496 Vibrations
 

I have just rebuilt a mercruiser 454 330hp bravo 3 with a 496 stroker kit. I also removed the mercruiser fresh water pump and installed a Johnson crank driven pump. The pump oscillates when running like it is off center or has a bent shaft. Either way I think I have a balance issue with the damper and flywheel. This is a Pro Comp gen V stroker crank that is internally balanced. My vibrations start at 1200 RPM and continue. My buddy used the same kit on his car with a gen IV without problems using the same damper that he had. My difference is of course the heavier flywheel for the boat and the gen V block. Can I use a Fluid damper to take care of this? I plan to remove the crank pump to eliminate this possible cause, but I think I have bigger issues. Please advise. Thanks.

if your stroker kit is internally balanced you can not use the counterweighted balancer&flywheel.i don,t use the pro comp stuff.do you have a part number for your kit?

did you have the engine balanced ? NEVER just throw in a kit like this without having a machine shop balance it..no matter what they say..pre-balanced etc. what Mike said is correct, most stroker kits are internally balanced and use a 396-427 balancer and flywheel, but with having this crap(what most of the pro-comp chinese junk is) checked for straitness, roundness, balance, the pin will have been removed..

my main concern is the mercruiser flywheel....since it is not a flex plate. I was under the impression these fly wheels were zero balanced. I was wondering if I can use a Fluid damper to solve this.....

if your internally balanced you need a neutral balancer and flywheel as Mike stated, you run a risk of breaking that crank if not done properly

the mercruiser flywheel is simply a manual transmission flywheel as opposed to an automatic trans flexplate. as has been stated you need the correct balance which in your case appears to be neutral on both balancer and flywheel.
a fluid damper isn't the answer. a machine shop could probably neutral balance them but would probably be cheaper just to buy the correct ones.

the balancer&flywheel from a 396 or a 427 will work,they are neutral balanced engines.

i would not continue to run your engine until you get it right,it won,t take long to eat the main bearings up,then it is all over.

i would look closely at the paperwork that came with the rotating assembly.it will tell if it is int or ext balance.with pro comp the balance is no doubt not right and should be balanced at a machine shop as already stated.

Right on. Many of the cast rotating stroker assm are externally balanced from I remember. Why I have no clue but remember seeing some that are externally ballanced but only the cast ones.

Like everyone said don't run it til you get this taken care of or you'll be pulling engine and not happy.

Stroker kits. Some balance and some not.
 

Here's an example and even same company. Note one kit externally balance and other internally balanced.

Scat Series 9000 Cast Pro Comp Stroker Lightweight Crankshafts 9-454-4250-6135
Thanks men, I don't plan on running it any longer....this is the P/N of the crank. I am trying to get a hold of a solid mercruiser contact to help determine the specs on the flywheel and outdrive coupler.

GEN V and GEN VI have externally balanced flywheels from GM and Merc. FYI Merc uses GM Flywheels, in fact, the whole damn motor is from GM, minus some of the accessories and hoses. :)

Edit in: and as stated from others, even if a kit comes 'balanced' and 'drop in' , one still has to have a machine shop check/balance and you or the machine shop needs to check all dimensions and clearances.

So should I get the crank, pistons, and rods balanced with the flywheel and damper?

Yes. Check with your machine shop...some will want everything including hat you said and wristpins/locks if used , rings, and etc.

Here is a good quote from this forum on flywheels that GM and Merc used. The Pat #'s are GM.

That sux....I hate to completely disassemble the whole damn thing 😠

Do some searching here and you'll see a few thousand of us have had to pull/remove/re-install. Multiple times.

Thanks man....lol

Can I use an automatic style flex plate in lieu of that heavy flywheel?

i have a 489 in the shop that i am rebuilding,i finished the disassembly today ,it has a forged scat crank and it is externally balanced.they offer it for folks that don,t want to replace the existing balancer&flywheel.it was built 13 years ago and the assembly was balanced at a machine shop,i know this because the shop that did the balance job scribed their name and the bob weight and the date it was done on the crankshaft.

no,you need the drilled&tapped holes in the flywheel for bolting on the drive hub,unless you go with a omc drive hub,it bolts on with studs that also bolt the flywheel on.absolutly nothing wrong with using a heavy flywheel,mercury marine sold a million of them that way.

i did not know and have never seen a internally balanced 454 from the factory,ya learn something new every day!

Pretty sure they didn't.

I think they just list it that way since 427 stuff isn't searched for much.

http://paceperformance.com/i-6255729...utch-only.html

3991469

DESCRIPTION
This 14" diameter manual transmission flywheel accepts a 10 1/2" and 11" diameter heavy-duty clutch. It can be used with all internally balanced Chevy big-block V8 engines. Technical Notes: Do not use with externally balanced 454 ci engines. Use with neutral balanced damper P/N 3879623. 168 tooth starter ring gear. For use with Mark IV engine only.

Doesn't surprise me at all. Honestly I think all those stroker assm kits should be internally balanced. I would never trust an already so called balanced kit anyway but that's just me. Easy to drop off flywheel and balancer at machine shop to have them neutrally balanced.

OP should contact where he got it from and just confirm what is what and go from there. He might get lucky.

that is why i asked him to post his rotating assembly part number,i was going to attempt to gather information about it but no number posted.

Scat Series 9000 Cast Pro Comp Stroker Lightweight Crankshafts 9-454-4250-6135L

Can you feel the vibration in the boat when it's running?

yeah it shakes pretty bad....I thought I had a miss or valve train issue but after inspecting every checks out.

the listed number is not a rotating assembly,it is a crankshaft.not knowing the rest of the parts used in the build it is probibaly not balanced,pretty obvious if the engine is shaking.time to remove engine and get the rotating assembly balanced.

Just from my build, I went with the eagle forged crank kit. I went with the externally balanced. My machine shop recommended what flywheel and balancer to go with. I had him put it together and balance everything. I know you already have it together but I would take it to a shop. You can't beat having proven data that it spins smooth and all the clearances check out. Also I found all dyno guy that was 500 to run it for 4 hours. In my opinion the everything Xtra $ spent is all for the piece of mind. This way I know that it is together and running correctly. This way I don't have to build it again and spend 10x the amount I spent to do it right the first time. Again just my opinion but pull it and spend some money to save a lot of money.

you cannot use a auto flywheel, coupler bolts to the clutch bolt holes, yes you are going to need to disassemble, if you don't it will...

Years ago I built a 496. Balanced my machine shop. Started it and it had a vibration at 1,200 RPMs. The pin to line up flywheel was removed and I lined it up wrong. Never make that mistake again.

If you didnt get the rods and pistons matched to the stroker crank its highly unlikely the rest is going to pan out on the external side.
On the oem gm side there are subtle bobweight variations based on which pistons used ,within the same crankshaft casting numbers , then there are are revisions in the flexplate balance based on that.some builders can make calculations based on the crank pn the rod and piston weight ,then mod the flywheel and balancer alone to make it work. If you have the part numbers to rods and pistons too ,that could be path of least resistance

Wd1548-060 pistons
41253 pro comp rods