Determining Reverse Rotation Motor- GM V-8s sb&bb
Chris D
I recently put up a post about which engines that I have. I have
since learned how to tell as the most that you will find will say turn
it over with the starter or things like that. Well, first of all, if
you are asking that question, it is because your boat probably doesnt
run or your possibly missing the starter or whatever. Why would you
care otherwise if they are running. 1) If you have a heat exchanger,
look at the raw water pump. Pull off the hose that goes to tranny or
H.E. turn pump by hand to see which way it draws the water from the
hull and that will tell you direction of crank. 2) If no raw water
pump, remove dist. cap. ALL GM distributors rotate clockwise reverse
rot. or not. Turn over motor by hand with 1/2 drive ratchet and look
at the rotor button to see which way it spins. ALWAYS CLOCKWISE
ROTATION. that will give you your answer. 3) Usually the standard
rotation engine will have the standard firing order of 1-8-4-3-6-5-7-2
in the cast of the intake near thermostat housing. This is not always
the case as if you had a bad intake, you would probably go get one for
a Chev truck for $50 bucks, rather than $500 for a new one because of
some numbers bieng wrong. That was the case with mine as both intakes
were the same. Check other methods I listed if you have same firing
order on both. 4) if out of the water, check rotation of prop. Does it
spin clock wise? if so than this is your standard rotation engine. 5)
If it is mercruiser, they all spin clockwise and have rotation
reversed in the tranny. 6) Usually V-Drives will have a higher gear
ratio on the side of standard rotation. Hope this helps and all info I
have listed worked for me on my 1980 twin 350's. Be aware that by the
early 90's and some late 80's, they all have a clockwise crank
rotation and are reversed in the trans.
FIRING ORDERS------------------
STD. ROTATION- ALL GM V-8
---FLY WHEEL---- 1-8-4-3-6-5-7-2
8 7
6 5
4 3
2 1
* CRANK TURNS CLOCKWISE FROM DRIVE PULLEY*
REV. ROTATION
---FLYWHEEL---- 1-2-7-5-6-3-4-8
8 7
6 5
4 3
2 1
*CRANK SPINS COUNTER CLOCKWISE FROM DRIVE PULLEY*
Hope it helps you. Some older models of GM motors Pre 78 I believe
have a different reverse rot. firing order. Call a marine shop to
verify the stamping number on the front left of block where intake
meets top of block. Good luck and happy boating!
gene
Great ideas, got to remember that one about the raw water pump.
One caution about the direction of the props: if you have straight
inboards that are mated to the transmission at the rear of the engine,
the right hand turning prop will have the opposite rotating (CW when
looking from flywheel) engine. My previous boat had the straight
drive transmission mounted to the front of the engine and thus an
exposed flywheel-standard engine was on the starboard side. V-drives
would typically have the front of the engine facing aft My Velvet
Drives will turn in either direction, but other models require a
reversing gear. With all of the combinations, you really need to
identify the transmission to figure things out. Frequently, it comes
down to looking at the plug wires coming out of the distributor:
find the #1 wire and then one engine will follow the standard firing
order and the other will be reversed. As you point out, most
manufacturers have the distributors turn in the same direction.
By the way, my neighbor has 454 Mercruisers in his 1978 Bertram, and
both have reversing straight drive transmissions-so starboard engine
is standard (turns CCW) yet prop turns to starboard, while port engine
is opposite rotating (CW) and prop turns to port. Cleaarly, boat
manufacturers just wanted to keep you on your toes.
Gene