Jump to content
SAU Community

Need help/advice with bearing taper clearance, eccentricity and arp studs.

Desean Strickland
 Share

Recommended Posts

Desean Strickland Contributor

Desean Strickland

Posted
Posted

Hey lads 

so im finally putting together my rb30 forged bottom end and ran into an issue. I measured my main bearing clearance with arp main studs torqued to 60 ft-lbs using ACL H series STD size bearings and standard, un-ground crank shaft journals and got an oil clearance reading of about 1.3 thou measuring straight up and down and about 2.8 thou measuring at a 45 degree angle (just above and below the parting line). My machine shop said they measured the main tunnel and it was all within spec (they didnt say the actual measurement) and to go with a standard size bearing, which i have done and the clearance is too tight, I'm guessing because of the extra clamping force from the arp studs distorting the main tunnel. I was wanting to run about 2.5 thou main bearing clearance. 

My questions are:

1. could i just use the HX extra 1 thou clearance ACL bearings? that would fix my straight up and down clearance making it about 2.3 thou, but then would the side to side clearance be too big at around 3.8 thou?

2. what actually is the recommended main bearing clearance for measuring near the parting line / side to side. i know its supposed to be bigger as the bearing has some eccentricity built into it but how much more clearance should there be compared to the straight up and down measurement? at the moment there is about 1.5thou difference, is that acceptable or should it be less?

3. If i took the engine block + girdle back to the machine shop and got them to line bore the main tunnel (like i told them to do the first time, but they said it didnt need it) what bearing size would i buy? the STD size bearing shells already slide in fairly easily with no real resistance, some even falling out if i tip the girdle up-side-down. If im taking material out of the main tunnel would i need a bearing with extra material on the back side to make up for it?

this is probably confusing af to read so if something doesn't make sense let me know and ill try explaining in a different way. My machine shop doesn't come back from christmas break until mid January, hence why i'm asking these questions here.

TIA for any help or info 

Duncan Grand Master

Duncan

Posted
Posted

I can't help with the clearance question, I've always taken my machine shop's advice on that. It is worth considering that a shop that does that every day for road cars will be looking for as good as they can get off the shelf, not perfect. If you want more careful race style "blueprinting" then you need a race shop to measure/machine the engine.

I do have an opinion on line boring the block though....don't do it unless you have to. The crank centre moves higher but the oil pump stays in the same place when you line bore the block.

  • Like 1
Desean Strickland Contributor

Desean Strickland

Posted
  • Author
Posted
2 hours ago, Duncan said:

I can't help with the clearance question, I've always taken my machine shop's advice on that. It is worth considering that a shop that does that every day for road cars will be looking for as good as they can get off the shelf, not perfect. If you want more careful race style "blueprinting" then you need a race shop to measure/machine the engine.

I do have an opinion on line boring the block though....don't do it unless you have to. The crank centre moves higher but the oil pump stays in the same place when you line bore the block.

Thanks for the response. I get why line boring the block could cause issues with a spline drive oil pump but I’m just using an extended flat drive collar, u reccon it could still cause issues? 

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • GTSBoy
      RB20DE NEO smallbox clutch.

      By GTSBoy · Posted

      Input shaft bearing. They all do it. There is always rollover noise in Nissan boxes - particularly the big box. Don't worry about it unless it gets really growly.
    • Kapr
      RB20DE NEO smallbox clutch.

      By Kapr · Posted

      For once a good news  It needed to be adjusted by that one nut and it is ok  At least something was easy But thank you very much for help. But a small issue is now(gearbox) that when the car is stationary you can hear "clinking" from gearbox so some of the bearing is 100% not that happy... It goes away once you push clutch so it is 100% gearbox. Just if you know...what that bearing could be? It sounding like "spun bearing" but it is louder.
    • GTSBoy
      Mistakes were made, my R34 Story

      By GTSBoy · Posted

      Yeah, that's fine**. But the numbers you came up with are just wrong. Try it for yourself. Put in any voltage from the possible range and see what result you get. You get nonsense. ** When I say "fine", I mean, it's still shit. The very simple linear formula (slope & intercept) is shit for a sensor with a non-linear response. This is the curve, from your data above. Look at the CURVE! It's only really linear between about 30 and 90 °C. And if you used only that range to define a curve, it would be great. But you would go more and more wrong as you went to higher temps. And that is why the slope & intercept found when you use 50 and 150 as the end points is so bad halfway between those points. The real curve is a long way below the linear curve which just zips straight between the end points, like this one. You could probably use the same slope and a lower intercept, to move that straight line down, and spread the error out. But you would 5-10°C off in a lot of places. You'd need to say what temperature range you really wanted to be most right - say, 100 to 130, and plop the line closest to teh real curve in that region, which would make it quite wrong down at the lower temperatures. Let me just say that HPTuners are not being realistic in only allowing for a simple linear curve. 
    • Kinkstaah
      Mistakes were made, my R34 Story

      By Kinkstaah · Posted

      I feel I should re-iterate. The above picture is the only option available in the software and the blurb from HP Tuners I quoted earlier is the only way to add data to it and that's the description they offer as to how to figure it out. The only fields available is the blank box after (Input/ ) and the box right before = Output. Those are the only numbers that can be entered.
    • GTSBoy
      Mistakes were made, my R34 Story

      By GTSBoy · Posted

      No, your formula is arse backwards. Mine is totally different to yours, and is the one I said was bang on at 50 and 150. I'll put your data into Excel (actually it already is, chart it and fit a linear fit to it, aiming to make it evenly wrong across the whole span. But not now. Other things to do first.
×
×
  • Create New...