5.7 merc. 260 rattle...

[270win]

At 3000-3500rpm the motor runs like a top all day long. But if I run it at WOT, after about 1 minute, I hear what sounds like valve train noise or spark knocking... If I back it down to 3,000 rpm it goes away immdiately. The speed hasn't decreased, but I have also noticed some minor bogging with big throttle position advances and it's become more difficult to start after the first start of the day...that could be totally unrelated.

Any ideas?

 

[capecodcruiser]

Detonation, check your timing at idle and at 3K+- RPM

 

[Hampton]

Agreed - ignition. Check all tune-up items: Plugs, wires, cap/rotor...

 

[270win]

Ok, I'll just completely tune the engine. I thought about detonation but figured it would do it throughout the rpm range.

Thanks!

 

[270win]

is the timing vacuum advanced on this engine?

 

[capecodcruiser]

detonation only really happens under a load, hence when you start to load it up, you hear the "pinging". You can also try a higher octane gas if your timing numbers end up being correct.

 

[270win]

I've been running only 93 octane. I'll replace the plugs and wires and then check the timing. I'm pretty sure I also have a separate issue with the carburetor.

 

[stevea661]

Advance is centrifugal. Inital advance is between 5 and 10 degrees depending upon regular or premium fuel. An additional 21 degrees comes in between 700 and 3000 rpm. Again between 26 and 31 total depending on fuel. That being said I did mine with my wife driving the boat and me working the distributer at wot and premium fuel. It worked out to be about 32 degrees total and 7 inital. The book is pretty close:grin:

 

[270win]

Advance is centrifugal. Inital advance is between 5 and 10 degrees depending upon regular or premium fuel. An additional 21 degrees comes in between 700 and 3000 rpm. Again between 26 and 31 total depending on fuel. That being said I did mine with my wife driving the boat and me working the distributer at wot and premium fuel. It worked out to be about 32 degrees total and 7 inital. The book is pretty close:grin:

that's what I'll have to do then...is the harmonic balancer marked pretty clearly on your engines?

 

[stevea661]

I used an advance timing light, you can adjust when the light fires. The timing tab goes 10 degrees in either direction, I marked the balancer with white automotive touch up paint. I scribbled over the black timing tab with yellow plumbers crayon (keel) and then whiped it off, it leaves yellow in the numbers and degree marks. It's way easier to see that way. The engine and timing tab is black and yellow works good with black. I checked it with the light after I was done just to see where I was. If you have someone run the boat and you advance it till it pings and then back it off a little, your good :smt001

 

[270win]

I used an advance timing light, you can adjust when the light fires. The timing tab goes 10 degrees in either direction, I marked the balancer with white automotive touch up paint. I scribbled over the black timing tab with yellow plumbers crayon (keel) and then whiped it off, it leaves yellow in the numbers and degree marks. It's way easier to see that way. The engine and timing tab is black and yellow works good with black. I checked it with the light after I was done just to see where I was. If you have someone run the boat and you advance it till it pings and then back it off a little, your good :smt001

I've used the touch up paint trick before.

How do you like the pertronics ignition setup? Is it like an HEI distributor or more like an MSD box and coil?

 

[stevea661]

The pertronix works well. It's a real easy install. It works with a magnet and a pickup. Its a simple system. I did have a problem with the original rotor and cap but I called pertronix and they set me straight with the right part numbers. But even with the part Numbers they gave me I still had to shim the rotor up some, It was at the bottom of the cap contacts. I used a plastic coffee can lid and a punch to make shims I think I used 3 shims.

 

[270win]

The pertronix works well. It's a real easy install. It works with a magnet and a pickup. Its a simple system. I did have a problem with the original rotor and cap but I called pertronix and they set me straight with the right part numbers. But even with the part Numbers they gave me I still had to shim the rotor up some, It was at the bottom of the cap contacts. I used a plastic coffee can lid and a punch to make shims I think I used 3 shims.

is this better than an HEI setup?

 

[stevea661]

I'm a Ford / toyota / dodge / honda / yamaha/ jeep guy on dry land, I'm not familiar with hei or how it works.

 

[270win]

Ah, I'm more of a GM guy. The HEI is basically the dist., ignition box and the coil all in one unit. But I never have seen them on boats...not sure why. Thanks for the info on PerTronix!

 

[270win]

detonation only really happens under a load, hence when you start to load it up, you hear the "pinging". You can also try a higher octane gas if your timing numbers end up being correct.

Apparently I was wrong, I said I only ran 93 in it. I must have bought some 89 octane somewhere. Yesterday, without changing anything else tune wise, I filled up with 93 octane. No rattles at all. I'll bet the timing is still too advanced...I plan to completely tune it once I pull it for the winter projects. Maybe that'll allow me to run 89.

Thanks!

 

[cpt. sundancer]

i had the same prob. on my '81 5.7,bumped up the timing and ping was gone. i have the old points system and will up grade with the pertronixs conv. kit in spring. i also was wondering if i could run my msd-6al and blaster 2 coil thats just sitting in garage?

 

[270win]

i had the same prob. on my '81 5.7,bumped up the timing and ping was gone. i have the old points system and will up grade with the pertronixs conv. kit in spring. i also was wondering if i could run my msd-6al and blaster 2 coil thats just sitting in garage?

I would think so, but the MSD distributors have an issue with rusting under the cap in cars...it would probably be much worse in a boat. I was thinking about an HEI, but I can't find anyone else who's used that setup.

 

[cpt. sundancer]

wonder if i can use the msd blaster -2 coil with the pertronics upgrade,this coil is not epoxy filled:huh:

 

[sprink56]

I used an advance timing light, you can adjust when the light fires. The timing tab goes 10 degrees in either direction, I marked the balancer with white automotive touch up paint. I scribbled over the black timing tab with yellow plumbers crayon (keel) and then whiped it off, it leaves yellow in the numbers and degree marks. It's way easier to see that way. The engine and timing tab is black and yellow works good with black. I checked it with the light after I was done just to see where I was. If you have someone run the boat and you advance it till it pings and then back it off a little, your good :smt001

This is good stuff. One additional tip is to watch your plugs after you get set up and run a while. You might benefit by moving up or down in heat range based on what your read is on the plugs.

White is too hot, black is too cold...tan is just right.:thumbsup: