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CRANKWALK FIX for 7bolt & others

Posted by bjones18, Dec 5, 2012

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  1. bjones18

    bjones18 Proven Member

    Joined Jun 3, 2004
    canton, Michigan
    THIS PROCEDURE REQUIRES MECHANICAL SKILL, and YOU ARE A BIG BOY. If you screw up or get hurt, look in the mirror do not blame me or this forum. IMO this procedure is relatively simple, however seeing the many FAIL compilations on the web makes me realize some people make poor decisions. I recommend you pay someone who is skilled to do this procedure for you.

    The summary below describes a procedure that I used to resolve crankwalk on a problematic 7 bolt 4G63. Essentially, the "fix" is relatively simple and costs under $20. It does however, require the crank to be removed from the block in order to implement the fix. While following this procedure may be relatively quick and simple for yourself, developing this fix was rather time consuming and expensive for me.

    Along the way, my cost included a block, crank, rings, bearings, and time for building, researching, and combing through a Clevite bearing catalog. Any donations to recoup my expense is greatly appreciated.

    <img src="http://www.dsmtuners.com/gallery/files/3/2/6/4/0/thrust_mate.jpg" alt="Thrust Mate" />

    When I purchased my '97 Talon the seller assured me it did not have crankwalk. It did however have clutch problems, which turned out to be a broken clutch fork. Upon assembly, after installing a new fork and clutch I noticed the flywheel "jump forward" when bumped by the transmission input shaft. This "endplay" discovery was the start of a long and tedious journey. I pulled the oil pan and found the thrust surface on the middle main bearing hanging on by a few shreds of metal. One hard clutch release would have ripped these flanges off. In attempt to fix this quickly, I slid in new bearings without removing the crank. This quick fix lasted less than 1000 miles before significant end play developed again. A subsequent rebuild using the girdle setting procedure did not last long either. I attribute these short lived bearing replacement episodes (rightly or wrongly) to a poor start-up procedure after rebuild.

    After a rebuild I recommend cranking the engine to distribute oil before firing up the engine: WITHOUT depressing the clutch (disable switch) and sparkplugs removed (NO compression loading) and crank position sensor unplugged (no spark). This quick procedure can help generate oil pressure quickly on startup, with NO thrust bearing load.

    To resolve my thrust bearing issues, two sources suggested adding a second crank thrust surface, Rick at Chuck's Engine (Westland, MI) and a tech I worked with at Ford who used to build Indy car engines. The next question was how. Rick suggested using shear pins to hold the bearing in place, short enough to sit below the soft babbitt bearing surface metal. With that as my plan, I poured through a Clevite bearing catalog looking for thrust washers having the correct dimensions: diameter and thickness (this is not as simple as you may think). For my first attempt at implementing this fix, I had Chuck's Engine turn the back side of the crank flange, and I brazed the girdle & block - to build a "seat" in order to mount both a top & bottom thrust washer to engage the crank flange. This was a mistake and cost me an engine. My second attempt at adding a 2nd thrust surface was successful. I punted on the lower and focused on mounting only an upper thrust secondary surface. Essentially,I installed the only the stock bearings and crank, and then measured the required bearing thickness for a second thrust bearing between the back of the block and the crank flywheel flange. In doing this, I slid my Thrust Bearing Washer (TBW) in place (no pins) and measured the gap with feeler gauges. It is paramount that you knock the crank back and forth while doing this such that you build a system in which the crank engages BOTH the stock thrust bearing AND the second TBW simultaneously. Pushing the crank in the "clutch load" direction, thus engaging the stock thrust bearing allows you to measure the required gap between your crank flange and block. It was easiest for myself to slide the TBW in place and use feeler gauges for measuring. I needed a thicker TBW than was available so I used JB weld to build a thicker bearing (back side of TBW). Epoxy is a perfectly acceptable material for this purpose, when adding thickness it is loaded in compression and shear. After cleaning the back side of the thrust washer with acetone it's rough surface is perfect for bonding. Applying the JB on back of the TBW and then filing/sanding it down was the easiest for me to get a correct thickness. I measured the thickness in many locations, although 9, 12, and 3 o'clock is sufficient if you use a flat surface for sanding. Keeping a constant thickness without angle requires some talent. The JB thickness is somewhere around 0.020". In order to hold the TBW in place, two 1/8" holes were drilled in both the TBW and the back of the engine block. Short shear pins were pushed into the block so the exposed pins were shorter than the TBW thickness. The pins sticking out of the block engage the holes drilled in the TBW. I chose to drill the TBW holes at the oil relief slots, this way I was not removing TBW surface area (Babbitt). Ensure the pins are set below the bearing surface by a good bit (est ~0.040") to avoid pin to crank contact. The block holes must hold the pins very secure; whereas the TBW holes should allow the bearing a small clearance or float. I drilled the bearing holes first, then lined the bearing up to the block and marked the block hole locations. Again, the block holes and the TBW holes are NOT drilled the same size. An interference fit for the pins on both the block and TBW could skew the assembled TBW if tolerances are not perfect. A skewed bearing could engage the crank surface without oil film (bad). I used a handheld drill on the block side. Again, the pins are "press fit" in the block and the bearing "floats" on the pins.
    It is a good Idea to assemble (without lube) the block, crank and bearings, including the TBW and recheck your thrust clearances with the crank knocked forward and back. Both the stock thrust bearing and the TBW should engage at the same time. When the crank is knocked forward you should have identical spec clearances at both the primary and secondary thrust surfaces. I used a stock, unmodified crank for this second, successful procedure.

