v8 flatty connecting rod question

I am rebuilding my 1949 v8 flathead and I am having a concern with the connecting rod clearances. I have a 4 inch crank cut 10 thousands undersize and am using 10 thousandth oversized bearings. I am connecting the rods to the crank and the clearances check out with plastigage, but I can move the piston end of the rods about 1/16th of an inch side to side. Is this normal. It just seems to worry me that I am missing something. Should the rods be a little wobbly, or should they be tight?

Any help would be greatly appreciated.

EdiRoy.

 

a 16th is .125 or 125thousands clearance

 

I can move the piston end of the rod about 1/16 of an inch. Maybe a tad more. Is this normal?

 

you need to check the rod to piston clearance when its in the bore and mounted on the crank should be .050-.300 on the crank end the side clearance is with both rods mounted and i dont think your using babbit bearings so ill say .020 - .050 should be fine

hth good luck

 

Actually 1/16" is .0625, not .125. I have always had success figuring 1/16 is close enough to .060 to visulaize some of these things (like overbores).

 

When the rod is torqued to the crank, I can grab the end of the rod and wiggle it. That is my worry. Shouldn't it seem tight with no wiggle? Any engine builders out there that can let me know if this is normal. I have checked the clearance with plastigage and it seems o.k. It just seems weird that I can wiggle the rod.

Thanks.

 

Just to be clear. The piston is not attached yet.

 

Wow! That's mighty loose. .050-.300 must be a typo or perhaps the clarity of an unpuncutated run on sentence is confusing me.The connecting rod clearance on the crank pin for a 1949-53 Ford 8BA is .0005"to .003'. Read the last paragraph here: http://www.reds-headers.com/html/red_s_engine_talk_32.html Also here:
http://www.secondchancegarage.com/public/406.cfm

 

If your rod bearing clearance is less than.0025 you are fine. Remember you are magnifying that .0025 by about 6.5 -7 inches. Go worry about something elese like what;s for lunch.

 

Are you saying that you are concerned about the the movement of the rods as they slide "side to side" when both are installed on the crank? OR Are you concerned that there is actually perceptible "Wobble" when you rock the end of the connecting rod that attaches to the piston? Post your question on www.fordbarn.com for other opinions.

 

HI 19fordy,

Yes, I am concerned that there is actually perceptible "Wobble" when you rock the end of the connecting rod that attaches to the piston. Not the side to side sliding motion.

EdiRoy

 

My clearances seem correct at about .0015 It just seems weird that there would be a wobble.
Maybe I am being too paranoid.

 

Don't risk putting the motor together that'll knock in a few miles. It's normal to get a little rock with connecting rods, but find someone with a dial-bore gauge that can accurately measure the clearance to .0001"

 

I will double check with a bore gauge. Better safe than sorry.

Thank you everyone for all your great advice.

EdiRoy.

 

It would seem logical to me that there would be a very tiny amount of "wobble" depending on the actual amount of rod bearing clearance you have. A smaller amount of clearance will result in a smaller amount of "wobble" when you "rock" the "piston end " of the connecting rod than if you have a larger amount of clearance. Remember also that there has to be some "clearance" as the rod bearing rides on a layer of oil. Zero clearance would result in zero wobble, and an oil starved bearing. I DID FIND THE FOLLOWING INFO. in Ron Holleran's book "NOSTALGIA Rebuilding and Modifying the Flathead ford V-8" first published in 1992 and again in 2006. His contact address is in the book just in case you desire a copy or have a flathead question. He is an expert of flathead engine rebuilding and knows his stuff.
Anyhow, below are the pages in his book that discuss rod bearings. He does not mention the "wobble" that you are concerned with, but he does discuss "side to side" movement of the installed connecting rods. It seems to me that if you have the correct rod bearing clearances you are "good to go." As you will find in the photos below .012-.015 rod bearing side clearance is acceptable. But .012 is best. Also, BUY his book. It's the best.

 

Thank you for the information 19fordy. I will definitely be looking into that book.
I am going to unearth my old kennedy tool box and find my bore gauges.
That will make me feel better about what I am doing.

EdiRoy.