Compression/overheat on Mercruiser 5.7 ski

cj7ole

Seaman
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Aug 17, 2009
Messages
74
I have a 1989 Malibu with the Mercruiser 5.7 Ski engine with 660 hours. I am the original owner. It overheated and stalled a month ago when the impeller fell apart. Been idling rough since. Did a full electrical tune up and that helped, but it still feels like it is missing at less than 1500 rpm. Plugs were not tight on the left front two cylinders. Checked the compression, 150 psi is spec, 145 psi on the 4 right cylinders. Starting from the rear on the left I got 140, 130, 30 and 60. Surprised it runs at all. Getting 4400 rpm at full throttle.
What is the most likely problem? I hope it is a head gasket, not valves or scored cylinders. Where should I start? Got tools. Any words of wisdom? What is the head bolt torque spec? I know that heads need to come off.
 

cj7ole

Seaman
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Aug 17, 2009
Messages
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Re: Compression/overheat on Mercruiser 5.7 ski

Slight update: with 3 squirts of oil in the 2 offending cylinders, one went from 30 to 35 psi, the other from 65 to 80 psi. Does that good or bad?

As I read the posts on compression, with two adjacent cylinders low, it is likely a blown head gasket, right?
 

Bondo

Moderator
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Apr 17, 2002
Messages
70,464
Re: Compression/overheat on Mercruiser 5.7 ski

Ayuh,... Pull the head,+ Look....

Manuals are in the Adults Only section for reassembley...
 

mikeneal

Senior Chief Petty Officer
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Jan 28, 2004
Messages
710
Re: Compression/overheat on Mercruiser 5.7 ski

Exhaust valves are one of the 1st things to go when overheat. Time to pull the heads.
 

cj7ole

Seaman
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Aug 17, 2009
Messages
74
Re: Compression/overheat on Mercruiser 5.7 ski

I checked out the Adults Only section, looks like I need manual 15, which doesn't appear to be available. Bummer. Next step, get a set of gaskets on order and pull the head. Priorities, Michigan summers are short. Looks like my Jeep painting project is on hold.

Edit: I found the manual.
 

sbbamafan

Petty Officer 1st Class
Joined
May 11, 2008
Messages
303
Re: Compression/overheat on Mercruiser 5.7 ski

Your compression issues certainly could be HG, but you will not know until you look, as someone else said. As far as how long it lasts, my boat will likely get to 1100 hours this summer (I hope). Take care of it and it will last a long, long time!
 

cj7ole

Seaman
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Aug 17, 2009
Messages
74
Re: Compression/overheat on Mercruiser 5.7 ski

I sold my last ski boat with 1070 hours, still ran good.

If the one head is warped a bit and needs to be milled, do I need to mill the other one also to keep things balanced? And it it necessary to spend 3 times the amount for Merc head gaskets, if not are there aftermarket gasket sets to stay away from?
 

cj7ole

Seaman
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Aug 17, 2009
Messages
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Re: Compression/overheat on Mercruiser 5.7 ski

Talked to my local engine rebuilder (Michigan Motor Exchange http://www.michmox.com/ ). They will mill the head and do a valve job for $150 for one head, $250 for both. 20 years on my baby and 660 hours, I guess she deserves to get both sides freshened up. Pulled the heads today, looks like I was getting gasket leakage between #1, 3 and 5. Valves on #1 and 3 looked questionable. The cylinders looked ok, but I could feel a slight fingernail drag on a small crescent shaped area on the wall of #3. I will have them look at that too, may be ok, may need honing.

Still debating on gasket sets.

Edit: feels good to wrench on an engine again, it's been a while. 14 years on my Jeep's 4.3 Chevy and 30 years on my old Martinique's 318.
 

cj7ole

Seaman
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Aug 17, 2009
Messages
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Re: Compression/overheat on Mercruiser 5.7 ski

They looked at the heads and definitely could see it was a blown head gasket, due to the rust forming where the gasket was between 1-3 and 3-5, also they confirmed the valves on 1 & 3 looked suspect.

I was able to mill the gasket seat for the riser on my mini-mill, cleaned up real nice. Cleaned up the mating surface on the exhaust manifold the old fashoned way, with a scraper and file.

My question: is a knotted wire wheel on a 4" grinder too aggressive to remove what is left of my intake manifold gasket after I stripped off the bulk of the seal? I swear they put that seal on with epoxy!
 

Bondo

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Messages
70,464
Re: Compression/overheat on Mercruiser 5.7 ski

My question: is a knotted wire wheel on a 4" grinder too aggressive to remove what is left of my intake manifold gasket after I stripped off the bulk of the seal?

Ayuh,.... Just be Careful....
And it it necessary to spend 3 times the amount for Merc head gaskets, if not are there aftermarket gasket sets to stay away from?

You can't go wrong with Fel-Pro gaskets...
 

cj7ole

Seaman
Joined
Aug 17, 2009
Messages
74
Re: Compression/overheat on Mercruiser 5.7 ski

It worked very well once the bulk of the gasket was removed.

I have a set of Felpros on order from my rebuilder. Very handy that a Merc dealer is right next to the rebuilder so I could order the riser gasket there.
 

cj7ole

Seaman
Joined
Aug 17, 2009
Messages
74
Re: Compression/overheat on Mercruiser 5.7 ski

Final update if anybody cares: boat is now back in the water and running good, having lost only 2 weeks. When I checked the timing, I was only off by one degree, that really surprised me. Fired right up without a problem. Compression on 1 & 3 now back up to 140+. Only leak was from the thermostat cover, added a one dollar gasket and I am good to go.

Yes I am going to add an overtemp alarm light and maybe a buzzer.

Total cost: under $500. Probably twice that if I had not done the tear down/rebuild.
 

gordond

Cadet
Joined
Oct 1, 2007
Messages
24
Re: Compression/overheat on Mercruiser 5.7 ski

.."Final update if anybody cares"

it's refreshing to see someone post their resolution. thx

Too often i read posts with no resolutions. They should be deleted. It's a waste of space & waste of one's time
 

cj7ole

Seaman
Joined
Aug 17, 2009
Messages
74
Re: Compression/overheat on Mercruiser 5.7 ski

New update. Starts and idles fine, pulls well up to about 3000 rpm but can't get it over 3600, used to hit 4400.Somewhere I lost 800 rpms. Had a inboard mechanic look at it and after he tweaked my valve adjustment a bit, he says now my distributor isn't advancing properly, only going to 24 degrees, he says I need to be advancing to about 36 degrees. Recommending a new distributor. All of this while sitting in my drive with a garden hose hooked up. I pulled it and took it apart, cleaned and lubed the weights. No help. Not looking to put a new $330 part into it just to see if that is it. Any suggestions as to what distributor to install? Traditional points and condenser. The mechanic suggested Prestolite. Don't think they even make it anymore.
 
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