Sputtering 1971 Merc 500

[Great Lakes Mike]

Need some help here.

I'll give you the current situation and the symptoms. Please help. Gotta get back out there while the fishing is good.

Facts:
~ 1971 Mercury 500 Thunderbolt (50hp)
~ Changed Plugs last Fall
~ Using Correct Oil/Gas Mix
~ Changed Gear Lube (Clean)
~ New Prop (Not the issue anyway)
~ Recently Changed Fuel Line

Symptoms
Reverse
~ When I put the motor in reverse it gives me a clicking/clanking noise, it's been happening for the past couple months
~ No real power in reverse, it seems like I get no pull, then again I'm not giving it much gas because of the noises it's making

Idle
~ Everything was fine until yesterday, now in idle I'm getting the same noises
in idle that I used to get in reverse
~ I burned the fuel off the carb yesterday, and it sounded terrible

In Gear (Low Speed)
~ Loud Cranking Noise when I first put it in Gear
~ Same Noises
~ Cut's off when I first give it the throttle, took me 5-6 times to get it going
~ Stalling issues at low speed

In Gear (High Speed)
~ Sounds Great
~ It opens up wide and runs its best

Thoughts????
I think Fuel Pump/Carb rebuild

I hope nothing major. Please help.

 

[BassnKY]

Re: Sputtering 1971 Merc 500

If it make a clanking noise, it sound like it might not be going all the way into gear. Could the shift control slide rail be cracked and opening up when you try to shift into gear.
Can you rev it up without it being in gear (BE CAREFUL TO NOT OVER REV IT)

 

[Great Lakes Mike]

Re: Sputtering 1971 Merc 500

It does rev up, but it's making those noises in neutral too. Do you think it may not be coming out of gear either in neutral either? It makes a lot of sense the more I think about it. I'll check it in the morning.

 

[BassnKY]

Re: Sputtering 1971 Merc 500

I does sound like something in the shifting.

As for not having power in reverse, the linkages do no let it go to full throttle. It limits the carbs to only opening up about 1/3. Kind of a safety feature. Could imagine running 5,000 RPM in reverse? I believe it also does this when not in gear to prevent literally blowing the engine apart.


Like I mentioned before the slide rail could be cracked/broken and flexing so the linkages are not working correctly. Keep you fingers crossed that it is not internal.

 

[Moody Blue]

Re: Sputtering 1971 Merc 500

From your description, I would guess lower unit issues. The sound you hear is the clutchdog "skipping" over the engagment dogs on the drive gears and chewing them up little by little.

The more it skips, the worse it will get until it won't engage at all. I'm in the middle of a complete rebuild on my lower unit for similar problems in reverse.

To eliminate the possibility of a mis-adjusted shift cable, disconnect it from the motor and try shifting manually.

 

[BassnKY]

Re: Sputtering 1971 Merc 500

Moody Blue has a good idea about trying to shift it manually. When you do this, you will see the part I was talking about.

However, I fear that Moody Blue is correct.

What is your serial number? That way I can look at the correct diagram and post a pic of the part I am talking about.

Do you have a repair manual? If not, I would definitely get one. It will make repairs A LOT easier.

 

[Great Lakes Mike]

Re: Sputtering 1971 Merc 500

Serial Number is 2738818. To Manually Shift, do you recommend disengaging the cable at the motor or at the controls.

 

[Great Lakes Mike]

Re: Sputtering 1971 Merc 500

Nevermind, I just read his post again. Disengage at the motor...

I do have a manual, but it's just the Clymer Mercury outboard manual. It's not very specific.

