02-07-2017, 09:43 AM
It's a good idea to use a thin film of sealer on the intake manifold gasket, stuffer gasket and the surface between the side cover and the block where the large o-ring groove is located. I use RTV as it is easy to remove when doing rebuilds. You can also use the spray on copper coat sealer on the head gasket. I don't recommend that you use any sealers on the gaskets above or below the reed cage as there is too much chance for blockage of the pulse holes to the carb.
Regarding setting the timing.... you can try the method I use.... here is how I do it.
Install the points and run the screw down till it is snug, then back it off just enough to allow the metal plate with the slot to be movable with light force and move the plate to a position that creates a large gap in the points. Rotate the crank around until the plastic arm of the points is sitting on the highest point of the cam on the crank then insert a .016" feeler gauge in between the points. With the feeler gauge held in place with the left hand, use your right hand to push the contact on the metal plate over to contact the feeler gauge and continue pushing enough to see the cam follower lift off the cam. Once you see that you have made the cam follower lift off the cam just a bit, gently release the assembly with your right hand and let the point spring tension return the cam follower back to contact with the cam and then use your right hand to tighten the screw. The process is easier if you have a small feeler gauge that allows better "feel" in the left hand while the right hand does all the work.
I like to use a 1/4" wide by .016" feeler gauge since it is pretty flexible and you can't influence the process much with sloppy work by the left hand. Once you have them set you can check to see where you are with a degree wheel or by measuring piston position relative to TDC.
On your Mac 91 25 degrees BTDC is equal to .100" from the top. Each degree plus or minus from that position is approximately .008" so .116" will give you 27 degrees and .084 would be 23 degrees.
Regarding setting the timing.... you can try the method I use.... here is how I do it.
Install the points and run the screw down till it is snug, then back it off just enough to allow the metal plate with the slot to be movable with light force and move the plate to a position that creates a large gap in the points. Rotate the crank around until the plastic arm of the points is sitting on the highest point of the cam on the crank then insert a .016" feeler gauge in between the points. With the feeler gauge held in place with the left hand, use your right hand to push the contact on the metal plate over to contact the feeler gauge and continue pushing enough to see the cam follower lift off the cam. Once you see that you have made the cam follower lift off the cam just a bit, gently release the assembly with your right hand and let the point spring tension return the cam follower back to contact with the cam and then use your right hand to tighten the screw. The process is easier if you have a small feeler gauge that allows better "feel" in the left hand while the right hand does all the work.
I like to use a 1/4" wide by .016" feeler gauge since it is pretty flexible and you can't influence the process much with sloppy work by the left hand. Once you have them set you can check to see where you are with a degree wheel or by measuring piston position relative to TDC.
On your Mac 91 25 degrees BTDC is equal to .100" from the top. Each degree plus or minus from that position is approximately .008" so .116" will give you 27 degrees and .084 would be 23 degrees.
Dave L.