Shims Under Main and Rod bearings

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Pompis

Pompis

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Hey guys and girls I just bought a 75000 mileage 318. After doing a compression test the cyl 2 failed because a cracked valve seat and cylinder 2 have bad pitting. So I sent the block to machine shop for sleeving cyl 2 because the other cylinders was in really good condition with minimal wear. I ordered a rebuild kit with new pistons, bearings, timing set and oil pump.

I measured the crank and rod journal with a micrometer and the numbers are: Crank journal 2.5005". Rod journal 2.124" which are STD size. The bearings mounted in the 318 where marked with AT20 which I first tought would be a .020" undersize bearing but since the journals measured STD that was what I ordered. The thing is when I test fitted the rod with the new bearing I had visible gap so I knew I ordered wrong bearings. So I measured the rods bore and it was not STD size they are .0020" "oversized". I should have measured the rods before ordering the bearings but the seller didn't have oversize bearings. My question are can I put shims that are cut out the same size as the bearings to mount under the bearing half?

Or is there any out there selling bearings that have material added on the "outside" of the bearing half to fill out where they removed material from the rod bore? AKA oversize bearings?

Thank you FABO
 
No I would not do that prob make them out of round, you are pushing the inside tighter get the right ones.
 
No. You need new rods if they were machined oversize.
 
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Not sure I follow you. The ID of a rod on the large end doesn't change when the cranks is turned. The bearing size increases.IE std,.010,.020, .030 etc. You probably need your rods checked and maybe resized/ reconditioned. Or replace them.
 
I cant see why the rod would be out of round if you fit thin brass shims between the rod and bearing half Halifax?

Toolmanmike if the engine left the factory with oversize rods with bearings that fit, why would I need new then? Doesn't machine shop sometims oversize crank bore and rods?

The crank and rod journal are STD size and not turned SGBARRACUDA. But on the rod big end side material is removed from factory by .0020". Normal undersize bearing which you choose when either crank or rod journal are turned down wont work. I need material added on the other side against the big end side of rod to take up the gap.

I found a link hear when someone did what I talk about. Deckwar Tapered Shims - Rod Bearing Shim Installation Guide
 
You can try it I was thinking the gap was between the crank and bearing not the rod and bearing.
 
halifaxhops said:
You can try it I was thinking the gap was between the crank and bearing not the rod and bearing.
Click to expand...
That is something mechanix did 50-70 yrs ago. I saw it done. Don`t know how long the car ran after he did it, but was running when I joined the service. He actually was replacing the shims in a 1953 6 cyl chevy that was stock. Wheather gm did it from the factory, I don`t know.
 
GM did this on the mains of their super shitty "every main journal is a different diameter" 6cyl. They are a major PITA to setup. OP-Do NOT attempt shimming anything. Get the rod and main housing bores correct and get the crank journals correct and then get the right bearings for the job and then check it all! J.Rob
 
I re-read the original post. I thought you measured the connecting rods big end without the bearings in. My bad. Still, you should not use shims for engine bearings. If the rods are the correct size and the crank journals are ground and polished to a certain spec, a quality bearing will get you the correct oil clearance within tolerance. You can sometimes order .001 or .002 undersized bearings to give you the proper clearance if the crank was polished but not turned.
 
Did you measure the big end bores both vertically and across the break in the end? Make sure they are not eccentric. And make sure the rods bolts are fully torqued; if you did not torque the rod bolts to spec, then your big end measurements will be off.

And did you mean the bearing materials was .002" thinner only on the sides? If so, those may be for AL racing rods.
 
I also think that having the correct bearings would be the best RAMM, but since I live in Sweden and parts are non existent and I have to order them overseas and that cost a lot. I now already have STD size bearings that fit like they should against the journals. But I have a small gap between the bearing and the rod which would require oversize bearings. Which I cant find on the internet, only undersize bearings which would not help my case at all since my rod journal measured 2.124" which is STD sized rod journal. I understand that shims is not best case senario.

Toolmanmike my crank isn't tourned or polished and the rod and crank journals all measures STD 2.124" and 2.5005" so undersize bearings wont help me unfortunately.

nm9stheham I did measured the big end after they where tourqued down properly. Measured at many places but not at the across the break.

Since this engine have never been apart before I am pretty sure MOPAR did remove the material on the big end side of the rod upon assembly at the factory.

