flyday58 Posted March 16, 2012 Posted March 16, 2012 Mello Greetings. With 100 miles on the rebuild of Ole Red, time to do some searching. I am noticing a vibration that I am associating with bearings. It becomes very pronounced at 3100-3200 rpm, then again around 4100 rpm. If I vary the throttle just a little, the vibes decrease to what I consider normal for a two-stroke. When I pit my palm on the flywheel casing I can feel the vibes as the rpm changes, but it's not scary, just I know it's there and wondering what the long-term import may be. Please, I must have your thoughts...
nayruf Posted March 20, 2012 Posted March 20, 2012 Hi A problem on my DT, might have some bearing on your post (no pun intended) My DT had a small end bearing fail and I sent the bottom half away to get the casings and the crank split to have new con rod and bearings fitted, this the shop did no problems, I then rebuilt the motor new piston and top end bled the oil and was running the bike in fine there was a little vibe similar to yours, but I figured that it was just loosening up a little, Just to be sure I brought a new oil pump. To bleed it and ensure the oiI had made it to the carb nipple I took the plug out and turned the engine over by hand 10 or so times, whilst doing this the engine locked up, What I found was that one of the main bearings the shop had fitted had collapsed and the crank had slid over to the right this had unfortunately allowed the inside of the magneto to contact the ignition/charging coils and they had become trashed. I can only assume that the shop had damage the bearings when they fitted them ‘ In my 30 + years in aero / auto and industrial pump industries I cannot recall new bearings failing like that with out being the victim of some mishandling, So if it were mine I would take the top off check out the small / bottom end and both main bearings looking for any untoward movement, the shop fixed the bottom end for me after a bit of wrangling, but getting a new magneto and coils cost me, If I had been a bit more inquisitive about the vibration I would of only needed to replace a top end gasket set and the shop would have had the bottom end to do under warranty.
flyday58 Posted March 21, 2012 Author Posted March 21, 2012 Thanks for the reply. This bike sat in a junk yard out in the elements for a number or years before I purchased it and started the restoration. I disassembled the the cases to give it a good cleaning and check for damage, and all seemed well (I worked on C-130 props and engines for 22 years, cars starting in '79 and bikes back to '72, so somewhat familiar with things mechanical, just your basic gear-head). I did not document anything for reasons which escape me. Normally I photo everything I do, but not this time. So I've got nothing to refer back to. I know the con rod had side play but don't know about up-and-down. A main bearing seems more likely to me, as I don't think the gear bearings turn as fast. I'm going to try putting it on the stand, going thru the gears and seeing if I can narrow this thing down. Cheers. Richard
Moderator Airhead Posted March 21, 2012 Moderator Posted March 21, 2012 take a hold of the magneto rotor and see if you can feel any movement there, if the rotor does start rubbing on the coils iron core it will cause a great deal of heat and trash the coils, i've seen the results but always assumed it was from a loose rotor...hey maybe its a loose rotor??? Did you torque up the nut to the specified amount?
flyday58 Posted March 21, 2012 Author Posted March 21, 2012 take a hold of the magneto rotor and see if you can feel any movement there, if the rotor does start rubbing on the coils iron core it will cause a great deal of heat and trash the coils, i've seen the results but always assumed it was from a loose rotor...hey maybe its a loose rotor??? Did you torque up the nut to the specified amount? Why yes. Yes I did. I didn't like the "slop" the rotor had when I installed the magneto stator I got on ebay, so I bought a new woodruff key for the shaft and that took care of most of the slop. I WILL go back and check the torque on the rotor nut. Ran outta time just now as severe weather is moving in and needed to get under cover. Come to think of it, I should get off the computer,too...
Moderator Airhead Posted March 21, 2012 Moderator Posted March 21, 2012 heres how i get a grip of the rotor to tighten / undo the nut...saves getting someone to jam the brakes on in gear Under the filter wrench chain there are strips of cloth backed rubber cut from 'gardening / industrial' type gloves...works a treat
Moderator Airhead Posted March 21, 2012 Moderator Posted March 21, 2012 Also check again you engine mounting bolts are tight
Moderator drewpy Posted March 21, 2012 Moderator Posted March 21, 2012 Why yes. Yes I did. I didn't like the "slop" the rotor had when I installed the magneto stator I got on ebay, so I bought a new woodruff key for the shaft and that took care of most of the slop. I WILL go back and check the torque on the rotor nut. Ran outta time just now as severe weather is moving in and needed to get under cover. Come to think of it, I should get off the computer,too... the woodruff key is only there to locate the rotor. Its the taper that grips the rotor and some peeps use grinding paste to get a good key and thus grip (wash off the paste first)
flyday58 Posted March 22, 2012 Author Posted March 22, 2012 Already went around retightening. The forward mount was slightly loose, the rest were fine. I did find the drive sprocket very loose, also producing a leak. With everything torqued back correctly I still have the harmonic vibration.
flyday58 Posted March 22, 2012 Author Posted March 22, 2012 heres how i get a grip of the rotor to tighten / undo the nut...saves getting someone to jam the brakes on in gear Under the filter wrench chain there are strips of cloth backed rubber cut from 'gardening / industrial' type gloves...works a treat Paul, is this procurable or did you make it?
Moderator Airhead Posted March 22, 2012 Moderator Posted March 22, 2012 yeah just google oil filter wrench chain Just had another thought about vibration! (at the risk of telling you how to suck eggs) Clutch plain plates need spacing equi-distant around a full 360 degrees...are yours? in fact you will see little circles marked on the edge of the clutch centre, 5 of them...this is where to place the little 'pips' on the edge of the plain plates...
flyday58 Posted March 22, 2012 Author Posted March 22, 2012 Clutch plain plates need spacing equi-distant around a full 360 degrees...are yours? in fact you will see little circles marked on the edge of the clutch centre, 5 of them...this is where to place the little 'pips' on the edge of the plain plates... Yes, all that was done on original assembly. Being a old git mech I am fairly fastidious to that sort of thing. Anal is a word I think that sums it up.
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