MTFCA Forum

Does anyone have any experience with this type center main? It was in an engine I bought to use in a speedster, wondering if I should use it or fit a regular cap. The spring loaded wedge forces the 1/2 bearing forward.

I am having a hard time getting my head around this device. The two main bearing bolts when tightened will not allow the bearing cap to move, as it should be. Is the "wedge" simply to keep the crankshaft from drifting within the confines of the bearing caps, just keeping the shaft against the thrust face on the rear main?

Allan from down under.

That one did not work as well as one that had a set screw to adjust and hold in place, that style wondered under load that you have.

You need to be very careful with the center Main. Sometimes the rear of the crankcase has dropped which will force the crankshaft to bent upward at the center main. If you tighten the cap with the crankshaft in that situation it will bend with each revolution leading to the broken crankshaft.
Norm

Allan, I’m thinking that the babbit-lined brass 1/2 bearing “floats” between the cap and the crank because of the clearance. As it moves forward assisted by the spring loaded wedge it’s prevented in the same way from moving backwards. So when the bearing cap bolts are tightened there is still enough clearance for the bearing to float and have clearance. It was in a stationary engine I bought with the magnets removed but I suppose it had previously been in a car with a working magneto for the end play to matter.

Hi Corey,
If the Babbitt in the block is good & the crank is true then YES replace it with a re-Babbitted or a very good used one. That looks kind of hokey.
It may have been installed because of a center main issue rather than a preventative measure. So check the bearings close.
Craig.