Flywheels the same or not
 

I have a pair of fly wheels from 1990 Mercruiser 330 hp (454) inboards and replacement 496HO's. I/O's
Are these the same and were the 454's internal balance or external.
I was going to use the ones from my old motors if they are the same..

454's are external.
Don't know about the 496 but I do know that between the Mark IV and the Gen V 454's there is a difference. It's small but enough that I wouldn't swap the 2.

they are MKIV so these are external bal. the new motors are 8.1 496.
also are the flywheels the same between inboard/outboard and inboard motors.

As for a I/O and a inboard it all depends where the starter is installed. An inboard the ring gear is on the outside and I/O it's on the inside (because the starter is mounted to the block). Some you can just pull off the ring gear and put it on the other side but not flywheels can do this.

/f_inscreenname thanks I just confirmed them and you were correct. Since the flywheel from my MKIV blocks appear to have a counter balance built in them with a few drill holes I assume they are External Balance correct?
So can the flywheel be neutral balanced.

counter weight on the flywheel is external
It can be neutral balanced but you would be better off just buying a natural flywheel. Just bought one for a 427 stroker I'm building. 78.00 bucks

http://www.summitracing.com/search?S...ord=atp%20z296

IF you are installing 496HO engines, you need to use the flywheel that came with them. If you will be using a TOP mount starter like a transmission boat, or inboard, then you need this flywheel.

http://www.michiganmotorz.com/inboar...nes-p-626.html

If it is for an I/O, you need this one.

http://www.michiganmotorz.com/sternd...nes-p-627.html

If its an I/O with bottom mount starter, you may be able to get a flywheel from a GM 8.1L truck engine. Like this

http://www.carpartkings.com/rhinopac...el-167576.html

[QUOTE=MILD THUNDER;4055263]IF you are installing 496HO engines, you need to use the flywheel that came with them. If you will be using a TOP mount starter like a transmission boat, or inboard, then you need this flywheel.

http://www.michiganmotorz.com/inboar...nes-p-626.html


This is the application that I am doing.. Can I just change ring gear on an I/O to the other side so it would work with top mount starter?

yes, as long as the flywheel is machined on both sides, mine were not from GM gen VI marine engines, I had a machine shop cut the other side and I put the ring gear on and was fine...best to use flywheel that came with the engines...

why is it best to use the flywheel that came with the engine?

Because it is matched to the motor.
I'm sure there is a balancer in your area that can match a new one if needed. Hell they can even match a flexplate to a flywheel if needed.

just fyi,they are not balanced with the engine,you would be suprised if you knew how gm does their balancing,it is not like a quality balance job done in a quality machine shop.the 454 and 502 flywheel,s are bolted on the already assembled engine,not done on a balancing machine.i have seen bbc engines that had all the pistons&rods so mismatched it would scare you but they still ship them out and they run forever at the rpm level they were designed to run at.

Not just Chevy. Took apart a Ford 302 one time that had 3 rods for a 289 in it. Now how does that happen and how do you balance that?

do the GM 454 and 496 wheels share same part number? I would think with the different stroke, they would be weighted differently. also, a truck 496 goes to 4k rpm, and driver (or trans) shifts to higher gear. then the motor runs along 95% of the time or more at less than 50% throttle at 2600 or so. 496 in a perf boat, engine hits 4k...sometimes driver throttles back and holds it there at cruise. mosta time he is heading up to 5k or more. get it balanced. really balanced. not assembled with GM parts that are in spec.

NO, they do not share the same part number. Actually, there are not many things that they do share. People assume a 496 8.1L GM/MERC engine is a stroked 454. It is not.

I personally don't have experience with the merc 496 engine. However, I would not be surprised if the flywheel, was identical to a GM truck flywheel. I highly doubt mercury got these engines shipped in from GM, disassembled them, custom balanced them, etc, and reassembled. Best guy to talk to, is Raylar. He would know.

aren't the 8.1 496 metric sizing in some way? in the prev. links posted they say metric.

I know the 496 manifold studs and bolts are.

Well so far the 496 is a unique engine.out of the 4 I have disassembled 1 of them being a junkyard truck motor with 215,000 miles. None of them have any cylinder wear. Manual says compression second ring end gap .0177 min. These motors old ring set measured .0180 in old bore that to me is freaking amazing. Rod and main bearings almost untouched where as in the surface looked to be "like new" shape. Coated piston skirts slight to no wear.
I am really excited about rebuilding these engines and can't wait to see how they perform in my 43ft 15ft beam boat.

I am havering the rotating assembly re-balanced for my peace of mind.

The 3 merc motors had bad blockage in the coolant crossover tube with a pinkish orange paste. Highly recommend flushing the coolant systems on these closed cooling units. I understand why merc. Recommends coolant flush and change

well they have several flywheels used on the same engines if you look in the GM parts, so if you can use the ones that came with that engine originally you are better off having the "correct" one...