Engine Knock...confirm my worst fear

[1bigdadeo]

My Johnson 175 started a slight knock at 4000 rpms but would go away at 4500 or 5000. No knock at low speeds. Engine still runs strong. Getting oil for sure and the water pump is still pumping. I think it's a valve knock. Sound right to anyone out there. Time for a re-build?????

 

[Will Bark]

Re: Engine Knock...confirm my worst fear

What year of engine, Model number, 2 stroke or 4 stroke, if 2 stroke there are no valves in it. Need more info for someone to be able to help you.

 

[SigSaurP229]

Re: Engine Knock...confirm my worst fear

if its a two stroke it may be a piston ring.

 

[Jayrock]

Re: Engine Knock...confirm my worst fear

Do a compression test. Run it as little as possible until you find out for certain what the problem is. Report the results of the test...

 

[dehydrated]

Re: Engine Knock...confirm my worst fear

timing could be advanced worst yet piston slap need more information

 

[boobie]

Re: Engine Knock...confirm my worst fear

Does this knock appear if you back off on the throttle ?

 

[emdsapmgr]

Re: Engine Knock...confirm my worst fear

Before you condemn the powerhead, make sure it is not a problem in the lower unit. Strange noises can transfer through the engine, and may sound like it's the powerhead when it could be lower unit-related instead.

 

[Joe Reeves]

Re: Engine Knock...confirm my worst fear

Your engine (2 stroke) does not have valves. Do the following check.

(Piston Play Check)
(J. Reeves)

This procedure will tell you if there is any wear or play in the Wrist Pin, Wrist Pin Bearing, or Connecting Rod to Crankshaft area.

Remove the spark plugs. Insert a screwdriver, dowel, punch, or some object of your choice through the s/plug hole and into the cylinder/piston area. Hold the tool lightly against the top of the piston. Turn the flywheel by hand, bringing the piston up to top dead center, then continue turning the flywheel to pull the piston down about a inch..... all the while holding the tool lightly against the piston top.

Now, at the point whereas the piston has been dropped down about a inch, grab the flywheel and hold it firmly. Now, push that tool solidly and firmly against the piston top.

If the piston moves without moving the flywheel, there is a problem (wear, play, clearance, etc) somewhere with the items mention in the first sentence. Be sure to check all of the pistons/cylinders.