21A connecting rod question

Seth Swoboda

Seth Swoboda

Well-known member
I have a nos crankshaft for my 1940 Ford, 2.4990" mains and 1.9990" rod journals. I have 21A connecting rods that measure 2.2250" inside big end of the rod. What is the bearing thickness and will they fill up that .225" of space? I thought that the 21A rods were compatible with this crankshaft. Machine shop asked me before they start reconditioning the rods.
 
Std size of big end bore of rod is 2.220. Those are the rods to use with that crankshaft; depending on what bearings you can find, you'll need std/ .008 [01-6211-K] preferably, you may get by with std/.004.
 
So I have .005" of wear on big end of rod. Would the floating type bearings wear rod end some or is this way out of spec? Should I be looking for better connecting rods?
 
Seth, look for a nos set of 21a rods,they are around,then get a set of std floaters ,heaps of those around,,the cost will be WAY less than getting your rods resized and bushed.
Lawrie
 
I spoke with the machine shop again. They told me they would check the rods with an "arnold gauge" to get a more exact measurement on Monday. They just took a quick reading with an inside micrometer. Meanwhile, I'm going to contact Mac VanPelt monday to discuss bearings.

Lawrie, I think you're right and I mentioned this to the machinist. I have never had an issue with full floating type rods before so that is why I was asking.
 
Seth Swoboda said:
So I have .005" of wear on big end of rod. Would the floating type bearings wear rod end some or is this way out of spec? Should I be looking for better connecting rods?
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Not necessarily that much wear. The rods could have already been rebuilt (honed oversize to a concentric size) to fit an over-sized bearing). If so may be more cost effective to try and find the correct size bearing. NOS rods are getting hard to find.
 
Like I said ,the costs involved in resizing the rods,fitting and honing the bush to size,checking the rods for straightness,here it can run into $600 or $700.
You can get a set on NOS rods with the bush fitted and sized for WAY under that,
Lawrie
 
Whilst I generally agree with Lawrie; [I use nos rods in my builds], Barn Junk raises a very valid point.Check what you have first. Incidently, even though I use nos rods, I always need to get the bushes honed to suit, also check all rods for alignment. Just because they're nos doesn't mean they're perfect! Always check everything.
 
I have a chapter in my book on fitting these bearings. The big end bore of the 21A rod is 2.220, I open this to 2.221/2.2215. I also turn the crank to 1,998. Next I go through the bearings foir sizing (I keep abox full of used bearings) to find the right clearance. This is done with alittle Math. The NOS bearings range from .108/110 in thickness. All this is for standard bearings, Ford made .004 and .008 oversize Outsid sia bearings for rebuilt rods. so a rod bore of 2.225 would be for one of these.
The next thisn you have to do is BEND them to fit the crank, they have a tendancy ti tighen up in the box. Have yur flywheel resurfaced for the next operation. De bure the edges of the parting surfaces ans place them on the Flywheel, us a rubber/ plastic hammer to spread them tto fit the crank and still turn in the rod. Once to have accomplish this you have to open up the side clearnce of the bearing. I use .015 for a street engine and .020 for the 4 1/8 stroker cranks. You also need .010/.012 side clearance on the rods. All this may sound complicated, and not all of these numbers are mine. they come from many of us old timers the ran thes rods in some real wild engines. My last 296 engine had over 50k hard miles on it and the ownde says it still ran good when he replaced it with a 294 blown engine.. My present race engine is also getting a set of these.
 
A lot of the Ford authorized rebuilders here in the states honed the big rods ends out to +.004 or +.oo8 to match the bearings that were available. Some of the rebuilders cut the rod caps a little and honed them back to standard. I found a nice set of 91As that were back to std at a local swap meet for $15 and they were very well done, probably in the 1950s. Have to keep your eyes out for all the stuff ya may run across.
 
With unknown history the "out-of-round" condition of the rod bore must be checked carefully. It is not unusual for the top-bottom to become oversize. I have saved many sets of rods with careful filing and sanding of the cap on a flat surface. Not a job for quick results or amateur measuring skills.
 
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