Merc 5.7 Bearing Replacement

[300sflyer]

Not sure if this has been asked before or not, but is it possible to replace both the crank and rod bearings in a 1998 Merc 5.7 by removing the oil pan, and then replacing them all, one at a time? The oil pan has never been off, so I would simply put a fresh set of stock bearings in.

I had to remove the engine anyway to replace the coupler, [badly worn splines] and while the engine is out of the boat, I thought it would be a good time to do this. The engine runs fine, however the oil pressure is on the low side, throughout the RPM range. I'm thinking a fresh set of bearings would remedy this. For some unknown reason, there was some water in the oil a year or two ago, and the engine ran like this for an unknown amount of time. [Previous owner] Engine compression readings are all normal, and the cooling system checks out fine with a pressure test.

Thanks.

 

[Bondo]

Re: Merc 5.7 Bearing Replacement

Not sure if this has been asked before or not, but is it possible to replace both the crank and rod bearings in a 1998 Merc 5.7 by removing the oil pan, and then replacing them all, one at a time? The oil pan has never been off, so I would simply put a fresh set of stock bearings in.

I had to remove the engine anyway to replace the coupler, [badly worn splines] and while the engine is out of the boat, I thought it would be a good time to do this. The engine runs fine, however the oil pressure is on the low side, throughout the RPM range. I'm thinking a fresh set of bearings would remedy this. For some unknown reason, there was some water in the oil a year or two ago, and the engine ran like this for an unknown amount of time. [Previous owner] Engine compression readings are all normal, and the cooling system checks out fine with a pressure test.

Thanks.

Ayuh,... The only way to know whether the motor's bearings are worn or not is to pull, 'n inspect 'em...
At that point, you'll also know whether the crank needs polishin' or not....

Many times, even the original factory bearings are all different by a thousandth or more,..
So,...
You won't know what sizes are needed til ya see what was originally installed, 'n you Measure the journals to see what sizes ya need...

 

[300sflyer]

Re: Merc 5.7 Bearing Replacement

Thanks Bond-o

I'll post the results with some pictures, once I have it apart.

 

[achris]

Re: Merc 5.7 Bearing Replacement

Get a hold a product called 'Plastigauge'. It's designed for exactly the job you're doing... We 'old-timer' mechanics use it (I'm sure Bond-o and Don know the stuff I'm talking about. ). It's basically a thin strip of plastic that you put on the journal, tighten up the cap bolts, leave it for a minute, remove the cap and then use the measure provided on the Plastigauge packet to see how wide the plastic strip now is. The more the plastic has been spread out, the closer the bearing tolerance... Too easy!

You may find that your bearings are all ok, but the oil pump is worn. How many hours on this engine? The other thing that can hammer out bearings is a prop too big...

Chris.......

 

[300sflyer]

Re: Merc 5.7 Bearing Replacement

Thanks for the tip Chris! I'll see if I can locate some. The engine has just over 500 hrs on it. It's one of two engines in a cruiser. The other engine is fine. Both engines have Bravo 3 drives, with the same props.

Thanks.

 

[achris]

Re: Merc 5.7 Bearing Replacement

Try here -> http://www.plastigaugeusa.com/

 

[300sflyer]

Re: Merc 5.7 Bearing Replacement

This afternoon I decided to run the engine, sitting on a skid. To double check the oil pressure, I removed the oil pressure sending unit, and installed a mechanical gauge. Am I ever glad I did! I have almost 30 PSI at idle, and close to 50 PSI when I rev it up. This is with the engine up to operating temperature.

Obviously, there is no need to tear it down, as the problem is either the sending unit, the gauge, or in the wiring.

I'm much happier today!

 

[Bondo]

Re: Merc 5.7 Bearing Replacement

This afternoon I decided to run the engine, sitting on a skid. To double check the oil pressure, I removed the oil pressure sending unit, and installed a mechanical gauge. Am I ever glad I did! I have almost 30 PSI at idle, and close to 50 PSI when I rev it up. This is with the engine up to operating temperature.

Obviously, there is no need to tear it down, as the problem is either the sending unit, the gauge, or in the wiring.

I'm much happier today!

Ayuh,.... I bet you are,.... That's a 'ell of a pile of Work, ya ain't gotta do....