8.1 Horizon knocking sound

[Pilot]

Been doing this past couple years when I initially start them. They will knock for 20-30 seconds, then settle down and run fine. Is this normal?

 

[scoflaw]

No

 

[sbw1]

Definitely not normal.

 

[scoflaw]

Define knock

 

[jmcdboater]

Initially start them each season? Or initial start after a day. Week, month, of down time?

 

[Strecker25]

Initially start them each season? Or initial start after a day. Week, month, of down time?

you’ll find countless threads on how the 8.1’s eat plugs and are very sensitive to old wires. The type of knock is the first thing to understand but it could simply need a tuneup

 

[scoflaw]

you’ll find countless threads on how the 8.1’s eat plugs and are very sensitive to old wires. The type of knock is the first thing to understand but it could simply need a tuneup

So what's the source of the knock and why does it only last for 10 to 20 seconds?

 

[Strecker25]

So what's the source of the knock and why does it only last for 10 to 20 seconds?

I don’t know, we don’t know what knock he’s talking about yet because he didn’t share a video

 

[ttmott]

tick, knock?
Lifter

 

[Bill Curtis]

Without a video, we can only guess, since every mention of a certain noise depends on the story teller.
Tick, rattle, click, knock, thud, bang, klunk are all pretty vague, but to the experienced ear, all are pretty specific.

What I look at first (after eliminating low / old oil as a cause) YMMV
Ticking = Bad lifter / roller rocker arm, exhaust manifold / gasket leak or spark plug wire leaking to ground.
Knock (single knock) = piston slap from a worn piston (usually worse on cold start and goes away shortly after piston heats up and expands), connecting rod bearing, crank bearing, clutch / flex plate related or in an 8.1, may be spark related.
Knock (double knock) = Piston wrist pin

 

[sejensen737]

Do yourself a favor and start with replacing the sparkplugs with correct AC plug. Especially if they have not been changed in the last 3 or 4 years. You could save yourself a lot of grief...

 

[dpvandy01]

change plugs and wires. If that doesn't clear it consider ignition coil packs. also check your tanks for water

 

[Pilot]

change plugs and wires. If that doesn't clear it consider ignition coil packs. also check your tanks for water

Thanks I will replace wires. Plugs were done @100 hours ago w/platinum AC 's.
The knock seems to be sporadic and short lived, always just during start up and first 30 seconds. Another thing I might do is dose the engine with a Seafoam cocktail directly into fuel lines. That should help clean and lubricate lifters.

 

[scoflaw]

How would Seafoam get from the fuel system to the oil system?

 

[Jacks-N-Rays]

I was told to never put Seafoam in anything that might see ethanol or had the grey mercruiser fuel lines, it eats the fuel line liners. Just FYI. Use Staybill.

 

[Thornton69]

Is it possible you do not have the correct oil filters installed? Honestly not familiar with your engine, but many of the gm engines use a filter with a check valve in them to prevent the oil in the filter and galleries from draining when shut off for extended periods. If you look through the outer ring of holes in the top of the filter, you should see a rubber washer if it has it. Just a thought.

 

[jmauld]

How would Seafoam get from the fuel system to the oil system?

It can work its way through the rings. But that’s not likely. First it would have to sit in the cylinders. Back when I was racing, some people used to pull the plugs and pour some in the cylinders.

 

[scoflaw]

Well if your trying to quiet noisy lifters do you think this is this correct procedure?

 

[jmauld]

I don’t really know the design of the 8.1. Do they use hydraulic lifters? If so, low oil pressure or carbon buildup on the lifters could cause lifter tick.

Pouring the sea foam in the oil as a cleaner also was a common practice.

 

[scoflaw]

Yes to all that