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Buick Brain Trust I seek your knowledge! Rebuilding a 1940 Model 41 and have poured through the forums here and seen some information both ways in terms of keeping the babbitt bearings or changing to insert type. The thought is to be a road and show quality when complete, so I do expect to put some miles on it. Just pulled two rods and they need some love... see below  Overall thoughts? 

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It is not only how many shims, but how thick are the shims in thousands of an inch. Need to know the total thickness on each side.  Shims come in many different thicknesses from .001" and up.

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Posted (edited)

Lets see the rod side. That's where any pounding shows. Oops top pic is rod side.  Also important is any out of roundness on crankpin.  If crank is good and there is still some babbitt on the rod I would just set them up and run it.  Not totally sure on Buick but it looks like a "thin babbit"  rod. if so, by the time it needs all the shims removed there's almost nothing left,  This is why they are asking the shim thickness. 

As far as changing to inserts, if the machine shop can do it and find shells, in my opinion that is the way to go. Commonly done on Chevy 216's.   235 shells work. 

Edited by Oldtech (see edit history)
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The babbit looks well bonded to the rods and shows no sign of crumbling.  If you can get the proper clearance with the plastic gauge by removing shims, I would not spend the $$ to rebabbit or replace with inserts.  Babbit is so much more forgiving than inserts on these systems without good oil filtration.

 

Bob Engler

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I agree with Bob. Babbit is very forgiving. Factory babbit is even better. If this is the worst bearing surface in this engine and it has good oil pressure in all operating conditions I would definitely run it. You may spend some time getting the oil pump in good condition. You can also play with oil viscosities some  to obtain desired oil pressures . If you drive her responsibly , you can have many years of use while avoiding thousands of dollars in engine rebuild cost.

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11 hours ago, Oldtech said:

As far as changing to inserts, if the machine shop can do it and find shells

OK, I can agree only after the bearings are completely worn out with no more shims to remove.  And then, change to inserts only if the inserts can also be inexpensively replaced down the road when needed.  Note that Babbitt is actually the bearing surface used in new replacement insert bearings.  The only real difference is the thickness of the Babbitt.  IMO, poured Babbitt bearings offer more flexibility to adjust for wear by removing shims for individual bearing journals while insert bearings typically require replacement of all rod bearings when only one or two are worn out. 

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I quite agree Mark, Run the current ones until all shims are gone. Now this comes from Chevy experience, but looking at the rods, they are spun babbit. Not poured.  The factory learned they could spin the rod and pour the metal, having it forced outward by centrifugal force. This makes a nice job but is thinner than poured. When the shims are gone you are close to contacting the steel rod. And that is never good. (Especially on a splash lube Chevy.)   Yes, there's a story. 

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  • 3 months later...

If you decide to do inserts, Terrill Machine in Texas (254-893-2610) does the rods on an exchange basis for $48.00 each. They are also cheapest on most

other internal parts. I sent the rods for my 1940 Super off to them yesterday. I used a USPS Medium Flat Rate Box that cost $15.05.

My engine was running fine with good oil pressure but had piston damage and had to be torn down due to excessive oil burning and blow by.

The bearings were not loose but the Babbitt had begun to separate on 3 or 4 of the rods. One probably would have failed had I driven the car to the shop 

rather than having it flat-bedded. I think I will feel a lot more confident with the inserts even though I got 50 years out of the engine that was in unknown

condition when I got the car. The car has been in the shop since March, but thanks to the pandemic they only got the engine out of the car a couple of weeks ago.

Since there have been no cruises or shows either I don't miss the car as much as I would have in a normal year.

 

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