 

[BassnKY]

Re: Sputtering 1971 Merc 500

Hear is a link to a blow-up of the sift linkage. I believe it is part 56 that I am talking about.
http://www.mercruiserparts.com/Show_Pictures3.asp?dnbr=%2048425&ivar=images/MERMAR/48425/26.png&inbr=437&bnbr=16&bdesc=BOTTOM+COWL+ASSEMBLY+AND+SHIFT+LINKAGE

Also, here is a link to the page that lets you select you engine:
http://www.mercruiserparts.com/selectModels3.asp?type_id=MERC

These diagrams are very helpful. especially if Moody Blue is correct (Which I think he is). It includes all the blow-up drawings for your engine. I use them in addition to me Seloc manual.

GOOD LUCK!!!

 

[Great Lakes Mike]

Re: Sputtering 1971 Merc 500

Thanks for the troubleshooting tips, it's not related to shifting. I disengaged and did everything manually. The noises are coming from the top of the motor. It seems like it's coming from the starter/flywheel area. When the motor is in neutral there is a vibrating noise coming from the top. The housing seems like it is loose. Is it normally like that? Any recomendations? I hope I can avoid taking it in, but I may not have a choice.

 

[BassnKY]

Re: Sputtering 1971 Merc 500

OK... time to switch gears... so to speak.

Can you give me a pic of the housing you are talking about?

If it is from the top, can you feel around and see if anything else is loose?

I know this sounds weird but when it is running, you can take a screwdriver and lightly touch various parts and it will amplify the sound when you get the correct part. But, You need to be VERY CAREFUL and not get near moving or electrical parts. From your description, I would start around the linkages.

 

[Great Lakes Mike]

Re: Sputtering 1971 Merc 500

The noise is coming from the starter (red). There is a wobble between the top section and the bottom (Geared) section. It makes a clanking noise when the motor is running. The reason I couldn't tell that it was happening at high speeds is either centripital force or it was just getting drowned out by the motor. In idle it sounds terrible.

 

[BassnKY]

Re: Sputtering 1971 Merc 500

Mike:
The geared red item in this picture is the flywheel. Is what is loose the top most piece? (the pulley for the pull starter) According to the attached schematic, this pulley bolts on to the top of the flywheel flex plate. Then the flex plate bolts to the actual flywheel. Have you checked these bolts? You might need to take both flex plate off to see what the problem is.

 

[Moody Blue]

Re: Sputtering 1971 Merc 500

That RED part is the flywheel, not the starter, and its sounds like it is coming apart. If it lets go at RPM, someone could be seriously injured or killed.

Wouldn't run that motor until whatever the problem is is fixed.

Is it possible the whole flywheel is wobbling? Could be that the upper crank bearing is shot and the whole crankshaft is wobbling ?

 

[Great Lakes Mike]

Re: Sputtering 1971 Merc 500

That part is listed as the "Flywheel/Starter" samething!!! Haha.

The bolts are tight, no doubt about it. It's gotta be the upper crank bearing that is shot. The whole thing is loose, and thus causing the wobble.

Now here's the big question. How tough is this fix? I'm no pro (obviously), but with directions I can do it. My extent of engine knowledge is oil change & tune-up. If I get the parts, and I only have slightly better than a handyman's tools, can it be fixed.

What type of problems may I encounter?
Other than basic tools, what do I need?

Thanks for all the help.

 

[BassnKY]

Re: Sputtering 1971 Merc 500

Mike:
First, I would get a repair manual and read through the procedure to see how comfortable you feel. To me, it is not to bad. But I am used to fixing everything myself. With the manual, as long as you pay attention, and be methodical, anyone with SOME mechanical ability should be able to get it done.

Here is a link where you can get an OEM service manual. http://www.marinepartsman.com/Mercury-outboard-manuals_5.html Find the "500" section and then just select the range that includes your serial number. Or you can get a Seloc or Clymer.

Just remember, it is going to require an almost complete tear down. And while you have it this far down, you mite as well to a complete rebuild to save future headaches. If you don't want to do that, you want to at least go ahead and replace ALL of the bearings on the crankshaft.

If you decide to do this, it would help a lot of others in your situation if you posted the progress along with pic's.

GOOD LUCK..