Broken flex plate?

Anyone ever experience a broken flex plate? My 85 2001 started making ugly knocking / popping sounds last Wednesday and I was told it could be a broken flex plate , or a thrown rod in my 454 engine. I'm thinking (ok hoping) it's he flex plate not the rod as I believe it would be an easier / less costly repair.
So does anyone know how to diagnose this short of completely dismantling it?
Please help, summer is here in Maine and I want my boat running.

That 10-18 gets real heavy/real quick at a certain point. The SN hull will help I'd guess.

Please clarify your response, my starter is cranking slower than prior to the onset of this problem I need answers not clever replies or sarcasm .

Bill,
By chance, have you been doing a lot of starting/stopping of the engine listening at the sound trying to figure out the problem? For a quick check on your slow cranking, check the volts on the battery and starter.

8122pbrainard wrote: Bill, By chance, have you been doing a lot of starting/stopping of the engine listening at the sound trying to figure out the problem? For a quick check on your slow cranking, check the volts on the battery and starter.

Yes , and I have been swapping in freshly charged batteries , volts are ~11.8 to 12 v/dc
Hence my concern it's actually a motor issue not the flex plate. Pissing down rain here in Maine today so no compression test. There's a local guy that runs a Marina nearby that does "dock calls" going to see if he can drop by this week and help diagnose the problem and will go from there.
Keep my fingers crossed its the flex plate.....

Did your oil pressure change from what it was before the noise started. Rod or main bearing failures usually result in oil pressure going down especially at idle as the clearances between the crankshaft journal and bearing increase. Flex plate noises are typically a higher pitched more metallic rapping type noise, while a rod bearing will have a lower pitched knocking noise.

11.8 to 12V open circuit voltage on a battery indicates its at about 25% of battery capacity, you really want to see about another 1/2 volt higher.

Terry,
What are the issues with the bottle jacks? I as well as many have used the method.

Thank you, great advice, I assume the boat will have to come out of the water then??
Probably way easier access to tools etc, plus should anything go south it's eaiser to have it closer to the tools.

ultrahots wrote: On a 454 no thanks. Seen enough cracked manifolds in my day to not help them out. A Cherry picker can be rented from most parts stores for $25. I have a bunch of issues with the bottle jack idea. I assume you are putting it at the rear edge of the manifold ? Getting bolts out of the way as well as wrestling the Velvet out of the way with bottle jack teetering on the edge. Sounds like a trip to the ER in training. Not putting pressure on the corner of a glassed over 30 year old stringer either. Just my .02 . I would rather use a come along and strong tree branch first but choose the correct tool for my safety.

Terry,
You've seen cracked manifolds from using bottle jacks? The front engine mounts are still in place so the engine doesn't teeter. If your stringers can't handle the base of a bottle jack, then they can't handle the engine mounts ether. The problem with the stringers should be addressed. I sure wouldn't say a tree branch is a " "correct tool" BTW, after the engine is tilted, I always set it down on a piece of wood at the keel.

I would never attempt this repair in the water if on a trailer was an option. Could it be done like that ? Sure I will bite. But WHY ?


Pete. Most of the posts I see by you are "By The Book" . Why attempt this repair in the water with crude methods at best. As I stated and I will stand by my comments this repair should be done on land with the correct tools, and not floating using bottle jacks. I would be more worried about the bottle jacks slipping as you are trying to get the velvet drive out of the way. Add possible waves and weather to this just seems out of sorts for you to even entertain. I understand you will not be holding all the weight up with the bottle jacks but old cast iron manifolds being used as a lifting device ? In an emergency..... Possibly. If I could do the job correctly with less of a chance of injury...My first choice.

Engine Hoist & Dry Land on Trailer = No Trip to the ER.

My comment above was I would rather use a Tree Branch than a pair of bottle jacks. It may not read like that but I think you got the idea.

We may be talking about different scenarios. Like most, I can detrans a windsor ford anywhere, mounts are in the middle of the engine in most modern marinizations. The 454 has its mounts adjacent to the second jug, and requires some more preparation about the extra leverage it exerts..

Bill,
Have you found the problem yet? Have you load tested the batteries you are using and made sure they aren't deep cycles?

8122pbrainard wrote: gpzstar wrote: I have been swapping in freshly charged batteries , volts are ~11.8 to 12 v/dc You must be using old crappy batteries. Run a load test on them. A fully charged 12V with be 12.7 to 12.8 and hopefully none of them are deep cycles.

With the slow crank, they sure could be giving you the wrong idea that you broke a rod. I leaning towards the damper plate. The poorly constructed (not Sachs) can make a pretty big mess inside the bell housing.

ultrahots wrote: Boat out of waster yes. Easier and safer for all involved. Pics of the boat would be great. Rare bird with a 454 in it.

Don't know how to get pics uploaded to forums , and yeah I'm an engineer ,but for some reason these forums confound me...

Bill,
A quick high jack question. Would you use a diode or a RC network across a switch contact that's welding itself together? The switch is rated for 50 A with a 25 A inductive 12 V DC load but I've gone though 2 that welded together.

steve600 wrote: Where in Maine?

Waterford , Maine , western foothills near Norway