    If you own a drill and a few bits, this fix will cost you under $20. The TBW is under $20 retail; if you are very frugal you can sell the other TBW half. Two shear pins (1/8") and JB weld is under $5 at a hardware store. In Developing this fix, my mistakes cost me well over $1000 in parts alone not to mention the hours and frustration.

    AFter fixing this historic problem, I thought about selling a kit, essentially "hiding" the TBW part numbers, but hassle of selling kits on EBay to fellow DIY-DSMrs is not worth it. If you feel so inclined, I would be happy to receive any donations to recoup my losses (I feel like WIKIP now).

    Parts required:
    1. Clevite Thrust Bearing Washer (TBW): Clevite part# TW-596 S.
    2. Steel split shear pins: QTY=2, Diam 1/8", length~1/4"
    3. JB weld


    1. Drill & bits. (shear pins are generally sized for interference fit with STD sizes)
    2. 220 grit sandpaper.
    3. Feeler gauges to measure gaps.
    4. Caliper to measure TBW thickness, drill bit diameters, and shear pins.
    5. Hammer to tap or press pins into block.

    1. Measure required TBW thickness (Block, crank, main bearings installed, TBW, feeler gauges).
    2. Use JB weld and sandpaper to achieve correct TBW thickness (measure w/caliper).
    3. Drill two holes in the TBW (not too close to edge – strength) for a clearance fit on shear pins.
    4. Locate TBW on back face of block and mark block for hole locations.
    5. Drill block for interference fit with shear pins (tight fit = good / loose pins = bad).
    6. Press shear pins into block, exposed pin shorter than TBW thickness (est ~0.040" shorter).

    <img src="http://www.dsmtuners.com/gallery/files/3/2/6/4/0/thrust_blockpins.jpg" alt="Thrust Blockpins" />

    7. Install TBW on pins (slightly loose fit = good).
    8. Ensure the crank flange mating surface is polished (machine shop or 400-600 grit wet/dry) BogusSVO posted a picture of a crank flange which would need polished.
    9. Check axial clearances: dry assemble bearings/block/crank & measure.
    10. When satisfied with engagement, disassemble, lube bearings, and install crank.

    <img src="http://www.dsmtuners.com/gallery/files/3/2/6/4/0/thrust_assm_14084.jpg" alt="Thrust Assm" />

    <img src="http://www.dsmtuners.com/gallery/files/3/2/6/4/0/thrust_assy.jpg" alt="Thrust Assy" />

    Below is some data I put together a couple years ago. It is not needed if you do your own measurements. If you find this info helpful, great... otherwise you can ignore it. These may pertain to having the step cut from the crank. Again, my current "fixed" 4G63 uses a stock, unaltered crank.
    <img src="http://www.dsmtuners.com/gallery/files/3/2/6/4/0/crank_assy.jpeg" alt="Crank Assy" />

    Spreadsheet with Clevite bearing numbers for similar dimensioned cranks. I think this data may be when I was looking for a full bearing since I do not see my TW-596 S in the list. Also the bearing length and Std, 010,020... designation is for full bearings, not TW:

    <img src="http://www.dsmtuners.com/gallery/files/3/2/6/4/0/clevite_bearings.jpg" alt="Clevite Bearings" />

    hello i read your post on crankwalk fix and i like the idea of it and am really considering doing it to my 7 bolt im in the process of building. i just have one question and that is why do you leave the new thrust bearing float instead of making it a tight fit on the pins? wont it eventaully rock on the pins and wear through? hope to hear from you and thanks for thinking outside the box.

    In my opinion (and other engine builders also) a "fixed bearing has much greater chance of "binding" into a less-than-perfect position. The float allows the mating surfaces to align the bearing. "Theoretically" stick your finger in the gap... then drop the clutch... That 2600 lb pressureplate will smash your finger into the perfect thrust surface. Shear pins are hardened steel; essentially the pins are taking a shear load... not a frictional rubbing - hence shear pins. Could they shear? yes... but most likely cause of that would be the babbit melting to the crank from lack of oil. I may have put a ~0.010" chamfer on the bearing-split mate edge to allow a lubrication path; but I cannot remember for sure.
    Last edited by a moderator: Jun 5, 2014

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    1997 Eagle Talon TSi AWD
    · 2G DSM
    mercaholik likes this.

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