VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1937-1945 Connecting rod bearing clearance

What is the clearance on connecting rod bearing for a 1938 216 motor?

The recommended clearance is 0.001-0.002".

Thanks, Chipper

I would suggest following the proceedure in the shop manual. Remove shims untill the rod can not be snapped back and forth by hand but will move with light tapping of a small 8 ounce hammer....Then install one silver shim. Should the be able to move by hand with a little effort. This will get the bearing as tight as possible without being too tight....especially on a "used" crankshaft. With the heavy cast iron pistons the rods can make noise with .002" clearence.

Chevygene how does one get them to snap back and forth by hand when I'm looking up at them with the motor over my head. They are in my truck. I can read the shop manuel too, but I'm taking the slop out because of wear and needed to know what the tolorance was or is. You have a good point though as to get them as snug as you can without being overly tight. Thanks to all.....

Just slide them back and forth on the crankshaft. They have a few thousands end play (front to rear) and when they have some miles on them its very easy to do. Just give it a try. When properly adjusted they should move with hand pressure. If tapping with the hammer is necessary they are too tight and a sim shold be added. When adjusting rods I remove the dipper until I am finished. This eleminates damaging the dipper by tightening the rod nut against it several times.
In 1938 the book didn't mention bearing clearences or torque figures. Torque the rod bolts to about 40 foot pounds. The rod bearing clearence will be correct by using the original factory method and I found its more accurate tha Plastigage.
You should also inspect the condition of the bearing babbit. The lower part on the cap will look OK. The upper part on the rod gets all the pounding and if run loose for a period for some time little chunks of babbit will fall out. Will look like big cavities.
When cleaning out the pan place the garden hose over the main oil feed pipe for the the pipes going to the troughs and make sure all the pipes are open. Very common to find one or two plugged with sludge. ...not good. They should all squirt in the same area on the side of the pan.

Now I should be OK with the info you just gave me chevygene. I have bought plastigauge today, but will try your way. It sounds like it might be better. Hope I can get them to spec out at about .001". I will be pulling the oil pan again some time this week. I have already checked for oiler tube flow. They are good and shoot to same spot on the opposite side of pan when I shot water through them. Still will have to inspect the upper babbit. I'll repost my findings and adjustments when I get the job completed.

I've done it a few times like Gene says and it works fine. One more thing to add that I do, especially on a higher mileage engine, is check the clearances like Gene describes, but do it at 90 degree intervals of crank rotation. If your journals are a little out of round, what may check out at say BTDC could be a little tight when the crank is rotated a 1/4 turn. Maybe I'm just being anal, but you don't want 'em too tight.

Bob

I am rebuilding my 38 Chevy 216 which I recently acquired on ebay and do not know the mileage or history of the engine except the numbers tell me it is correct for a 1938 Chevy Master Deluxe (fan blade dia was the give away on the Master deluxe / Master choice)

The following nubers may be useful to you to give you an idea of a typical Out of roundness and taper that occurs on the journals:

I have measured my 1938 Chevy 216 crank accurately for Wear (average of 4 readings of the reduction of diameter of journal, 2 axially along the journal top to bottom and 2 associated with each of these but side to side[90 degrees to first set]), Out of Round (difference between two diameters chosen randomly but at 90 degrees to each other) and Taper (difference between the diameter at one end of journal and diameter at the other end of the journal along the axis of the crank).


My measurements of Crank:
Main #1 = 2.6790 to 2.6808 in.[Out of Round =.0018::Taper =.0008]
Main #2 = 2.7102 to 2.7106 [O.of R. = .0004::: Taper = .0004]
Main #3 = 2.7410 to 2.7418 [O.of R. = .0008::: Taper = .0008]
Main #4 = 2.7728 to 2.7728 [O.of R. = .0000::: Taper = .0000]
Main #4 = 2.7736 to 2.7739 (frwd, rear on journ)[O.ofR. = .0003]

Rod #1 = 2.3067 to 2.3070 inches [O.of R.=.0003:: Taper = .0005]
Rod #2 = 2.3059 to 2.3077 [O.of R. = .0003::: Taper = .0018]
Rod #3 = 2.3069 to 2.3061 [O.of R. = .0008::: Taper = .0010]
Rod #4 = 2.3052 to 2.3068 [O.of R. = .00015::: Taper = .0007]
Rod #5 = 2.3052 to 2.3064 [O.of R. = .0013::: Taper = .0003]
Rod #6 = 2.3066 to 2.3063 [O.of R. = .0003::: Taper = .0009]

