Merc 470 Hard Cranking when Warm

[cshirley]

I was out on the lake this weekend and each time I killed the engine and went to start it again, it cranked slower. It ended up I got back to the ramp and it died switching between gears and It cranked over a couple times and then wouldn't crank anymore at all like the battery was dead. I just did the alt conversion (used alt), disconnected the stator, and assumed the used alt wasn't producing voltage so the battery was dead.

I got it home, let it sit overnight, went out to try it and it cranked fine, battery voltage shows full according to the charger.

I know this can be heat related but the engine temp never shows any higher than 120F, I know that is pretty low for this engine so I'm wondering is something is wrong there.

It has the newer aluminum exhaust manifold and 4" heat exchanger.

The battery is a Walmart EnerMAXX Marine 875CCA that is 2 months old. Its been completely drained one time (left the key on accidently) and re-charged.

I'm not really sure where to go from here, I'm going to test the alternator for a good output but it seems like maybe it IS working ok. I can't see the battery voltage going from no crank and clicking to perfectly fine overnight with no charger on it.

 

[IVAZ]

Re: Merc 470 Hard Cranking when Warm

Does it run smoothly? Improper timing can cause difficult starting once the engine gets warm.

 

[cshirley]

Re: Merc 470 Hard Cranking when Warm

Yeah it actually runs fantastic. I've replaced points with ignitor electronic ignition and flamethrower coil. Adjusted timing by ear like I do with cars and checked it several times when warm and it was fine. When cold, I pump it a couple times and it fires immediately and idles very well. The only issues left are this one, and if I goose the throttle it wants to choke but as long as I ease into it, it throttles fine and will hit 4500 rpm at wot although I run about 4200 rpm max. What gets me is even at 4200 rpm for 10-15 min straight, it still never gets over 120F on the temp gauge and it takes a good 15-20 min from a cold start to reach that.

Curtis

 

[IVAZ]

Re: Merc 470 Hard Cranking when Warm

You need a timing gun. Your ear can get it close but not exact. Is the thermostat installed?

 

[cshirley]

Re: Merc 470 Hard Cranking when Warm

I didn't check the new manifold, it was off another motor so I just assumed but even with the old manifold, it didn't get warm and I know there was a thermostat in it.

I have timing light, but it quit working and cheapest i found locally is $40 bucks but if i have to i guess i'll get it.

 

[IVAZ]

Re: Merc 470 Hard Cranking when Warm

Yeah, you really do need to check the timing with an instrument. You can?t rule out timing being out if you don?t know where it?s at. You?re going to need to check the temp with something else besides the onboard gauge (IR gun or different gauge). Your temp gauge might not be accurate. Some people here do a "touch" test to roughly check temp on the risers. Might be worth searching to see if you can find them.

 

[a1nowell]

Re: Merc 470 Hard Cranking when Warm


CSShirley,
I have an '84 M/C 470 that does exactly the same thing. It starts pretty quick when cold. The longer I run and then shutoff, then the harder it is to start until it gets to where it will not crank. Sounds just like the battery is dead. When this happens and I let it set 45 minutes then it will crank right up. Temperature guage never reads over 160. Battery is a brand new Exide marine 800 cca and I have a brand new WalMart battery like yours that I carry as a spare. When it won't start and I take my spare battery and jump it to the Exide, it makes no difference, still will not crank.

I will check the timing, 8 degrees BTC I think.

Keep me posted on your solution.

Larry

 

[cshirley]

Re: Merc 470 Hard Cranking when Warm

I found out that my alternator is bad, not charging the system. This was most likely my problem. now my next problem is I went and got a new alternator, turning my bad one in for the core exchange and I don't believe the new one is a marine alt. Can someone tell me what the difference is?

Thanks,

Curtis Shirley

 

[abj87]

Re: Merc 470 Hard Cranking when Warm

You should see screens on the air inlet ports and a tin cover over the back of the alternator.