flywheel/flexplate question

[Mike Harry]

Alright boys and girls, Ive got a tech question for you all. Im doing away with the old school 350 (1985 block 2 piece rear main seal) that takes a heavy flywheel and am purchasing a brand new crate 5.7 (350) this will be the newest version (roller block vortec style).

In automotive use this new engine would require a much lighter flexplate than the old school flywheel.

My question is this, how does this translate in marine applications? Will the flexplate work with my velvet drive transmission or do I need to adapt to a flywheel somehow? I am concerned with 2 things (tell me if I should be concerned with more)

1. If the flexplate is the way to go, will my starter still work in this application (remember I am set up right now for old school flywheel)

2. If the flexplate wont work and I must adapt to a flywheel (if thats possible) how would I balance to the flywheel to the new engine or engine to the flywheel heowever you want to look at it.

Hopefully Im just looking at this to deep and there is a really simple answer. Hopefully the flexplate will work properly and that is all there is to it, but I want to be sure before I purchase anything. Dont want to have to replace velvet drive as well just because Im upgrading to a newer style engine.

Thanks as always,
Mike

Pictures are always nice 

[Mike Harry]

Holy Crapola, Ive been trying to figure this out on my own...... what a pain in the azz.

From what I am reading and understanding they do make flywheels for marine use on a 5.7 One is a 14 inch and the other is either a 12 or 12.5 inch. (Remember were talking about a newer style vortec here)

The 14 says not to use with top mount starter, so Im guessing I need the 12 or 12.5 (whatever it is I cant recall right now)?

Thats another 200$...........

Am I looking in the right direction here?

[backfoot100]

Mike,

Now keep in mind that I'm no scientist and a somewhat knowledgeable backyard wrench at best so the following description could be completely wrong and if I am, I welcome any corrections. With that said this is purely my interpretation of this phenomena.

The flexplate is designed to be used in cars with an automatic. The flywheel is for manuals.
The engine crank needs to have some external mass to keep it moving in between each power stroke of the cylinders. Without that weight the crank would want to stop rotating until the next power stroke kicks it in the a** again. The engine would be very erratic and hard to keep running.
The flywheel (in manuals) and torque converter (in automatics) supplies that weight mass and the centrifigal forces keep the crank rotating in between each power stroke.
Now comes the really cool stuff. How much weight do you need? 
If the weight is lighter it'll move considerably faster up the RPM range (and it also slows down really fast too!) but you'll start to run into the erratic and hard to keep running problems.
Heavier weights keep things nice and smooth but the acceleration of the engine through the RPM range is slower.
There are some power-to-weight ratios involved way over my head. The physics theories of "bodies in motion want to stay in motion and bodies at rest want to stay at rest" as well as centrifigal mass on rotating forces that apply here so the engineers will have to get into those explanations.
To answer your question, our direct drive boats need a flywheel.  I'm not sure if your engine is internal or external balance as that will have an effect on what type of flywheel you need. An external balance will need the flywheel to be weighted heavier on one side and be balanced as part of the engine rotating assembly. Internal means the engine rotating assembly is "0" balanced and the flywheel is "0" balanced and just bolted on. Internal balancing is generally preferred but the design of the rotating assembly and the engine itself determine if that can be done.
I have been wanting to experiment with lighter flywheels over the stock ones but haven't been able to accomplish that. For your application, I would just stick with a stock or close to stock weight flywheel. A couple pounds lighter probably wouldn't hurt but stay as close to stock as you can. I do know one guy that has played a little with lighter flywheels (he's running a 500+HP dynoed 408) and he ended up running a stock or close to stock weight to my knowledge. He in fact had to put a SPI rated flywheel on his CC when he fragged a stock flywheel into a dozen pieces. Needless to say, he's turning quite few RPM over stock.

There are also different diameter flywheels that can make a big difference but then you need to worry about starter locations and how many teeth are on the flywheel and the starter. I believe your stock starter is for a 153 tooth flywheel which I think is a 14". I'll have to look back at my engine info to see what I needed but I'm still not sure if the Vortec is the same or not.

Hope this helps.

[Mike Harry]

Helps, but I'm still in the dark a little. Vortec crank to flywheel assembly bolt pattern is different from the old school bolt pattern. I was almost sure it needed to be a flywheel but wanted to check with the experts. The engine is internally balanced, I know where to go as fat as that's concerned.  Mostly needed to know the size, but also wondering about the weight issues as well.

Come to think of it the coupler may not even bolt to a flex plate to begin with...... so........

[Joel]

Mike,

I'm gonna throw out what I think Ron would say...  ( Ron will probably correct me     Does the manufacturer make a marine application with this engine?  What does the manufacturer recommend?