Did draw a picture better showing what I'm talking about since this stuff easy gets confused.
Rod_zpsrlo4xua8.png
 
There ain't chance in HELL I would do that.
I realize you are concerned about the cost, but what about the cost of doing it all over again?
 
You could have them milled on the parting edges and reground again, but the costs would be way higher than a fresh set of rods.
I would throw them away and get some other ones.
It's not like 318's are scarce around the world.
 
Pompis said:
nm9stheham I did measured the big end after they where tourqued down properly. Measured at many places but not at the across the break.

Since this engine have never been apart before I am pretty sure MOPAR did remove the material on the big end side of the rod upon assembly at the factory.

Did draw a picture better showing what I'm talking about since this stuff easy gets confused.
Rod_zpsrlo4xua8.png
Click to expand...
Something is not right.. I have never heard of bearings made bigger on the outside. Measure across the break and see if they are .002" oversized there. If not, then the rods caps may have been stretched due to hard use.

It is very odd that you could see a visible gap between the rod big end and the bearing shell. The length of the rod bearings should be slightly longer than the inside circumference of the big end, and the ends will crush together to hold the bearing in tight into the big end. I have to question if the rod bearings may the wrong ones. What brand is this engine kit?

What actual inside dimension did you measure in the rod big end?
 
nm9stheham I will measure the rods tommorow at the break.

But I think I may found the problem now when I was calculating the measurements taken on the rod big end from mm to inch. The measurement at the rod is actually 2.250" so a STD size bearing should fit then. The old bearing fit tight when mounted on the rod journal. The new STD size bearing does not fit tight on the journal and you can hear a small "klonk" if I pull the rod against me. I had to put a 0.0020" feeler gauge under the bearing to make the rod stop "klonking" and feel like the old bearing did.

The new bearings must be wrong in size. When I mic the new and old bearings the new ones are thinner which they should not be if my other measurments are correct. It is hard going from mm to inch and then translate and explain it in english it is easy to get confused.

I have no idea what brand the bearings are, I ordered this kit from ebay: 74 75 76 77 78 79 Dodge Truck Van SUV 318 5.2L OHV V8 - ENGINE REBUILD KIT | eBay
 
Pompis said:
nm9stheham I will measure the rods tommorow at the break.

But I think I may found the problem now when I was calculating the measurements taken on the rod big end from mm to inch. The measurement at the rod is actually 2.250" so a STD size bearing should fit then. The old bearing fit tight when mounted on the rod journal. The new STD size bearing does not fit tight on the journal and you can hear a small "klonk" if I pull the rod against me. I had to put a 0.0020" feeler gauge under the bearing to make the rod stop "klonking" and feel like the old bearing did.

The new bearings must be wrong in size. When I mic the new and old bearings the new ones are thinner which they should not be if my other measurments are correct. It is hard going from mm to inch and then translate and explain it in english it is easy to get confused.

I have no idea what brand the bearings are, I ordered this kit from ebay: 74 75 76 77 78 79 Dodge Truck Van SUV 318 5.2L OHV V8 - ENGINE REBUILD KIT | eBay
Click to expand...

The size of the bearings should be stamped on the back of the shell....
 
It's better to simply not convert to milimeters when dealing with US inch-sized parts.

BigBlock Mopar engines usually had a Maltese cross mark, or something like that, on the engine casting if something was different with the bearings.
Not sure if they did this also on Small Blocks?

Why did you buy a truck rebuildkit?
The pistons are probably super low compression and basicly ashtrays.
Do some math the 1.741 Compression Height to see where you end up on the static compression.
 
The OEM bearing are marked AT-20 so that's why I thought something was 20 something of. I made a mistake when measuring my rod at first so that's why I assumed it was the rods because the mistake measurments was 20 thou off on the rods. I'm not sure any more what to think but I will measure everything again.

d55dave I am not going to shim. I know understand from some help from this link: Mopar Rod and Main Bearing Guide - Mopar Muscle Magazine
"Because of bore-shape variables, the most desirable bearing shape is provided with a slightly oval inside diameter. As a result, bearings are manufactured with an eccentric wall. In most cases, the bearing wall thickness is greatest at the top and bottom (90 degrees from the parting line). The bearing ID tapers slightly at the parting line area." A shim would not work with the taper I guess.

