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How to increase oil pressure on MBL

Posted: Mon Jul 02, 2018 8:10 am
by Kerry Price
I just installed a fully rebuilt MBL long block and while the oil pressure was showing to be around 40lbs when tested prior to putting into the boat it is now reading at only 15 +/- lbs on the dash gauge when running at around 2500RPM on the water. The oil gauge itself was rebuilt and has less than 15 hours on it and was reading 30lbs on my prior engine which has been replaced with this newly rebuilt one so I don't have any reason to suspect that the gauge is the problem (though it may well be)
I spoke to the engine restorer and he said that there is an oil pressure adjustment that can be accessed from a side panel on the forward lower section of the block (starboard). I wanted to check in with my fellow CC club members and connect anyone that has ever made this adjustment and how to go about it. Any pictures of what this looks like would be great!

Re: How to increase oil pressure on MBL

Posted: Mon Jul 02, 2018 11:45 pm
by jim g
Its accessed through the access plate on the side of the oil pan. Remove it and you will see a bolt sticking out towards you. Loosen the lock nut and turn the bolt in 1/2 to 1 turn. You will need a new gasket for the plate.

Now before you go through all of this. You need to get a manual test gauge from a parts store hook it up and run it. Keep in mind the oil pressure will drop 10 or so pounds when the oil warms up. You should have around 35 at speed when hot and around 7 at idle. A cold engine will be higher.

How many hours do you have on the new engine? Did it happen while running or after the engine set for a time?

The big question was the oil pump rebuilt when the engine was?

There is a set distance the bolt should stick out if its been rebuilt. I'll have to measure a rebuilt one I have and let you know.

If there are internal problems no matter how much you crank the bolt in. Its not going to change the pressure much.

One last thing to check before you try adjusting it. Behind the lock nut is another hex nut. Unscrew this one as it will have some tension on it from the oil pressure relief spring. Once you have it off there will be a disc in the end of the spring. Take it and the spring out. With a small parts magnet ( you can get one at the parts store) slide it in the hole and you should be able to pull the cup out. If it won't come out at all. Then its stuck in the open. You will need to get it out and take fine sandpaper and polish the sides of it. Put it back in and make sure it moves freely back and forth with the magnet. Reassemble and test the pressure.

Hopefully you using a good 30 weight break in oil.

Re: How to increase oil pressure on MBL

Posted: Tue Jul 03, 2018 7:05 am
by Kerry Price

Thank you for your thorough explanation and fast response on this.
According to the restorer, who incidentally was Van Ness Engineering, the oil pump was completely restored prior to shipping off to my mechanic up at Lake Muskoka, Canada. I will take your advice and first attach an oil gauge directly off of the engine and see if the pressure is good. If not we will dig in and follow your adjustment instructions. Fingers crossed!