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1725 Main Bearings Housing Bore Dimension

Discussion in 'Rootes Racing' started by dla248, Mar 14, 2011.

  1. dla248

    dla248 Gold Level Sponsor

    I would appreciate some help in finding out what was the original stock dimensions for the main bearing caps opening, my engine builder calls this the main housing bore dimension. I see from past postings here and a crankshaft specialist that there no listings for the Rootes 1725cc engine dimensions for this. I see the 2.375 inch dimension journal diameter in the workshop manual, but usually there is a reference to the opening diameter that seems to be missing for this engine. I need to get a new crankshaft line bored, but they would like to know the original specification.

    Thanks for you help, please email me at dla248@comcast.net

  2. V6 JOSE

    V6 JOSE Donation Time

    Hi Dave,

    What is the reason you are wanting to line hone the block? Did you spin a main bearing? Unless a main bearing has spun, there rarely is a reason to line hone the main line. I know that line honing the block is something that high dollar race engines get, but unless you plan to race the engine, I wouldn´t worry about it.

    When you line hone the block main line, you move the crank center line closer to the cam line, which in your case doesn´t pose a whole lot of trouble, because your engine uses a chain, but when the timing is done by gears, like in the Ford 2.8 V6, then you run the risk of too close a tolerance between the cam and crank gear.

  3. sunbeam74

    sunbeam74 Donation Time

    Jose, I am pretty sure Dave is building a replacement race motor.
    Unfortuantely, I don't have the dimension myself.

  4. dla248

    dla248 Gold Level Sponsor

    From a race shop I managed to get the dimensions below from a 1970 Vandervell Bearing Reference Listing (all in inches):

    Crankshaft main shaft 2.3740-2.3745
    Main bearing housing 2.5197-2.5205 (this had an .0008 spread listed but all others were .0005)
    Bearing shell .0723

    Crankshaft rod shaft 2.1255-2.1260
    Rod Housing 2.2710-2.2715
    Bearing Shell .0723

    Hope it may help someone else

  5. jumpinjan

    jumpinjan Gold Level Sponsor

    Thanks Dave for researching this.
    Everyone, remember these rod dimensions are for the 1725. The 1600 has a 2.000" crank pin.
  6. mightyohm

    mightyohm Donation Time

    I have a question about these rod bearing numbers.

    If I subtract twice the bearing shell thickness plus the rod journal diameter from the rod housing diameter, I get a range of clearances that are considerably less than the big end running clearance numbers in the WSM.

    The WSM specs the rod big end clearance as 0.0015 - 0.002".

    However, if I do the math using the numbers above I get a clearance of 0.0004 - 0.0014. Considerably smaller than the WSM specs.
  7. Barry

    Barry Bronze Level Sponsor


    The correct way to determine the rod bearing I.D. is to install the rod bearing shells in the rod big end and cap, torque the rod bolts to spec. and measure the rod bearing I.D. with an inside micrometer. Subtract the measured rod journal diameter (outside micrometer) to get the clearance.

    Alternatively, use the PlastiGauge system.

    Just my opinion / experience; YMMV.
  8. mightyohm

    mightyohm Donation Time

    Barry - I've done that in the past on a previous motor build. The problem is that my bore gage tends to gouge the soft bearing surface.

    At one point I tested both ways and found that the bearings-out method (subtract the shell thicknesses from the bore) agreed very well with the bearings-in method you describe.
    Last edited: Nov 16, 2017
  9. mightyohm

    mightyohm Donation Time

    Barry - I wanted to double check what I just said, so I installed a bearing in the rod and measured as you suggested. I'm getting a slightly larger clearance using your method. I suspect it's due to a couple things - first is the slight mark that the bore gage leaves in the bearing (let's call that 0.0001) and the second is that your method has less accumulated error than the original method I was using. So I think it's a useful way to measure, I just wish I had a better bore gage with a larger plunger to avoid the marks. I think Mitutoyo discontinued their 545 series as I wasn't able to find one online, and the Sunnen style bore gauges with multi-point contact are very $$$$. I'll have my machine shop check my work before cutting any metal..

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