okay I spun a rod bearing, damit. so I took the crank to the machine shop, and the guy said he could fix it , but then he said that the rod would need to be replaced, is this true?? it looks fine, and my finger nail is not catching on any thing, and I thought it only need to be replaced if your finger nail caught on something.

If there are no scratches on the crank, why did you take it to a machine shop? If the surfaces are not scratched at all, just replace the rod bearings and you should be fine. I have done this in one of my cars and it solved my knock. The crank was pristine, and that's the key. If there is *any* roughness or scratching on the crank though, just toss it, if you ever want to be able to trust your motor again. It is not worth having it reground. The clearances for an sr20 crank are incredibly tight. They sell standard bearings in several grades to accomdate this. Undersize bearings are only sold in a specific size though. This means that while Nissan themselves couldn't produce cranks close enough to spec to maintain clearances (instead using the bearing grade to accomodate variations in crank measurements), a machine shop is expected to hit the tolerance right on the dot when they machine the crank, since they have only one grade of bearing to work with. Do you really expect a machine shop to be able to do this? I'm sure there are some that can, some of the time, but I do not trust one enough to make machining worthwhile. I speak from experience on this - one of my cars has had a regrind job (before I bought it, unbeknownst to me). The rod knock of course came back. I just replaced the rod bearings in it again last week, and it lessened the knock, but didn't completely eliminate it. If you go to the trouble of removing a bad crank from the car, why would you want to put it back in there? Chances are whoever regrinds it, if they don't know SR20s like the back of their hand, will grind it to tolerances appropriate for old american V8s. This isn't an old american V8. A crank ground to their specs is not going to solve the problem. You will spend a couple hundred on labor and bearings for a regrind that probably won't really fix your engine, so why not just get a primera motor and be done with it.

End of Rant. If you can't tell, I am damn tired of looking at SR20 rod bearings at this point.

Josh

What do you mean that a crank should've been reground and that they have one type of bearing to work with. That is exactly why they have oversized bearings. When you get a motor rebuilt it is in your best interests to get the journals reground and oversized bearings put in. is 30 plus differeThat's why there nt sized bearings from Nissan and other oversized bearings from other aftermarket companies. Engine building is engine building period, there are tricks to the trade that transcend American to Japanese motors, they're not functionally different. They all have crank, rods, pistons..... and when you get your motor rebuilt it's on the reputation of the builder and not if he's used to doing American motors. So you're saying that in Japan they can rebuild a 4 cylinder better than they could do a 8 cylinder, because they're from Japan and probably rebuil more 4 cylinders than they have eight. That's really a bad generalization to make.

I made no generalization. When I went to Napa to buy plastigage to check my bearing clearances, the smallest plastigage they sold didn't even measure all the way to the low end of the SR20 specified bearing clearances. They sell the plastigage specifically for use in determining engine bearing clearances. That tells me that our clearances are quite a bit tighter than most other engines, if the smallest plastigage they sell doesn't even measure that small. I am not saying a crank *can't* be reground right, just that in my opinion it isn't worth the trouble, especially when a JDM motor is only a hundred or two more, and you already have the motor out of your car anyway. Look, the FSM doesn't even mention methods for regrinding the crank. They tell you to replace it if it's damaged or out of spec. If you want to second-guess Nissan on this, fine, but don't be surprised if it doesn't work out well. They do sell undersize bearings, yes, because they know people will still try... the FSM says "grind to specified clearance" as a note next to the listing of undersized bearing. They don't give a specific size to regrind the pin to.

You'll also see undersized bearings aren't sold in closely spaced grades like standard bearings are. When you buy undersize bearings, you buy bearings for a specific undersize - 0.25, for example. That's what the regrind in my car was. You don't have the option of different grades at that undersize, so you have to hit the clearances dead-on by grinding. And you also don't have the option of going a grade tighter if you have to replace bearings again at a later date (since you often have to go a grade tighter due to wear when replacing standard bearings). So if those clearances are off, or the crank undergoes future wear after a regrind, then there's nothing you can do to get those clearances right again.

I just used american V8s as an example, since we are in america, and more of those go through your average machine shop than anything else. If the guy who grinds the crank doesn't know Nissans, he might not grind it to a close enough clearance. And he won't have the chance to make it right using a different grade bearing. Bottom line is any builder who I'd trust to regrind an SR20 crank to the proper specs would probably cost at least as much as a JDM motor does. Good work isn't cheap, and it's pretty much mandatory on these motors.

