Bad oil leak/crankcase pressure on 91 Prostar? Advice needed

[mikeg205]

Originally Posted by [email protected]

Perhaps you are thinking of compression numbers, you are wrong, minus 7 mcocd points for you.

Ack.... you are correct... dang tequila... oh well it's 5 o'clock somewhere...

[SWGA Boater]

Originally Posted by [email protected]

Yes a normal motor will show 10-15% leakage, your numbers are mostly good, cylinder 8 is iffy at best, I would start looking at #8, anything above 15% and you need to start thinking about investigating and possible rebuild. I recently did a leak down test on a 5.6L titan with 135,000 miles none were over 8%. I would clean top end, pistons etc. Mix up some atf/ water mix 50/50, (marvel mystery oil can also be used)remove all spark plugs insert several teaspoons full of mix into each plug, let soak for 10-20 minutes while slowly rotating engine over by hand every few minutes, then spin engine over with starter motor, plugs still out to remove excessive atf mix, install plugs, it will smoke like a chimney until all atf is burned off, run it for a while, let cool down and recheck leak down.

Thanks for the suggestion. I talked with a mechanic yesterday and he suggested the same thing, except pouring down carb throat until engine dies and then letting it sit over night. Last resort before going into engine i guess.

Any idea what is the difference betweeen the oil the engine uses and atf for the rings? Why would atf be a better choice?

[Spork]

Originally Posted by SWGA Boater

Thanks for the suggestion. I talked with a mechanic yesterday and he suggested the same thing, except pouring down carb throat until engine dies and then letting it sit over night. Last resort before going into engine i guess.

Any idea what is the difference betweeen the oil the engine uses and atf for the rings? Why would atf be a better choice?

Atf will dissolve the carbon build up and free the rings, oil will just sit there. yes pouring down throat is an option I typically don't recommend that method for the fear if not done correctly rods can be bent, fluids typically don't compress well, also you don't know if the mixture actually got into all 8 holes, either way just ensure you get a good soaking to dissolve the carbon.

[JimN]

Was compression/leakdown tested when the engine was cold, or hot?

[SWGA Boater]

Originally Posted by j.mccreigh[email protected]

Atf will dissolve the carbon build up and free the rings, oil will just sit there. yes pouring down throat is an option I typically don't recommend that method for the fear if not done correctly rods can be bent, fluids typically don't compress well, also you don't know if the mixture actually got into all 8 holes, either way just ensure you get a good soaking to dissolve the carbon.

That makes sense...i have a little squirt can so i will go with your recommendation. Will report back afterwards.

[SWGA Boater]

Originally Posted by JimN

Was compression/leakdown tested when the engine was cold, or hot?

Leakdown was done when engine was hot.

Thanks

[SWGA Boater]

No change in my engine situation, but I have found a used engine out a 91 Ski Nautique. The mechanic is telling me it will be a straight swap for the 351 in my boat, in that the Ski Nautique engines are standard rotation (looking from rear engine turns left) same as a MasterCraft. I had always thought SN had a different prop rotation (RH prop). Is the change made in the transmission?

The engine can be had for a reasonable price ($500), but I want to make 100% sure before I tell him that I will take it. Also, the engine is 5 hours from me so its quite a haul.

Will this engine work in my 91? I hope so....

Thanks for any input!

[Spork]

Originally Posted by SWGA Boater

No change in my engine situation, but I have found a used engine out a 91 Ski Nautique. The mechanic is telling me it will be a straight swap for the 351 in my boat, in that the Ski Nautique engines are standard rotation (looking from rear engine turns left) same as a MasterCraft. I had always thought SN had a different prop rotation (RH prop). Is the change made in the transmission?

The engine can be had for a reasonable price ($500), but I want to make 100% sure before I tell him that I will take it. Also, the engine is 5 hours from me so its quite a haul.

Will this engine work in my 91? I hope so....

Thanks for any input!

I do remember someone saying nautiques did have a lefty motor and the change was in the transmission causing a RH prop. If the engine is truly a LH you should be all set, as it sounds like it's already a marine motor their is no need to swap freeze plugs, etc.
Perhaps the question should be raised on http://www.correctcraftfan.com/forum/default.asp
Or PM this guy he knows CC http://www.mastercraft.com/teamtalk/member.php?u=4253

[SWGA Boater]

Thanks for the quick reply! I will also post over on the CC page.

[SWGA Boater]

Ran the boat this past Saturday with no oil leak issues. My problem may have been a stuck ring, I'm not sure. I filled the cylinders with a few teaspoons of a combination of sea foam and mystery oil. I let it set for about 30 minutes and rotated the engine every 30 minutes for so for about 3 hours. I then ran the engine. Afterwards I added a few teaspoons of ATF into the cylinders and let it set overnight. Ran the engine in the yard and then changed the oil and headed to the lake. Finger crossed it will continue to run fine. Dipstick popped up a few times when I ran wide open, but not when running 2000-2500 rpms as before.

Engine still seems to have excessive steam coming out of the exhaust at times. Engine never ran over 160 degrees though. Any thoughts or run as is?