OzVMX Forum
Clubroom => Bike Talk => Topic started by: alexbrown64 on February 12, 2015, 06:28:20 pm
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Well, after considerable time, cost and effort, i started putting the engine back together on the 1983 YZ125K. All new bearings, seals, rod,etc.. When it came to tightening up the cases, in the last 1mm, the crank tightened up. I did all the usual stuff, a tap here, tighten it all up, back it all off etc.. but the crank would go tight on final torque. If i backed everything off a whisker, the crank would loosen up. Anyway, i knew there was a problem so i ripped it all apart again. Checked main bearings. All OK and seated right in. I checked the newly rebuilt crank and measured up the new rod. Its 17mm wide. I grabbed my genuine Yamaha rod. Its only 16mm wide. The ProX rod says it for 1980-85 YZ125 but it is too wide and thus i am unable to torque the cases together without the crank getting tight. My question is this. Do i have a case against ProX if i email them all the details. Can the bike shop rectifiy the problem or is it an OEM rod to get it right. Also, in my heavy handed way, i bent the end of the crank where the threads are that tighten the rotor on. Also, f*cked the threads a bit. Can this be heated, straightened and rethreaded. Might be best to start again with a used crank and all OEM rod, spacers, bearings etc..
Thoughts..
This is the rod.. http://www.vmxunlimited.com/connecting-rod-kit-1980-85-yz125-pro-x/ But i got mine from Partzilla
Cheers,
Alex
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Hate to say it but straightening out your bent crank won't be easy, much easier to start with another crank that isn't damaged.
Is the original rod available still? It may be possible to surface grind .5mm off either side & fit a genuine big end bearing which will be the right width
Part number for the 83 rod kit is the same for 82 & 84 models so I'd say that pro-x has made a mistake
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99% sure I've got a new genuine rod kit for an 84 YZ125 that I never used. You can have it very cheaply if you want it.
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Tony, i just checked and the original crank is not available. I have just emailed a long letter to ProX explaining the problem as i believe they have sold an out of spec part which opens a can of worms. I have checked FleaBay and i can get an old crank for about $100 delivered. I have only bent the skinny end where i whacked it. Are you sure you cant just heat em up a bit and get it straight? Its only the last 20mm where the nut goes on. Nathan, thanks very much for the offer. I may take you up on that depending on circumstances.
Cheers,
Alex
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I may have found the problem and solution. The original 16mm crank + 2 x 1mm shims and a 1mm gap gave a 19mm space between the crank halves. The shims used in the crank rebuild were 1mm, the same as OEM ones. This took the crank (17mm) + 2 x 1mm shims plus a 1mm gap to 20mm. The ProX kit comes with 0.5mm shims as well which the bike shop did not use and gave back to me. If they had spec'd it all up first to keep the correct width they would have noticed that using the 0.5mm shims and only a 1mm gap would of given me an 19mm gap between the two crank halves and i would of been in spec. Back to the bike shop.... but i still may need another crank if i cant straighten and fix the threads on the tip.
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I would say that your crank rebuilder made mistake.They should have pick this up. They usually measure , compare and record all crankshaft dimensions before disasembly and when assembling/trueing the crankshaft.
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Yes the thread can be brought back onto centre, as long as you have not mushroomed it over too much. Clean the thread up and see if you can get the nut started - slowly pulling it back into shape... be patient and don't use a hammer
Do you own a set of Vee blocks and a dial indicator ??? as they come in handy for times like this ;) as it will tell you if the crank is still within spec and spinning on the same centres.
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Even though a bent thread is ugly, the taper is the strength of the assembly, and the nut holds the flywheel firm onto it. I have seen plenty of cranks over the years with bent threads that still work fine. As long as the thread itself is ok and the nut is a nice firm fit on it, and there is no damage to the taper, it will be fine. i use a crank removing tool mostly, and I never hit the end of the crank if possible, or if i have to i press the crank out of the cases in a press. Worst case scenario if you have to hit the crank, use a copper hammer, and spin the nut on first till it is flush with the end of the crank. Always, always measure the crank width before splitting it, and always, always , check side clearance once the crank is reassembled and trued. I have had some where I have reassembled a crank to the width it was before it split it, and using the same width thrust washers, I have found the side clearance is too little. Most manafacturers will have the width of the crank listed in workshop manuals, or if not the correct side clearance.
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Turned may a stuffed external thread crank into an internal thread with no adverse effects. Just cut it off, drill & tap & you're good to go without spending any money.
K
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with the bent end, they're guaranteed to get damaged by someone at some stage without the proper gear [sorry], but the shop probably won't be using the centre of that to true up the wheels on assembly. They'll have rollers or something or in my case [cheap ass] assuming [or hoping] the other end is still straight so as to use the centre--i run the chuck of the lathe tail stock thingy up to just before the keyway then a centre in other end [primary end] & dial gauge close to the wheels. Shop may have knife edge rollers set close to the wheel & do the reverse of what i do pretty much. Both work.
