Hello and help please: 90hp 1989 Mariner knocking.

[solyd]

Hi all!

New to the forum and to boats.

Recently purchased a defective 1989 90hp, 3cyl 2stroke engine that knocks at higher RPM. At idle and low RPMs it does not knock but once the throttle is opened, the banging is very obvious and loud. It sounds as either a piston is hitting the head, a connecting rod bearing might be kaputt or probably the lower crankshaft ball bearing may need replacement. The upper roller bearing was changed but the problem remains.

The engine has not run in it's current state for longer than a few minutes.

I've rebuilt a number of motors in the past but never worked on a marine outboard and would need some input from the experts.

What should I start looking for, how to troubleshoot and what should I expect based on the description above? I want to know what to expect before I get into something I can't finish or costs too much for what it's worth. Want to take this thing on the water this summer and summer is really short around here...

Thank you all in advance!

 

[solyd]

Re: Hello and help please: 90hp 1989 Mariner knocking.

wow, nobody with info?

I know it's not a specific question I'm asking. Maybe I should re-formulate:

- is there a way to diagnose the problem without taking the entire powerhead apart?
- what's the best/worst case scenario in terms of damage?
- how high of a repair bill would I be looking at if
1 ---- done by myself
2 ---- sent to a shop


Any input greatly appreciated.

 

[Ram57]

Re: Hello and help please: 90hp 1989 Mariner knocking.

How is the compression in the cyclinders? You can take the plugs out to see how much rod end play you have in the pistons by pressing down on them with something on there downward stroke through the plug holes.

 

[solyd]

Re: Hello and help please: 90hp 1989 Mariner knocking.

Thank you Ram57.

I only checked the compression on cylinder #2 (center) but I don't think it's an accurate test as I didn't want to run the engine in its current state long enough for it to get up to operating temp. The reading I have on cyl2 is 112psi.

As for the 'push-the-piston-through-the-plug-hole' test, I must say it's a great idea. Something I didn't think of. I'll do it later tonight. So, I guess that if only one piston/rod has some play while the others don't, I know it's a rod bearing. If all 3 have play, it's the crankshaft bearing. Correct? Whichever it is, what are the chances that the crankshaft got damaged?

Thans for the reply, anything else I should check for?