Fitting Rod Bearings

[ursus]

I am working with new rods on a reground crankshaft and wondering about something I read in the old Victor Page book on Model A mechanics. He states that a rod and piston assembly should be able to fall by its own weight from a vertical position. That seems too tight as a rod fitted using the 0.002 foil method seems to fall by its own weight without the additional weight of an attached piston.

Am I OK with a rod that will fall from vertical by its own weight?

[cadillac512]

Yes, that will work fine. I agree with you...any rod that requires more weight than its own is too tight for me.

[nkaminar]

With precision machining of the rod bearings then the rods should fall without the pistons. With hand scraped bearings in the past, they were not all that accurate and were fitted tight. They were carefully broken in so that the high spots were worn down. The Model T engine was assembled very tight and smoked in on the assembly line using an electric motor. The engines were upside down without the pan on and a worker would stand over the engine pouring oil on the bearings while smoke was pouring out of them.

[ursus]

Originally Posted by nkaminar

With precision machining of the rod bearings then the rods should fall without the pistons. With hand scraped bearings in the past, they were not all that accurate and were fitted tight. They were carefully broken in so that the high spots were worn down. The Model T engine was assembled very tight and smoked in on the assembly line using an electric motor. The engines were upside down without the pan on and a worker would stand over the engine pouring oil on the bearings while smoke was pouring out of them.

I went back over the details of Victor Page's section on engine assembly and now understand the point made by nkaminar. There was a lot of bearing scraping back in those days.

[Dan McEachern]

How much clearance do you measure between the crank shaft and the rod bore??
I would suggest .0015"/.0020" total clearance. If you don't have a good way to measure, plasti-gauge is better than nothing.

Or- install the rod on the crank pin with assembly lube or motor oil, torque to 50 ft-lbs. If no drag at all, start peeling shims evenly from both sides until you feel moderate resistance turning the rod. Add one shim back to one side only and you should have just the right amount of clearance. This is based on shim layers of about .002/.003" thick.

[alexiskai]

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Originally Posted by Dan McEachern

If you don't have a good way to measure, plasti-gauge is better than nothing.

Just for reference, what is the preferred way to measure this clearance? I assume you mic the OD of the crank and then tighten the rod without the crank in it and use a bore gauge to measure the ID of the rod?

[cadillac512]

Originally Posted by alexiskai

Just for reference, what is the preferred way to measure this clearance? I assume you mic the OD of the crank and then tighten the rod without the crank in it and use a bore gauge to measure the ID of the rod?

That is correct. Measure several places on the crank journal looking for size,taper and roundness. Same with the rod after torquing it to spec.