overheated and now makes rattling sound?

[conron]

I have a 1986 Starline 16" with a merc120 and alpha one. It overheated on me and I did not notice until it was making this rattling noise. Shut it down and got a tow to the dock but I guess it was too late. I went back to the lake to check it out after changing the water pump and the noise was still there and the power is greatly diminished, more than half I would say. So my question is what do I need to start checking to find this problem. I am new enough to boating that I still dont know much about marine engines. Thanks

 

[conron]

Re: overheated and now makes rattling sound?

forgot to mention that I can't hear the noise when idling or at home on the muffs

 

[conron]

Re: overheated and now makes rattling sound?

could exhaust shutters do this

 

[Ky Baja Blast]

Re: overheated and now makes rattling sound?

First thing you need to do is check the compression and post results it may not be that much wrong

 

[conron]

Re: overheated and now makes rattling sound?

First thing you need to do is check the compression and post results it may not be that much wrong

bad news
cyl 1) 120
cyl 2) 115
cly 3) 50
cyl 4) 50

Looks like a rebuild?

 

[dubs283]

Re: overheated and now makes rattling sound?

Looks like a rebuild?

not necessarily

might just need a head gasket (cheap end) or...

burnt valve(s) (more expensive), or...

cracked head (even more expensive)

 

[conron]

Re: overheated and now makes rattling sound?

so whats the first thing I should do to determine course of action?

 

[dubs283]

Re: overheated and now makes rattling sound?

well, you know that you have low compression on at least two cylinders, and the first step in determining what is causing that low compression is to pull the head and look for:

blown head gasket, burnt valve(s), cracked head, etc...

 

[wire2]

Re: overheated and now makes rattling sound?

An overheated head will typically take a cupped shape; the hottest areas in the middle will distort up. In your case, it's lifted between 3-4 and allowed the gasket to fail. Pull the head, take it to an engine machine shop to check. They can take a few thou off to true it, a new gasket and you're good again. (been there, done that).

 

[Bondo]

Re: overheated and now makes rattling sound?

so whats the first thing I should do to determine course of action?

Ayuh,... Yank the drive, then the Motor...

It's easier to work on, on the bench, than in the boat...

My guess is, yer lookin' at a new/ rebuilt Long Block...

 

[conron]

Re: overheated and now makes rattling sound?

I was going to pull the head this afternoon to check it and the valves but the rain got to me first...I will post my findings as soon as I do. Thanks for the post

 

[Pete104]

Re: overheated and now makes rattling sound?

If you can hear it, it blew towards the intake/exhaust manifold. I go with Bond-o, it's over!
To bad too, those engines cost as much as V-6.

 

[conron]

Re: overheated and now makes rattling sound?

so is it a waste of my time to pull the head....

 

[PuddleJumper]

Re: overheated and now makes rattling sound?

Since it's a 25 yo boat, Go ahead and pull the head. If it's just a gasket or maybe a valve job you are in the hundreds rather than the thousands to keep boating.

 

[conron]

Re: overheated and now makes rattling sound?

looks like a simple blown gasket....is there anything else I should look at or "do while I'm in here"? Looks cut and dry

 

[Pete104]

Re: overheated and now makes rattling sound?

Make sure the block didn't get burned away between the cylinders or where it blew thru at.
If run long enough with blown gasket, cast iron will burn away!

 

[conron]

Re: overheated and now makes rattling sound?

it looks a little burned...how will I know if it burned away?

 

[Pete104]

Re: overheated and now makes rattling sound?

If you feel a "low spot" or divet with your finger, that's not good. Probably be best have someone locally look at it. What you see vs. what someone knows is a big difference. The people that are doing the valve job would know. Ask'm.

 

[Rhadley]

Re: overheated and now makes rattling sound?

I have the same engine and have also had it overheat. It got so hot it melted the Mercruiser sticker, but did not cause any damage. It did, however, melt the shutter rubber and cause the metal part to fall down towards the water/exhaust exit and it rattles when I hit bumps while trailering it.