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View Full Version : Low Compression in 91 prostar 190 HELP


Creeklife
07-29-2009, 06:43 PM
My 91' Prostar 190 wasn't running right. I did a compression check on the cylinders and #3 and 4 were at 30 and 40. What is my next step??? Don't know much about Head repair and I need some advice on how to proceed from here. I'm looking for my options. Do I need a new engine, or is it worth it to repair the problem on the old engine? Can it be rebuilt. How much for Repairs, or new engine? Any help and advice would be greatly appreciated

blackcreek
07-29-2009, 08:03 PM
Talk to the really good looking older man with the prostar who lives across the canal. I will take a guess this is Brian, welcome to the forum.

Creeklife
07-29-2009, 08:29 PM
Hey Jim. That's funny. I got excited when I saw there was a reply, and when I read it, I about fell out of my chair laughing.........I got you message. Thank you and welcome home.

JimN
07-29-2009, 09:11 PM
My 91' Prostar 190 wasn't running right. I did a compression check on the cylinders and #3 and 4 were at 30 and 40. What is my next step??? Don't know much about Head repair and I need some advice on how to proceed from here. I'm looking for my options. Do I need a new engine, or is it worth it to repair the problem on the old engine? Can it be rebuilt. How much for Repairs, or new engine? Any help and advice would be greatly appreciated

Was this test done cold or at normal operating temperature? Had all of the spark plugs been removed?

You'll need to drain the water from the motor- completely. If that's the only thing wrong, it's definitely worth repairing.

The linkage, fuel line, wiring and anything that 's on top of the motor will need to come off, but most of it can just be laid to the side. The exhaust manifolds need to come off (just lay them on some towels, at the side of the motor), you'll need to mark the distributor rotor and base so it can go back in the same position- don't crank the motor after the distributor comes out. Remove the hoses from the intake manifold and remove the intake intact, blotting up any water that drips into the oil gallery. Remove each head. Use gasket remover and after the gasket material is soft, scrape them off completely. You need to have completely bare metal, but don't use anything that's too aggressive, like files or a flexible sanding block. Permatex makes that and it comes in small cans.

I don't know how much of this you want to do but some NAPA stores have a machine shop- your area will have someone who can check heads for cracks, shave and flatten them, grind valve seats, etc. Use only marine gaskets (FelPro are good).

FelPro also has a bolt pattern sheet and torque specs that you may be able to download.

Did someone use gasket sealer on the head gaskets prior to it overheating, or something?

blackcreek
07-29-2009, 09:18 PM
I will be around this weekend. If you still have the exhaust manifolds off we can take a look inside the cylinders with my borescope to see if your pistons have any holes in them or just pull the heads and look. If it were me I would just replace the 18 year old motor and be done with it but pull the heads, maybe it won't look so bad. Did you figure out the ignition problems?

JimN
07-29-2009, 09:22 PM
I will be around this weekend. If you still have the exhaust manifolds off we can take a look inside the cylinders with my borescope to see if your pistons have any holes in them or just pull the heads and look. If it were me I would just replace the 18 year old motor and be done with it but pull the heads, maybe it won't look so bad. Did you figure out the ignition problems?

Ignition problems, like idling on the trailer pretty well and running like crap in the water, under load?

blackcreek
07-29-2009, 09:40 PM
Hey JimN I took a look at his motor last week and gave him my compression tester and told him how to do the test, the numbers don"t look good. I fear that the block may of been a victim of a freeze last winter because one head has a crack on the outside of the head above the number 8 plug that is really pissing water, and the other head has low compression. No water in the oil, he just bought the boat a short time ago so the history is unknown.

blackcreek
07-29-2009, 09:54 PM
Ignition problems, like idling on the trailer pretty well and running like crap in the water, under load?
I test drove the boat it was missing badly, we came back in and I put a timing light on it and it was advanced about ten degrees, I put the timing back in spec and the boat would barely run until we pushed the idle setting way up, I ran the light on each wire and one or two were dropping spark at idle, probably just bad plugs or wires. I had to go out of town and told him to do the compression test before we went any further. I am pretty sure the last owner had the timing advanced to cover up the idle problems, the cracks in the head were found while working on the ignition.

JimN
07-29-2009, 10:02 PM
I test drove the boat it was missing badly, we came back in and I put a timing light on it and it was advanced about ten degrees, I put the timing back in spec and the boat would barely run until we pushed the idle setting way up, I ran the light on each wire and one or two were dropping spark at idle, probably just bad plugs or wires. I had to go out of town and told him to do the compression test before we went any further. I am pretty sure the last owner had the timing advanced to cover up the idle problems, the cracks in the head were found while working on the ignition.

Cracks in the head or just bad head gasket? I asked that specific question because I had a guy come in for a tuneup and the first thing I told him was that gasket sealant isn't used on head or intake manifold gaskets (Ultra Copper next to blue metallic paint was a dead giveaway). I told him I'd check it out and it idled well but in the water, once I tried to go past idle, it was terrible, so I took it back to the shop for some tests. #2 had 15 pounds and #3 had no compression, so I told him what I needed to do and found that the gasket had eroded from hot gases. I called and asked when it overheated and he just stammered that it was the first time that season.

Long story, but he was one of those people who shouldn't own a boat because he didn't know the basics of how to maintain it. Turns out that it had frozen the year before and a new casting plug (freeze plug) was installed but nobody caught the cracked cylinder where it froze. He ended up trading that one in after he got a used MC as a loaner for Memorial Day weekend. First thing I told him was that he needs to check and clear out the oil cooler every time out and first time he took it out after he bought it- really bad overheat.

blackcreek
07-29-2009, 10:26 PM
The head is cracked above the plug on the corner of the head, well above the gasket.

JimN
07-30-2009, 09:17 AM
Might be a basket case, unfortunately.