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TALK TO ME ABOUT LINE HONE/LINE BORE OF MAIN BEARING SURFACE


DENNISWEBER47
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SOMEONE PLEASE EXPLAIN TO ME THE REASONS FOR AND THE RESULTS OF LINE BOREING AND/OR LINE HONEING THE MAIN BEARING SURFACE OF BLOCKS AND CAPS. I HAVE, IN THE PAST, HAD AN ENGINE THAT I TRIED SEVERAL TIMING CHAIN AND GEAR SETS ON AND COULD NEVER GET A TIGHT FIT. I FINALLY BUILT IT WITH THE LOOSE CHAIN AND WAS NEVER SATISFIED WITH THE PERFORMANCE. THIS BLOCK HAD BEEN LINE HONED, PER THE SELLER. NOW I AM FACED WITH A SIMILAR PROBLEM, WITH A PURCHASED LONG BLOCK. I HAVE TRIED TWO NEW TIMING SETS ON IT AND STILL HAVE ABOUT 6 DEG. OF SLOP (DAMPER TO ROTOR). WHEN THE NEW SETS ARE INSTALLED ON THE OLD CORE MOTOR, THEY ARE TIGHT WITH NO PLAY. CAN THE GEOMETRY BETWEEN THE CRANK AND THE CAM BE DISTURBED BY THE BORE / HONE PROCESS ?????? THANKS DENNIS WEBER

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Line boring/honing is to assure proper fit and alinement of main bearings. Should have no relationship to timing gears/chains or geometry of crank to camshaft, unless I am missing something about your problem. What do you mean re 6 degree of slop?

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I CAN ROTATE THE BALANCER ABOUT SIX DEGREES BEFORE THE DIST. ROTOR BEGINS TO MOVE...THE TIMING CHAIN HAS THAT MUCH SLOP IN IT. I HAVE INSTALLED SEVERAL NEW SETS WITH THE SAME RESULTS. HOWEVER, THESE SAME SETS ARE QUIET TIGHT WHEN INSTALLED ON THE OLD ENGINE. I AM WONDERING IF SOME HOW THE CENTER TO CENTER DISTANCE FROM CRANK TO CAM HAS BEEN ALTERED BY THIS BORE/HONE PROCESS.

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Line boring assures that all of the main bearings are in perfect alignment with each other allowing the crankshaft to rotate as freely as possible with no distortion and minimal friction. It also assures that the centerline of the crank is exactly 90 degrees to the centerline of the cylinder bores. I think you are correct in assuming that excessive boring will allow the crankshaft to become closer to the camshaft causing a loose timing chain, although 6 degrees sounds excessive. I believe a block requiring more than a few thousandths of metal to be removed during boring should be discarded. If you must use the block I would suggest considering a gear drive kit which allows you to adjust the backlash. These kits come in either quiet or noisy, noisy simulates the sound of a blower,(straight cut teeth vs. helical cut).They can be purchased at speed shops and a leading mfg. is Pete Jackson.

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I agree w/Impala also. If excessive material was removed from the caps in order to keep the hole round when lineboring and honing, the centerline distance between the cam and the crank is reduced causing excessive chain slap. I also agree that 6 degrees sounds excessive and would investigate the connection between the camshaft and the distributor as well.<BR>

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THANKS FOR THE RESPONSE, I THINK THATS WHAT I REALLY NEEDED TO KNOW. THAT DURING THE REFURBISHMENT OF A BLOCK, THAT SOMEONE MIGHT REMOVE MATERIAL FROM THE CAPS, AND REBORE THE BLOCK, CAUSING THIS DEMINSION TO CHANGE (SHORTEN). LIKE I SAID EARLIER, THIS IS ON A REMANUFACTURED LONGBLOCK, PURCHASED LOCALLY. DO THESE PLACES REGULARLY DO THAT TO "SAVE" AN OTHERWISE USELESS BLOCK ?

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Machines generally do not make errors - unfortunately the same cannot be necessarily said for all machinists. It happens! Since you have not identified the engine it is difficult to suggest that the best alternative to to give up or try another fix.

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Dennis,<P>I have watched this progress, and held my thoughts as I could not believe any machine shop could be this sloppy in a line bore. I now understand, as you now say its a remanufactured engine. I did not catch that part before. My father use to handle remanufactured engines for many different companys in his business over the years. We had many arguements over why he wanted to sell these "Boat Anchors". What you have makes plenty of sence now. You can not believe the lack of quality in these engines. Not all, but most of them. Go get your money back.<P>Rick

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Blocks are only linebored if warped or the caps stretched, otherwise the bearing material is the only thing that is bored. This can be either rebabbited shells or babbit poured in the block. Late model engines are generally not line bored, cranks are ground and undersized bearings installed. Older engines with babbit are line bored as mentioned by impala, but must be bored on the proper centerline, if bored off that, towards the cam, the chain will be loose.<BR>This is actually not an uncommon problem. Even if the block was excessivily line bored, quite a time comsuming process, the hole must still fit the crank, so that is not your problem, it is most likely centerline related. You might also have the wrong timing gears, with the wrong tooth profile, which could also make the chain loose.

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IT IS UNLIKELY THAT LINE HONING WOULD CHANGE THE RELATIONSHIP OF THE CRANK CENTERLINE WITH THE CAM CENTERLINE.THE AMOUNT OF METAL REMOVED IN LINE HONING IS NOT ENOUGH TO CHANGE THE TIMING 6 DEG.IMPROPER LINE BORING CAN SINK THE CRANK CENTERLINE INTO THE BLOCK THUS DECREASING THE DISTANCE BETWEEN THE CRANK AND THE CAM.

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I agree that the 6 deg. sounds like a lot for normal line boring procedures, but the distance could also be increased between the crank and camshaft and with timing gears this may be enough to create slop in the gear mesh, and maybe 6 deg. is not too unrealistic.

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Several years ago, I had a 1935 Cadillac V-8<BR>come into my shop, which ran poorly. One thing I found was that the centerline of the crank was nearly 1/8 of an inch closer to the cam than it should have been. The main bearings were noticably off center. Since this engine does not have a chain tensioner,the chain was very loose and easily had 6 degrees of slop in it if not more when turning the crank back and forth.

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