Author Topic: RD250/400 SHAKE DOWN  (Read 278 times)

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Offline dobeuk

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RD250/400 SHAKE DOWN
« on: April 14, 2018, 09:59:24 PM »
Bit of a story really, i did a nut and bolt rebuild on the 250 and finished it a year ago and had it as a museum piece in the house then i thought no this thing needs running. The last couple of weekends i have been getting it set up and checked over , covering short runs back home checking everything is tight all well. Then the turn of the 400 i had the engine rebuilt as you all know from previous posts did the same as the 250 so i thought , went for the second run out to a coastal town all well then started to head home nice long straight traffic in front weaving in and out about 70ish , dropped into the next village slow traffic in front doing about 30 lost all drive, pulled over engine still running, clutch ok selecting gears ok . A car pulled up that i had overtook and told me they had seen on the last bend something fall off and bounced down the road . Turned out to be the front sprocket tab and nut had come loose and dropped off which let the sprocket slide off the shaft. Cut a long story short a phone call to RDdave who came out in his van and recovered me, a special thanks to him , god must of being looking down on me , on inspection back home no damage to absolutely anything phew , could of been  destroyed casings and a wheel lock up. Ordered the bits from fowlers lets see what next weekend brings.
To be continued.

Offline Adeyone

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Re: RD250/400 SHAKE DOWN
« Reply #1 on: April 14, 2018, 10:12:17 PM »
Wow, you were very lucky, as you say it could have ended in tears.
Mark it up to experience and be sure the lock tab water is doing its job!   8)

I too had a quick ride out this afternoon on my RD350, at long last, due to foul weather.  Made me smile all the way - what a joy to ride these special bikes.
Looking to buy an RD400 now!

Ride safely.

Ady
Yamaha RD 350 1973, 1 of first 700, Not Smokin
Lambretta Li 150 special 225cc TS1, Not Smokin!
Honda ST70 Monkey bike, Now finished! Just needs an MOT!

Online 5port

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Re: RD250/400 SHAKE DOWN
« Reply #2 on: April 15, 2018, 08:48:44 AM »
Hmm. :o  We have had a few similar cases reported by members.  The tightening torque for the front sprocket nut is given as 47ft/lb.  You really need two of you to do it with one doing the back brake and steadying the bike.  ;)   This sprocket tightening and locking must be done well, because this type of arrangement WILL undo the sprocket nut if it is not fully torqued and locked.  Pretty much on the level of making sure that the wheels and suspension bolts are on tight.  Glad to hear no more damage!  :)

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Offline Barnett

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Re: RD250/400 SHAKE DOWN
« Reply #3 on: April 15, 2018, 10:25:19 AM »
How does a tab washer come loose, Dont understand that.
Yamaha 1974 RD125 (AS3) in bits!
Kawasaki 1977 z650 B1 being ridden
Yamaha 1972/3 U.S. early RD350 just acquired

Online mervin

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Re: RD250/400 SHAKE DOWN
« Reply #4 on: April 15, 2018, 11:26:09 AM »
Dunno but i had one crack on my TDR 250 just after a chain and sprocket change ,the tab that i bent over came off , 
luckily no damage when sprocket came off we fouind the nut sprocket and old tab washer in the road ,
the suspension adjuster spanner under the seat fitted the sprocket nut luckily , but there is a spacer that holds the gear box oil in it fits over the splines of the shaft and into the seals , so oil pissed out, we put it all back together ,
 A stone and screwdriver managed to  bend some bits of the old tab washer to stop it  coming undone ,

 Nathen dug into his panniers on his Stelvio and produced a litre of oil and off we went , I now reckon i will fit new tab washers evry time and stuff the expense
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Online 5port

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Re: RD250/400 SHAKE DOWN
« Reply #5 on: April 15, 2018, 03:14:17 PM »
The big or multi-tab washers can be reused if they are in good condition and you can bend an unused part of the tab to do the locking.  The thing that should really keep it together is, the torque loading.  If it is not tight, it will "worry" against the tab and possibly still work loose.   :'(

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Offline betty foRD

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Re: RD250/400 SHAKE DOWN
« Reply #6 on: April 15, 2018, 04:03:32 PM »
How does a tab washer come loose, Dont understand that.

Normally it doesn’t come loose as such but if the sprocket doesn’t bed down correctly then there can be enough gap for the tab washer to jump the shaft and just unwind with the nut.

So the learning ‘take away’ is that it’s not all about torque, the sprocket and tab must be seated properly so check before you fit. Sadly as I Get older my eyes find it harder and harder !
Rev 'em till they rattle

Online 5port

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Re: RD250/400 SHAKE DOWN
« Reply #7 on: April 15, 2018, 06:06:22 PM »
Yes, there always seems to be relatively little of the spline for the tab washer to engage. The retaining nut is counterbored to help the fit but, I always find that I have to hold the tab with fingers and make sure it is caught on the spline while tightening the nut fingertight.  If the nut is stiff on the thread and/or you just run the nut/tabwasher up tight from loose with a wrench, you might catch the tab splines on the end of the shaftsplines and get a badly seated tabwasher.  Also, if you fit the nut with the counterbore outwards, you might end up just tightening on the end of the spline.   :'(
Cheers

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Offline Barnett

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Re: RD250/400 SHAKE DOWN
« Reply #8 on: April 15, 2018, 09:50:48 PM »
So if the tabs are in good condition and fitted correctly it should be impossible unless part of the tab washer fails in service. Agreed its important to tighten nut correctly and to the correct torque, as 5sport says a loose nut can fret agaunst the washer but most importantly its a major cause of output shaft spline wear which is expensive to repair! Watch out for poorly fitting sprockets also, they must be a good snug fit and not too thick to take up the space reserved for the tab washer teeth. I have seen some awful examples in the past and now only use jtc, or is it jct which seem to be quite consistant.
That was a lucky escape merv!
Yamaha 1974 RD125 (AS3) in bits!
Kawasaki 1977 z650 B1 being ridden
Yamaha 1972/3 U.S. early RD350 just acquired

Offline kawazonkey

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Re: RD250/400 SHAKE DOWN
« Reply #9 on: April 15, 2018, 10:03:23 PM »
A narrow squeak, glad all is ok!

Offline Blackhat400

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Re: RD250/400 SHAKE DOWN
« Reply #10 on: April 16, 2018, 09:09:59 PM »
Yeh " i think sprocket thickness is the problem,[ aftermarket,],  i like the ones that have 2 small holes 180 degree,   that you can punch the tab into,  as a secondary lock,