identifying plastic ring in front of prop 150 4stroke

[Alumarine]

I was seeing if one of my old aluminum props could be used as a spare on a friends 2012 Mercury 150hp 4-stroke.
It has a plastic ring that has 3 tabs and fits into the bearing carrier nut and seems to fill in the gap at the front of the prop.
My spare aluminum prop seems to rub a bit too much on it.

Does anyone know what the part is called and what it's purpose is?
I can't find any parts listings online for this motor.

thanks

 

[Faztbullet]

Sounds like a blow out ring,,,,,,,

 

[Alumarine]

Thank you! I think you're on to something.

I've never head of those and not sure why his Vengeance prop would even need one.
We'll have to try it without it and see if it does anything.

Sure having trouble finding it online anywhere.

 

[Alumarine]

Update. I contacted Mercury and they left a message for me.
It's called a Prop Bore Sleeve part no. 8M0054695.
I'm sure you're right that it helps prevent blow outs.

It might be because this gear case is 4.88" as opposed to the more common 4.75"?

Here's a quote from a tech on another sight "It's essentially a protective sleeve (to protect the gearcase bore/carrier nut area from scarring). "

 

[elkhunter338]

the ring is actual a shim to prevent exhaust gases from causing prop cavitation, my merc 150hp won't work without it. Loose way too much speed, motor over revs. very poor design, Mercury should make a good fix for this piece of crape plastic shim. only there because they went to a larger gear case, some are talking about selling there motor because the ring won't last for more than a few hours, mine lasted 250 hrs. Mercury needs to step up and fix there design problem.

 

[QBhoy]

Very common on new mercs. Happened to my ct other week. Apparently can be put back on by heating up tabs and bending to a tighter fit. Yet to try it.