[pogo1000]

Have a 4 cylinder, 3.0 liter Mercruiser I/O that is making a "knocking" or "pinging" noise when put under a load. It idles fine and doesn't make this noise until I get the rpms up above 2000 when trying to get on plane. Anybody have any ideas as to what it may be? Valves or lifters? Thanks.

 

[3bees]

out of time

 

[pogo1000]

Thanks 3bees, I will check the timing this afternoon. I hope that is the problem!

This was the first trip of the year for me and I didn't adjust/move the distributor from last year's setting.

 

[country_bunkin]

I had a similar problem with mine two years ago. When the mechanic looked at it I believe that one of the cylinders(Not sure though) was bad. Final diagnosis was to get a new top end. Hope yours is not that bad.

 

[pogo1000]

Hey country, by top end you meant the head, right? How do I diagnose that? What about trying to adjust the valves?

 

[Bob H.]

Pogo - a deep toned knocking is lower end (crank) and tinny noise is upper end (valves). I'm not familiar with that engine but it probably has hydraulic lifters, no adjusting, check oil level. Occassionally the lifters go bad and won't pump up, making a racket. Timing shouldn't change unless the cam sprocket is worn, timing chain is stretched, or distributor is worn. Check the timing since it's easy to do. If the noise is pinging it's probably just a case of bad fuel. Dump some octane booster in the fuel tank until there's room to add some good fuel.

 

[country_bunkin]

Pogo I just had the mechanic look at it. I changed the plugs checked the distributor cleaning the carbon build up off of it and that was all I did. When neither of those fixed the issue I figured it would be eaiser and quicker to get a professional to look at it.

 

[tony james]

I have an '89' 3.7 Mercruiser. My pinging is noticed at idle. My mechanic told me to check the stator located at the front middle of the bloch where the front pullie is located. After someone converted to an alternator, he thinks maybe something was left in and is now coming loose.

 

[billfish]

Tony,
I have 2, 3.7 engines. Pinging on that engine could be timing, or bad fuel. The 3.7 engine has a very high compression. It was made to run on 89 octain fuel. Many machanics and engine rebuilders will set the timing 2 or 3 degrees lower to make the engine last longer and prevent pinging. Do pull and check the risers and gaskets every 2 years. The riser and head gasket problems have killed many of our engines. If you need any advice on this engine I have been through alot with mine!!
Billfish[sad]

 

[tony james]

Thanks for the advice on my engine, Billfish. After logging-off, I thought I should have mentioned the timing when I responded to Pogo1000's question.

 

[pogo1000]

Got it fixed! I checked my dwell and timing and found out that both were off. At first I noticed my dwell reading was high and erratic. Upon checking my timing, I couldn't even read it! I loosened the distributor and adjusted it. Seems to run fine now. I am just wondering how my timing got that far off??

Anyways, thanks guys!

 

[Bob H.]

Time to check the crank & cam sprockets and the distributor gear. The Dist is probably the easiest to get to. Make sure you marke the rotor position before pulling it out. Check the shaft for bad bearings (shaft shouldn't wobble) while you have it out. Dist gears are easy to replace. The problem won't fix itself and it's not something that can be repaired while away from the dock.

 

[billfish]

Something to watch out for on a 470. The waterpump seals ride on the end of the cam. They will cut into the cam and cause a leak. Watch out for the problem some where around 500 hrs +. You may have to pull the engine get to the cam. Some people put a sleeve on the cam. I could not make it work. Some say that you can put another seal on the shaft in a different place. Just watch out for ant freeze leaking out of a hole in the front of the motor. I pulled mine and had the cam cut down and a sleeve placed on it and cut to the right size, Also had the engine rebuilt while they were at it. I had 570 hrs on the engine.[tongue]