Replacing melted piston 91 Evinrude 150 XP

[trimmers]

Re: Replacing melted piston 91 Evinrude 150 XP

I feel your pain. I got the exact same issue on my no.5 cylinder (175 TLCU). I tore her completely down and prepairing to replace all the rings on the pistons and spot check all the bearings on the crank. Not sure how my issue happened. But feverishly looking. Luckily, no damage whatsoever is found in the cylinder itself, just localized to the top of the piston. I am looking at about 150 to 200 dollars in rings, seals and o-rings but ya know, when she is all done, atleast i know the engine is freshened up and ready for a fun summer of boating. Good luck bro

 

[TheStinkMan]

Re: Replacing melted piston 91 Evinrude 150 XP

Took the power head and pistons to the machine shop. They say the #6 (cylinder with melted piston and small groves) can be cleaned up boring .020. They also mic'd the 5 pistons:
#1 3.492
#2 3.492
#3 3.493
#4 3.493
#5 3.489
#6 Not mic'd, melted piston

He says the pistons show some wear. I'm hoping I can re-use them. What do you think?

Thanks...

 

[emdsapmgr]

Re: Replacing melted piston 91 Evinrude 150 XP

The spec for a new factory 150 piston is: 3.4955-3.4965.
The new factory bore spec is: 3.4995-3.5005
A decision to replace pistons should depend on the stackup of total tolerances. You did not say how dimensionally worn each of the bores is. That needs to be part of the overhaul decison. If the bores are tapered and egg-shaped you may need to bore and go with new pistons anyway. Generally, you can reuse pistons if they clean up well. Reusing worn pistons (with new rings) in worn bores can work, but will reduce the long-term life of the overhaul. You need to compare costs to overhaul with other options.

 

[TheStinkMan]

Re: Replacing melted piston 91 Evinrude 150 XP

The boat is a recently aquired 92 Nitro 180 that has had a rough life. I'm not looking for new just reliable enough to cut across the lake for a couple years without worring to much.

Thanks...

 

[Faztbullet]

Re: Replacing melted piston 91 Evinrude 150 XP

Are those measurements the top or skirt of piston? If they are the skirt spec's pistons have a lot of wear, and the cylinders are most likely worn in the port transfer area. I would just go ahead and bore the rest .020 and have a good engine instead of a ok engine as you may find another hull later and will have a good engine to install on it.

 

[TheStinkMan]

Re: Replacing melted piston 91 Evinrude 150 XP

Picked up the Powerhead today. Shop bored #6 .020 and said cylinders 1-5 mic'd at 3.499. I'm going to hone the 5 cylinders, clean up the old pistons and put new rings on them. #6 is getting a new piston. I plan on using the old wrist pins unless they look bad when I remove the old piston. Bearings all look good. Ohm'd out the stator it checked ok. New Recitifier / Regulator. Cleaned carbs (were full of snot). Plan on cleaning everything and putting it back together next week.

I'd like to thank everyone for the great advise...

Thanks...
TheStinkMan

 

[TheStinkMan]

Re: Replacing melted piston 91 Evinrude 150 XP

Thanks...