BigBlockMopar since my micrometer is in mm I kinda have to :) The old piston have 1.720" CH so I will gain something and with a deck height of .074" and at the machine shop they removed .020" from the deck. Going to end up somewhere at 9.0 in compression, I need to CC the 302 heads and check the deck height with the new pistons to be 100%. Going to run comp cams XE250H so I think the comp will be perfect. The 302 heads am I only using since my other heads have a cracked valve seat. I know I'm not going to have a effective quench.
 
Your new bearings should be marked as KrazyKuda states, with a marking like STD, .010, .020. There were such bearings as .001" and .002" and even .003" undersized back in the old days, but they are rare now. And sometimes bearings are marked wrong on the boxes and on the bearing; I bought a set of old .001" undersized rods and they were marked .001" but were actually STD.

Also a .002" shim inserted OK in the gap between rod and crank journal may be OK; it sounds like that is your bearing-to-rod-journal clearance. You need to check this with the rod cap torqued into place. If your measurement on the rod journal of 2.124" is accurate, then the rod journals are slightly worn by about .001" and the bearing clearance will be larger than standard. You can tolerate a clearance of .002", and to .003" range absolute maximum. (I personally would not like to run .003" if I could avoid it and would turn the crankshaft journals to .010" undersize rather than do that.) You should measure all of your crankshaft rod journals carefully to make sure they are round (same dimension all around).

Does you local machine shop have something called Plastigage? That is an easy way to measure your bearing clearance.

Also, measure your bearing shell thickness in the center, not at the ends. Place a round rod in the center and measure the thickness of the bearing shell and round rod together. The rod has to be perfectly straight across the bearing. Then subtract the rod thickness. The reason for the taper in the rod bearing shell thickness is because the ends of rod bearing shells get crushed a small amount when installed, and the ends get a small amount thicker when they are crushed.

It is good to hear that you have a taller piston, and that the block is decked. Do your pistons have the recess in the center like shown in the picture on eBay? That will lower compression ratio. Can you measure the depth and diameter of that recess? I have made a guess but would like to know the actual dimensions

I have run some computations on your compression ratio, assuming that your 302 heads have 64 cc combustion chambers. The Static CR depends the head gasket type and thickness. With the standard Felpro 8553PT head gasket, it computes to 8.15:1. With the Mr Gasket 1121G, it computes to 8.55:1. Dynamic CR is about 1 point less for the XE250H cam.
 
Having trouble with all the descriptions...........

What happens if you take one rod and one set of rod bearings and assemble them out of the engine? Are the shells loose in the rod bore?
 
DDodger said:
Having trouble with all the descriptions...........

What happens if you take one rod and one set of rod bearings and assemble them out of the engine? Are the shells loose in the rod bore?
Click to expand...

Shouldn't be loose fitting at all, they should "snap" in--this is what bearing crush is. J.Rob
 
Thank you nm9stheham for taking your time to answer and explaining. Also appreciate all you others for taking the time.

My guess is that the bearing fitted from factory is a .002" bearings and that's why the factory bearings are marked "AT-20". When I measured the rod journal again today it was 2.123". I have bought plastigage in different colors so I was in the process to plastigage the new bearings when I first discovered this mess. The old bearings are not bad and when I get the block back from the machine shop I am going to plastigage them.

This engine has minimal wear and I do not feel worried at all to put it back together with the old bearings if I have to. I am already $2000 in debt know because of this engine so I hope you guys can please keep that in mind. I would love to turn the crank and do all sort of machining put I think this engine is in good condition after measuring different parts. I'm new to use micrometer and it's a learning process that's why this thing have been confusing for me and you. If it wouldn't be for the lack of compression in cyl 2 this engine would already be in my Valiant since the other cylinders almost reached the full 150-160 psi at the first stroke and that's a healty indication to me.

When I cc my 302 I ended up at 62 after some minor work in the compression chamber. But going to redo it to be 100% sure after I get them back from the guide and valve job. The new valves are more recessed than the older ones.

But I must have smoked crack or something because the old piston are not at 1.720" CH they have the same CH as the new pistons. I remember that I did a comparison of the CH when I first got the piston but when "double" checking it today I was wrong again. I guess I never did a comparison.:realcrazy:

The measurment for the recess is 1.06"x0.39"x0.074". Here is a picture of my piston with me putting 2 cc of water total in the recesses. The water sits way above.
DSC_1246_zpsnfstogru.jpg
 
Subscribed. I wonder if the rod ends were machined for some reason? If they were balancing them they usually grind the flat machined part dont they?
 
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