Flex plate or Flywheel

[Cas]

it's been awhile since I've seen anything about the pro's and cons of each.
The reason I bring it up is I went out to fire up the engine and the starter kept disengaging. After a little investigation, I noticed the flex plate is warped. As soon as the starter rotates the flex plate to the warped side, it disengages.
is one better than the other?

[flat broke]

well, considering we don't need the extra inertia of the flywheel for anything in a jetboat, the added weight and cost would probably be reasons enough not ro run a flywheel.
Just get a good SFI approved flexplate and you'll be fine.
Chris

[steelcomp]

straighten the flex plate. It's not hard.

[UBFJ #454]

Steve - What FlexPlate are you running?

[Cas]

Bear,
Although I can't remember the manufacturer, the flex plate I have is SFI approved. When I did the rebuild last year I purchased it from the machime shop.
At least I was told it was SFI approved.

[UBFJ #454]

The reason I asked was that we ran a FlexPlate up until the NJBA Summer Break of this passed year ... Then changed to an AL FlyWheel ... Added weight ... About 6 +/- Oz., no big deal since it's rotational mass ... Loss of maybe a fraction of a HP.
The reason we changed was we kept popping the Allan Head Bolts that held the Steel Starter Ring to the AL FlexPlate ... The manufacturer was kind enough to reinstall the Ring three times with no charge before we decided to go the FlyWheel route ... The manufacturer maintained that we had the starter misaligned, but, we Know that was Not The Case, so we changed over to the AL FlyWheel.
What we determined was happening was that the Allan Heads that held the Ring to the Al FlexPlate were spot welded to the heat treated Steel Starter Ring after being installed ... The spot welds crystalized and weakened the Allan Heads resulting in their popping off over a period of time ... Realize that the FlexPlate we were using was SFI Approved and has been used in Funny Cars ... The only difference is that in a Funny Car there is an Inertial Ring and Tq Converter where on a Jet Boat Installation, there is only the FlexPlate held on to the crank by a small mounting ring. What this allows (w/out an inertial ring to stabilize the plate) is the FlexPlate to FLEX like a drum head and work against the weakened Allan Heads ... This combined with the High Compression 'Ms. MoneyPenny' has led to the Allan Head Failures.
As a result of the above, I would recommend that FlexPlates Not Be Used On Jet Boat Motors ... Use an AL FlyWheel ... While the cost for a top end AL FlyWheel is on the order of about $125 more than a SFI FlexPlate, I believe it is well worth it given the damage and injuries that can result from a starter ring "Flying Off". Of course, one must make sure that the starter pinion is properly aligned and its clearance with respect to the starter ring is right.
Just conveying our experience with A FlexPlate on our Jet Boat. Note that while the FlexPlate we were using was a SFI Approved Plate, the particular case of its use in an 'UnBound State' on a High Compression Jet Boat was probably not taken into consideration ... I may be wrong, but, I think the SFI Approval only has to do with the RPMs that they can be Safely Spun At?

[MikeF]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7946872517&category=33732
I asked Jack about this in the past. He said, early on, they used heavy flywheels way back in the racing days cause when the pump would unload (while racing) the engine would not spin up quite as fast. No rev limiters back then. He also says you tend to be a better reader of the water w/ experience. :boxed:

[Floored]

I use a steel flywheel, like someone would tool up aluminum for an olds, and dont notice any dif from previous boats with flexplate. It still revs easily , no heavy torque converter, and no flex or starting problems. In a continous high RPM use it may also help with crank harmonics like using a larger harmonic balancer.

[UBFJ #454]

We're running a Billet AL Flywheel, not a cast.

[wsuwrhr]

I run a reactor products (http://reactorproducts.com) flexplate, nice peice that can be had with or without SFI.
Not cheap, but it works.
Talk to Olan.
Brian

[Mr.&Mrs.Budlight]

The problem with most flexplates is it was designed to have a torque converter bolted to it. Thats what straightens them out. They were never designed to be run without a converter. most guys have it hidden in a bellhousing so you don't see it wobble. The hp aftermarket ones are thicker so they wobble less. I have a flexplate on mine but I think Bear is right. Buy a billet aluminuim one and it will last you forever. Plus when the ringgear gets a chip, you can turn it over and put it back on. My two cents. Budlight

[UBFJ #454]

Your definately right about being able to turn the ring around ..... That's a Definate Plus.

[steelcomp]

Jack, I think most of the guys here would be using one piece steel flex plates, not a two piece aluminum/ steel which is sort of over kill for a flex plate IMO. Sometimes a part can get too trick, if you know what I mean. Why not just use the steel type? Not trying to be argumentative, just curious.
Every steel flex plate I've ever seen wobbles, a little or a lot. They are real easy to straighten...do it right on the motor. You're not going to bend it enough to compromise it's strength, and most jets that don't even run 6000rpm really don't even need an SFI plate. OEM replacements are around $40.

[shaun]

I posted this exact questions a while back, here's the link incase you want to check it out. http://***boat.com/forums/showthread.php?t=46151&highlight=flywheel

[jim@pj]

Cas, Be careful. Depending on what type of drive joint that you have,you may end up changing how much the spline slips over the pump shaft if you change to a flywheel. They are thicker at the hub. You need end play on the pump shaft,1/8 inch will do. In your case the thick SFI flexplate would do fine. Either way, make sure that your drive joint doesn't bottom out in your jet. How have you been Cas? Are you missing that Panther Jet? Jim

[Cas]

Bear,
Thanks for the in depth post! That's the kind of info I was looking for to help make a decision. Totally makes sense in what you've posted, you too Budlight. A good friend of mine lost the ring gear at the races back in the mid 80's that cut a nice 1/2" x 10" hole in the bottom of his boat.
Steel,
I can relate to what you're saying, sometimes there is overkill on a lot of the things we do with our boats. My biggest issue with the parts I buy is I want something that will cut down troubles on the water, especially when the wife and kids are out there with me.
Jim,
What you alluded to with the end play is a very good point and i'm glad you brought it up. I guess I need to check that before making a decision. I still have the Tahiti with the Panther, just haven't used it in awhile since it doesn't have a power plant. That will be remedied shortly as I'm going to go with small block power to see what it'll do.
wsu,
Thanks for that link, I'm going to check into that as they look pretty stout.
The other one I'm leaning towards is this one by CSR
http://www.csr-performance.com/pics/CSR_flex.jpg
CSR Torque Master Flexplates are designed to withstand the stresses of today’s high horsepower engines with nitrous oxide and high stall torque converters. Flexplate center is constructed using 3/16” thick chrome moly steel that is fully machined. With a fixture welded ring gear to ensure minimum run out and has a gold irradiate finish for lasting protection. CSR Flexplates are .062 thicker than OEM units and are double welded to withstand the rigors of high rpm racing. Torque Master Flexplates are approximately 3 lbs heavier than stock to improve reaction/and 60 ft. times. Torque Master Flexplates greatly exceed SFI. specification 29.1. SFI Certification valid 3 Years

[Liberator TJ1984]

Cas , that is a good choice ...$ 175.00 on Doug Herbert web site and it looks Hell for Stout, on my boat all flywheel does is turn over motor to start, drivehub bolts thru flywheel directly to crank, it seems it would be in alot less of a strain than even in an automotive application, better to have Overkill though :cool: