Gap setting for plugs on a 3.7 470 Merc

[Pst76]

I need to confirm plug gap setting on my 470. Its an 84 Mercruiser. The Manual spec I have shows 25 to 30 on the plugs and 17 on the points.
When I pulled the plugs that were in the boat the plug gap was in the 35 to 40 range.
I am figuring the manual spec would be correct but wondering if there would be a reason to over gap.
THanks

 

[Don S]

Re: Gap setting for plugs on a 3.7 470 Merc

Not sure what manual you are getting your specs from, but they are't what's in a Mercruiser manual and way off from the specs.
The 470 should have a plug gap of .035"
Points should be gapped at .022" then checked with a Dwell Meter and readjusted to 28° to 32°. Then the timing has to be reset to 8° BTDC @ idle rpm of 650 to 700 rpm

 

[Pst76]

Re: Gap setting for plugs on a 3.7 470 Merc

Thanks Don, The manual spec I got was from the Marina yesterday where I got the parts for a full tune up. He looked it up while I was there. So much for that.
The reason I wanted to confirm is because the plugs I took out had a much larger gap and got me wondering
. I guess I will stick with parts only from the guy I spoke with yesterday.
Is there a technical manual I can get for the Mercruiser model motor? Motor S/N 6890496
Most of the ones I have seen on line are for the 3.0 not much on a 3.7

Thanks

 

[Don S]

Re: Gap setting for plugs on a 3.7 470 Merc

You need service manual number 3 for your engine, it's part number 90-95693.

Your local Merc dealer can order you one, or you can order one directly from Mercruiser.

https://appcenter.mercurymarine.com/litreq/orderForm.jsp?type=mc

If you order from this link, add a 0 to the front of your serial number.

No manuals online for your engine that I am aware of.

Many have found them on ebay.

 

[Pst76]

Re: Gap setting for plugs on a 3.7 470 Merc

thanks Don I will get one ordered