VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 1928 Engine Knock - Removing Main Bearing Shims

My Son and I have a 1927 Chev Landau with a 1928 engine. The engine runs great and has no issues other than being quite loud with a pronounced knock when at speed. The knock intensity changes when I retard the spark, but the knock does not completely go away. I have read a number of posts on this forum about similar engine issues, and from that have deduced that it is most likely the clearance on the main bearings.

Apparently the way to fix this type of issue is to remove a shim from each of the 3 main bearings.

I am a handy, but a complete novice at this type of thing. I am hoping you Guys (or Gals) that know, could give me a bit of advice: Can I access the main bearings and remove one shim from each bearing by simply removing the oil pan, or does the engine need to be out of the vehicle ? To ensure I don't leave the engine too tight, how can I check this after removing a shim?

Really appreciate your help.

You don't rremove one shim. You remove the required amount (one or more) and is done by just removing the oil pan. I would suspect it could also be a connecting rod bearing too loose. Remove one spark plug wire at a time. If the knock lessens on one cylinder in so doing that rod is loose or burnt out.

Yes, you can access all the bearings (main and rod) by just taking off the oil pan. I suggest checking all the clearances and clean out any sludge while you are down there. Be sure to look at the oil pockets with a mirror. Sludge hides everywhere!

When I checked these clearances on my '28 engine, I found that the previous owner had smushed some of the shims so they were folded over in spots, so were falsely tight. I cut off the folded parts, cleaned up the shims, and checked each bearing clearance.

I loosened all the bearing caps and worked with one at a time, so I knew each was what it should be. I removed two shims (one from each side of the bearing), tightened it, and then spun the engine by hand to make sure it turned freely (spark plugs out). When I felt it bind, I put one shim back in. The clearance for each ended up about .0015 of an inch (as measured by plastigage).

Cheers, Dean

You can also use the old mechanic trick of a large screwdriver or a dowel, with the thumb over the end, placed behind the ear, and place the other end over the three main bearings and then each rod. Also follow the recommendation of the trick of removing a spark plug one at a time.

Don't get excited, and jump to a conclusion, but quickly, remove the oil, then the pan. Start the engine, with someone with good ears lying under the car, listen quickly for the direction of the noise. DO NOT run the engine over 1 minute, and DO NOT race the engine.

As to the fix, and this will also draw a certain number out of the grass, use Plastigage to measure the adjustments for each item that you wish to change. After making the change, use some of the tricks mentioned in the repair manual. Such as the use of the hammer to check rod bearing adjustment.

Thanks very much for these answers.

When removing shims, is it important to always leave the same number of shims on both sides of each individual bearing?

Common practice says an equal amount from each side.

I had a serious knock in my 28 and after playing around with the shims (with no luck) I found that my knock was reduced by adding some lead replacement additives in my gas tank. I took a couple tanks worth of gas to hear the difference but the knock slowly went away.