Checking the Bearing Clearances

F

frank55a

Well-known member
I think it is about time to check the bearing clearances of the engine in my roadster. The engine is installed and I would be doing this by my self. Every procedure I have found so far such as in the Mcree Engine book and Les Andrews book discusses this being done as an engine rebuild on the bench. I know people have done this procedure with the engine installed.

The engine was rebuilt at sometime before I acquired the A, when and how many miles ago I do not know. However, I believe it was rebuilt in the late 80s and considering the condition of the A when I acquired it (about 4 years ago) do not believe it had that many miles on it, probably less than 5,000 on the rebuild and I have put about another 5,000 miles on it.

Has anyone checked their bearing clearances themselves? Is there a web site or article that provides instructions. Apparently Mcree does not use Plastigage they do it by feel whereas Andrews does it with Plastigage. I recall years ago talking with people about this and it seems it was a mixed bag about half and half.

Thanks,
 
Use plastigage.

I recommend starting with the center main since that has the most wear. Then check the rear [ which is the hardest to do.] The front main rarely needs anything. The rods are easy to check.

I set them to .0015" and the rear maybe a tad tighter. If the shim pack doesn't want to come apart then I sand them on a piece of glass to the thickness I want and measure them at each end and the center. Remember to use oil on the strip of plastigage. I prefer to keep the shims on either side of the cap the same thickness.

Yep, and, I usually do this laying on my back. I've welded up a 'wrench' for the rear main nuts. I want to do this only once so I take my time.

I forgot to mention I use a small bottle and lightly add pressure to the crank to keep it seated up into the top bearing.
 
Last edited:
Bob C said:
Here's a video on adjusting the bearings. He doesn't use plastigage.
https://www.youtube.com/watch?v=8MH3HtTnshQ
Click to expand...

I use a different method again from that. After removing a shim, I soak a small piece (say, 1" x3/4") of newspaper with oil. I put that in the bearing and do it up. With all of the other bearings backed off a little (rods and mains), I try to turn the crank. I look for a bit of drag when I turn the crank handle but it will turn. When I open the bearing again, the paper talks. If it is squeezed dry, the bearing is too tight (you will know that already because it was hard to turn). If the paper is still soaked and not compressed at all, take out another shim. As the guy in that clip says, the weight of the flywheel make the rear main the most difficult. I like his method best for that but mine is fine for the others, including the big ends. When they have all been done, you should be able to turn the crank handle and feel some drag.
I NEVER use plastigage and as I assemble a bearing for the last time, I give it a wipe of a Teflon assembly lube I use.
 
If you are thinking that is only has about 10,000 miles or even 20,000 miles on the engine and it isn't making any noise then I wouldn't worry about it.
Leave it be.
 
1crosscut said:
If you are thinking that is only has about 10,000 miles or even 20,000 miles on the engine and it isn't making any noise then I wouldn't worry about it.
Leave it be.
Click to expand...

Tend to agree. At most, just check for any perceptable play manually by trying to move the rods. I am a plastigage fan but never tried to get a reading with the engine installed - seems like it would be difficult and prone to error. Would need a technique to hold the rod firmly on the crank while torqueing down the cap. If it sounds good just enjoy that ride.
 
It can be done under the car but it is much easier with the engine out of the car. Oiled Plastigage is the goto method. A little oil will keep the Plastigage from sticking to the journal or bearing. You can alternate sides to take a shim out if you want to reduce the gap by half the thickness of the shim.

In the day I would take up the bearings on a car that had very few miles. The bearings would seat in after a rebuild. Today the babbett is done better so that may not be needed. The bearings will let you know. Tap tap tap.
 
When you do this place a rag in the flywheel opening to catch a nut or cotter pin if you drop it. I have a lift and have checked the clearances often. Not a tough job but a slow job. Good Luck
Dan
 
If you where to do it this way, would you back off and loosen your previous main or rod to not influence the one you are currently working on? Then when completing all, go back and torque all of them to spec.
 
