Flex plate

[25ss]

Need a flywheel flex plate for a 25ss.
Are they still available from merc. if so anybody know the part no.
Thanks Dale!

[David_L6]

I need one too if anyone has a source.

[nbass]

What is it?

What is a flywheel flex plate?
25ss ignorant,
Neil Bass

[snyder]

25SS Flexplates for sale

I have remaid the flexplates. 4130 steel. $40 ea. + shipping.
snyder@phelonwis.com.
Del Snyder

[crankbearing]

Hardening

Del,

Are those hardened as well?

Regards,

[snyder]

Flex plates are not hardened. They work harden and crack. Mercury used a plain high carbon steel and heat treated them just slightly hard, but 4130 is a superior steel and I have not had 1 of mine fail on a 25 mod yet.

[crankbearing]

Right.

Flex plates are not hardened. They work harden and crack. Mercury used a plain high carbon steel and heat treated them just slightly hard, but 4130 is a superior steel and I have not had 1 of mine fail on a 25 mod yet.

Sorry Del,

Yes right thinking wrong terminology.

Thanks,

[ZUL8TR]

25ss flex plate

What is a flywheel flex plate?
25ss ignorant,
Neil Bass

The flex plate is the circular thin steel plate (about 7" in diameter with about a 3" hole in the center) that secures the outer magnets and the inner tapered keyed connector that provides the securing location for the the crank shaft. Basically Mercury came up with a 3 piece flywheel and the flex plate was the middle securing piece. The idea was that the flex plate would allow limited vertical motion of the outer magnet ring in order to reduce vib harmonics. I believe the idea sounds good on paper but in the field there were many stress cracks in the plate that rendered the plate useless and dangerous unless replaced. Mercury sold lots of parts.

I presently have 2 good plates, one in the box and the other mounted in a complete flywheel. I plan to run the 25ssh mod so will be keeping them.

[ricochet112]

What is a flywheel flex plate?
25ss ignorant,
Neil Bass

Older Mercs have a 3 piece flywheel; an inner hub, the outter ring (with magnets and teeth) and a thin piece of steel that connects the 2 together to allow the flywheel (outter ring) to actually flex up and down.

[jeff55v]

A picture's worth a thousand words?


Just a generic Merc flywheel. NOT the particular application in question. For informational help only.

[mac19f]

Flex plate purpose

The flex plate purpose is to reduce stress on the crankshaft. The large weight of the spinning flywheel acts like a very strong gyroscope. It allows up-down and directly sideway movement. But a gyroscope greatly resists tilting off of its spinning axis. With the engine at high rpm and the boat (especially a race boat) rapidly bouncing and tilting, the loads on the crankshaft are tremendous if not somewhat isolated by the flexplate. And since these are high cyclic loads, fatigue failures of the crankshaft would be likely. The flexplate absorbs the fatigue stresses and then becomes the sacrificial failure part.

[proprider]

Thanks Mac19f

The flex plate purpose is to reduce stress on the crankshaft. The large weight of the spinning flywheel acts like a very strong gyroscope. It allows up-down and directly sideway movement. But a gyroscope greatly resists tilting off of its spinning axis. With the engine at high rpm and the boat (especially a race boat) rapidly bouncing and tilting, the loads on the crankshaft are tremendous if not somewhat isolated by the flexplate. And since these are high cyclic loads, fatigue failures of the crankshaft would be likely. The flexplate absorbs the fatigue stresses and then becomes the sacrificial failure part.

Thank you for that great explanation of the flexplate purpose. That helps me swollow better after shelling out megabucks for a 44xs flywheel.

[alanaker]

flex plate

Jeff- I think the 25ss had the smaller 6 bolts on the outer edge style instead of the larger 8 bolt outer edge style in your picture. This one is for a larger motor, although I don't recognize that ring gear.
Alan

[G Stillwill]

Alot of the Merc 200's had the same flex plate even though the outer part was different. I needed a couple of them and just got them off of ebay for next to nothing just for the flex plate.