Connecting rod shim adjustments - how-to

M

mcgarrett

Well-known member
Just purchased a '30 Roadster and the engine sounds like it might have loose connecting rods. I plan to drop the pan and remove shims, but I am requesting advice from those who have actually done it successfully. Would appreciate it if someone would walk me through the process.
Thanks,
Mike
 
If the crankshaft was out of the engine, you'd adjust them one at a time and "feel" the drag in the bearing by moving the rod by hand. With the motor in the car, the drag from pistons in the bore and other places makes that a non starter. I'd use something like Plastigauge to check clearances. I'm sure a search will bring up the information you want from earlier threads on the matter.
 
Bob C
Helpful video - thanks for posting. The process is pretty much what I expected. I have never done it myself, but have heard others talk about doing it and wanted to confirm what I think I already knew! :)
 
Plastigauge is one way. One other technique is to take shims out, alternating side to side, until you cannot turn the crank, then add one shim back in. I have done it both ways. Inspect the journal to make sure it is not damaged. Use assembly lube during the final install of the bearing caps.
 
nkaminar,
I think I'll go with the latter of the two methods. Seemed to work well for the fellow in the video.
 
I'm a plastic-gauge guy and set them at .0015".
I try to keep the shim pack per side equal thickness and if they don't what to peel apart I just sand them on a piece of glass.

Usually the center and rear mains are the ones that require tightening.
 
I'm suspicious that my noise problem is loose connecting rod bearings, so I'll be working on them primarily using the same methodology.
 
A rod noise is a light clicking sound when there is no load on the engine. It can be heard by running the engine up to a fast idle (1,000 rpm) and then slowly backing off the throttle. It can also be heard when running down the road with no load on the engine, neither accelerating or decelerating.

A main bearing noise is more of a deep thump and can be heard when the engine is under load such as running up a grade or accelerating.

Sometimes a rod noise can be heard at idle but most of time not. A valve tappet noise or a camshaft gear noise can be heard all the time.

Synchro, are you being effected by the heavy rains in the east?
 
nkaminar,
The noise I'm hearing is a knocking sound that is more pronounced when the spark advance lever is pulled all the way down. I don't hear it near as much when I retard the spark to about half way. When traveling at 35-40 mph and then getting off the throttle, the noise goes almost completely away. When I first got the car, it was noisier than described above with the lever settings the same. I checked the timing and it was way off (too advanced), so I corrected that. I'm thinking the knock was due to pre-ignition. It's some better now, but still think some shims need to come out. We'll see...
 
Sounds like you have the spark lever to far down. This is from the instruction book.


The Spark Control For average driving the spark lever should be carried about half way down the quadrant. Only for high speeds should the spark lever be advanced all the way down the quadrant. When the engine is under a heavy load as in climbing steep hills, driving through heavy sand, etc., the spark lever should be retarded sufficiently to prevent a park knock.
 
Having the ignition too far advanced can ruin rod bearings in short order.

Timing: The trick is finding the knee in the advance curve. That is where one click further advance will not improve engine performance and one click retarding will hurt performance. The optimum timing will change depending on conditions, such as pulling a grade. Or, as the instructions say, driving through heavy sand. Last time I did that was in 1965.
 
Last edited:
nkaminar said:
A rod noise is a light clicking sound when there is no load on the engine. It can be heard by running the engine up to a fast idle (1,000 rpm) and then slowly backing off the throttle. It can also be heard when running down the road with no load on the engine, neither accelerating or decelerating.

A main bearing noise is more of a deep thump and can be heard when the engine is under load such as running up a grade or accelerating.

Sometimes a rod noise can be heard at idle but most of time not. A valve tappet noise or a camshaft gear noise can be heard all the time.

Synchro, are you being effected by the heavy rains in the east?
Click to expand...

Thanks for asking but we are fine. The rain is further north. Boy oh boy, have they copped a bucketing this year. Many places have gone under for the fourth time this year. This flood is higher than the others. Crazy stuff.
Where I am (in Melbourne - 640 miles south of Sydney), we have a much smaller rainfall every year than Sydney where the floods are this time. In fact, it has been a little on the dry side so far.
I don't know which is worse flood or drought but it is home. As Dorothea McKellar said in her 1908 poem about Australia:
I love a sunburnt country,
A land of sweeping plains,
Of ragged mountain ranges,
Of droughts and flooding rains.
I love her far horizons,
I love her jewel-sea,
Her beauty and her terror
The wide brown land for me!
 
Finally got the pan off the Roadster today to try to correct a profuse oil leak and made a disappointing discovery. The rear main had NO shims! Without them, can't make an adjustment to control the oil leak. Sure isn't good news - looks like a major teardown/engine replacement in my future. :(
 
First, measure the clearance with some Plastigauge. You can lap (sand) off some material on the rear main cap to close it up but it will ruin the cap for future use with shims.

The rear main will leak if the cap does not seal well on the sides. Some sort of gasket goo is commonly used when mounting the rear main cap.

All this work is more easily done with the engine out of the car and up side down on an engine stand. You may be right that an overhaul is needed. Examine the rest of the engine. Is the Babbett cracked or missing parts and is the cylinder worn so that the piston moves a lot sideways when at the top? If that is the case then consider the Burtz engine instead.
 
As mentioned,
I've sanded caps on a piece of glass taking 3 measurements on each side, which means you'll need a micrometer. It'll get it by for another decade.[smiley face]
What are the main clearances now?
 
You must log in or register to reply here.
Back
Top