MCM 470 Starter Shot? Replacement options?

[Shrek6737]

So I have an old 1977 MCM 470 that I have removed from boat (need to do some fiberglass work) and placed it on a pallet. I semi-rebuilt the engine by cleaning and then replacing intake/exhaust manifold and gaskets and a carb rebuild. Prior to taking engine out of boat, I tried to start it and the starter (old Prestolite 50-72550A1, looks original) seized up (smoked). I took off the starter and then got it working on the bench after cleaning to where it spins with battery applied. All work done and excited to get engine tested, and starter doesn't even get the engine to crank. Battery suspected dead, I then used jumper cables off of my truck battery and still the starter would not crank the 470. I can hear it trying but it just seems like it has had it. Is my assumption correct and I need to be looking to replace it? If so, any ideas what I need to search for to try and get something at the auto parts store. I'd like to avoid a $300 starter, but if i have to go that route I guess better safe than sorry?

I should add, I can hand crank the engine with no issues, so it doesn't seem seized up to me, but maybe I'm missing something.

I'm certain this has probably been asked a bunch so sorry if its a repeat thread. I couldn't find anything with the searches I was using.

Thanks for any help.

 

[Scott Danforth]

could be a bad starter.

I would have it rebuilt vs replaced. however you can do either. its your boat

BTW, no such thing as semi-rebuilt. you just did maintenance until you have the head off, new components such as pistons, etc and a machine shop is involved. nothing was rebuilt. just gaskets changed which is maintenance

 

[ROY WILLIAMS]

the starter motor takes it out then use the battery is rotating ... then the engine uses the person cranks it rotation ... do not put in the starter motor ...
then open up the starter motor brushes .... probably the brushes are the brush holders rusted a bit .. also clean the armature contacts ..

 

[kenny nunez]

Sierra # 18-5907. Delco No core required
Sierra# 18-6949. PMGR style new.
The Prestolite never did hold up on the 470s. They make good drift anchors.

 

[Shrek6737]

Sierra # 18-5907. Delco No core required
Sierra# 18-6949. PMGR style new.
The Prestolite never did hold up on the 470s. They make good drift anchors.

I had ordered the 18-5907 and it doesn't seem to fit, the bolts dont slip through to mount. Am I missing something on this or is this the wrong part. If I get the 18-6949, any idea if I would have the same problem?

 

[kenny nunez]

If you shorten the bolts they will fit. Or have some 1/2” 13 studs turned down to stepped 7/16” 20 so a 5/8” o.d. hex nut will fit. That is what the Mercruiser conversion kit used to come with when converting from the Prestolite to the Delco style.
I do not know if the other starter is easier but that would be the one I would have used.

 

[ROY WILLIAMS]

I had ordered the 18-5907 and it doesn't seem to fit, the bolts dont slip through to mount. Am I missing something on this or is this the wrong part. If I get the 18-6949, any idea if I would have the same problem?

MHA7016 STARTER MOTOR ,,,,,MCM470 1978

5660 - Mercruiser Starter Motor - OBB Starters and Alternators

Mercruiser Engine Marine Starter Motor, Mercruiser Stern Drive Starter Motor Replacement for Prestolite Dd, 12v, 9t, Cw, Remanufactured, 5660, Mercury Marine 50-72550, 50-72550a1, Prestolite 46-2273, 46-3599, mha6104, mha6104s, mha7016

www.obbstartersandalternators.com

Application: Mercruiser Engine - Marine
Model 470 MIE Mercury 3.7L - 224ci - 4cyl 1980-1981
Mercruiser Stern Drive
Model 470 Mercury 3.7L - 224ci - 4cyl 1976-1982
Model 485 Mercury 3.7L - 224ci - 4cyl 1980-1982

 

[Shrek6737]

If you shorten the bolts they will fit. Or have some 1/2” 13 studs turned down to stepped 7/16” 20 so a 5/8” o.d. hex nut will fit. That is what the Mercruiser conversion kit used to come with when converting from the Prestolite to the Delco style.
I do not know if the other starter is easier but that would be the one I would have used.

Thanks all for the help. I got some 1/2-13 shorter bolts. I think when I was checking the fit of the original bolts there was some paint in the new motor's bolt holes and I was scared to use some force on the bolts since I wasn't sure if I was returning the motor. Good news is, the shorter bolts seem to work so far. This might migrate off topic, but any idea if the solenoid on the Delco style replaces the stand alone solenoid that the Prestolite was using? I was able to get the starter and engine to crank using the attached solenoid with 12v to the 'S' terminal, but not sure if I just use the 'R' terminal as the wiring equivalent of the 'I' terminal on the old solenoid. Still digging through info on that.

Thanks all again.
I do think next time I'll go with the PMGR version.

 

[Eric 3.7LX Alpha 1]

Here are two wiring diagrams. The first is from manual 2, page 3E-12 covering your current version of the 470 which use the starter without a solenoid on it. The 2nd diagram is from manual 8, page 4E-7, which covers newer versions of the 470 with starters with a solenoid on them. It still shows the separate solenoid wired in.

Older manual #2:



Newer manual 8:

 

[Eric 3.7LX Alpha 1]

On your existing set up, on the solenoid, the S terminal should have a yellow wire, that is 12 volts coming from the ignition switch while cranking the engine to start; The I terminal should be a tan wire that runs to the coil (+) terminal. It gives full 12 volts to the coil from the solenoid while cranking over the engine only. It looses that voltage when you release the key. The coil has a 2nd "resistance" wire on the (+) terminal that gives it lower voltage like 8 or 9 volts while the ign switch is in the run/on position to save the life of the points.

You need to be able to separate that voltage so the starter doesn't get power still when you release the key from cranking from the 2nd resistance wire on the (+) on the coil.

How many smaller terminals does your new starter solenoid have? maybe snap a pic of it and post it. It's been too long I don't remember..... If you have two, it might be possible to eliminate the separate solenoid. The starter has to be able to provide 12 volts to the (+) on the coil while cranking, and not continue to get 12 volts back from the coil when the key is released to run or the starter will continue to crank the engine over with the key released.

 

[kenny nunez]

Leave the small tan and yellow wires where they are on the original solenoid.
Relocate the main battery cable to the large post on the new starter. Remove the large yellow cable from the original solenoid and make up a #10 gauge wire to replace it from that post to the “S” small terminal on the new starter solenoid. Make up another #10 gauge wire and connect it from where the original battery cable mounting post was on the original solenoid to the large post on the new starter. Now the original solenoid is the slave solenoid.

 

[ROY WILLIAMS]

Here are two wiring diagrams. The first is from manual 2, page 3E-12 covering your current version of the 470 which use the starter without a solenoid on it. The 2nd diagram is from manual 8, page 4E-7, which covers newer versions of the 470 with starters with a solenoid on them. It still shows the separate solenoid wired in.

Older manual #2:
View attachment 369312

the mercrusier manual OEM is in my 1978 .. the manual is a different manual later on the change of the MCM470 . I changed the voltage regulator to the DC generator 70amp.. output ...my starter motor took it out and inspected it and lubed ,and cleaned the commutator and the brushes/brush holder..the manual inspects the starter motor and repairs it ...MHA7016 prestolite starter motor ..

View attachment 369311