Tap rod bearings into shape??
 

I got .010 undersize rod bearings for the 36 LB engine we're rebuilding/having rebuild. Part 48-6211-C. (.010 under, STD on the rod)

The rebuilder says they don't fit the rods. Neither of them. Seems odd to me. Parts are NOS. I suppose 1 set could be mixed up at some point the last 70 yrs, but all 4...

In the Flathead Rebuild book I read it's common to tap them into shape. When I mentionned this to my rebuilder, his eyes almost popped out. [emoji28] They've done 1 or 2 newer Flatheads before, but they rebuild for a wide variety of cars, mainly top notch stuff (Ferrari, Maserati, etc.)

Is it really common practice to tap those bearings into shape? Do they really get a bit misformed from laying on a shell all those years?

Thanks.

Dennis
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Re: Tap rod bearings into shape??
 

Yes. I've never done it, but reshaping the rod bearings is an important part of the process. There are more experienced people here on the barn that will hopefully add more comments. Note this only applies to floating rod bearings. People have mixed up the instructions before and tried to do this with insert rod or main bearings.
A thought: Some bearings are oversize on the outer diameter, to suit oversize rods. Make sure the bearings are sized to suit both the crank and the rods.

You can check the thickness of the bearings by measuring the crank diameter and the bore of the rod and doing some sums to get the bearing thickness.

Mart.

Re: Tap rod bearings into shape??
 

Thanks Mart!

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Re: Tap rod bearings into shape??
 

First of all, you need to make dang sure that you have the right bearings. There are TWO dimensions that come into play -- the ID for the crank journal and the OD for the rod big-end bore. One frequently sees oversize bearings on BOTH dimensions. Hopefully the box and/or bearings are marked correctly.

1) If your machinist has an accurate bearing mic, they can measure the thickness of the shell and get an initial idea if these will work. Measure the crank journals, measure the rod big-end bore, measure the bearing thickness and do the math. You want about .002 clearance. This is your starting point.

2) If these appear to be the right bearings, then it would be rare for NONE of the sets to fit. Usually I have to "tune up" a couple sets (with a rubber mallet), but not all sets.

3) I polish the outsides/insides with fine ScotchBrite and lacquer thinner. This is part of the process as well.

4) Make sure you do all the mic measurements - before you start working on the bearings themselves.

5) Checkout this little video I made a few years ago - might help you guys:

https://youtu.be/CyVLsPdbhS8?si=c8Qzhkq6HmtMDmLh

6) Also, some guys like "Ole' Ron" will open up the big-end of the rods about .001 just to give a bit more clearance. Keep in mind that these surfaces are bearing surfaces - so whomever is running the hone needs to be able to use the hone in a manner that polishes the big-end surfaces - as the bearings need to "float" in there. This is different than typical modern rods where the bearings are "tanged" and don't float in the rod.

Re: Tap rod bearings into shape??
 

Ha, that's a coincidence. I just saw your video when looking for more info on those floating bearings. Thanks for the info.

I just talked to the rebuilder. They're not that familiar with Flatheads, but were open to the info I showed them on making the bearings fit.

Thing is, I got virtually 4 different sets, all supposedly .010 under and STD on the rod. I'm new to this, so I didn't notice before. 1 set seems a different size, the others are all different material. They don't want to use them.

So I'll be looking for another complete, identical set. Either .010 or .020 under.

Dennis

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Re: Tap rod bearings into shape??
 

The earley rods measure 2.220 stock. if my memory is correct. That is a good starting point putting the two halvs to gether they should measure 2.217 . Normaly the pair will not be round so smack them with a large hammer??? Just kidding, but the flanged bearings are hard to correct. I like the floaters. The Ford bearings were made from Cad/silver and run forever.
Gramps

Re: Tap rod bearings into shape??
 

I watched John Forces bottom end man, on tv, replace rod brgs in johns top fuel car and he tapped one of the brgs with a mallet, on the floor, to get it to fit!

Re: Tap rod bearings into shape??
 

If you can find rod bearings that are undersize for the crank pin and oversize for the connecting rod bore, your machinist can then hone the con rod big ends to fit the bearing thereby restoring to original clearances.

Re: Tap rod bearings into shape??
 

Yeah, I have NOS rods and the rebuilder prefers to stick to undersize on the crank only.

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Re: Tap rod bearings into shape??
 

That is how I'd do it. You'll have a much better chance of finding bearings - both now and later.

Re: Tap rod bearings into shape??
 

Good, then that’s one less thing to worry about.

Re: Tap rod bearings into shape??
 

Great information about the bearings!!!
Do you have a video or write up about the polishing process???
If not, what scotchbrite pads used ???
How did you insure that the bearing thickness was even!
Thanks
Tim

Re: Tap rod bearings into shape??
 

I’ve been building engines since the early ‘80’s and it is not uncommon to have to “fit” the bearings to the shaft. I agree that you need to make sure you have the correct size bearings before you start. Make a visual check since some bearings actually had the size stamped (ink or mechanical) on them. Unfortunately, experience in properly fitting a floating bearing has a sound and feel which no one can describe in writing. Most times they need opening rather than closing as your picture shows. If your machinist has properly resized the rods and the crank is ground correctly, he may test fit each set of bearings by installing a single rod on the bottom side of the crank (outside of the cylinder bore).That way you have access to half of the bearing(which you can hold) and a rod (which you can move to check for clearance). Everything can also be checked with Plastigauge or .002 shim stock without the risk of piston or ring damage. I hope this gives you some additional ideas.

Re: Tap rod bearings into shape??
 

I used floating bearings in all my race engines back in the 60's. I used an old flywheel re ground as the surface I used to tap the bearing in place. you need a bearing mike which has a ball on the anvil side fo measuring the thickness'.
To start with, measure the ID of the rod with the cam torques in place. The 21A rod measures 2.220
Crank measures 1,998 and the bearing thickness is .108
now I'm doing all from memory so they maybe wrong, I put a small amt of oil on the old flywheel place the two bearing halfd to gether and measure roundness place the bearing on the fltwhell to spred the bearing and on edge to decrease the size I use a smal ight hammer to accomplish this
This is is a putzing job, do enough of them. and it gets easier.
whit I look for is .002" On both the rod and the crank, total of .004 plus alittle
I also like .012/.015" clearance between the rods to allow for ore oil flow. keeps the bearing cooler
Lastle I save allltthe old bearings from the junk engines so I have a supply of different thickness bearings
It's fun to relive this. Take care
Gramp
PS all engines come with a surface plate. us it.