How do I know which bearings to get for main journals/rods?

[sil80drifter]

I have a 1990 240SX, and have a 70k old block which I've taken apart,and the stamped grade numbers on the block and crank lead me to the conclusion that I need the following grades for my bearings/pistons:

Main bearings (1 to 5): 3 3 1 3 3Rod bearings (1 to 4): 2 2 2 2 Piston grades (1 to 4): 1 1 2 2

What does this translate to in terms of bearing/piston sizes? When I look to buy them online, what should I order? How come the numbers are different (wfor main bearings and pistons)?

sil80

[sil80drifter]

bumphelp?

sil80

[180fan]

Look at the bottom of the block. Write those numbers down in the sequence you see them. Look at the front of the crank. Where the #1 rod bolts up, you'll see two rows of numbers. The top row you'll see 5 numbers. These correspond to the crank bearings. The lower 4 numbers correspond to the rod bearings. The rod bearings you use em just flat out when ordering your parts. The 5 numbers you got from your crank correspond to the 5 numbers you got from the bottom of your block.

ex: from block suppose you get 1 0 2 3 2from crank suppose you get 1 1 2 3 0

now here's where kindergarten math comes in. You ready? Take the sums according to columns.

first column = 1 + 1 = 2, this is your grade bearing for the first set of bearings.2nd column = 0 + 1 = 1, the second set of bearings for your crank is a grade 1 bearing3rd column = 2 + 2 = 4, your middle bearing for your crank is a grade 4.

The piston grade you'll see stamped both on the tops of the pistons and on the top side of the block. Take these values for what they are.

[180fan]

Oh, ask for those specific grade bearings. The grades are different sizes. For the KAE, I'm too lazy to check what each grade translates to in measurements. When you order, tell them what grade bearing you need, they'll know what you're talking about.

[sil80drifter]

Will they be stamped, or color coded or something? Or will I have to measure them myself when I receive them? Yeah the numbers listed above are already calculated, I actually made a spreadsheet that helps do that, it's in the technical thread in the KA forum.

Also, how come my numbers are not all the same (like for the rod bolts they are, but for the pistons and main bearings they are different) from a factory made block I would expect an identical sequence like 11111 or 4444, not 33133

sil80

[180fan]

Color coded if you get em OEM by a dot on the bearings. OEM, you don't need to measure jack...unless you're a paranoid mofo. Rod bolts are the same cuz they're not subject to the tight spaces that the bearings and rings and pistons are. The bore sizes ala your different piston grades, beats me why they're different, just that they're different is all you need to know. Main bearings are different because it's effing hard to keep the same size uniform throught, since you're cutting away at metal, the tools you use wear down, or it takes more time than it's worth to measure everything out to the same size, etc.

[sil80drifter]

I'll try calling them and askign for my specific grades, thanks so much.

sil80

[s13sr20chris]

the grades are a good thing. a lesser manufacturer would just use one bearing for all the rods regardless of fit.

[sil80drifter]

Does piston grade number have anything to do with ring size? my first two pistons are grade 1, and my second two are grade 2. what rings do I get based on those grades?Or is it irrelevant, as long as the bore is stock?is the bore stock when the piston grade number is 1 or 2?

sil80

[180fan]

I think the piston grades are slightly different sizes. I tried grade 2 in grade 1 (or was it the other way around?) in the spare SR block I have and didn't fit. The rings, it don't matter if it's stock bore. They'll come in a set of 4. The thing I noticed was that even compared to my CP's ring set, the new set I bought for stock bore was larger and thicker than the ring set for my cp's which were 0.5mm overbore. You'll need to get em filed down a bit and squared.

[s13sr20chris]

as usual 180fan delivers the goods on internal engine work!

