed here too as it depends on the exhaust valve being open for it to get in there. That is why it won't happen every time. If it is a manifold leak you will know it. One hole will be just pumping water out of it.

 

[vinney]

Re: Compression Results- Help

This engine is known for the risers to last about five years. This engine needs new manifolds and risers and because its been pulling in water in thru the exhaust it has rusted up the valve seats. Thats why the compression is all over the place. This engine needs the cylinder heads remove and a valve job done on both sides. Text book water ingestion problem. They do make after market manifolds and riser that sit higher than oem manifolds and risers. Vinney

 

[geriksen]

Re: Compression Results- Help

There you go.

 

[digitaldav]

Re: Compression Results- Help

Thanks for everyones replies you have been very helpfull. Especially Vinney and geriksen.<br />Ok I will start replacing the manifolds and risers. I will hold off on the floor replacement until it starts to warm up again. Vinney you seam very confident in your diagnosis, do you work on many of these motors 5.0? Can you give me some places to purchase these after market manifolds and riser?

 

[vinney]

Re: Compression Results- Help

Im not a big fan of osco but they work and the material osco uses on there after market manfolds and risers will usally out perform what was on the engine to begin with. The weight is always more. When you pull the cylinder heads use new head bolts. Vinney Osco can be found many of these after market online market places.

 

[digitaldav]

Re: Compression Results- Help

Vinney,<br />Osco does not carry this type of man. THis engine has Log style man. I was told were only used for two years. Any other replacements?<br />The #'s on man. are 913683 and 913682-port