Deposit on 79 140hp Evinrude piston crown

[Jack Mears]

I just pulled the heads on a 1979 Model 140943R bubbleback. All pistons are stamped .030 on the crowns. Three of them are almost new and the crosshatching is still visible on the cylinder walls from the rebore. The port lower piston crown and plug have what looks like lead deposits on them. Heavy lead deposits. The cylinder wall has a little apparent aluminum in one area just above the exhaust ports. This deposit can probably be taken off with some 180 grit wet or dry.The neoprene water deflector in the water jacket of this cylinder is displaced and in the wrong spot according to the Evinrude repair manual.

My question is: Am I going to have to tear down this motor or is this apparent lead deposits allowable. If so- anyone have an idea what would cause this? Could this cylinder been running hot/cold because of the water deflector being in the wrong position?

Thanks Guys

 

[1946Zephyr]

Re: Deposit on 79 140hp Evinrude piston crown

I would see if you corrected the problem with the water deflector. I wouldn't tear it down, unless the compression went bad.

 

[emdsapmgr]

Re: Deposit on 79 140hp Evinrude piston crown

Good catch to note that the water deflector is misplaced. It is not obvious to many.. That may actually be the root cause of the failure-an internal overheat, probably causing a lean conditon on that cyl. The aluminum that has transferred from the side of the piston to the cast iron cylinder liner is from the side of the piston. It is deteriorating. You can probably clean up the cast iron liner with a little acid, but if the piston has started to delaminate-that is the problem. It may continue to run, but there is increased friction in that area of the piston. It will need a new piston and ringset at some time in the future.

 

[Jack Mears]

Re: Deposit on 79 140hp Evinrude piston crown

Thanks for the replys guys.

What kind of acid would remove the aluminum from the cylinder wall?

I'm on the fence as far as a teardown before I put it back in the water. I just finished tearing down a 78 140hp and it's a pain-for sure. Bad block. Salt water engine and that makes the teardown more difficult. This 79 has never seen saltwater.
I think a compression check will be the first thing I do after mounting the motor on the boat. If the compression is down on that particular cylinder, I'll bite the bullet and tear it down.

Thanks again guys!

Jack Mears
Concrete, Wa.