crancase top thru-bolt causing leaks?
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  1. #1
    Member chainsaw's Avatar
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    I love my TW.

    I hate chasing down leaks, and this one has me baffled. I suspected, as was mentioned on the forum before, that the base gasket was going south, or even that the long flange bolts had shaken loose.

    Well-they had shaken enough that vibration from the engine had caused quite a bit of shear on the threads.



    This, my fellow tw-riders, was not my Eureka moment. To remove the top left flange bolt, I had to literally hammer it out, shave away a "casting lip" specially designed to piss off Mother Teresa.

    The folks at Yamaha just hammered the bolt in, screwing up the threads. I guess they figger what I don't know won't hurt them.



    Anyway, once all the metal filings were very carefully and forcefully flushed out, I put the new flange bolts in, getting all giddy about riding a leak-free tw.



    I didn't have a torque wrench, but I did fit them carefully, warmed the bike up, then rechecked them and threadblockered them.



    Fast forward to the next day when I take a good hard 50 mile run, turn the bike off, and gaze in wonder at oil weeping from the same spot behind the cylinder head, then down the left clam, proceeding down my pant leg, shoe and foot peg.



    Now, if this was a much larger bike with greater oil capacity, I probably would just throw a shop rag over the oil, then top it off before the next ride, but I'm just anal enough to obsess about problems like this to the bitter end, so here's the "rest of the story":



    After spending countless hours, sleepless nights and a trip to the local shrink (LOL), It ocurred to me that the 6mm through-bolt, both holding the clams tight and preventing seepage, might have been roughed up, threads sheared, allowing oil to leak right at the seam on the right clam, then leak more out of the bolt hole.



    I'm so far past throwing good money after bad (adhesives, bolts, various hardware), I'm going to put a new bolt in there, but I'd hate to put a long, skinny 6mm one in-this is definitely one of those places where size and strength do matter.



    Here's my question: Is it possible to tap an 8 or 9 mm hole without much weeping and gnashing of teeth? The threaded area of the hole inside is only about 1.5" long. I implore you dear friends-do I tap-and die for a thicker bolt, or use a self-tapping 8 mm, or keep a fresh supply of weapons-grade 6 mm through bolts on hand? If you have any suggestions, please be so kind as to help a guy going through his third childhood and just wants to ride.



    Thanks in advance for your help,

    Thom

  2. #2
    Senior Member Gerry's Avatar
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    Thom, you seem to be in a pickle. You went into some detail to present your predicament but I am not sure of the meaning on a couple of words, like "left clam". Not sure if you were talking about a clamp bolt or cam bolt. There again Yamaha may have a "left clam" and I have never heard of it. I am not trying to make fun of you, or your post, it is just that this 'detail' leaves me confused. In any event, should you have the room to move up to a large size hole/bolt, I personally would have no problem doing this. Make sure you use lots of cutting oil to get a nice defined thread. I would as well, paint that bolt red to remind me that it is different and not to be tried in the other holes... Good luck, hope this helps you out... Gerry
    Take care my Friend.........

  3. #3
    Member chainsaw's Avatar
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    Mr. Gizmow, I was hoping you would answer. You seem to have your finger on the TW's pulse.

    I'm an old guy, and we used to call the halves of the crankcase "clams" or "clamshells"

    I'm leaning toward these ideas in the following order:



    1. Get more 6mm bolts, but made of sturdier metal, redblock 'em in so Moses himself couldn't even part the bolt from the clam.

    2. Using a slightly larger bolt that would cut it's own threads-6.5mm maybe?

    3. Throw caution to the wind and just tap a hole for an 8mm bolt



    It still amazes me that these days, the metal (or aluminum) on bikes (and cages) just feels so cheap. In 1974, I bought my first Honda while living in a DOD suburb outside of Kanto, near Tokyo. It was an SL90, cousin to the CB90, tremendously overbuilt and tragically underpowered.



