1951 - rod & main clearance

whizzernick

whizzernick

Well-known member
I have an original 1951 ford eng. I plan to use it but thought as it is on eng stand why not check rod and main clearance's. I have .003 on both(plasticgage) std bearings. should I install new std bearings or is .003 OK ?
I have run this eng ---ran good -- good oil pressure when above idle rpm---little or no smoke.
 
Ford calls for ,001 to .002 clearances, is the copper showing thru the babbit in the bearings, if so I would at least replace the bearings with new ones, that should tighten things up a thousand or so, been awhile since I built a flathead, been taking cancer infusions treatments, but they used to make 1 to 2 thousand under bearings, if you can find them buy .002 under, using them will give you exceptable clearance, but at the least I would install new bearings
 
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Plastigage doesn't tell you if the bearings are egg-shaped. Miking the journals would be better.

How do you plan to use the engine? Long trips, local duty, etc.? Mine had similar clearances and ran fine, no noise, decent pressure, but I wanted it to last a long time so I had the crank turned.

Does your engine have hardened valve seats, or the rotator-type valves? If you are going to push it at all, I'd get hardened seats put in.
 
You could confirm with red.As .003" is the upper end of green. But .003 is too much.

Specs for colors

Green: 0.001" to 0.003",
Red: 0.002" to 0.006",
Blue: 0.004" to 0.009"

R
 
I'd like to bring up the subject of oil viscosity here. With .001-.002" Rod and main bearing clearance, do you still feel running 15-40 oil is a good idea?
 
As much as I used to love high oil pressure, I've changed my way of thinking. If you are running your pump over relief, seems it is overworking your pump and creating excess heat. Didn't Ford specify 30 wt summer and 20wt winter? Certainly they were considering close tolerances here. I'm leaning toward a viscosity that would produce just under 50# warm at cruising speed.
 
If your just try to get by with an engine with a lot of miles, here is a trick we use to do when we didn't have money to buy bearings. Take a piece of aluminum foil, that's usually .001 thick, cut it the width of the main bearing and put it in the main bearing cap under the bearing, that will take up some clearance and won't hurt a thing. Walt
 
Walt
That reminds me of stories about combat boot leather tongues being cut to fit Model A rod caps. My last boss remembered a guy doing that every weekend that he got leave from the army. Can you imagine pulling the pan just to make a trip home for the week end. Folks did a lot worse back in the day.
 
This is sort of "on the subject". Coating of bearings (and other parts as well) is very standard today. There are companies that coat bearings OR you can coat them yourself with the right equipment. The typical moly coating on a bearing is .0005" thick for each bearing shell or .001" for both halves. Where is this used? On just about every Nascar engine every week!

When I built my flathead 276" I also coated the pistons and combustion chambers-----helps to keep a little more heat in the combustion chamber. You can also moly coat the sides of the pistons----helps to reduce "piston slap".
 
You don't mention anything about your oil pump, but the Melling M-19 will "cover" the .003"/.003" clearances. Those numbers are somwhat loose but should not be an overall issue! We have built many with .003" (mains) and .0025" (rods).

You can't do much with the main clearance but you could "shrink" the rod clearance at home (or in a shop) with some slight labor! You just need to be very careful. The plastigage would make this procedure somewhat more difficult.

(Add) The only coatings (Teflon) we use now are on our cam brgs, it helps "tighten" the room very slightly in that area.

Thanks, Gary in N.Y.

P.S. We don't place much reliability in using plastigage for measuring, believing it isn't really accurate enough?? This is my own take on it.
 
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