Volume 5 of the MAFCA restorer series of books has a procedure. They use plastigauge.
The instructions for use on shell type bearings is to put a smear of grease on the journal and a small quantity of silicon release agent to the bearing surface prior to putting the strip of plastigauge on and putting the cap back on for torque up. Some use lacquer thinner on a rag to remove the plastigauge material after the measurement is complete. Some folks use oil but this is what the product manufacturer recommends. I would not used a plastigauge material that has set around for too long. Use a newer batch to prevent indentation. A bit of indentation likely wouldn't hurt the babbitt but is may affect further checks.

Using plastigauge will give a reasonably close tolerance dimension to work with where other ways are just a guess. It would give a better "feel" for what kind of adjustment needs to be done.
 
rotorwrench said:
Volume 5 of the MAFCA restorer series of books has a procedure. They use plastigauge.
The instructions for use on shell type bearings is to put a smear of grease on the journal and a small quantity of silicon release agent to the bearing surface prior to putting the strip of plastigauge on and putting the cap back on for torque up. Some use lacquer thinner on a rag to remove the plastigauge material after the measurement is complete. Some folks use oil but this is what the product manufacturer recommends. I would not used a plastigauge material that has set around for too long. Use a newer batch to prevent indentation. A bit of indentation likely wouldn't hurt the babbitt but is may affect further checks.

Using plastigauge will give a reasonably close tolerance dimension to work with where other ways are just a guess. It would give a better "feel" for what kind of adjustment needs to be done.
Click to expand...



Yep, its pretty important to use fresh plastigage.
 
Thank you all for your time and comments.

Perhaps an explanation here is due, I can explain my reason for doing this check in one word, that is “confidence”. I am a driver, specifically my As do not get a ride anywhere. I have been in the hobby and driving Model As since 1963 when I got my first one.

The engine was rebuilt at sometime before the previous owner acquired the A, when, by whom, and how many miles ago the previous owner did not know. However, he believes it was rebuilt sometime in the mid to late 80s and considering the condition of the A when I acquired it (about 4 years ago) do not believe it had that many miles on it, probably less than 5,000 on the rebuild/restoration and I have put about another 5,000 miles on it.

At this time I do not know what the condition of the bearings or Babbitt is in, I think they are good but without a check it is unknown. With Covid winding down, we plan on catching up with our distance driving the As. To start we are planning a 1,000 mile plus drive in May. I would not be concerned about the bottom end of the engine if my As rode on a trailer most places or we did not plan to drive much more than an hour or two from home.

I think those of you that are drivers will understand.
 
Last edited:
Sometimes hornets nests can be opened. If you own this car from a friends estate in Oregon you will need to mark every rod nut and replace it exactly. The fellow that built this engine did a very carful balance to the rotating mass. The only thing I didn't like was he used the rod nuts to +- the final weights. If you own this car the engine was recently rebuilt with few miles.
 

Attachments

  • Ken's A.jpg
    Ken's A.jpg
    83.6 KB · Views: 29
Good afternoon...I agree with those above that are telling you, if the engine is quiet...then leave it alone...it will tell you when it needs to be tightened up. Also, I would not do the job alone without some experience. Even if someone with experience simply watches you do the work and coaches you. Again...if the engine is quiet...leave it alone...if it is making noise...then give it some love...Ernie in Arizona
 
A person can sometimes tell most of what you need to know by pulling the pan and inspecting what's laying in the bottom. Pulling the dipper tray can sometimes be tricky but they do come out. While in there a person can "shake" all the rods and check crank journal end play to make sure the thrust surfaces are still there. A good oil pump screen clean is a good idea as well.

If it had the babbitt done then it should be good to go. If pieces of babbitt are sticking out or laying in the pan then that's not good.
 
Last edited:
And old guy once showed me his technique for determining if a rod bearing needed to be adjusted. He used a small lead-headed hammer to tap on the rod cap after rotating it to bottom dead center. If too loose, it made a different sound than when sufficiently tight. It made sense to me but probably required an experienced ear for the determination.
 
I learned that hammer method and it was more the action of the rod on the journal that told the story. Also a finger on a wrist pin to piston with a (trusted) friend rocking the crank can reveal looseness there.
 
Last edited:
You must log in or register to reply here.
Back
Top