RicardoMarine
Gold Medal Contributor
Mark, I'll answer your question the best I can, but first I'll respond to what Jack posted.
Yes, if making a change from Pre-1986 Engines, note that there will be certain parts that will and will not interchange.
Intake manifold bolt angle, oil pan, flywheel type, etc. Pre-Vortec Engine intake manifold uses 12 bolts.... Vortec cylinder heads require only 8 intake manifold bolts.
However, it sounds as though you are going to be replacing complete engines, not mixing/matching components!
This takes us to two aspects of the Re-Power that may involve some planning:
1.... after 1990, the mechanical fuel pumps were no longer used, therefor the cylinder blocks were no longer fully machined for the mechanical pump. (actually, the mounting surface is there.... the push rod bore is NOT)
If you go to electric fuel pumps for carburetors, you must incorporate the N/O Low Oil Pressure switch as a safety feature.
If Hell Bent on mechanical fuel pumps, the block casting can be drilled to accommodate the fuel pump push rod.
The camshaft must offer the push rod cam lobe, or this does not work.
2.... The AFT end of the crankshaft flange is quite different after 1986. GM changed from a 2pc rear main seal to a single 1pc seal.
This created a major change to the crankshaft flange, which in turn created the need for a different flywheel mating area.
The starter motors don't care...... as long as the Straight accross bolt pattern is used for the 153 tooth, and the Staggered bolt pattern is used for the 168 tooth..... these will all work.
Borg Warner drive couplers will mate to either style flywheel.
As for the rotating assembly and balancing........, your Engine provider should advise you regarding flywheels and balance.
If not, make certain that you bring this up and ask the question so that this is covered.
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OK.... as for reversing Engine rotation, here's what you'd first need to know:
The GM cylinder block, cylinder heads, crankshaft, etc, are the same between the two.... LH or RH rotation engines.
The crankshaft itself and the connecting rods don't care which direction they spin.
The ignition distributor is driven by the rear camshaft gear. The distributor shaft also drives the oil pump.
We DO NOT change the rotation direction of either of these.... we simply let the oposing hypoid gear cut create the correct rotation.
In other words, either RH or LH engine's distributor will rotate CW, as will the oil pump.
Ignition Spark sequence begins @ #1 cylinder and moves around the distributor cap in the same CW direction, just as it would with a Std LH Engine.
(like this, but with a firing order of 1-2-7-5-6-3-4-8 )
Ignition Distributors:
The camshaft offers a hypoid cut distributor "drive" gear at the rear area. The distributor has a hypoid cut "driven" gear that mates to this gear.
When the LH rotation camshaft is turning the distributor and oil pump, the hypoid gear cut causes an "Up-Lift" force against the distributor's driven gear. The thrust surface above the "driven" gear checks this force and reduces friction and wear.
When the camshaft direction is reversed, the hypoid gear cut corrects the distributor shaft rotation..... But..... it now undergoes a "downward" force.
The REV RH Engine distributor must account for this force.
Examples:
Mallory YLM 624 AV = Std LH Rotation.
Mallory YLM 624 BV = REV RH Rotation.
Engine circulating pump (aka water pump) will need to be bi-directional.
On either rotation Engine, conetic energy forces are at work against the connecting rods/wrist pins/piston skirts.
In order to check these forces and minimize rocking and distortion, the wrist pin is off-set for this particular crankshaft rotation.
When we reverse the direction of the Rotating Assemebly (I.E., REV RH Rotation), we must also change the wrist pin off-set by 180*.
With a completely Ambidextrous piston (such as the GM full dished piston w/ double valve reliefs), we simply reverse each piston direction on their respective connecting rod. (rods remain the in same orientation)
This is easy and simple to do by aiming the piston orientation "notch" AFT, instead of FWD.
This is not quite as simple with a LCQ, D-Dished or a correct Quench style piston profile.
These are not quite as Ambidextrous.... but it can be done.
Since the REV RH crankshaft is the same as the Std LH crankshaft (yet it's being turned in the opposite direction), the sequence of intake and exhaust valve operation and spark timing must also be reversed.
This calls for a completely different camshaft profile.
REV RH Engine camshafts can be chain and sprocket driven, twin gear driven or quad gear driven.
Chain and sprocket and Quad gear driven spin the camshaft in the same direction as the now reversed crankshaft.
In either scenario, the cam profile is unique to the REV rotation Engine.
The #1 cylinder is always the furthest cylinder forward on most any engine.... it does not change.
We still index components from #1 cylinder while @ TDC, and we begin our ignition timing sequence from #1 cylinder while @ TDC.
Std LH Rotation SBC firing order is 1-8-4-3-6-5-7-2 . When we reverse rotation, the SBC firing order now becomes 1-2-7-5-6-3-4-8
Front and Rear main crankshaft seals are specific for the engine rotation.
Tiny spiral serrations wick oil back into the crankcase area. If not correct for the rotation, they will wick oil out of the crankcase area.
For a good machine shop, building a REV RH SBC should not be an issue.
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