Main # 1 Wear = .0041
Main # 2 Wear = .0046
Main # 3 Wear = .0046
Main # 4 Wear = .0042
Main # 4 Wear = .0033

Rod # 1 Wear = .0047
Rod # 2 Wear = .0047
Rod # 3 Wear = .0050
Rod # 4 Wear = .0055
Rod # 5 Wear = .0057
Rod # 6 Wear = .0050

All of the above wear readings are based on the 1939- Chevy Shop Manual Specifications. The 37 and 38 Shop manuals both may have errors in the diameter of the main bearing journal for mains only.

First the 39- listing Specs:
Main # 1 = 2.6840 +/- .0005 inches
Main # 2 = 2.7150 +/- .0005
Main # 3 = 2.7460 +/- .0005
Main # 4 = 2.7770 +/- .0005

For All years (both 37-38 listings and 39 onward listings) Rod Specs: Journal Diameter = 2.3115 +/- .0005 inches

Now the 37-38 listings Specs:
Main # 1 = 2.6860 +/- .0005 inches
Main # 2 = 2.7170 +/- .0005
Main # 3 = 2.7480 +/- .0005
Main # 4 = 2.7790 +/- .0005

Mike

Looks good for a used engine. Should tighten up and be just fine. Wonder what happened to # 2 rod? Is is a little bent?

I found it easy to move the bearing( end to end, horizonally) in #'s 5&6 connecting rods compaired to #'s 4,3,2&1.

#4,3,2,&1 were snug and did not bang up against end of crank shaft shoulder, (unmachined part)

#'s 5&6 were way loose and when I moved them they made a distinctive sound of metal against metal when they hit the crank shaft shoulder.

I found that #'s 5&6 connecting rod only had two shims (brass looking) on each side. I have not checked for # of shims in #'s 4,3,2 &1. The book states there should be three shims on each side.

Are the three shims that are suppose to be there all .002" shims or is there suppose to be two .002" shims and one .001" shim on each side.

I removed one (brass looking) shim on the cam side of # 6 connecting rod. I then retorqued the nuts and now I find the # 6 connecting rod is so snug it will not move at all from side to side (horizonally).

When I removed the one brass shim was that a 002" shim. And when I removed the .002" shim was I actually only removing .001" clearance since I only removed the one shim on the cam side??

I have not checked it for movement in any other position than position where I took the shim out.

Has someone already removed shims in this motor?

It would be VERY unusual to find an engine that old that did not have shims removed. t was common to adjust rods and mains every 40 to 50,000 miles. Also usually done with and engine overhaul.
When new there were four shims on each side. Two brass (.002") and two silver (.001"). It is permissable to remove what ever shims required for adjustment. Do follow the "remove till rods will not slide and add one" method....Even the ones that presently do not move freely before adjustment may be loose.

Thanks for that info chevygene. I now have #6&#5 adjusted right on the money. The rest are prety snug. I think those two were the ones giving me the trouble. Im down to 2&1 shims (brass) on #6 and down to one chim (brass) on each side on #5. Never saw any silver .001" chims on either #6 or #5 though. I will put the oil pan back on tomorrow and see if the problem is fixed. I'll post again after I have tested it.

Install the pan gasket in the proper order. The side gaskets must be stuck to the block first. I use grease. The end corks go in last as the ends but up against the side cork tabs. The end corks from modern gasket sets are not pre-curved like the originals. Would help if you could "bend" them before installing so the stay in place.
I make studs out of 1 1/2" long bolts by cutting off their heads. (1/4" bolts)...thread the studs into the side of the block, two on each side. They help keep the gaskets in place and make sure the pan is correctly positioned so the end corks stay in place.

you did not say what your problem is . if it is a knock that im chaseing i put the rods up with luberplate start the engine with the pan off and listen . if you dont run at idle very long it will not heat the rods . a knock can be very deceving . piston pin , piston , main bearing , timing gear , loose flywheel on and on hope this helps pushrod

Problem was push rod crank wear. Making noise from 5 & 6 cylinders.
I managed to get everything back together after removing the right amount of shims today.
The old truck sounds good going down the road now. I learned a lot from you guys here on the forum the last few days.
A special thanks to you chevygene, you were right on the money with everything you stated.
Maybe I can just read here for awhile and not have to post more anymore messages for awhile.