Mercruiser 470 hard to turn over

[Dehn]

I am purchasing a Mercruiser 470? 4 cyl. 170 HP. from a mechanic friend. This engine is very hard to turn over on start up ( he told me to get at least a 950 cold crank battery). My buddy says that it has always been this way since he owned the boat (12 years ) He has replaced the starter, added a 2 battery switch etc. I am wondering if this is normal for this engine if not what should I look for as a problem. Thaks for any advice

 

[Trent]

Re: Mercruiser 470 hard to turn over

Its not normal. Look for internal corrosion on the battery cables and engine grounds.

 

[jfc092]

Re: Mercruiser 470 hard to turn over

I have a 1978 470 Merc. and have the very same problem. Once started, it runs great. But, it does crank over slow. Some one told me earlier to check the timing. I did and its fine.<br />If someone knows a solution, I'd love to hear it.

 

[MrBill]

Re: Mercruiser 470 hard to turn over

My experience has been that wear...particularly brushes in the starter motor initiate hard starting in this motor. As the others have suggested, check all battery cable connections and ends for corrosion, along with grounds, etc. This problem is not normal. Rule of thumb: 2 cold cranking amps per cid should be sufficient and is usually the manufacturers recommendation.

 

[petryshyn]

Re: Mercruiser 470 hard to turn over

To take away all guess work, <br />>measure voltage across battery (post to post) while cranking<br /><br />>measure voltage from starter housing, to starter motor terminal(copper strap coming out of starter barrel) while cranking<br /><br />If these two readings are within 1 volt, starter is at fault.<br /><br />If these two readings are more than 1 volt difference, you have a cable, connection, solenoid or ground issue.<br />

 

[johnkc]

Re: Mercruiser 470 hard to turn over

may i ask what weight of engine oil is being used in it ?? and is it the cold starts or warm starts or both??

 

[Dehn]

Re: Mercruiser 470 hard to turn over

Coincidentally this is also a '78 470, It has new cables, battery and starter. Oil is 10W30, hard turn overs occur both cold and hot. After starting, the engine runs great so I don't think it's a timing problem. My friend ( an Auto mechanic) says not to worry about it as it has been doing this for 12 years for him with no associated problems. I am at a loss to understand why this would be the case and for my own peace of mind I thought I get outside opinions, thanks for the suggestions and please keep them coming.

 

[Bob_VT]

Re: Mercruiser 470 hard to turn over

Mine acts the same exact way but it always starts.<br /><br />1985 Mercruiser 470/170<br /><br />Bob

 

[beckerdg]

Re: Mercruiser 470 hard to turn over

I don't think this is normal to crank slow, of course our description of slow may be different. <br /><br />I have an 86 mcm170 and use straight 40wt oil per recommendation of manufacturer and it cranks and starts fine. It did get slow for a while once, but cleaned all terminals and replaced corroded leads and that straightened things up. You really ought to use at least a 25-40 or 30wt oil. Automotive 10-30 will shorten the life of the engine. That is if something else does not get you.<br /><br />You may not want my advice though was out this weekend and the ignition went dead. No spark, no go. Have not had time to trouble shoot. :~( Still cranks fast enough, just no go... Ha!

 

[johnkc]

Re: Mercruiser 470 hard to turn over

try using mercruiser 4cycle oil or straight 40w motor oil. seems to me we had a service bulletin or a lenghty conversation on this subject some years back at service school. and i know that this sounds too simple to cure the problem,but 10w30 is the wrong oil to use any way. good luck ,

 

[jfc092]

Re: Mercruiser 470 hard to turn over

In my '78 470 Merc. I use straight 30 weight oil. When this engine sits for a couple of weeks It won't start unless I prime the carb with a little gas or the canned starter fluid. I assume the fuel evaporates from the carb while sitting for a lenth or time.<br />My definition of slow cranking is so slow that it will slow to a stop if there's no gas in the carb to fire it up. I've noticed that the positive cable will get hot during this cracking.<br /><br />I have removed all the cables, cleaned them and checked the timing. The next step is to remove the starter and have the brushes checked. But after reading some of the posts here, even a new starter may not be the answer. Aside from the problems, this engine pushes my 19 footer very very well.

 

[petryshyn]

Re: Mercruiser 470 hard to turn over

If the actual cable is hot, its likely undersized....do the above voltage drop checks and it will indicate a problem area...

 

[chiefmike58]

Re: Mercruiser 470 hard to turn over

dehn, it definitly sounds like a faulty ground connection or a tired battery. I had the same trouble with one of my twin 470s and changed starter to a spare I keep on board and it turned over fine. I've gone through quite a few starters on these two engines and don't feel that they last that long, thats why I keep a spare around. I think schematic gives the best advise to get to the root of the problem. Great motors though.

 

[chiefmike58]

Re: Mercruiser 470 hard to turn over

dehn, I meant tired starter, not tired battery, although that could be it also.

 

[DJ]

Re: Mercruiser 470 hard to turn over

Follow Schematics advice. Voltmeters are cheap and handy.<br /><br />If your cables heat up, they're either dirty at the ends or undersized.