[sil80drifter]

if my pistons are different sizes, then the bore on the cylinders is also different. lemme rephrase my question: if the grade 2 piston stands for the corresponding cylinder being 0.02 over bored, does that mean I'll need different sized rings for it as compared to stock bore (grade 1 piston/cylinder)? it seems to me that i do. please confirm or deny. with reasons if you could.

sil80

[180fan]

I believe they're a single set of rings. You must fit them to your block. You can call your dealership to verify, however the set that I had purchased from Courtesy was a standard bore, for grade 1. Check my post in the RWD SR20DET parts guide. 12033-53j20 is the part number for the ring set for the SR20DE. Like I said in my previous post, although my CP pistons are 0.5mm larger than stock pistons, the rings were smaller diameter when closed. My guess, is that you will need to file the end to fit your motor to the end ring gaps as follows.

Top ring: 0.20mm - 0.30mm with the limit being 0.39mm

Middle ring: 0.35 - 0.50mm with the limit being 0.59mm

Oil ring: 0.20mm - 0.60mm with the limit being 0.60mm

This does involve putting the ring into the cylinder and with a feeler gauge, checking the gap. You must also make sure the edges are squared and filed.

If you need a set of piston rings, I have an unused but opened set of OEM rings that I could not use as I went with CP pistons.

I will have a second look at the OEM rings I got and compare them to the bore of the block I was going to put them through if you'd like. However, it might be easier to find out from just a comparison of the part numbers if there is just one set of rings that requires filing and squaring.

[sil80drifter]

I have a KA-E, so your SR OEM rings will not fit, but thank you for offering. So you have a forged piston that's 0.5mm larger than a stock piston, but does that mean your cylinder is actually 0.5mm larger? From what I understand, one can get slightly larger forged pistons into stock bores because they do not expand like the stock pistons do. This would mean that the rings you get would also be stock sized (granted they would be filed as needed) and they would still fit, because they would be going into a stock bore.So before you go out there and measure anything for my stupid sake, can you tell me what size the bores are that you have use your oversized piston on? Is it a stock bore? Is it an over bored bore?

Also, should I want to safe and get all 0.02" oversized rings, could I file them down to a "stock sized" ring size if needed? Or is the actual width of the ring different from stock?Tnaks again, and sorry for being so dimwitted about this.

sil80

[s13sr20chris]

stock sizes are measured in grades(piston) there is one size of ring that fits all grades of piston. .010 and up is considered to be a "service" overbore and will need special rings.

[180fan]

Yep, my cylinders are 0.5mm larger than stock. Thus, stock pistons will fall in and flop around like a fish out of water. But, the OEM rings I got my motor are still larger than the rings that came with my CP piston ring set. I had to get my block bored out 0.5mm to make space for the pistons that are 0.5mm larger than stock. Nah I wouldn't really bother with getting oversized unless you need it. First though, while you've got the motor out, I'd bust the glaze off the cylinder walls and give it a fresh hone and then fit in the new rings.

[sil80drifter]

is it true that when honing/deglazing, one should stay away from the top and bottom inch of the cylinder walls, to avoid egg-shaping it?

sil80

[180fan]

use of a bore gauge and an accurate thermometer can tell you if it's getting oval shaped. After doing a hone/deglaze give it a day to cool off before taking measurements. Record the ambient temps as well. Those fluctuations in temperature can cause the aluminum to expand/contract a pretty good amount that is trackable by the bore gauge (if you get one that's accurate enough).

Or better yet, take it to a machinist. Bore gauges are expensive and cost more than getting it done by a machinist.

[sil80drifter]

I have a KA, which is an iron block, does the same go for it as an aluminum SR block? And I already bought a honing tool and my friend has a bore gauge.

sil80

[Touchdown038]

Sorry to bring this thread back, but I'm still a little confused after reading through it.

So the numbers added together represent the grade of the bearing, which apparently is the same thing as the size? And when I'm ordering new bearings, I should just stick to the numbers and not pay attention to any size change recommended by the machine shop (yet to do)?

For example, say that my block had a 1 and the crank had a 1 for the first main journal. But, if my crank has wear on it and they need to machine it undersize, how does that effect the grade of the bearing?

[NISTECH]

you'll need to plastiguage it to determine what you need then as the sizes will no longer apply.