My engine has developed a knock so I pulled the inspection cover from the bottom of the engine, hoping not to find mass quantities of metal. The pan was clean but upon inspection I found a very unique center main bearing set up with a spring attached. Can anyone help me identify what I have and could it be the reason for the knock. As always all help will be greatly appreciated
you have an adjustable "thrust" ... aftermarket center main bearing cap ...probably not the source of your knock UNLESS that bearing is too loose ...always an optimist...gene french
harvey, The problem that i have seen with the adjustable center main is it keeps pushing the crank forward. On a couple of the engines i tore down with these in it the flywheel was hitting the field coil and that will give you a knock!
I guess my next question is, should I replace the adjustable cap with a standard? I was able to tighten the bolts holding the cap on by hand so perhaps it is just loose but in the long run would I be better off replacing it?
I took one of those out of an engine also. The bearing is not bonded to the cap and under constant forward pressure. Gene and Joe are the experts here but I think a crankshaft is designed to spin in a circle and not try to screw itself forward. I hope your rear main thrust isn't gone and the rod bearings are not egg shaped by running off center. I would remove it and put it in a display case.
Tighten the bolts on the center main and check the others, then put it back together and see if your knock goes away. Finger tight main bearing bolts could easily cause a knock.
That adjustable center main cap is a band aid to cover another problem. The thrust surface on the rear main cap is worn and no longer holds the clearance needed in the magneto. Chances are you engine needs all new main bearings.
I have been unable to find a picture of this cap, When I drained the oil a nylon lock nut and a 5/16 lick washer were on the magnetic drain plug. I don't know where they could have come from but possibly part of the adjustable bearing. Does anyone have a picture of this bearing complete? The opinion of most is that I should remove this cap and replace it with standard. Harv.