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AKA OhOneWS6
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Discussion Starter #1 (Edited)
I tried to search on this and didn't find any real discussion on it. I know of 3 that failed in the last 6 months. I know two of those were flywheels. I am not sure on the third. What is your choice and why? It might also be good to include how you use your boat and what your HP & torque numbers are.
 

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Failures....

The majority of the flywheel/flexplate failures I've seen were related to starters and ring gears... I have personally "flexed" an aluminum flywheel so quickly the ring gear fell off, twice.... I've seen several chewed up ring gears from those small "high torque" aftermarket starters, 4 on Allerton's PS52 boat alone..... I currently use an aluminum flywheel from Bergeron, bought from Brockhouser at LB in 08, and it's worked great with 13.1:1 and a bone stock GM high torque starter mounted Powerglide style to the bellhousing with 39* locked out in the mag...... I've used flexplates, GM, or Jeg's, in several recreational jet boats for decades, also with stock GM starters. In 40 years I've never had to shim a Chevy block mount starter, Pontiac yes, Chevy no......Another area to think about is the battery. You NEED a good HOT battery to crank anything without busting something.... If the motor CAN kick back, it will...
Ray
 

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Try to use the best you can buy . I have seen a sfi flex plate peel the ring off ,kinda rare but it happened. last weekend a buddy of mine had a flywheel explode tore a hole in the bottom and side of a pc tunnel and it sank . once upon a time ihad an external balance bbc weight come off the flywheel and lucky enough went thru the bell housing without damaging anything else . What scares me if it can tear up that much stuff on the boat imagine what it could do to the boat you running along side
 

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AKA OhOneWS6
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2,637 Posts
Discussion Starter #7 (Edited)
The majority of the flywheel/flexplate failures I've seen were related to starters and ring gears... I have personally "flexed" an aluminum flywheel so quickly the ring gear fell off, twice.... I've seen several chewed up ring gears from those small "high torque" aftermarket starters, 4 on Allerton's PS52 boat alone..... I currently use an aluminum flywheel from Bergeron, bought from Brockhouser at LB in 08, and it's worked great with 13.1:1 and a bone stock GM high torque starter mounted Powerglide style to the bellhousing with 39* locked out in the mag...... I've used flexplates, GM, or Jeg's, in several recreational jet boats for decades, also with stock GM starters. In 40 years I've never had to shim a Chevy block mount starter, Pontiac yes, Chevy no......Another area to think about is the battery.
You NEED a good HOT battery to crank anything without busting something.... If the motor CAN kick back, it will...
Ray
Thanks for the input Ray. So far you are the only one to post that is using a flywheel. Is there a reason why? I understand it is a nice piece and not a stock GM flywheel. The failures I have seen are catastrophic. I believe all three were stock flywheels. All that is left is a couple of very small pieces at the crank flange. These were way more than just a ring gear failure. I totally agree on the hot battery. Not sure why your reply is divided into 2 quotes. I tried to fix it but it keeps changing back.

Try to use the best you can buy . I have seen a sfi flex plate peel the ring off ,kinda rare but it happened. last weekend a buddy of mine had a flywheel explode tore a hole in the bottom and side of a pc tunnel and it sank . once upon a time ihad an external balance bbc weight come off the flywheel and lucky enough went thru the bell housing without damaging anything else . What scares me if it can tear up that much stuff on the boat imagine what it could do to the boat you running along side
Was this at the Winter Nats in south TX? That is the one that I was unsure if it was a flywheel or flexplate. the 3 failures I know of have been very lucky that no one was hurt.
 

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Was this at the Winter nats in Houston? That is the one that I was unsure if it was a flywheel or flexplate.
It was an sfi aluminum flywheel. There is not one spec of it left to be found anywhere in the boat, just a piece of the ring gear. There is a gap between the pto and crank with all bolts like it was never there! Check your installations guys and make sure you have done all you can do to prevent a failure! Parts still fail when everything is right, but this type of damage not only cost a lot of money, but could get you hurt or someone next to you.
 

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"BOATLESS"
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After i saw what can happen like "Dominator" on the forums, his flywheel exploded at the track and left some nasty scars on the transom, lucky it was not sawed in half:))eek:))
I bought this SFI approved billet one off of Jegs or summit, i think it was like $300-$400 but the piece of mind is worth it with high HP applications.
I have a deep cycle battery ive had sense i bought the boat, high torque starter and 950+hp on the nitrous, i dont want shit to break laying down a pass at the river.:)
 

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i run a flexplate on my blown alky in a jet, my family ran flywheels in their PE and TE hydros
 

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Was riding in my old daytona with the the new owner and we heard a rattling noise it ended up being the sfi flexplate and it broke loose at the crank!
I had a blown 540 pushing 1000hp using that plate and it was fine but it is now on a 870hp 572 and it was destroyed
 

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TCI sfi flexplate on a 15:1 n20 motor with a top mount IMI mini starter and a lithium ion battery. No problems at all.

Make sure everything lines up properly, that the starter is correct for the application in terms of gear ratio (speed) and motor torque, and that you have good power to the starter and you shouldn't have problems.

I frequently check the flexplate for cracks and rust because it does get wet after all.
 

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Stay away from China flexplates and stock iron flywheels, but as said above even SFI stuff breaks so check your stuff often if you are running large power.
 

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TCI sfi flexplate on a 15:1 n20 motor with a top mount IMI mini starter and a lithium ion battery. No problems at all.

Make sure everything lines up properly, that the starter is correct for the application in terms of gear ratio (speed) and motor torque, and that you have good power to the starter and you shouldn't have problems.

I frequently check the flexplate for cracks and rust because it does get wet after all.
I run the Exact same setup in mine , TCI SFI flexplate, IMI high torque with li battery.... 15/1 n2O-No issues.

Darin
 

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We run and have had great luck with Mcleod sfi billet aluminum marine flywheels, carfully measuring the depth of flywheel in relationship to depth of pto drive flange, they sometimes need to be massaged for proper "crush" on flywheel and registration. Other times have had machine shop stack flywheel and pto on crank, and have two dowel pins drilled and reamed as an assembly so to "lock" it all together, not just relying the six bolts to do the job

Also ring gear is attached to aluminum by six small tabs tig welded to ring gear that are bolted to small pockets machined into flywheel held by small bolts, very secure
 

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AKA OhOneWS6
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Discussion Starter #20
Great info. It sounds like a quality SFI certified flexplate is the popular choice even over an SFI certified aluminum flywheel. Seeing 3 flywheels gernade in 6 months really had me thinking. I would imagine that even if you did fling the ring gear off a flexplate it would do far less damage to the boat than a flywheel coming apart. I have a stock 454 with a stock GM flexplate now. I will be ordering a new quality SFI certified flexplate for mine before spring.
 
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