OzVMX Forum
Clubroom => Tech Talk => Topic started by: D project on March 05, 2013, 08:41:00 pm
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After doing a full rebuild on my 125.It seems to have a bottom end vibration >:(
All bearings have been replaced.Crank rebuilt,rebore etc.
After it started the first time I suspected the main bearing were spinning in the cases.
Also seemed not as bad when you pulled the clutch in.
Checked out the clutch basket which had some movement,in/out back and forward where the gear connects the the back of the basket.
Belted down the rivets that hold it together. Which took out the play.
You could jiggle the crank/flywheel up and down.
Removed and replaced the bearings either side, put some locktite liquid metal in which cured that.
Checked the crank width which is a little over the standard in the manual.
Re assembled and ran it again it still seems to be there ::)
Would it be the crank out of balance when it has been re assembled or could something else be the cause?
Don't want to pull it down again just to start scratching my head.
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Is the mag running true ..... put a dial indicator on it ;)
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Is the crank balanced properly? Sounds like the cases are rooted if you had to use liquid metal to hold the bearings in. Did you replace all the gearbox bearings also?
Are the engine mount holes in the cases or frame flogged out? That can also cause vibration.
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Is the crank balanced properly? Sounds like the cases are rooted if you had to use liquid metal to hold the bearings in. Did you replace all the gearbox bearings also?
Are the engine mount holes in the cases or frame flogged out? That can also cause vibration.
Only had to use a smear of loctite which seems to have done the job.
All the bearings had been replaced.
Checked the bolts/holes etc.
Had that problem on another bike ,so I knew about that one.Is the mag running true ..... put a dial indicator on it ;)
I guess you mean the flywheel/rotor?
Can that not seat on the taper correctly on the crank half?
Should I try another flywheel?
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I know this sounds stupid but I once forgot to tighten the engine bolts?
And don't forget the rear engine mount is held by the swing arm. (On some models)
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While repairing a bike years back I found the clutch shaft was bent.
Can’t imagine what the previous mechanic did to it to cause this.
Another bike had a clutch basket that had the Cush drive rubbers disintegrate
The trouble with your clutch basket makes me think of both of these problems.
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Jase, Have you checked the crank itself for runout? who rebuilt your crank, did you do it yourself or outsource it ? - when you do it yourself at least you can spend the time to make sure its running perfectly true. also as per what GMC mentioned , i had a 1990 RM125 that was running as sweet as a bird, then all of a sudden it developed a horrendous rattle and vibration. THe clutch basket was the culprit, replaced it and happy days again.
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From my experiences, the main clutch basket bearing & bush need replacing every season on the late 80s-mid 90s RMs. Once they start to wear, the complete basket starts to pivot around (like A gyroscopic effect) & can make a horrendous vibration. If the vibration decreases when the clutch is pulled in, this may be the culprit.
Hope this helps.
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first thought is engine bolts not tight enough including swing/arm bolt through back of motor if it's that type. Secondly, if it has a 'full' flywheel--i had one once where the rivets were loose [broke off in the end & flywheel took off--roadracing RT1 Yam minus the cover, long story. Thirdly the pipe isn't touching the frame or solid mounted without rubbers etc. Also--piston [just] touching head. Gotta go but will think of more later. Cheers.
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Thanks for the tips so far.
Jase, Have you checked the crank itself for runout? who rebuilt your crank, did you do it yourself or outsource it ? - when you do it yourself at least you can spend the time to make sure its running perfectly true. also as per what GMC mentioned , i had a 1990 RM125 that was running as sweet as a bird, then all of a sudden it developed a horrendous rattle and vibration. THe clutch basket was the culprit, replaced it and happy days again.
Had the crank done by Ken Colvin. Seemed to be pretty old school, did a good job on the re bore. Champhered the ports etc.
Can you do a crank at home :o.
How do you go about checking it to see if its ok?
Re the clutch. Maybe that is part of the problem but it seems that the vibration is coming more from the flywheel side.
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Check that the crank isn't bent at the flywheel taper, I've had one bend when removing a flywheel.
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Take the barrel off again ;D and put a dial indicator on crank half's while hand turning your crank should tell you whats going on with out splitting the cases.
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Take the barrel off again ;D and put a dial indicator on crank half's while hand turning your crank should tell you whats going on with out splitting the cases.
Good thinking Stewart :)
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Take the barrel off again ;D and put a dial indicator on crank half's while hand turning your crank should tell you whats going on with out splitting the cases.
You would need a dial on each web and that still wouldn't tell what happening at the journal. Engine bolt or mount maybe the clutch thing would be more likely IMO.
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Just took pity on the neighbors 200 4 wheeler [loncin engine non name quad]. Just knew it was gonna give me grief. [look what i just bought]The old--it's only a small bike, their can't be much wrong with it trick. Anyway--Vibration--sorted it's various electrical problems etc but it 'vibrates' quite bad. Motor sounds good [no noises],so not going to go looking as all mounting bolts are supper tight & someone said once that these cheapy things built out of very thin gauge steel can play havoc in that respect. Remember when we were bucket racing, one of us put a mudbug or ts100 in an RG50 frame & vibrated bad [maybe he hadn't tightened it up].
Build my own cranks at home & get them close with a steel ruler then finish in the lathe with a center in the good end & the open the tail stock chuck up to fit up the taper to just before the keyway seeing the thread is nearly always bent from years of abuse. Set a dial gauge near the wheels & start from there. Wouldn't say i'm good at it but [needs must] get them pretty close whacking them around or squeeze or spread as required. Forgot where this is heading but probably trying to say that more often than not-vibration is caused by something else other than the crank being set up 100% true. Jut to tell another story re-out of true, back in the day [AJS 6 day trial factory bike--was before i got to it], boss wanted it roadworthy overnight for a road trial [nz], lights hadn't been on it for years & on fitting the alternator [direct lighting] found crank 'so far out' that it poled & couldn't turn the motor so Fk it [don't tell the boss] i just machined down the rotor till it gave clearance!!, went around in a gyration but worked & gave lights. Think i know who has that bike now--must tell him the story if he's given up on why the lights are 'dull'. Sorry, none of the above is probably of any help to you. Cheers.
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Did you replace the crank pin when the crank was rebuilt? If so was the replacement crank pin the same weight as the original? Some crank pins are solid and others are hollow. If you mix the two you're going to get some horrible vibrations as I found out years ago back in my road racing days.
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Pulled the motor down again to find that the loctite had not worked to hold the bearing in place.
I could get a feller gauge in between the bearing and casing.
I was able to locate another set or cases (thanks Bahnsy!) and have run with the motor and all seems well!
So conclusion was too much main bearing clearance in the cases ::)
Thanks for all the input!
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Pulled the motor down again to find that the loctite had not worked to hold the bearing in place.
I could get a feller gauge in between the bearing and casing.
I was able to locate another set or cases (thanks Bahnsy!) and have run with the motor and all seems well!
So conclusion was too much main bearing clearance in the cases ::)
Thanks for all the input!
Bearings are pressed or shrunk into a tight hole, at the end of the day it is still called an interference fit. with the right tools measure the hole, it shall or should be always smaller than the bearing OD, It can be felt in a hand operated press as "resistance". No bearing or body likes a loose hole.
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http://www.youtube.com/watch?v=dq6T5BojXc8
;D ;D ;D, :P