Author Topic: HELP! 78 yz250 kicker sprocket grinding inside of case  (Read 1821 times)

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Offline rob86

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HELP! 78 yz250 kicker sprocket grinding inside of case
« on: November 09, 2014, 07:31:41 pm »
Hi all,

I had my 78 yz250 out at the sunday slide last week for its first proper ride now that I thought it was sorted.  I pulled in a after a few laps to pull the plug and have a good look over the bike to check the tune etc. I noticed a grinding noise once I had my helmet off and killed it fearing it was the crank bearing.
I finally got a chance to properly go over the bike this afternoon and surprisingly everything seemed really good and clean to the point where it appears to have had a full rebuild not too long ago or the possibly the easiest life an old dirt bike has ever had...

What I did find was that the sprocket on the kicker shaft had made contact with the inside of the case. I took the kicker assembly out completely, put the cover back on and oil back in then bump started it in the drive way. The noise was gone and I guess confirmed that the sprocket was the source.

The problem is that the kicker shaft shows no signs of wear at least from what a novice can see) nor do any of the other components to it or where the shaft sits in the case.

Is there something I'm missing? Is this a known problem? Any help or advice would greatly apreciated!
Cheers - Rob


oldfart

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Re: HELP! 78 yz250 kicker sprocket grinding inside of case
« Reply #2 on: November 09, 2014, 08:22:44 pm »
If it is assembled as per schematic.... I would be looking at part 21 not located in correct position to 20.
This is quite common  on Suzuki rebuilds  ;) by not paying close attention ... dots must be aligned.

Offline rob86

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Re: HELP! 78 yz250 kicker sprocket grinding inside of case
« Reply #3 on: November 09, 2014, 09:10:27 pm »
Thanks guys, I'll take another look at it and make sure it's all seated properly and in proper order

Offline OverTheHill

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Re: HELP! 78 yz250 kicker sprocket grinding inside of case
« Reply #4 on: November 09, 2014, 10:26:05 pm »
Without studying it closely, do you think it 'is' grinding on the case as by memory they're machined there for clearance where the teeth wizz past but suppose wear in the outer cover [not un-common] could let it move slightly over on the outer end & if it's a close call to start with then it might just make the difference [but don't think so sorry]. What i'm wondering [or thinking] 'is' the ratchet staying partially engaged [not releasing fully back out of the way]. Could operate it [plug out-or clutch off] & see how far it moves back when against the return stop. Maybe pack the shaft more to the outer cover side if possible which will take the gear further away from the ratchet in the returned [up] position--[fully up that is] as only disengage on the last little bit. Might be able to bend the steel stop to make it pull the ratchet more out of the way. Dot on the shaft [without looking] is possibly only to do with kick start spring tension & is still important within reason from the spring point of view. Might be a bit of leeway there to wind the spring up a notch to make sure the lever is hard up after starting. A static test [for the ratchet] would be--plug out & turn the mag flywheel backwards by hand & see if it comes to a stop due to the ratchet picking up [seen that cause havoc on old points ignition AG bikes running backwards, touch the kick start & bang--all over--or all over the floor more like. If yours revolves backwards it might be just touching the top of the ratchet but not enough to catch & lock backwards but enough to to rattle when running. If i'm up the creek then sorry about that--open another beer & carry on. Cheers. ps, with motor running try pulling the shaft towards you, if it's got say a couple of mm end play & the noise stops then pack the other end --something like that.

Offline rob86

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Re: HELP! 78 yz250 kicker sprocket grinding inside of case
« Reply #5 on: November 10, 2014, 11:09:43 am »
Thanks overthehill that gives me a few more things to go on.

Anyone else experienced this on their yz?