Engine Knock or Clanking in Mercruiser V8 5.7L Valve train ...What is this SOUND?!?

[Bamaman1]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

Find yourself a good Chevy mechanic. Put a water jacket on the lower unit, and let him listen to it. A really good mechanic can often tell you exactly what's wrong by the sound--at least an educated guess.

Working on a 350 or 454 engine in a boat would be a snap for a quality mechanic. You don't have to work over fenders and under hoods--and can get to them so easy.

As far as you having to push the engine so hard to stay on plane--invest $450 in a set of Bennett hydraulic trim tabs. Problem will be solved immediately. Have you ever noticed that all planing boats (Sundowners, Cigarettes, Fountains) all have trim tabs. They'd never get those long noses down without them.

 

[Timboat]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

After many of the recent suggestions led back to the exhaust manifold gasket being the source of the noise. I decided put my lifter/rod theory on hold and focused on removing and inspecting the exhaust manifolds connection to the cylinder head.
As predicted......... IT WAS THE GASKET! check out these pics. It was melted, crispy, and often missing entire sections when I (carefully) pulled it off the head.
Needless to say I will replace both sides of the engine's gaskets. Is there a better quality material of gasket that would work better for me? I just installed these gaskets last season! Guess they didn't like the extreme heat of running at 4300rpm.

On to reassembling the engine now, good thing I didn't take off the carb or intake manifold....
Also I'm in the market for a better and more appropriate prop for my "people moving" at 24mph. Perhaps a 16x13" 3 blade will get my 6000lb boat on a plane at a low RPM? I have 15.25 x 15" 3 blade aluminum now AND CLEARLY it is getting me in trouble.
Any suggestions?




Thanks!

 

[fishrdan]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train ...What is this SOUND?

Good to hear it's nothing serious.

When the exhaust gasket were replaced, did you re-torque the manifold bolts after running the engine, first heat-cool cycle?

I've used those "paper" exhaust gaskets before and would never use them again for the reason you experienced, blowouts. Get a good set of FelPro gaskets. The green riser gaskets are questionable also, I'd replace them with a set of graphite coated (Mercruiser/Quicksilver) gaskets. You don't want the riser gaskets leaking or you will have some serious problems...

 

[tpenfield]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train ...What is this SOUND?

That is about the least invasive thing that could have happened. The boat engine Gods were looking out for you!

Easy fix and you'll be out with bikini clad passengers in no time.

 

[netting one]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train ...What is this SOUND?

Man good to hear! I got my exhaust gaskets at summit racing parts. Also put a straight edge on the surface to check if they didnt warp a little bit. Glad it worked out.

 

[Bondo]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train ...What is this SOUND?

I've used those "paper" exhaust gaskets before and would never use them again for the reason you experienced, blowouts. Get a good set of FelPro gaskets.

Ayuh,... Fel-pro, # 1404 is the metal. graphite exhaust gaskets for the SBC...

 

[Silvertip]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train ...What is this SOUND?

Glad you found the issue and that it's an easy fix. Yet another example of the importance of a logical and systematic approach to "diagnosing" and "isolation" of a problem. Shotgunning a problem is rarely time or cost effective.

 

[PBarrett]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train ...What is this SOUND?

Good for you, you ended up with the best possible scenario. Easy and low cost.

Going forward, I don't think there is much you can do to keep an underpowered boat on plane, when you are carrying that kind of load. Changing your prop will have little affect, but maybe you can try and shift more weight to the bow and try and work the trim and tabs to your advantage. Short of adding more usable power, you are kind of stuck. One idea would be to just take the bikini girls and leave their heavyweight BF/spouses on shore. Or, maybe go through your boat and remove any unneeded weight that you find.

I have read that some 2556 owners have installed larger trim tabs with pretty good results, quicker to plane and at lower speeds. The problem is the standard 12" x 12" tabs are rather small for such a short, wide, stern heavy boat. Since most 2556's came with Bennett Trim Tabs, maybe you want to contact them and see what they say.

Good luck,
PB

 

[Timboat]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train ...What is this SOUND?

Bigger trim tabs are a good idea. What about bolting on some sort of trim tab extension to the existing ones to make them larger?

Also, is a bad idea to move two of my house batteries forward in the bow of the boat under the sleeping berth in the interior of the cabin to shift weight forward? Will lead acid batteries off-gas, over heat, explode, melt or fill my cabin with toxic fumes???

 

[Thalasso]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

After many of the recent suggestions led back to the exhaust manifold gasket being the source of the noise. I decided put my lifter/rod theory on hold and focused on removing and inspecting the exhaust manifolds connection to the cylinder head.
As predicted......... IT WAS THE GASKET! check out these pics. It was melted, crispy, and often missing entire sections when I (carefully) pulled it off the head.
Needless to say I will replace both sides of the engine's gaskets. Is there a better quality material of gasket that would work better for me? I just installed these gaskets last season! Guess they didn't like the extreme heat of running at 4300rpm.

On to reassembling the engine now, good thing I didn't take off the carb or intake manifold....
Also I'm in the market for a better and more appropriate prop for my "people moving" at 24mph. Perhaps a 16x13" 3 blade will get my 6000lb boat on a plane at a low RPM? I have 15.25 x 15" 3 blade aluminum now AND CLEARLY it is getting me in trouble.
Any suggestions?


View attachment 127598View attachment 127599View attachment 127600View attachment 127601

Thanks!

I'll bet you didn't get this good of advice on the other site.

 

[tpenfield]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

About those gaskets . . . from your photos it looks like you used those pale green after market gaskets. You are better off with the more OEM style gaskets that are gray in color, and I believe are laminated metal, etc for durability.

I just threw a couple sets of those pale green gaskets out during my recent engine rebuild.

 

[joewithaboat]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

ThanksPB. Yeah I have the 2556 with the Alpha I gen2. It's a fantastic boat except for the underpower issue.
When I get the motor issues smoothed out, I'll pickup a new prop for a more realistic cruising speed. Would you recommend your 3 blade aluminum 16x13?
Also how much are we talking to have a mechanic install a more powerful Mag 350 or a 383? and will all my exhaust risers and components still fit on the 383?

Glad to see the problem was easily resolved. Lots of good diagnostic suggestions were given. Luckily the simplest was your problem.

A friend of mine owns a performance oriented boat shop. He charges $1,500.00 to $2,000.00 labor to change out a long block. It depends a lot on the interior removal/engine hatch room etc. A 383 or 406 would make your boat much more enjoyable. Buying a rotted out boat that has a good 454 and a bravo drive to swap might be the best option. His shop frequently performs these small to big block conversions. I'm guessing but would prob cost $2,500.00 labor.

As i was reading the post and thinking about possible lifter problems...
On your current set up make sure you are running the appropriate oil for flat tappet cam protection. Most of the oils these days are not made for flat tappets and will lead to a flat cam eventually.

 

[Bondo]

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

Re: Engine Knock or Clanking in Mercruiser V8 5.7L Valve train .. UPDATE

Now, Now children,...

This ain't no danm Oil thread...

Those that I've deleted know who you are,...
Cut it out.....