Clacking/tapping noise due to blown head gasket

[roos]

Hi,

I have a Supra Launch 22 SSV with a 2002 Indmar Marine small block, 350 / 5.7 litre engine. Block-wise the same as a mercruiser.
The engine is a TBI (throttle body injection), is salt water cooled and has about 800 hours on it (first 400 in sea water though).

This saturday I was out wakeboarding and while I was behind the boat after I will down the first/second time and we were getting on plane again my girlfriend pulled off the gas. I heard a strange noise and she obviously did as well.
I got in the boat and there were no strange noise at idle. Put it in gear and everything was fine until we tried getting on plane. Then the clacking / tapping noise began. It seem to follow engine RPM, though we quickly got off the gas. In neutral we can rev her up to 4000 rpm without any strange noise.

I checked my oils on both the v-drive and ZF hurth tranny, and they seemed fine. Might have been on the low side, but still, in the range.
I checked the engine oil which was also a bit on the low side but still on the good side of "minimum". I added some oils to top them off closer to the "max" mark. I tried again, no change. (Thought this might be relevant further on).

I went online and found thread about a guy having a TBI 350 and what sounded like the same issue. An other one chimed in on his thread that had the same issue. Turned out both of them had a blown head gasket between two cylinders and the clacking was believed to be pressure releasing from one cylinder into the other causing the valve to smack open. Both of them changed the head gasket and the result was that the engine was fine afterwards.

I, of course, went down to the boat yesterday with my compression gauge and meassured compression on all cylinders. I removed all spark plugs at once, disconnected the ignition coil and wired an accessory switch to be able to run the starter engine without the ignition on.
I am a little unsure about the cylinder numbers, but since I have a v-drive and the engine is put in backwards I guess the starboard-stern one should be number 1?

In that case I had between 195 and 210 in compression on all cylinders, except 4 and 6 that read 0!!
Yes, zero.

In the other guys threads they seemed to read about 100, but it was unclear if they had in fact removed the number 4 spark plug when measuring compression on number 6.


My conclusion is a blown head gasket between cylinders number 4 and 6.
Repair seems straight forward = replace head gasket, resurface cylinder head if needed etc. (Though I haven't done this before and would greatly appreciate any advice, usually I am able to find the instructions online).

Now to the questions:

A fel pro 17030, would that be a good head gasket for this?
The engine is a vortec engine if that matters.

Should I exchange gaskets on both sides? I sure don't want to fix what isn't broken.

I think I saw a small droplet of water on the number 4 spark plug. Might be condensation, might also have ingested water and that caused the blown head gasket I guess?

Anything else I should look at when I pull the heads?

Do I have to pull the intake manifold to be able to pull the heads? In that case, do I need a new gasket for that as well?

Best regards,
Mike

 

[DeepBlue2010]

Yes, you need to change both head gaskets unless you are positive that the old one has the same thickness as the new one otherwise you will have two different compression ratios on the engine.

Change your oil and see if you have water in it.

Grab the shop manual for your engine, you will need some torque settings and procedures from it. Heads needs to be torqued in certain sequence (as in what bolt to start with and which one is next) you can't just pick one bolt and start with it.

Yes, the intake needs to be removed and you will need a new gasket for it. you can't torque any gasket twice, once it was torqued before, replace it. The gaskets that comes for the intake has some pieces for the front and back of the manifold, trash these and use fat bead of silicon instead. I am not talking about the gasket between the manifold and the heads, I am talking about the ones that go between the manifold and the front/back edge of the engine.


You will need to make sure that rocker arms, push rods, springs, retainers (simply everything) go back to the same exact location they came out of. Make sure you mark everything and your marks will stay put until you done. If you mix them, you will have excessive wear. After you done, you will need to adjust the valves again. Simple procedure you can find on youtube but make sure you understand that the lash is an up and down movement not turning movement. They turn it to make sure it is not stuck but the zero lash happens when it is not moving up and down.