Johnson 225 engine knock

[diamondback]

I have a 96 Johnson 225 that developed a knock after I accidentally over revved it.Other that the knock it runs fine.Any idea what it might be?powerhead,rod,bearing?It had recently had the lower unit replaced also.could something there have come loose?Thanks.

 

[ezeke]

Re: Johnson 225 engine knock

Run a compression test.

If you want, take all of the plugs out and use the eraser end of a pencil to feel the pistons while you turn the flywheel clockwise.

 

[diamondback]

Re: Johnson 225 engine knock

thanks,what would I be feeling for on the piston?Movement that shouldnt be there?Or just the position for the test?Seems like I remember someone saying it should be over 100 and pretty even on all cylinders,but also remember something about the time it takes for leak down of pressure.Is the correct?

 

[tashasdaddy]

Re: Johnson 225 engine knock

you would be feeling for a rough spot or clunk, as the piston moves. it should be a smooth movement, with no play. 100 psi, with in 10 % of each other. remove all plugs, and turn over equal # of times. 4-5.

 

[ezeke]

Re: Johnson 225 engine knock

Movement that should not be there (or lack thereof) or differences between pistons.

Leak down tests are fairly useless and difficult on two stroke engines. The compression test will tell you if the cylinders have adequate compression for combustion and help to find weak cylinders.

2 strokes have ports in both sides of the cylinders, so to do a leak down test you have to have the piston perfectly balanced and held at the top of the stroke.

Screw in compression gauges hold the highest pressure achieved while cranking so that you can compare the readings. A weak hole will show up in a poorer reading.

 

[Benny1963]

Re: Johnson 225 engine knock

is it a knock or cosistant ticking sound . i picked up a ticking sound
tuned out to be rod bearing and collapsed piston skirt
sometimes a knocking noise can be in the lower and sound like its the engine
get a piece of hose and put to your ear helps pinpoint noise
could be flywheel magnet chek for slop in your pistons by putting something hard thru spark plug hole to stop piston and rock flywheel you should not have any play .run a comp check ,if ya have a cyl with low comp pull
that head and look for slop in cyl and scuffing push on piston while holding fly wheel see iff th piston moves ,