Broken case half during rebuild, need advice
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Thread: Broken case half during rebuild, need advice

  1. #1
    Senior Member TheLuigus's Avatar
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    Broken case half during rebuild, need advice

    Hi, again. Sorry i haven't posted in a while. I mentioned a couple of months ago, that I was close to starting my rebuild, and that I would document everything to post at the end. Well, I encountered a problem that I need help with, so y'all are hearing from me early.

    When I was reassembling the crankcase, I thought I was being even more careful than was necessary, and anyone I asked for advice made me feel like I was over thinking it. Anyway, as I was tightening the left side onto the right, I heard the crankshaft bearing squeezing into its cutout, and rather suddenly, there was a bang. Turns out, one of the rods that hold the shift forks in place had poked through the right side of the case. Nothing else was harmed, and the hole is very small. There will be a picture below showing the hole and the broken piece.

    IMG_20170320_153443.jpg

    Bottom line, is this fixable, or do I need to buy a new case half? Also, is that particular rod longer in the XT/TTR motors, because I used all of the transmission pieces from the donor motor except the machined output shaft.

    Thanks everyone, and sorry for bothering you on a Monday.
    Last edited by TheLuigus; 03-20-2017 at 04:40 PM. Reason: Added photo
    Soon to be TW250! - Jimbo Shield, Mule Nuts, Cyclerack, Tinman's Tool Tube and Pannier Mounts, DMO Footpegs, Lizrdbrth Cooler

  2. #2
    Member wmgeorge's Avatar
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    Is this your first motor overhaul? If so or even with experience a good repair manual helps. Generally speaking, welding thin aluminum, unless your really experienced with the TIG process can be another heart breaker. I have done it and could do it but no longer have the HF and AC TIG welding setup.

    So the piece you broke out, is there a hole behind it that supports that rod? BTW when you seek help on the internet you get advice, not the skill of the person giving the advice. Skill in being a mechanic comes from experience and making mistakes sometimes until you learn.
    Last edited by wmgeorge; 03-20-2017 at 05:17 PM.
    Retired guy Central Iowa, Lots of Hobby's

  3. #3
    Senior Member TW-Brian's Avatar
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    Just to clarify things, it sounds like you are using TW crankcases and XT/TTR tranny parts with a modified TW output shaft, correct?
    site:tw200forum.com

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  5. #4
    Senior Member TheLuigus's Avatar
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    Thanks for the quick response guys!

    To wmgeorge: Yes, it is my first engine build, and I'm learning a lot as I go. I have the official service manual and another aftermarket manual with pictures, both of which have helped tremendously, as has this forum, but there are questions that come up sometimes, leading me to ask those who are far more experienced than I. There are frustrations, but overall it is enjoyable and a source of pride to work on the bike myself. I hadn't considered how it would be fixable yet, maybe just that there was something I could do, although if I must get a new part, it wouldn't hurt too bad.

    To TW-Brian: Indeed that is the case. In fact, I believe you were the one who helped me (among others) to get the output shaft machined, so thanks again for that! I have tried to read through every conversion thread on the forum, but I can't remember if those rods were mentioned or not. I suppose I had assumed that other than the output shaft, the rest of the transmission assembly should be migrated whole. I was probably wrong, knowing my luck, haha.
    Soon to be TW250! - Jimbo Shield, Mule Nuts, Cyclerack, Tinman's Tool Tube and Pannier Mounts, DMO Footpegs, Lizrdbrth Cooler

  6. #5
    Senior Member christddel's Avatar
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    Hello,
    Sorry for my translation

    I just know that there are 2 axes of different length.
    The part number is different for the XT125 & 225.
    But when opening the engines, I never noticed different from these engine parts,
    TW BV 5 - 6.JPG
    Perhaps you have reversed the axes?

    Part list fork gear.jpg

  7. #6
    Senior Member TW-Brian's Avatar
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    When I did my 6-speed conversion I used all the TTR225 parts and just substituted the TTR output shaft with the modified TW output shaft (and one bearing) and I did not experience any problems. I have also not heard of any problems like yours from others who have done similar conversions.

    According to christdel's post, it appears that there is at least a part number difference in these parts between the TW200 and the XT225. I do not know if there is a dimensional difference between these two part numbers.

    On the TW, these two shafts are the same diameter but one is about 3/8" longer. That means that the correct shift forks could be loaded onto the incorrect length shafts. If this is what happened, and if when the crankcase was reassembled with the short and long shafts switched, the longer shaft may have punched through the right side crankcase when you tightened the crankcases together as your picture illustrates.

    Can you check and see if the now protruding end of the shaft is still restrained by the crankcase, or is it able to be pulled through (don't actually try and pull it through, just see if it could be). If these shafts were indeed interchanged, and the shaft is still restrained within the crankcase, then you may be able to just tear it apart and reassemble it with the shafts in their proper position without replacing the right side crank case.

    Or, I may be completely wrong!
    Heli-Mech likes this.
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  8. #7
    Senior Member ronnydog's Avatar
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    I may have a set of center cases. You would want to use a matched set.

    ronnydog

  9. #8
    Senior Member TheLuigus's Avatar
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    Christddel: Thanks for doing all of that research! As soon as I can split the case and remove the rod, I'll use calipers to check the length against the one that came out of the original engine.

    TW-Brian: It would be quite embarrassing if I had just swapped the rods on accident... Just to be sure, the longer rod should be the one with two forks, right? I have checked, and the rod is not going anywhere. Are you saying there is a chance to salvage this?

    Ronnydog: Thanks, man! If I end up needing a set, I'd like to buy them from you.
    littletommy likes this.
    Soon to be TW250! - Jimbo Shield, Mule Nuts, Cyclerack, Tinman's Tool Tube and Pannier Mounts, DMO Footpegs, Lizrdbrth Cooler

  10. #9
    Senior Member TheLuigus's Avatar
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    So I got the cases apart...
    Christddel was right, they are different, I'll post the pics when I get home, but I have the measurements.
    TW short shaft: 93mm
    XT short shaft: 90mm
    TW long shaft: 102mm
    XT long shaft: 106mm

    TW-Brian, the rod can be pushed through the hole, but the piece that broke was originally a protrusion, so it fits back flush. Since it is not something under pressure, can the piece be epoxied back on?

    Edit: Here are the pics. The darker rod on the left is from the TW, and the chrome-colored rod on the right is from the XT.
    Short rod comparison:
    IMG_20170321_162349.jpg

    Long rod comparison:
    IMG_20170321_162300.jpg
    Last edited by TheLuigus; 03-21-2017 at 06:01 PM.
    littletommy likes this.
    Soon to be TW250! - Jimbo Shield, Mule Nuts, Cyclerack, Tinman's Tool Tube and Pannier Mounts, DMO Footpegs, Lizrdbrth Cooler

  11. #10
    Senior Member TW-Brian's Avatar
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    I am sorry that you had to be the one to discover this difference!

    I don't believe that these rods see much load in their lengthwise direction, so it shouldn't take much to hold it in place. I would suggest using something like J-B Weld. I would not feel very confident trying to bond the broken piece back on as there would not be much for the adhesive to grab onto, and I would worry about the bond letting loose leaving a good size piece floating around in there. You might want to consider cleaning the area well and using the adhesive to create a plug in the protrusion to hold the rod in place. If you use the shorter TW rod, this plug could extend 4-5mm into the case plus some buildup on the outside to grab onto the fractured area. What do you think?
    site:tw200forum.com

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