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NEED HELP WITH MREC 470 ENGINE NOISE

intrepid

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"I have been having trouble wi

"I have been having trouble with a mysterious noise coming from my enigne - similar to another post here - but I want to include more info in the hopes that someone else has had the same problem. A couple of marine mechanics are scratching their heads over this one!

I have a 1981 Hourston Glascraft with a Mrecruiser 470. I assume original engine the same vintage. About a year ago, the engine started making an intermittent sound at rpm's above 3200. The sound, to me, as like a knife edge or chisel being lightly touched to a grindstone - a tinny, mettalic "zzzzZZZTTT" sound that would appear for a second or two then disappear. Sometimes there would be a short interval in between sounds (7-8 seconds), sometimes minutes, and sometimes I would not hear the sound for an hour or more. In general, the sound would disappear if I throttled back to 3200 rpm, although recently when the boat was heavily loaded the sound appeared at 3000 rpms.

Took the boat into the shop and they checked everything external to the engine and could find nothing. First suspicion was a loose piece of magnet flying around in the stator, and the list went on from there. I suggested maybe flapper valve and was told that was new. Eventually the shop stated the problem had to be internal and that the engine needed rebuilding (it had been rebuilt only 380 hrs previously). So, the engine was rebuilt, and $6000+ later the sound is still there. Then the suspicion was faulty timing and the distributor checked and adjusted - no joy.

Does anyone have any ideas???"
 
"Engine was just out of the bo

"Engine was just out of the boat last week and all measurements etc up to spec. This was due to a blown head gasket 50 hours after latest rebuild (under warranty thank god). I didn't include this information with the original post as I thought it wasn't relevant, but perhpas it it. The shop had the head planed, new gasket, piston rings and bearings installed, and the noise is still there. Wondering now if maybe backwash got into the engine from the exhaust flapper/shutter and caused the head gasket to go??? Is this possible???"
 
"if the power plant was recent

"if the power plant was recently rebuilt, i would suspect a spun bearing even more. Nothing you did likely caused it. If its under warranty... let em tear it down."
 
In essence the engine has been

In essence the engine has been rebuilt twice since last November.. with new bearings both times!
 
"Richard.
I don't think


"Richard.
I don't think so on the flapper. It would have hydro locked the cylinder first depending on what point the stroke was at when the water was allowed in.
So the engine was rebuilt and the noise has not gone away.
Now they must have removed the crank balancer which also has the magnets for the stator inside it and would have seen any damage at that point.
That engine has a inertia drive starter.
The starter does not have a power asist system like most starters to hold the starter drive into the flywheel. The drive is thrown forward when the starter motor begins to spin.
A very simple explanation,there really is more to it than that.
These starters will make some strange noises at times if they have a problem.

But this is about the only thing left that could make that noise that I can think of.
Of course I'm assuming there is nothing else hitting the flywheel.
If this is the case I have no idea of how it could have been missed when the engine was removed.
But check that the starter drive is not loose/weak return spring and hitting the flywheel.
If the spring is weak for the drive return and the stern is down the starter drive could move towards the flywheel.
I doubt it would engage but it may bounce aruond some. Other than that I'd look for a bad bearing.

Hope you find the cause."
 
Richard.
Let me ad by looking


Richard.
Let me ad by looking for a bad bearing I mean other than internal engine bearings.
 
"Thanks for that input. I had

"Thanks for that input. I had a nagging thought that the starter could be the cause as there isnt a lot left that it could be, and I had heard that the 470's were notorious for being hard on starters... We should know soon enough"
 
"I have the same problem, the

"I have the same problem, the starter hits slightly ever since I had it rebuilt. Has a noise now and then at lower rpms. Plan on yanking it out and adjusting it just a small amt"
 
I also posted that my 470 was

I also posted that my 470 was making noise at high rpm's.I pulled the distributor and rotated it about half a turn.re-set the timing and is running great with no more noise.Give it a try.
 
"We had the distributor out an

"We had the distributor out and checked, put back in and timing set while boat at idle and at higher rpms. The timing did seem to be advancing too far at higher rpms, but was adjusted and everything cinched down tight. Noise did not appear on test run but on next trip was back!"
 
"Richard.
You say the noise w


"Richard.
You say the noise was gone on a test run but then returned on the next trip.
Was the air temp higher on the second trip?
My last thought on this is calibration.
Are you burning a high enough octane fuel and are the main jets the correct size?
Is the noise any different when it is cool out than when it is hot?
Just a thought but try setting the timing back a little and see if there is any change.
If not,reset the timing and then have someone close the choke a little when the noise is there and see if there is a change in the sound.
Last,did you check the distributor for any problems? (bushings,screw dropped in it etc).
Have you tried running it without the belt?
This is a good one I must say."
 
"AIr temp was about the same a

"AIr temp was about the same as far as I know. Fuel is marked marine gas, a mid-grade fuel. Noise seems to be the same regardless of outside temperature. Almost exclusively appears once the rpms go above 3200, but last week they were there at 3000 rpm when the boat was heavily loaded. The noises stayed right up through 3800 rpms. Lots of experimentation with timing and the distributor was taken out, tested, and weights adjusted etc. so that isn't the problem.

What belt are you talking about? I'm suspicious of the starter, so maybe the way to check that is to start the engine, drop the starter and then go for a run and see if the noise is there...?"
 
"The belt I,m asking about wou

"The belt I,m asking about would drive any accessories like power steering. If there is no belt on the front of the engine this is not a concern. My reason for asking was to make sure anything driven by a belt was not making the noise.
Have you tried a better grade of fuel?
That is a high compression engine and requires hi octane fuel.
Are you sure that you are not hearing pinging from low octane fuel?
The way it makes the noise more under load kind of sounds like this may be part of the problem."
 
There are some postings on thi

There are some postings on this site about the distributor not being installed in the proper position. There have been 2 that say a strange noise in the engine went away after rotating the distributor and reinstalling it.
 
"You can tell if the starter d

"You can tell if the starter drive is contacting the ring gear by pulling it out and inspecting it. It is possible that, at that magic rpm, the bendix rattles about enough to scrap onthe ring gear.

On pulling the distributor, then putting it in in a different rotation... Long as the timing is set right in both places it won't make any difference at all.

Jeff"
 
"Thanks to all who offered sug

"Thanks to all who offered suggestions. I had the shop swap out the starter, and ran the boat for the past couple of days - about 6 hours... at all rpm ranges from 3000 up to 3800. Not a peep. Maybe too early to say for sure, but the engine noise seems to have disappeared based on the noise appearing on almost every trip!!!"
 
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