470 mercruiser help,blowing air out valve cover

[skipper6567]

I just baught this motor from a guy,complete engine ready to plug in and go.i thaught. It starts and runs perfect except it blows huge amounts of air out the valve cover.I ran it yesterday for 10 mins and then blue smoke out the exhaust.The smoke stopped after 5mins of 2k rpm running.The air was still comming out the valve cover breather hole. It seems like oil mist. there doesnt seem to be oil in the antifreeze.the antifreez seemed to be ok but maybe had some carbon in it,very fine blackish stuff in the bottom of my bucket when I emptied the cooling system today.I did a compression test.1=60lbs 2 160 3 160 4 160 give or take couple lbs. did the compression test with the starter only,didnt have any of the plugs in. The exhaust manifold is dry inside,oil color is ok.so because the compression test results and so much air/staem comming out that if I block that if I put my finger over the breather oil comes out the dipstick. I decided to do head gasket,took off the valve cover,seemed clean but had some antifreeze drops inside. the intake is good,dry. the head seems clean,i flipped the head and filled the chambers with kero last night, all help fluid overnight except #2 cyl, has 005 over pistons.the pistons look good,cyl walls good. inspected all water passages in the block,no cracks.also it does not seem to leak any antifreeze while sitting. I lapped the valves and they all help fluid.The cylinders were filled last night with tranny fluid,the #2 was only one that held fluid.Sorry for this book but I know when i read post the more info the better. I just want to know how cyl 234 have 155lbs of compression and yet still leak the tranny fluid by the rings. Will one cylinder with bad rings make that much pressure in my block? I just finished and started the engine and same fing prob! going to chack the compression in the am..if I didnt walk away tonight..i may accidently drop a cigarette..lit in my gas tank.mercruiser does some real crazy stuff..makes pistons for that motort,standard,.005 .o15 .030 and only sells rings that at=re standard or 015 or 030..no 005 over rings..,one last thing that engine has not run for 6 years,is it worth a try of just runing it to see if it just has stuck/frozen ring..i figure thats what the blue smoke was..now that ive done the head gasket.

 

[Alpheus]

Re: 470 mercruiser help,blowing air out valve cover

Will one cylinder with bad rings make that much pressure in my block?

Absolutely.

You should have done a leak down test before you went and tore everything apart. You could have learned in 10 minutes where the leaks were. Piston rings are not 100% air tight...

 

[Biged007]

Re: 470 mercruiser help,blowing air out valve cover

Skipper I believe your answer is in your post.First yeah you wrote book But! I do believe one has to we aren't there. Okay with that said no.1 is most likely the reason for the "blow-by" at 60# that is a major prob. also as I read your post and I'm guessing here .005 over pistons = a rebuild and as you state the lack of .005 over rings leaves no choice but to use std. rings. The fact that the other 3 cyl.s are norm. you may have a shot at a set of stuck rings start her up get her warm and throw some Marvel Mystery oil down the carb. at a high rev 2k or so warning this will smoke out the neighbor hood and let it sit a day or so. Then try it again after it warms a little test that cylinder again to see if there is an improvement if there is keep cycling it (hot/cold) thing that concerns me did the 6 year hibernation cause the rings to stick or did they never seat causing the 6 year lay up (PO gave up) Either way I guessing you have a fairly fresh engine there and is worth saving. one last thing if you do get it to straighten out I would change the oil imed. as I will bet it has a ton of gas in it from that bad cyl.

 

[NHGuy]

Re: 470 mercruiser help,blowing air out valve cover

You might run some seafoam in the oil too. That stuff can do a lot from underneath. It claims to free rings, I can only tell you that when I thought I had a problem with a high mileage Dodge 4.7 engine I put some in the crankcase and got a big power improvement. It had seafoam in there for 200 miles.

 

[Bondo]

Re: 470 mercruiser help,blowing air out valve cover

Sorry for this book but I know when i read post the more info the better.

Ayuh,... Lovely book,... My eyes are Bleedin' trying to read it.....

Have ya ever heard of a Paragraph,..??

From what I could read, that motor needs a Complete Rebuild....

 

[coheej]

Re: 470 mercruiser help,blowing air out valve cover

You should have measured the cylinder bores when you had the head off to see how much wear you had. If there wasn't much wear, then you might just have a ring problem. But I agree with bondo I think you need to go through the whole thing.

I never heard of .005" over pistons unless they were custom made.
Does Mercruiser actually sell a .005" over?

 

[Aloysius]

Re: 470 mercruiser help,blowing air out valve cover

Listen to bondo.

Compression is made/held with the piston at the top of its stroke. 0.005 oversize just compensates for wear. If the top of the cylinder is tapered/out of round you won't get sealing.

The cylinders need to be BORED to the next clean-up oversize. The rings need to be properly fitted and gapped.

Piston ring seal in the piston lands is just as important as the seal on the cylinder walls. Damaged or worn lands will NEVER seal properly. The rings cannot be allowed to rock excessively.