Where is my oil going?

My 94 Nautique with a PCM 351, carb is burning oil. It has 575 hours on it, 490 of the hours were from the previous owner. I do not know how good they were about care. I'm meticulous about care, and so I notice the oil burning. I notice oil smoke when I cold start it and a little at idle. I never smell oil smoke while skiing or see it while on the throttle. The motor runs great, with good power, and tone. It only holds a tune up for about 50 running hours; this may not be related (see my carbon in distributer thread).

I'm wondering how it's burning the oil. Do you guy's think it's valves and I could get away with doing a valve job or do I need to do rings as well?

If this were a European car with moderate to low miles like the hours represent on the boat I would do valves and not consider the rings. I'm not as familiar with the Ford stuff in a ski boat.

Fuel smoke is more black, and Oil smoke is more blue.

79Tique, Run your engine and get it to operating temp. Then pull your oil filler cap then remove the PVC hose from the valve and plug it. Start the engine and see if you see smoke puffing out of the valve cover. If you do the rings are worn and a valve job will not do you any good. You may be in luck though because a little smoke at startup only usually means worn valves.

Yes...the one going from the carb spacer to the PVC valve at the cover.

Eric,

I have changed the plugs a few times as the motor only holds a tune up for about 40-50 hours. The plugs are black,wet and oily.

I think the hour meter is correct as I have been inside the dash to install the Perfect Pass and the wire connections on the meter are original and unbroken. The guy who owned it was not mechanical at all and I suspect they did not change oil as he should have. He and his brother were pretty good skiers and they used the boat to ski the course at 34-36 mph and that is about all they did. So it was pulling pretty hard most of the time.

The rest of the boat is in fantastic shape the trans runs great. I replaced the alternator, starter, all the ignition parts, and a bunch of other stuff this spring so after the motor is fixed it will be a like new boat. I'm committed to fixing it, but don't want to do more than what's needed.

I'm thinking because of the low hours and how smooth the motor runs that I might have some bad valve guides. I'm inclined to pull the heads when the season is over do a good valve job, but if experienced folks think I should do rings or more I'll take that project on.

I'm looking for some opinions.

How is a leak down test done? if you have the time to describe it.

Thanks for the the suggestions.

Gabe

That's great. Thanks for your explanation and the attached. I'll do the test over the next few days and see what's up.

Thanks again for the help; this is exactly what I was looking for.

79nautique wrote: explaination if you remove the PCV valve or breather on the other side and hear it there it's the valve guides,

How can air leak past the valve guides without leaking past the valves first. And then wouldn't you hear it in either the intake or exhaust?

I think it's safe to say that you can't check valve guides with a compression tester.

OK, Thanks I'll figure it out.

nuttyskier2002 wrote: How can air leak past the valve guides without leaking past the valves first. And then wouldn't you hear it in either the intake or exhaust? I think it's safe to say that you can't check valve guides with a compression tester.

got to keep you on your toes was expecting Billy to chime in.

nuttyskier2002 wrote: 79nautique wrote: explaination if you remove the PCV valve or breather on the other side and hear it there it's the valve guides, How can air leak past the valve guides without leaking past the valves first. And then wouldn't you hear it in either the intake or exhaust? I think it's safe to say that you can't check valve guides with a compression tester.

At least I can find out if I can get away with just a valve job. It would be nice to leave the motor in the boat.

[/QUOTE]
After you have done all the compression tests wet and dry, decarbonized the engine and everything is healthy but you still get cold start oil smo0ke then...
Valve seals can be done in the boat using compressed air in the sparkplug hole(or cotton rope pressed in the combustion chamber) and then a valve spring compresser to remove the keepers, spring, and valve seal.
Two tips- use the regular rubber seals as they are most forgiving and give all the valve keepers a good rap with a wooden mallet before you start.[/QUOTE]

When you say wet and dry do you mean with and with out oil? How would you recommend decarbonizing the motor?

Does the black oily plugs make you think rings?
I'm hoping do get away with just pulling the heads and doing a valve job. I ordered a leak down test from the local auto parts store so I should get a this figured out this week.

If I use my compression test gauge and turn the motor until cylinder #1 is holding compression I can assume I have close enough to TDC for the leak down test?

I don't think this motor is carboned up. The PO ran premium fuel and at pretty high RPM all the time. It has done very little idling. I still have not done the leak down test, but I'm thinking it might have some broken valve seals.

As I said above the motor runs great; 44MPH with the stock 351, and idles smooth starts easy. Just blows a lot of blue smoke right when started.

A couple of squirts with an oil can. Use motor oil....preferably the same as you are running in the crankcase. Spin the engine over several times to get the excess out. You don't want the oil to take up any volume in the cylinder. That would give you a false higher reading.

The lowest and highest cylinders should be within 10% of each other to be acceptable. Your readings fall into the marginal category. Post back with your second test using oil in the cylinders.