motor rattle

[shelbert]

Hi, I recently took out my grandfathers 1972 40hp evinrude and got it running. It seems to be a fine motor, changed lube, water pump, spark plugs and cleaned carbs. I cleaned and set the points. <br /><br />The thing starts like nothing i have ever seen, it never fails to start at about 1/4 the pull of the rope. It idols great and has lots of power.<br /><br />The problem I have it is rattles so much, that it drops parts in the lake, so far I have had the bendex bolt on the starter, 4 of the water jacket bolts, the lower starter bolts that hold the thing together, the carbs almost fell off,@ starter mounting bracket bolt, and 2 times the plugs have almost rattled off.<br /><br />Did these motors rattle like this or is something wrong?

 

[Xcusme]

Re: motor rattle

Shelbert, Perfectly normal...those old motors always drop parts, just keep a box of any old spare bolts you have in the boat.<br /><br />I'm KIDDING!! Gees.<br /><br />If your motor starts and runs as good as it does, there can't be too much amiss with it. I'd go over the motor with a good torque wrench and tighten up all the bolts to spec. A light coat of gasket sealer on the threads can help prevent loosening. Perhaps you're seeing the results of a previous attempt to rebuild the motor or parts replacement without much attention to fastener torque values.<br />You did mention that the motor shakes alot. Perhaps you're dropping a cylinder. Do a compression test and test for good spark at each hole and report back. Take notice of the spark plugs too, is either plug fouled or wet??

 

[rickdb1boat]

Re: motor rattle

Check the prop and propshaft to make sure it is true. Spin the prop by hand and see if you notice a difference in the way it turns. Really need a dial indicator to make sure.

 

[Paul Moir]

Re: motor rattle

Most of us have problems getting bolts out of outboards, not keeping them in. I'm sure there's lots of jelous readers wishing their corroded and stuck water jacket bolts would simply rattle out. <br /><br />Just to add to Xcusme's excellent advice, make sure your sparks can jump a 3/8" gap, and you might want to pull the flywheel to examine the crankshaft taper. If the flywheel ever sheared it's key, and the taper wasn't cleaned up perfectly, the flywheel would be out of balance and cause some nasty vibrations.<br /><br />EDIT: And rickdb1boat's excellent advice too.<br /><br />Another possibility is a primary compression problem. But that would turn up in your spark plug comparison.

 

[shelbert]

Re: motor rattle

Checked the spark today, it seems fine. I just had the flywheel off last weekend when I started working on it to check points, caps and points. cleaned up points, set gap. Everything under there looks like new. Compression is a even 120 in both cyl. There is no play in the pistons, or the flywheel. Ill try rest of sugestions tommorrow, ran out of daylight today.<br /><br />The prop shaft seems to be running strait as far as I can tell. The motor seems to vibrate when in gear, neutral or reverse. <br /><br />One other thing I noticed also today was I took it out with my brother so I could fine tune the carb settings. The engine runs good but seems to miss a beat now and then when running at full speed and doesnt quite open up like think it should. I played with the lean/rich mixture and it runs best when its all the way in firmly seated. I am not sure what would cause this, any ideas?

 

[Paul Moir]

Re: motor rattle

If the engine idling well with the idle mix screw all the way in, you're getting too much gas from somewhere. The needle and seat in the carb may be leaking - you can check this by pumping the primer bulb and making sure no fuel comes out the carb's throat.<br />Another possibility is that your fuel pump diaphram is leaking. Since when it leaks, it pushes gasoline into one of the crankcase chambers, it causes one cylinder to run rich. That would also explain your vibration problem since the cylinders wouldn't be firing evenly. This will turn up on the spark plug comparison. Or you could unbolt the fuel pump from the engine, pump the primer bulb, and make sure no fuel runs out the pressure pulse port on the back of it.

 

[shelbert]

Re: motor rattle

Thanks for the ideas on the carb and fuel pump, the rubber has been sitting for a long time, the gas lines felt like plastic they were so hard. I did replace all fuel lines but did not take the pump off. The fuel system will be where I go over next then.

 

[DJ]

Re: motor rattle

Shelbert,<br /><br />Also look for an air leak at or near the fuel and/or carb.

 

[shelbert]

Re: motor rattle

Well things are a bit better on the motor. We have tightened all the bolts down good. <br /><br />I took the fuel pump off and changed it with a new one off another motor. It ran well, very smooth up to about the last 1/8th of throttle. Thought I had something figured out but when I put the old one back on it still ran without the miss. <br /><br />That last 1/8th throttle seems to bog it down a bit. I am pleased where it is now, but any ideas on the last bit of throttle would be nice.