'Anyway'--the thread--either just grind a taper up to where the nut will wind on or better still [used to do this at work] find someone with a descent tap & die set with adjustable die jaws & back it off to get past the damaged bit then tighten the jaws on the good thread & wind it back off--that'll sort the thread & just forget it's bent. [won't be bent on the taper so won't matter--my theory anyway, the old fix it but 'dooon't spend any money trick]. Cheers.
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After your first post I was going to tell you that those kits normaly come with .5 and 1mm thrusts but I see you have worked that out. The shop that fitted the kit for you would be at fault as they should have measured the crank width before taking it apart. The threads can be straightened without the use of heat. I normaly use a soft drift to knock the main part of the thread back in line and then set up the wheel in the lathe to screw cut a new thread through the mushroomed section.
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Lots of great feedback guys. I will try to straighten and fix the end of the crank and then take it into the bike shop to explain my case. What a pain. I had everything together and the cases wiped with Three Bond etc.. Now its all back to cleaning it all up and starting from square 1.
Thanks again and i will post up the results of my endeavors..
Cheers,
Alex
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Alex , Your case is strong as you state that they gave you the alternative shims back. Don't rant and scream, just request the owner and senior mechanic/technician and firmly explain and display the results.
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The bike shop probably sent it off somewhere to get done. Not many bike shops do crank work in house. Just out of curiosity how much did you get charged to have the rod fitted?
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Thanks again for all the input fella's.
Well, i got up early this morning to have a fresh look. The threaded section on the end of the crank where the rotor goes on was about 25mm. I straightened it up as best i could and then used a dremel to cut off 15mm which was the damaged section. I tidied up the thread and spun a 12mm nut on no problem. So the repair worked great. Straight, clean and useable. I had the crank sealed in a plastic bag while i was doing the work, but i still blew it all clean with compressed air and then took it all back to the bike shop. They do their own cranks there and have done my rm80n crank. for the N, i supplied the parts and they rebuilt it for about $100. For this K, they said it was a bit tight and took a little longer so they charged me $130. Before i went in the shop, i drew everything up and showed all the measurements and where they went wrong. I showed it to the manager and he was great and understood the problem, especially when i showed him the 0.5mm shims he had given back to me when the mech had used the 1mm shims. Manager reckons he should get the crank rebuilt and within spec by this afternoon.
I think i have arrived at a good outcome.
Lessons learnt. Before you hand over your crank, write down all your specs and then check them when you get it back as i guess silly little mistakes can happen and you could save yourself a heap of time and effort.
Hopefully can restart the engine rebuild tomorrow.
Cheers,
Alex
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Will you still have enough thread left? 10mm of thread doesn't sound like much. $130!! I better start charging more.
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Sleepy, i inserted the PVL rotor on the shaft before i cut it and it went past the good threads and only needs a small nip to tighten it on the taper. After that, i dont think you would even need the nut as you have to use a puller to get the rotor back off. Saying that, i will use a good quality nut and some loctite and it will be perfect. I worked it out that the end of the nut and the end of the shaft will be flush. When i get to that part of the rebuild, i will put some pix up in the Yamaha section.
Not sure how you charge sleepy, but if i was close to you i would bring it over, but i have 3 bike shops only 5 minutes away and they just charge by the hour so usually it can differ a bit depending on how stubborn the crank is to pull apart and press back together. Do you just have a flat rate for a crank rebuild?
Cheers,
Alex
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Alex ..Serco up here in sunny Qld are under $100-00. and it's normally a 24 hr turn around.
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Oldfart... i am in WA... with the mining boom, labour prices are through the roof. I was quoted $660 just to paint my rm80b tank and i was to supply all decals and pick up/deliver the tank. My knees start shaking if i have to get any work done at a bike shop, hence i do most of my own work.. but sometimes i f*ck it up. In this case, the bike shop made a small error which has cost me heaps of hassles. At the moment, Eric Gorr in the US is working on my cylinder, Ash's Spoked Wheels is rebuilding my wheels with gold takasago rims in QLD and Terry Hayes Shock Treatment has my 3 monoshocks which they are rebuilding into 1 good one. My bike is all over world at the moment. This is an international project with a budget to match.
I have heard that Serco are really good for all sorts of work and are very professional.
Cheers,
Alex
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Alex - they ( Serco ) have been around for along time and I have never had a problem with their work. Most Business have a bad day ( as you have experienced ) and a business that wants repeat customers are more than happy to fix the problem if it's their mistake. ;)
I try to do most of my stuff in house ... hence this is why my projects take for ever ;D
Geez you don't mind sending parts to all four corners of the world :D
Cheers Stewart
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OK guys, thought i would post the outcome of the whole process. As described previously, i bent the tip and damaged the threads but i straightened it up and cut the threads down and it worked great... got away with it just this once. I then took the crank into Witch Cycles. They pulled it back down and said that because of previous damage from a mechanical failure, the crank needed to be machined. They machined it up which must of thinned the inside, because they used the 1mm shims again but reset the specs using Yamaha crank data. They were happy to do this and not charge me, so hopefully it is all good now. Below is a pic of the re-re-built crank showing my thread repair on the left side and everything ready to go back together. The threaded section on the left was about 25mm long and now it is 10mm but long enough to get a nut on to pull in the rotor and hold it there.
