Mercruiser MCM 7.4 l 454 1996 Gen VI OF809461 W/ bravo III. Timing ?

[Paul2222]

Doing a tune up: My Operation & Maintenance Manual says to set "Timing @ idle RPM 10*BTDC with a Spark Plug Gap = .035 in (0.9mm). But my Service Manual #16 under section 1B maintenance : "Timing @ idle RPM 8* BTDC" .

Which one is the correct setting? 8* or 10* BTDC ?

The engine has a Weber 4 Barrel Carburetor/Thunderbolt V Ignition Systeam.

Tia. Great Site!

 

[Bt Doctur]

Re: Mercruiser MCM 7.4 l 454 1996 Gen VI OF809461 W/ bravo III. Timing ?

with todays fuels, go with the 8, you can always increase it if there is no ping or detonation.

 

[Paul2222]

Re: Mercruiser MCM 7.4 l 454 1996 Gen VI OF809461 W/ bravo III. Timing ?

Thx Bt D
Is there a service bulletin for this matter?

TIA

 

[Bt Doctur]

Re: Mercruiser MCM 7.4 l 454 1996 Gen VI OF809461 W/ bravo III. Timing ?

not a service bulletin but considering all the things that move ,crank gear, timing chain, cam gear, dist drive spirals on cam, dist drive gear, add up all the .001`s and you find that the actual setting may be off a few degrees. say the motor is worn internally and the timing chain is loose, sprockets worn, etc.
a setting of "0" would actually be 10 deg ATDC. In this case you would simply bump up the timing to get it to run better.take the 10 add 8 and the actual reading you would see with a strobe light is 18 BTDC at idle to compensate for worn parts. This ethanol fuel is a rather poor substitute for the leaded fuel we once had.A lot of motors have a run lean condition that contributes to detonation and holed pistons.
too much timing , a lean mix either carb or injected and you can melt a piston.Better to err on the side of caution (less agressive timing curve) than risk damage.

 

[Fun Times]

Re: Mercruiser MCM 7.4 l 454 1996 Gen VI OF809461 W/ bravo III. Timing ?

Hi there, your timing specifications for your engine should have been on top of the flame arrestor sticker that say's 7.4l, That is as long as you still have the original flame arrestor cover sitting on top of your carburetor/engine.

http://www.boatfix.com/merc/Bullet/94/94_02.pdf

Serial number OF809461 is a 1996 MERCRUISER TB5, W/PS, TWOPCEX, WORO, GEN6 7.4L BRAVO Model number 474B110JT.

 

[Paul2222]

Re: Mercruiser MCM 7.4 l 454 1996 Gen VI OF809461 W/ bravo III. Timing ?

Thank you both. FTimes, what is the meaning of " W/P5, TWOPCEX/, WORO"

I have the original flame arrestor cover, I'll get it tomorrow and will let you know what it callsl for.

thx

 

[Paul2222]

Re: Mercruiser MCM 7.4 l 454 1996 Gen VI OF809461 W/ bravo III. Timing ?

The flame arrestor sticker specs; 10* BTDC. Thanks all!