I'd go to them and see what they say.   It probably wont be the first time someone has asked the question.  Thats it...  I'm done.  I know, not much help      I could help more if you were trying to put in a 26 year old Porsche 5.0, 32V, V8   

Joel

[Mike Harry]

Long story short Joel,  I'm mixing new school engine with old school velvet drive. I know it can be done, just wanna be sure I do it right the first time. I'm not purchasing my crate engine from a marine supplier 

[backfoot100]

Hey Mike,
I just did some checking in one of my reference books that I have. An excellent book by the way. If you have a chance to pick one up, definitely do it. It's called Small Block Chevy Marine Performance by Dennis Moore. I understand that it's no longer in print so if you can find it it can be pricey but the info in it is outstanding. He also has a another one for BBC's.

There are two flywheels available in the SBC. A 24lb. 12 3/4" with 153 teeth and a 30lb. 14" with 168 teeth. The flywheel you have depends on the type starter you have. If your starter has the two mounting bolts side by side, the smaller flywheel is what you need. The large flywheel starter has a diagonal staggered bolt pattern. I know that mine is the large one so I would assume that you would have the same one. 

You also need to make sure that you get the later model bolt pattern flywheel that will fit '86 and newer SBC's. This one has a 3" bolt pattern. Pre '86 bolt patterns are a little over 3.5".

I'm not sure if you are getting a new balancer either but your old one is 6 3/4". It can be reused but I would recommend a new 8" while you're at it. If that's something you're interested in let me know and I'll get the you the info on the one that I got. It's a Professional Products unit that is really nice compared to the factory unit and much better built. If you do go that way, then you'll need a new timing chain cover and timing pointer that will work for the larger diameter balancer.
That snowball thing thing that jumped up and bit me more than once

[Mike Harry]

Somewhere along the line my starter was changed to a gear reduction starter (more torque and spins faster) Damn thing costs a fortune.

Of course this will throw another wrench in the plans. Im guessing once I pull my engine I can just measure the one Ive got and I would bet that thats the size I need.

I was really just trying to get things together on paper so I knew where I stood as far as $$$ is concerned.

While doing this I guess I might as well come off another couple hundred bucks and buy a new coupler while Im at it............

[Mike Harry]

And yes, I had to have the starter rebuilt...... it is a marine starter.

[backfoot100]

Gear reduction or standard starter shouldn't matter. The bolt pattern to mount the starter is whats important.
Staggered bolt pattern = large flywheel.
Side-by-side bolt pattern = small.
I'm guessing it's the large one.
I also reread the orginal post. Your engine is an '85 with the two piece rear main seal? If it really is, you won't be able to reuse your flywheel then. You'll definitely have to get a new one. The bolt patterns are different.

I also want to confirm that the engine will definitely be internally balanced. All SBC's '86 and later (with the one piece RMS) are actually external balance from the factory as far as the flywheel goes. It's kinda weird because the balancers are internal balance but the flywheel is external balance. I;ve heard a name for that type balancing but I can't remember right now. It's that age thing . It sucks.  A crate motor could truly be internally balanced but I would verify before you have to go spending any money on the right flywheel.

[Mike Harry]

Exactly. I need to bite the bullet and buy the heart then go from there. Waiting on the Monet tree to sprout.

[Mike Harry]

While I'm on the subject of the flywheel might as well try and cover this as well, is there any improvements on the 1986 version of the coupler that bolts to the flywheel?

I mean, I'm guessing my best plan is to go ahead and buy a new one, but do I buy the same style or is there something better out there? The one I have now is the triangular shaped coupler. I see there are different versions out there........ any comments on whats good, whats better, whats best and if any of these make a difference in our applications?

[backfoot100]

That triangular shaped damper is perfectly fine for your tranny. There isn't anything any better right now. The center splined piece that mates to the tranny input shaft is attached to the outer triangular piece which is bolted to the flywheel by numerous springs that look kinda like really small valve springs. Those springs help take up any shocks between the crankshaft and the tranny input shaft. It's instrumental in preventing things like crankshaft harmonics being transferred to the tranny and vise versa. When you shift into gear or hit something with the prop those springs are very important for elimiinating any shocks getting transmitted to the crankshaft which could be very damaging. That's also why having a proper propshaft alignment is vitally important. The stresses and harmonics produced by an out of align propshaft are being transmitted directly to the damper and potentially the crankshaft.
There is a guy at CCFan from Ohio that owns his own marine shop. His specialty is tranny's. He's very adament that you change the damper anytime you pull the tranny and/or engine if that damper has any more than 50 hrs. on it, has been badly out of alignment or the prop has been hit something. He gives the CCFan guys a pretty good deal on them but the one you have is exactly what you want to replace it with.