Cheers,
Alex
(http://i40.photobucket.com/albums/e249/alexbrown64/crank_zpsbe636bbe.jpg) (http://s40.photobucket.com/user/alexbrown64/media/crank_zpsbe636bbe.jpg.html)
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rather than send rims to Qld have you tried Spoked Wheel Services in Beechboro?
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Spoked Wheel Services rebuilt the wheels on my XR500R and did a great job. I asked them to use my old rims as i wanted to keep the bike original. They fitted new SS spokes, blasted and painted the hubs, new bearings, tyres etc... When i finished the XR, i thought the rims let it down but i wanted to retain them so i called Spoked Wheel Services and they said they dont recondition old rims. I called Ash's Spoked Wheels and they said they would strip the anodizing, sand the rims and get them re anodized. Originally the rims were silver but i always wanted gold, so they did them in gold. They came out great and i retained my original DID rims and the bike looked fantastic. Since then i only use Ash's.
(http://i40.photobucket.com/albums/e249/alexbrown64/xr2_zpsb13f09f5.jpg) (http://s40.photobucket.com/user/alexbrown64/media/xr2_zpsb13f09f5.jpg.html)
(http://i40.photobucket.com/albums/e249/alexbrown64/xr1_zps7e41e203.jpg) (http://s40.photobucket.com/user/alexbrown64/media/xr1_zps7e41e203.jpg.html)
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OK - good point Alex. Have just removed the front wheel from my 80 CR250 and didn't want to buy a new rim but the original could do with a tidy up so may do the same thing myself.
cheers
Rossco
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OK guys, thought i would post the outcome of the whole process. As described previously, i bent the tip and damaged the threads but i straightened it up and cut the threads down and it worked great... got away with it just this once. I then took the crank into Witch Cycles. They pulled it back down and said that because of previous damage from a mechanical failure, the crank needed to be machined. They machined it up which must of thinned the inside, because they used the 1mm shims again but reset the specs using Yamaha crank data. They were happy to do this and not charge me, so hopefully it is all good now. Below is a pic of the re-re-built crank showing my thread repair on the left side and everything ready to go back together. The threaded section on the left was about 25mm long and now it is 10mm but long enough to get a nut on to pull in the rotor and hold it there.
Cheers,
Alex
(http://i40.photobucket.com/albums/e249/alexbrown64/crank_zpsbe636bbe.jpg) (http://s40.photobucket.com/user/alexbrown64/media/crank_zpsbe636bbe.jpg.html)
Are you sure they just didn't machine .5mm of each outside without pulling it apart again? Bit hard to see from your photo but what they told you sounds a bit odd.
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Sleepy, they said they pulled it apart and there was some internal damage which didnt allow the use of the .5mm shims. Not sure why. But they reckon they machined the inside surface of the crank halves. Then they reused the 1mm shims as because of the machining, the .5mm shims would allow to much slop. I have measured the internal gap and it is back at 19mm with the 1mm shims which is the spec that it originally had. The first time they gave it to me, the internal gap had gone from 19mm to 20mm which effectively widened the crank and thus got tight in the cases. I am re-fitting it all this arvo so i will report back on fittment but should be good now.
P.S - hope all you Queenslanders are OK with that cyclone bearing down. Good luck and take care...
Cheers,
Alex
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Ok. still seems a bit odd that they didn't notice that damage the first time around. Main thing is that it is fixed. I have the outside width as 56mm for the YZ125's
Weather is best described as wet here in Bris. They tell us that the cyclone or storm will get here on Saturday sometime but will be just rain by then. I hope not to much rain as our local bridge has water about 1 meter from going over already and if it gets much heavier I will be stuck here with me feet up.
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George..... Feet up, not likely :)
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George..... Feet up, not likely :)
Can't even dream of a bit of time off, thank a lot.
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Roscoe, they do warn you that a rim can crack when re-anodized. Mine were fine.
Sleepy, i went out and measured the crank up and bang on 56mm. I installed everything this morning and shut the case halves up. All fitted up perfectly. Again, lesson learnt is to check crank against specs before refitting it or you will be in for a world of pain.
Cheers,
Alex
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Just had 2 rims re-anodized by the so called experts.....both cracked. Only did it because it's a special bike......would never do it again.
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Just had 2 rims re-anodized by the so called experts.....both cracked. Only did it because it's a special bike......would never do it again.
I reckon you're on borrowed time the minute you strip an old wheel. With the amount of work they've done over 20+ years, the sooner you can lace them back up again the better.