Engine Tapping

[brodie123]

Hi Everyone;

I rebuilt my Mercruiser 205 inline 4 - 165 hp inboard a year ago and she ran beautifully. (Dual engine in a 30 ft cabin cruiser)

That is until a line fell off the stern and wrapped the prop - luckily at low speed.

After that though, the dreaded "tap tap tap" noise.

I pulled the plug on cylinder 4 and the noise went away. The other 3 had no effect.

I pulled the engine and the rockers, lifters and rods all look fine.

I could not find any play on any piston - tapping lightly with a small mallet.

I removed the piston caps for cylinder 1-3 and all looked fine.

I removed the piston cap for cylinder 4 and the bearings 'popped' out rather than staying seated. Ooops, I forgot to check the torque on the piston cap bolts prior to removing to see if they stretched.

There is 'no' damage that I can find at all - not even a scrape.

I am assuming that the piston bolts stretched? Should I be looking for anything else?

When I re-assemble, new bearings is obvious. But what about the rod bolts? Do I replace?

Any guidance here is appreciated - I don't want to put it back in and hear tap tap tap. lol

thx!!!!

 

[kmarine]

I would replace them while everything is appart. This way you don't have to worry about it.

 

[flipbro]

You could try new rod bolts. New bearing and some plastgauge to cheak bearing clearances. I personally would check the rod big end for roundness as well. Especially after new rod bolts are installed.

 

[Scott Danforth]

I would get new rod bolts.

 

[Bondo]

Ayuh,..... Does the 470 use pressed pin pistons,..??

I'd bring that rod to a machine shop, 'n have it checked, 'n resized,....

 

[Mercruiser420]

Pressed pin pistons..possibly bent connecting rod.

 

[Scott Danforth]

collapsed piston would also cause a tick. what ever you find, you also need to find the cause. Did the motor ever overheat?

 

[FreeBeeTony]

collapsed piston would also cause a tick. what ever you find, you also need to find the cause. Did the motor ever overheat?

Did you mean lifter?

 

[Scott Danforth]

no, collapsed piston from overheat - skirt collapses and piston rocks in bore. Very common piston failure. collapsed lifter is another type of tick - usually due to dirty oil.

 

[FreeBeeTony]

no, collapsed piston from overheat - skirt collapses and piston rocks in bore. Very common piston failure.

​Interesting, never heard of that...........learned something new today........thanks!

 

[brodie123]

Thanks everyone, that's all good advice.