I messed up redrilling rear mount

Discussion in 'Frame Mounted Engines' started by moonlake3, Aug 11, 2010.

  1. moonlake3

    moonlake3 New Member

    Here's what I done...I broke a rear mount stud. Instead of using an easy out, which I don't have, I drilled out the broken stud. I then used a self taping screw to make some new threads. I guess I didn't do a good job because now my rear mount spacer won't go all the way down the studs to be flush on the engine. I tried making the holes in the spacer a little bigger. Not much there to work with. The spacer goes over the studs and part way down. Just not far enough. The studs measure about 1/8" closer together at the engine that at the ends...:tt1:
    All this being said, I am trying to help my brother long distance. He has no computer understanding either. He is in need of an idea what to do. I told him probably looking at another engine.
    I hope I explained the problem well enough. He has only a few tools and little patients.
    I will wait for a few suggestions before I go on. I probably would have tackled the problem differently.

  2. spad4me

    spad4me Member

    Is this a happtime engine?
    My rear mount kept shearing off flush with the engine not the spacer.
    At first I would slot the broken stud with a dremel and unscrew the broken stud piece.
    I tried red locktite once BAD MISTAKE.
    I could not unscrew the broken studs.

    Place the spacer against the engine a little higher than normal.
    Just on top of the flush broken studs.

    Using the spacer as a guide redrill both holes being careful to align the holes, and not go to deep into the engine.
    Redrill with a drill sized for a 7/16 th tap to about 3/8 inch be careful.
    Tap the hole's with the 7/16 tap.
    But a correctly sized grade eight bolt.
    Its fixed and stronger than stock.

    Any hardware store will sell you the correct drill bit and tap as well as the grade eight bolts.
  3. moonlake3

    moonlake3 New Member

    messed up redrilling

    Good idea. I should have used the spacer for a guide the first time. My stud isn't broken off. I have another hole there now.Crooked. I'll have to look and see if there is enough room to move a little. With the other hole there, I wouldn't want to be right next to it. No strength.
    I was checking out the "rear mount overkill" idea. Might consider that also. I do have 2 holes to mount the plate. Just too close together for the mount spacer. Thanks for the input.:rockon:
  4. Al.Fisherman

    Al.Fisherman Active Member

    If it was my engine this is what "I" would do....

    Split the case and remove the crankshaft. Re drill the mounting holes starting with a 5/16 and working my way larger as need be, Drill ALL the way through the case. Tap hole, de-bur hole and clean case. Use Grade 5 studs with "RED" lock tite. Replace studs "before" assembly so you can see how far the stud goes into the case...you don't want it to protrude, just flush on the inside. Drilling and taping with the case together won't let you get enough good threads for the over sized stud. A tap has to go completely through the hole and not bottom out. They do make bottom taps but I feel it's use in this cast junk aluminum won't work and just screw up the upper threads. If the engine is mounted correctly, you will never have a rear mount issue under "NORMAL" operation.

    **5/16-18 drill "F"
    5/16-24 "I"
    **8x1.25 6.8
    **3/8-16 "5/16"
    3/8-24 "21/64 or Q"
    7/16-14 "23/64 or U"
    **7/16-20 "25/64"
    ** preferred sizes

    By the way I have done this to a front mount, as an experiment, but also changed it to the picture below. I can't see how this can be done with a rear mount tho.
    Last edited: Aug 12, 2010
  5. moonlake3

    moonlake3 New Member

    Rear mount repair...

    At this point, nothing is out of the game...Nothing ventured..nothing learned..:detective:
  6. GearNut

    GearNut Active Member

    I used a bottoming tap on all 4 of the mounting holes before I even began mounting the engine. The bubblegum aluminum that these engines seem to be made out of did not give me any issues, although I did maintain moderate pressure on the tap to try and prevent the existing threads from "pulling" the tap into the hole.
  7. Al.Fisherman

    Al.Fisherman Active Member

    Keep in mind that you using a bottom tap was basically used as a thread chaser, not for cutting new threads. Secondly we know what we're doing, and what to look for as it's being done.
    Last edited: Aug 15, 2010
  8. moonlake3

    moonlake3 New Member

    tap guidance

    thanks for the guidance. I didn't know that about bottom taps.good info to know.
    for now my brother has re drilled 2 new holes for the rear mount. not perfect but usable i guess. he does not live close by me. he may be moving to my area soon.
    I sent him pictures of the "overkill rear mount plate". he likes that idea. He is waiting on a new rear mount spacer now. the other one got modified and now is not usable.
  9. Al.Fisherman

    Al.Fisherman Active Member

    Hope it works out. If it doesn't you always have the option of splitting the case. If that is what needs to be done, take a piece of either angle or flat iron, drill the holes the correct distance apart and use it for a guide (like I did in my front mount save)...don't use the factory mount except for marking the plate.
    I drilled the holes in the angle iron, then using it as a guide drilled through the aluminum.
    Last edited: Aug 16, 2010
  10. moonlake3

    moonlake3 New Member

    messed up on rear mount

    Good series of pictures on the front mount...thanks for taking the time to take the pictures and post them..picture IS worth a thousand words..:detective: