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Thread: Motor Mount height???

  1. #1
    Join Date
    Mar 2010
    Grafton, OHIO

    Motor Mount height???

    OK. Gonna try to make long story short.

    Swapped a "known good" JY motor into '89 XR7 with spun bearing. Used new solid motor mounts that were in my collection of mystery parts from all over (I buy up stuff I know I'm gonna need when ever I can if the $$$ is right). Trans mount and cross member mount feel look very good. Also installed 24-2600 rpm converter and B&M shift kit (would not recommend, can't tell any difference from stock, get a constant pressure valve body tweeked to your preference, eliminate stupid TV cable), and new exhaust front half (ported manifolds to flowmaster mid pipe). Everything VERY good for 500 miles. NO leaks of any kind, no oil consumption. Successful swap

    Noticed significant wear on oil pan from failed motor mounts in "new" motors past B4 install. THOUGHT it was OK. Good for 500 or so miles, then a SUDDEN bad oil leak. Oil pan cracked on passenger side directly over K member where an obvious wear spot existed from rolled lip in hole in middle of K member directly over rack on pass side (can't tell if wear is new or old).

    During the 500 miles, I noticed a light/minor clunk/pop/bang on passenger side during hard upshifts intermittently. Expected to find a place where new exhaust hit chassis... NONE (also, although close, NO exhaust rattles at any time). Space between K member and pan LOOKS OK, 1/2 inch(?) or more... Can stick my fingers around it as far as I can reach all over.

    So. I decided to drop K member to swap pan instead of motor pull. When inspecting K member found NO "witness marks" of pan contact. Obvious marks on pan, but as I say, can't tell if any are "fresh".

    So why would pan crack after 500 miles not leak from the get go? I talked myself into believing I just made a bad call on pan wear, and heat cycling caused crack, but the more I think on it, and the amount of work if it does it again...

    My concern/thought is motor is torquing over allowing pan to hit K member (The thunk/clunk I am hearing) causing already thin spot to crack. If I have an incorrect shorter mount I could see this being the problem. Not enough clearance between. BTW the drivers side mount does have the "limiter" spacer thing in good shape.

    What is the "stock" motor mount height? I have NEVER seen a stock fluid filled mount that hadn't failed, so I have no idea what the measurement SHOULD be. The solid mounts I have installed measure 2 3/4 inches (solid rubber puck between the 2 steel halves of mounts). Supercoupe performance makes a big deal about theirs being custom made stock height and NOT RAISING motor center of gravity, which I read to mean are not TALLER than stock (ie parts store stuff IS too tall) . Are other applications (minivans, F series, mustangs with 3.8) SHORTER?

    OK then. That's my novel. Not so good on the long story short thing I do feel that any and all info IS critical to this sort of trouble shooting...

    So has anybody out there experienced similar fun, got ideas, suggestions, just wanna tell me I worrie to much and am a dumb ~~~ and put the new pan in and drive the wheels off it?

    Hep me out here



  2. #2
    Join Date
    Feb 2003
    Tinton Falls, NJ
    If there are no witness marks on the K-member, then it was probably just worn too far through before you dropped the motor in, and the heat cycling caused it to eventually crack. At this point, since the K-member is already down, I would grind flush that ridge that always makes contact with the pan, put it back together with the existing mounts and a new oil pan, and just keep an eye on it. If it does wind up making contact again, I would just install some washers between the motor mount and the top plate to raise the motor up slightly rather than replacing the mounts.

  3. #3
    Join Date
    Mar 2010
    Grafton, OHIO
    Thanks Mike.

    With new mounts I had myself convinced the same, but the mystery clunk on shifts concerns me. Had not considered grinding down that lip, but you are right, I see no reason not to while it is out it'll be easy insurance


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