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Author Topic: Would you use this case  (Read 3566 times)

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Offline alexbrown64

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Would you use this case
« on: January 15, 2015, 05:24:01 PM »
Hi fella's, well, my original cases for the YZ25K rebuild were rooted as the mains didnt have an interference fit anymore plus they were well worn.  I have purchased another set for under a hundred bucks from the US which included post.  They are supposed to be in great condition, which they are except for 1 problem  The left case has had a lug welded and machined.  The lug is one of the ones that a post goes into that holds some of the shift forks.  Its a big weld and i think its been used for a while like it but im just not sure and would like opinions on what others have done.  Yamaha used to sell case halves individually for this model.. K, L and N so i dont think case matching is an issue as i can get a left half if necessary.  Are the shift fork posts a heavy load area?  I believe the inner cases are ally so do you think ally welding will be up to it on inner cases?  I have provided 2 pics below so you can see a normal lug and my welded lug.
Also not that in the welded lug was a small hairline crack and the post fits in quite loosely with a bit of side to side wobble.  More movement than in my existing old cases lug. 
Cheers,
Alex
Normal lug below... next to the transmission bearing.. it holds a shift fork post....

My new case below which is good except for the repaired lug...
« Last Edit: January 15, 2015, 05:32:48 PM by alexbrown64 »
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Offline tony27

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Re: Would you use this case
« Reply #1 on: January 15, 2015, 05:54:07 PM »
Probably do something about the tightness of the hole, a decent engineer should be able to reweld & machine the hole or rebush it & repair the hairline crack.
The shift fork only really needs to be located properly for a couple of millimeters but more is better
Certainly a better starting point than your cases with the loose bearing housings
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Offline FourstrokeForever

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Re: Would you use this case
« Reply #2 on: January 15, 2015, 07:25:58 PM »
Looks like a pretty bloody good weld to me. If the shift post is a snug fit in the hole, I'd use it for sure.
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Offline 80-85 husky

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Re: Would you use this case
« Reply #3 on: January 15, 2015, 08:32:57 PM »
wack it together and see if it shifts ok.....
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Offline alexbrown64

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Re: Would you use this case
« Reply #4 on: January 15, 2015, 08:45:59 PM »
The hairline crack was only 0.5mm deep when i uses a screw driver to scratch it.  It is a chunky weld so i may just "whack it together".  There is another set of cases for 35 bucks from an 84 so i may get those as well for a back up.  This bike is fighting me all the way.  Tony, i dont want to go down the repair road.  Its expensive in WA, and i just want a decent set of cases.  It may take a few sets to get it right.
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Offline gus58

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Re: Would you use this case
« Reply #5 on: January 15, 2015, 09:52:11 PM »
Shim it, I'm not sure for very small stuff, but bearing shops supply shafting shims, or put some verniers on the shaft and in the hole, find the difference and shim it yourself. Buy the right thickness shim steel so it has a very small interference fit when rolled into a cylindrical shape. Or if the hole is seriously elliptical, get it machined out a touch and have a sleeve turned up on a lathe.
« Last Edit: January 15, 2015, 09:57:05 PM by gus58 »
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Offline OverTheHill

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Re: Would you use this case
« Reply #6 on: January 15, 2015, 10:23:32 PM »
can you machine the hole round & inline with other side without much cost or drama, lightly bronze the end of selector shaft then machine it to a reasonable fit, probably wouldn't want to be a tight fit just incase of slight mis-alignment. Done worse things than that & got away with it ok. Think you mentioned loose mains which takes me back to a yz125 i had which mains felt loose but that year [think was an F "79] had the case cast around an alloy ring for the main bearings & the ring came loose but was shrouded by the case by a few mm or more at the visible edge. Caused a few headaches. Ended up grub screwing it with half a dozen 1/4 whitworth allen driven straight screws [whatever they are]. Must've chipped the few mm away at the edge to see where the ring & case meet [35 years ago now]. Worked a treat as cases were expensive back then. All i'm saying is could still be a trap on cases made like that if not aware of it. Had an RMX250 "81 with the same issue exactly but the ring had fallen to pieces on one side & almost as bad on the other. Packed a sad & sold it as was, bugger it.
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Offline gus58

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Re: Would you use this case
« Reply #7 on: January 15, 2015, 10:39:35 PM »
Good option, BUT, depending on the size of the shaft I'd be wary about putting too much heat in it, it can't be re heat treated once brazed. If its diameter is big enough then go for it....
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Offline Tomas

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Re: Would you use this case
« Reply #8 on: January 16, 2015, 12:10:03 AM »
Would be good to know what caused that sort of damage. I would get it welded and remachined to correct size. Weld that is already there looks pretty solid. The actual repair looks stronger than original design. In my opinion it was only drilled with press drill rather than on milling machine. Should be an easy job most of japanese stuff is metric so there are not odd sizes to deal with. Good sharp slot drill should do the job.  Get it rewelded and machine it properly and it will last for another thirty years. I would not use shims, grub screws or other nonsense. You will just butcher it further. When you take it to the machine shop, get them to sleeve the other set of cases you have. You can buy another set of cases but who knows what may be wrong with them. You may just invest the money in repairing the sets you already have knowing that you have a good set with no issues.
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Offline gus58

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Re: Would you use this case
« Reply #9 on: January 16, 2015, 12:33:10 AM »
Quote from: Tomas on January 16, 2015, 12:10:03 AM
I would not use shims, grub screws or other nonsense.

Nothing wrong with shims, rode a Bonneville 750 for 12 years with a shimmed needle roller on the inner layshaft without a prob..... the bearing shit itself and wore the bottom of the gearbox case, simple fix that works, word of warning though, make sure the shim can't work its way back into the gearbox if u go with that option.... the bonnie had thrust washers so kept it in place....
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Offline alexbrown64

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Re: Would you use this case
« Reply #10 on: January 16, 2015, 12:49:08 PM »
Thanks for the input fella's.  I have decided to purchase another set of cases that came up for $35 and they are in the mail to me.  I will choose the two best cases and rebuild the engine with those.  I dont really want repairs in the engine if i can help it.  All the spare cases will be shelved for the future, as if my son has this bike at my age, he may need them as the bike will be 70 years old by then and you wont be seeing cheap sets of cases popping up on Ebay, or whatever they will have in the future.  He could probably just print himself up a set.
Cheers,
Alex
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