    Thanks for all your help.

    Thom

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  5. #4
    Senior Member thumper's Avatar
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    Quote Originally Posted by chainsaw View Post
    Mr. Gizmow, I was hoping you would answer. You seem to have your finger on the TW's pulse.

    I'm an old guy, and we used to call the halves of the crankcase "clams" or "clamshells"

    I'm leaning toward these ideas in the following order:



    1. Get more 6mm bolts, but made of sturdier metal, redblock 'em in so Moses himself couldn't even part the bolt from the clam.

    2. Using a slightly larger bolt that would cut it's own threads-6.5mm maybe?

    3. Throw caution to the wind and just tap a hole for an 8mm bolt



    It still amazes me that these days, the metal (or aluminum) on bikes (and cages) just feels so cheap. In 1974, I bought my first Honda while living in a DOD suburb outside of Kanto, near Tokyo. It was an SL90, cousin to the CB90, tremendously overbuilt and tragically underpowered.



    Thanks for all your help.



    Sir, lets back up a minute shall we...

    Leaks on these little motors can be very miss leading. After rebuilding my top end, I found oil again on the motor as you described also.

    It turned out to be the valve inspection cover o-rings. You MUST replace these any time you open them up or they will flatten out and leak.

    Also it could be your oil galley bolt (right rear side of the head) they sometimes leak and the oil follows the fins down the left side and wanders all over the place.

    Those would be my first two guesses. however, I have a very simple way to find/locate an oil leak!

    First take contact cleaner or brake cleaner and spray the entire engine clean.

    then go down to a supermarket or drugstore and by a spray can of foot powder.

    Spray all over the engine (won't hurt it) until the engine is completely covered.

    Then start the engine and see where it starts leaking.

    If anyone watches that tv show fact or fiction, I met the guy in the show (rides a buell) at a local HD shop.

    His Buell had a leak and the shop could not find it. I pulled him off to the side and told him about my method.

    He thought I was a genius! Shop hated me because they wanted to charge him 10 hours to "dissasemble the entire engine" and "find the leak"

    Hope this helps.

    Ride safe

    Thom

  6. #5
    Senior Member thumper's Avatar
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    I'm not sure why my reply ended up in the box with the prior reply.

    sorry for any confusion.

  7. #6
    Senior Member lizrdbrth's Avatar
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    Can we assume you're referring to the longer Phillips head through bolt that passes through the cases directly behind the cylinder?



    If you are there doesn't appear to be much meat on the right clam to accept much of an oversize. Your 6.5 plan seems wisest if one can be found.



    I'm with Igofar on this one. It sounds like you know what you're doing, but double check the source of your leak before proceding. Most leaks I've seen on these bikes migrate from other sources like the base gaskets and valve cover o-rings eventually depositing themselves in odd and misleading places. Rarely do they occur at the case halves.



    I can explain it to you, but I can't understand it for you.

    Powdercoated '87 frame, extended swingarm, YZ fork legs, ATV tire, 14/55, XT350 tank, spliced quick-release seat, disc brake conversion, beeg headlight, beeger rack, Lizrdcooler, Lizrdventz and bunch of other stuff all covered in invisible ink.

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  8. #7
    Member chainsaw's Avatar
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    Well, the original bolt was a flange type with a simple rubber washer. Funny thing is, it didn't start leaking out of that bolt until after I put the four larger flange bolts that run the length of the cylinder (that problem leak is solved for the most part). Tends to make you think that at some point, all the outside bolts are tightend in a sequence of sorts, so that nothing is too tight or too loose. But yeah, I did use my foot powder after a thorough engine clean to determine the leak point. The screwiest part is that I don't think it actually starts leaking until after I put the bike on the kickstand-while the bike is leaning to the left. There have been many times where I would prop the kickstand on a brick after a ride, and there was not a drop of oil to be found.



    Still flabbergasted,

    Thom

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