MERC 470 HARMONICS

"My 470 has started to make a

"My 470 has started to make a noise, nothing serious I think but wondering if anyone out there has the same issue. Only change to the engine or drive before the noise showed up was a larger (14.5 inch prop 19 pitch vs. the former 14/19).

The engine runs fine, temp stays at around 140 - 145 degrees (even with the 3 inch heat exchanger) and oil pressure is good. After crusiing for a while at around 3600-3800 rpm the engine noise changes, just slightly... makes a little lower pitch sound. The temp and oil etc stay the same and the boat runs fine. Just the noise, or harmonics change... one fellow that I had onboard told me he thought it could be the venturi/fuel icing in the carb?

Still looking for a solution to the hard start when engine is hot problem. The boat is all tuned up and just have to look at it when it is cold and it fires right up, but when hot I have to crank the starter for 8-10 seconds before the engine kicks over. Once running it is fine. I have new plugs, wires, everything all tuned. It is a two barrel carb, would a four barrel halp?"

The "HOT START" issue

The "HOT START" issue could be fuel percolation from the heat of the engine.

Prop noise: prop not balanced; is it a vented prop? yes--put the vent plugs in it and try it again.

"Fuel Iceing in the carb!!! TH

"Fuel Iceing in the carb!!! THAT's GREAT!!!
Thanks for the laugh. I can't see that being an issue unless you are in a piston driven aircraft at 20,000 feet in winter. Or mabey on a boat in Alaska fishin "The Deadlyist Catch".
My 470, as well most others, start the way yours does. The previous owner of my boat put a new ARCO starter with an Big FAT battery and fresh FAT battery cables. No more hot start problems.
ALSO, you have a Fresh Water Cooled engine. Your temps should be 160-180!! The 470 was never known to be a quiet engine. Perhaps if you got it to run at the proper temps it would quiet down.
Chris"

"Richard

Did you know that

"Richard

Did you know that a Uni Student once designed a jet engine as a major engineering project just to chill a beer........ Just thought i would mention that seen icing of fuel in the venturies was mentioned.
Actualy given the right circumstances you can get minor icing in the venturi area of a carburetta but with your engine I can guarantee you it is not a problem.
Engines continually change noises as they expand and contract through operation but if you think that the noise is a harmonics type noise I would suspect an out of balance drive line possibly caused by an unbalanced prop or dicky Uni's or Gimble bearing.
As for your hard starting problem when hot, If all your tune side of the engine is spot on I would bet money that Guy is very close to the mark.
When you turn off your engine it actually gets slightly hotter before it starts to cool and you can get some percolation or boiling of the fuel.
Next time you turn her off when hot, lift your engine cowel while you are stoped and then try to start it as per normal and see what happens, if you can dissipate the heat quicker from the engine area you will eliminate the problem. Simply installing a bigger, higer volume bilge blower to assist in cooling the engine bay may fix your problem.

Cheers
Peter C"

"Thanks for all the comments.

"Thanks for all the comments. The fellow who made the comment about icing in the carb claimed to be a "master mechanic"....

I guess the hot start issue will go away when I drop a V-6 in to replace the 470. Incidentally, I had replaced the original 3 inch heat exchanger with a new 4 inch one about 3 years ago, salt water did a number on it and it started to leak so I picked up a used but pressure tested 3 inch heat exchanger and put it back in. The tem differential was 10 degrees at best. Now the new marine shop I am going to has suggested that the 3 inch heat exchangers only do marginal cooling and I shoulf get a 4 inch one back in there - yet I have not seen the temp go above 150 degrees with the 3 inch!!! Hard to get a straight answer from any shops it seems."

Richard:

I did what Peter s

Richard:

I did what Peter said and installed a 4" I/L blower and went one step further by installing an additional fresh air intake. The original 3" intake goes to the bilge so I opened the closed intake port and attached a 3" flex hose to it and hung it up high so that as the blower pulls air out of the bilge it is also pulling fresh air over the top of the engine which is also used by the intake. The 4" exhaust outlet is very warm and my 4.3L runs quite well. 6" fresh air inlet and 4" outlet not including the intake useage.

my 470 on the garden hose 140

my 470 on the garden hose 140 in the lake 160 3500rpm 180 idle for 5-10 mins. back down to 160 is this normal ????

"To me it sounds about right.

"To me it sounds about right. My 470 runs like this.
160 on the muffs and at idle and no wake speed in the water. On plane in the water, 170 at 3000 rpm. 180 at 3500-4000 rpm. Temp will immediately go down to 160-170 when I throttle back. This is with water temp at 75 degrees and a 3 inch heat exchanger and a new impeller in the drive.
Your cool down at idle may be a bit long, how old is your impeller in the drive? When was the last time it was changed?
Chris"