thebigtman

I'm hoping someone can lend me some advice....here's what happened.

Well, what a bad weekend. After repairing my engine hatch cover, putting in a new stereo and speakers and replacing the distributor cap and rotor and checking the plugs, I dropped in the water, fired it up and CLACK, CLACK, CLACK, CLACK. After trying to mess around and see what it could be, I determined that its an internal problem. I had started the engine the previous day after the work was done to make sure there were no problems. There was NO noise then...how could I have something wrong between trailering it there and firing it up the day before????

I couldn't mess around with it until Sunday since I was in Houston for the Texans' game. I pulled the valve covers and tightened all of the rockers (comp cams roller tip rockers) since they were out of adjustment. I also changed the plugs and rechecked the cap and rotor. The previous owner had a different set of plugs (Champion rv15yc4) installed compared to what I have in there now (NGK br6fs). The NGK's are what the local dealer told me to install. In fact, the Champions are about .25" longer than the NGK's. No change. The funny thing is that I pulled #6 plug and the tip looked crushed slightly (it still had a little gap but it was closer). The others were at the correct gap. A few of the plugs were a little loose when I checked them but other than that, they were ok and the boat ran fine with them.
Now I'm stuck. The engine has 40 hours on a complete rebuild and it doesn't sound like a rod knock. I couldn't see any metal shards in the oil or laying in the rocker arm area. Could this be a gimble bearing or something like that? I tried cranking over the engine and I can't duplicate the sound. It only does it when the engine fires up. The valvetrain is tight but the noise sounds very similar to a loose rockers except it's much louder. I can't isolate what side the noise is coming from.
Help! Can anyone lend some wise advice?

Stuck on land in San Antonio...

Tim

thebigtman

BTW, it's a 1990, 454 with Thunderbolt Ignition. It has about 40 hours on a complete rebuilt. The engine ran fine up until this problem. I noticed that I also have some slop in the steering, which was there before. I recently greased the fittings on the outdrive (top and bottom)too. I don't know if any of this helps but I thought it can't hurt to give you more info.
I'm going to do a compression test this week. My gut is telling me it's not the engine though.

Tim

z.zuperboat

If The Plug Was Bent You Must Have Hit It With The Piston.first Try Accounting For All Of Your Tools.if All Accounted For Try Indexing The Spark Plugs.i Use To Have To Do This With Dome Pistons.some Times It Takes 2 Boxes Of Plugs To Get It Right.you Took The Plugs Out And Reinstalled Now The Noise.thats My Guess.

HeavyChevSS

How loud is the noise and how "fast" is it, does it change with engine rpm?? Did you put the same plugs back in or another set. Try pouring some oil down the carb throat to see if it goes away or quiets down. Just trying to remember the steps my mechanic went through when I had a clack noise, wished it was an AFLAC commercial with the stupid duck..
Good Luck

thebigtman

It does change with engine rpm. The engine has the NGK's in it now, but it did have the Champions. I should clarify that the #6 plug wasn't "crushed" but the gap was closed up a little. It should've been at .035 but it was closed up to about .020. I suppose the previous owner could've goofed on the plug gap on that one, but it seemed suspicious to me. The NGK's are a bit shorter and the engine still starts fine.
I can't get the noise to happen when I'm cranking the engine, even when the plugs are out so the engine can turn faster. It will only do it once the engine fires up and runs.
You can't hear the noise outside of the boat, only when you're inside it.
Could it be something with the drive (gimble)? My damn exhaust is so loud that it's hard to tell exactly where the noise is coming from. I'm going to pull the intake tonight and inspect the valley.

rchevelle71

iTrader: (1)

Internal exhaust flappers???????

blackhawk

rchevelle71, that's the first thing I though of but he didn't mention changing his exhaust tips. I replaced my stock tips with some stainless marine tips with internal flaps over the winter. The first time I started it up in the spring I thought a rod was going to fly out the side of the motor. Turned out it was just the stainless flaps making noise at idle. SCARY!

HiPerf2000

iTrader: (2)

Internal exhaust flappers???????

DING DING DING !!!!!!! I think we got a Winner!!!!

thebigtman

My tips are stock with the external rubber flaps. I took a flashlight and looked inside but I couldn't see a thing. Are they up further and if so, how can I check them?
God, I hope that's all it is.

rchevelle71

iTrader: (1)

Stock Like Corsa Bell shaped tips???

If they are, thats not it, no flappers in dem!!!

Does it have a Y pipe, or just straight thru-hull??

Could it be the ones in the y???