92nsx

1994 model 502 Mag EFI. Aprox 610 - 650 hrs total. I haven't scanned the computer yet due to being pissed, could be lower...
87 hrs on new rebuilt top end due to blowen head gaskets 2 seasons ago.

Always had a very slight valve tick, or tick.

Running accross the lake to head home for the day, ran fine, all gauges reading fine. Middle of the run there was a "hickup" or what felt like I hit the rev limiter, but I was right at 4900-5000 rpms according to a uncalibrated tach. Didnt think nothing of it. Didnt loose any speed, engine sounded fine. Hitting on all 8 cyls.

I open the hatch to let some hot air escape idling in, and Very LOUD knock, knock, knock, knock, WTF! Oil pressure was 30 psi at idle, reved fine form 800-1500 rpms. Didnt try any highter, just wanted to get back to dock.

I enlisted the neighbor kid to help pull the manifolds and remove the valve covers, hopefully it is in the valve train... No luck, rockers, push rods, springs, ect look perfect. Plugs look ok for 2 year old normal coppers. So the engine is coming out,

Start guessing as to what broke or let loose.

Budman II

iTrader: (1)

Sounds like a connecting rod - sorry to hear about your luck. The timing really sucks. Hopefully you can get it out in a hurry and the shops around you aren't too busy. Good luck with it.

Try running it on the muffs and systematically pulling plug wires and see if the knock quiets down. That will at least isolate the problem cylinder. A length of hose held to your ear and the oil pan can help isolate it. Also, pull the filter and have a local shop cut it open for you. That will tell the tale if it is a bearing.

On another note - sure wish that neighbor kid of yours lived on my street! I would love to have a little grease monkey like that to send down into the tight confines of my bilge! I'm getting too big, fat and old to contort myself into yoga-like positions to get in there.

mike tkach

iTrader: (3)

without hearing the noise it is just that,a guessing game.i have seen engines with spun bearings carry decent oil pressure so that really does not tell much.i would do some investigating before removing the engine,it could be something simple.

Unlimited jd

iTrader: (5)

Did you check if noise changed turning the wheel? Could be as simple as a gimbal bearing

SB

iTrader: (1)

If the sounds is from the top end could be a broken valvespring. I've run into many on boats and cars where the break wasn't noticeable until the lock/retainer was taken off, and then notice the several pieces.

I've run into that on 502MPI's and also once a lifter lost it's retaining ring/clip that holds the innards to the lifter. Suprisingly, the innards stayed in the lifter. And the clip was sitting in the lifter valley.

92nsx

I really dont want to restart the engine since it could cause more damage???!!? . Anything lower then the valves the motor has to come out anyways. Anything that is "normal" that goes out on the bottom end of BBC's? wrist pin, broken skirt, rod bearing?

Or a maybe a Collapsed lifter ? Any way to test that? or Pull intake, and pull the heads?

The slight tick I had before sounded like a valve or lifter tick before The KNOCK KNOCK i have now.

Now I dont know BBC's, however I know my Supra engines(7m's) and snowmobile engines. This knock resembles when I burn down a piston and 1/4 of it is missing. Piston slapping the F away. But this is BBC and plugs looked fine, and this is a knock, not a thud, thud.

I have a compleat spare 502 mag efi, but it has been sitting for 5 years since it ran last. So I want to clean it up some and go threw it before I run it.

Yes I moved the wheel docking the boat (single engine ), same noise, not gimble bearing.

Full Force

iTrader: (5)

A sid "knock" is more often a spun bearing and the rod beating crank, but like Mike T said it could be many things.

Heads been done before? Could be non inconel and exhaust valve broke and beat things up, but that pretty much always messes a plug up, I broke one it was a clean break went right out exh without barely damaging anything...

4bus

iTrader: (4)

First, carefully cut the oil filter open and hang the paper on a line to drip dry and inspect for metal. I will look like the chest of a stripper in the light if you have lost a bearing. If nothing go to valve train. It can get messy, but usually not too bad at idle to run engine with valve covers off and inspect valve train.

Every boater should own one of these http://www.amazon.com/Lisle-52500-Me.../dp/B0002SQYSM

I have heard drive issues, u joints, exhaust flappers, and even a fly wheel bolt coming out all sound like a knocking engine. At this point I don't think you are going to do much more damage running it at idle.

Black Baja

iTrader: (2)

Plug to the right of the top left has some slight peppering on it. I'm gonna guess broken piston. Do a compression test on that (better yet all) cylinders. And or hammered Rod/main bearing.

mike tkach

iTrader: (3)

i knew if anyone could diagnose the problem by looking at the plugs it would be you,lol.