1959 Atom Skier Gray Marine 4 knocking

New varnish on my boat this winter. Running great this year THEN... Last weekend I was cruising to the boat ramp when she started knocking and loosing power. Oil pressure dropped to zero. Shut her down immediately.    Problem was a ruptured line to the oil pressure gauge. Repaired and replaced the two lost quarts of oil. Restarted engine. Ran quiet and smooth as before with 40lbs oil pressure on trailer with siphon.   

Launched. Ran quiet and smooth as on trailer. BUT, over about 2,000 rpm she starts knocking and loosing power. Oil pressure stays at 40 lbs. Please tell me something other than to rebuild the engine. I do not have those skills.

My 56 Atom, 70hp, had a similar issue last season. On the first fire up the engine ran great up to 3000+ rpms. Then it suddenly capped out at 2400 RPMs. Tried to re-set timing, fuel/water separator filter, rebuilt generator, carb adjust and the same. At end of season a gentleman at the dock suggested a new spark advance spring. Did so, and rpm shot up to 3400. If you open your distributor cap you should be able to assess the spring, should be fairly tight, hard to pull on with your fingernail. It is a cheap fix attempt. If you get the same, then at least you have a spare set of points/spring for after the motor gets looked at.

zwoobah wrote: Also, get rid of that live oil feed line and run an electronic sender gauge.

What? An oil line is just a sound as a fuel line. They do not rupture. I suspect a loose fitting after the varnish job?

There was a six inch long rubber/fiber line that connected to the copper line under the floor board. Pretty rotten on both ends. My bad for not seeing and replacing it when I had the floor out.   

I am thinking a lower bearing problem. I have discussed the issue and fix with my boat mechanic.   He is ready to pull the motor next week and check it out. I will be getting the parts.

Where do I find the right bearings?   My assumption is that all should be replaced. What do I need to order the bearing? Do I need a different size from the stock?

Is it a good idea to replace the oil pump since I have the opportunity?

Any coaching you can provide is greatly appreciated.

Barry,
One additional thought and that is your mechanic should also check the cam bearings. I believe with those Continental blocks, the oil goes to the cam first and then to the main bearings/rod bearings. So, the cam bearings would see the lost oil first.

Speaking of oil, what have you been running in it? Hopefully an oil with a good ZDDP content.

Yes, I'd replace the pump. May want to replace the timing set as well. Cheap insurance. Your mechanic will likely recommend replacing all the usual seals - front and rear mains, oil pan, etc. It's smart to do while everything is accessible.

Don't order bearings until the engine is apart. If it has been rebuilt in the past it may already have oversize bearings and you will need to order the matching size. If the crank is scored and it needs to be turned, you'll also have to order a different size. Unfortunately this will slow down the rebuild by a few days, but there's no way to know what is in there until you can measure.

Gary S wrote: and you can start using a detergent oil    Also measure the pumps clearances it may be ok and a new one close to unobtainable.

Plus 1 on the pump and the oil