Josh

Understood and agreed. Yeah, the cost on regrinding journals on a crank at a reputable shop (at least one I would spend money on) would end up costing near the price of a used JDM motor. I was just under the impression that you felt that it's an unnecessary step in rebuilding a Nissan motor, especially after having a rod knock. That's what confused me. I, for one, would junk a motor that started knocking and put in a used one with a warranty than start to screw with a bottom end. I would rather rebuild the whole motor, including boring and honing that just re-bearing a crank. I've seen a Toyota motor rebuilt with just putting new bearings in and it not even spin because of a hair that got in between a bearing and the crank journal. All foreign manufacturers have this high of standards, that is exactly why their motors last so long, it's not just Nissan. Plus I think that you could find a correct plasti-gauge for your application, but maybe not through Napa.

well my bearings, and cranck will be ready fo me tommorrow, and we will see how it goes. the place I took it to does all the hondas, toyotas, and nissan in town, everyone I knows says that their the best, and it isn't costing much more than a hundred. I picked up the correct plastiguage, and will check the journals with the bearings they give me. also the plasti guage wasn't hard to find here, picked up all three sizes for $1.50 also if you have trouble finding the bearings, call a couple machine shops, they had no problem finding them in different sizes all the way to 30 over/under however you wanna say it.

I know what it means to "spin a bearing" but I'm not sure I know what is the cause. I'm afraid of it happening to me some time. Is it from driving the car really hard? High mileage?

Spun bearings is usually caused by impurities in the oil. If you don't change the oil, that's what can happen. Keep in mind, it's the bearing's job to wear away and not the crank's.

I have two motors with spun bearings. The rod journal or crank pin on each crank is a little scratchy to the fingernail, but no particularly deep grooves. My dad has been a machinist at Caterpillar large engine center for about 20 years and here is what we are going to do tomorrow. We are going to use different grades of emory cloth and smooth the crank pins back down as close to the other, good pins as well as we can. We have micrometers and my dad is an expert with one so we will measure them before we start, and as we make it smoother and smoother, we will keep measuring. The FSM S.D.S. spec page on this will be open right next to us so we can see where we are at. FWIW Jay Stewart has done this before and the motor is running find today. I should get my new digital camera today so I should be able to take good close up pics of our work.

I appreciate your input Josh, but I just cannot believe the two cranks I have are scrap. You said there is 1 size of undersize bearing. That is true for the MAIN bearings, but what we have problems with with are ROD bearings, of which there are 3 normal and 3 undersize bearings for in the FSM. I really think we will be able to salvage these cranks for the cost of the emory paper, a proper micrometer, and micrometer measuring skill, all of which I happen to have for free. :)

Thanks blackb13

I didn't mean to discourage you from trying to rebuild your crank, Ben - I know what it's for. I just wouldn't do it for a street car that you depend on. Another factor is that nobody seems to know for sure whether our crank journals are hardened or treated in some way - if they are, then machining through that probably does ruin the crank.

Also, what I meant about the undersize bearings is that they come sized, not graded. This means you can't pick a bearing for whatever size crank you end up with, you have to pick a bearing size and grind to achieve those clearances. This is a lot harder than just picking the grade that fits what you have. Like you said, your dad is a machinist - I'm sure a better one than I :) - so he'd probably be the guy to try it. My advice wasn't to you, it was to someone going to a machine shop who doesn't have the expertise and tools that you have on hand, for free.

I still wouldn't put that crank in the cherry NX though :).

Josh

My dad was here and looked at it today. Got me some emory paper and looked at the cranks with me. He doesn't think I will get even close to a thousandth of an inch of metal off there. He showed me how to use the micrometer really well too. Since on the crank was printed 2222 for the rod bearings, that would mean Grade 2 in the FSM, and what we measure was in line with those specs (one was 1.8887 which is Grade 2). So I feel very confident that I can smooth them back to almost a factory surface and just make sure I'm within the oil clearance spec for whatever bearing I get with Plastigauge. Simple. :) Just need to know how to use a micrometer.

The way I will use the emory paper to be extra careful to prevent and out-of-round situation would be to use it on one half of the crank pin counting my strokes and do the same on the other side. My dad said that probably isn't necessary, but would be good to do since it's easy to do.