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OMC 30 knocking

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alleykat

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"Okay A buddy bought this boat

"Okay A buddy bought this boat 2 summers ago and it had seized up. So he took it to the oldest and most trusted machine shop in town and had it rebuilt from the bottom to the top. On the maiden voyage it spun a main and KNOCKED it's way back to the dock and was trailered directly back to the same shop. EVERYTHING was in pristine condition except the bearing. The shop owner not wanting to see this vessel ever again (as this time the labor was on his wallet) ordered another rebuild kit and gave it another top to bottom rebuild. I've been on the boat the 3-4 times it's been out since the second rebuild and it's ran like a top. It only has 11.5 hours on the rebuild. Fast forward to this year, my buddy bought a bigger boat and offered me a deal I couldnt pass up. I got the boat home, hooked up the muff's and within 2 minutes it overheated. The impeller and impeller housing were melted beyond recognition. He winterized it without the muff's.
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As soon as temp reached two hundred I shut it down and went to my local shop for the impeller. Installed the new pump housing and prop, fired it up and it never ran over 100 degree's. (no thermostat) On to the new problem, I have discovered an intermittent knock that doesnt happen at higher rpm's but does at idle through 1500. I know he tinkered with the timing without owning a manual and I am not really sure what spark knock sound's like to positively id it. It does sound like it's coming from the block and not the head though. Any Idea's?"
 
step 1: compression test the e

step 1: compression test the engine.


how long has it been running without a t-stat?

Have you ever greased your gimbal brg. or u-joints?

might as well grab a timing light and set the timing before you damage the engine not knowing where it's been tinkered to.
 
"I'm going to get the ligh

"I'm going to get the light sometime this weekend, The outdrive has been serviced very recently, and it's a motor knock coming from down below. It changes tones and frequency at the same rpm and the engine does have a substantial miss. The timing is set at 3 degrees after TDC. Does anyone know the specs on timing for this motor? The previous owner's "neighborhood mechanic" set the timing so the engine would idle. He said it wouldnt fire set anywhere else."
 
is the oil pressure lower at i

is the oil pressure lower at idle? does it happen when warm ? could be the melted exhaust flappers but they would be more like a tink or tick (more like a lifter-light metal knock)
 
The oil pressure is lower at i

The oil pressure is lower at idle by a few pounds. I thought maybe there wasnt enough exhaust back pressure to seat the valves properly. It is definately not a valve sound though it's more metal on metal. I checked with a home made stethascope (garden hose) to locate the origin and it seems to be where the head meets the block.
 
I can actually feel the knock

I can actually feel the knock if I place my hand on the timing cover. I know that the cam could hit the cover if it was loose but that doesnt make sense does it?
 
"Chris, on the inline engines,

"Chris, on the inline engines, 4 & 6 cyls the cam is held in place by a retainer and 2 bolts, it is very unlikely but not impossible. Could be water pump bearings, with the engine off see if you can wiggle the water pump pulley. unfortuneately not much else will knock except for rod bearings and piston wrist pins but they are lighter in sound than a bearing knock but heavier than a loose lifter/rocker and would have a quick double knock. I guess the engine builder didn't check the bearin clearances before assembly? remove the engine, drop the pan and tap the connecting rod end caps "lightly" with a hammer, the hollow sounding one is the loose one."
 
ps if they didn't clear ou

ps if they didn't clear out all of the oil passages including the oil pump some left over pieces probably found it's way to another rod bearing. Or it's a bearing to journal clearance issue. - good luck
 
"Thanks Brian. I spoke with th

"Thanks Brian. I spoke with the guy I purchased the boat from, and he is just as miffed that this is happening AGAIN as I am. I know that there is a cam "retainer" plate that I will surely mention when I return the whole package back to the machine shop. The warranty on the rebuild is a verbal contract and were trying hard not to break it. The builder has no idea it's been sold if you catch my drift. My train of thought is it's only been about 12 months and less than 20 hrs run time since the second rebuild, roughly the same as last time. So purchaser and seller alike are hoping to see this "warranty" take care of the issue. (especially the purchasers wife) This is an auto shop so maybe they arent thinking max potential and I'll be sure to mention the plate and the water pump.

Can anyone else think of anything else I should mention when I drop it off at the shop?

I was also wondering about direct bolt in replacement, what else would bolt up to the bell housing and wouldnt be too much of a pain exhaust and gear ratio wise to just purchase maybe a vortec V-6?"
 
"a 4.3L V6 175-210hp will fit,

"a 4.3L V6 175-210hp will fit, but then you need a Y-pipe, and a bigger prop. I've used a inline 6 which was supposed to have a 1.65r drive, I used a 1.98 drive from a 4cyl with no problems with a bigger prop 23p, I did some calcs and that's about what matched up with a 1.65r and a 19p, so a 4.3L v6 uses a 1.80r with a 19, drop a 21p on and you'll still have tons of out-of-the-hole power. good luck."
 
"oh, the engine mounts on a V6

"oh, the engine mounts on a V6 & V8 are in a different place than the inline 3.0L"
 
"Yeah I thought about the moto

"Yeah I thought about the motor mounts as well, this vessel has what I'm assuming are 4x4's wrapped in fiberglass in the bilge for mounting motor mounts so I'm guessing the possibility's are endless. If I'm understanding you correctly anything chevrolet with a flywheel that matches will be an easy enough fit with a little pitch tweaking as to not stress the outdrive."
 
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