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1981 XR250 balancer chain adjustment does't match manual

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Howdy Fellow Thumper Drivers!

My newest bike is a 1981 XR250.  It made some tappy sounds, so I adjusted the valves and the cam chain as outlined in a manual I found on internet.  The manual was written for a 1979 XR250 and has addendums up through 1983.  I also wanted to clean the oil pump screen, adjust the balancer chain, and get a general look at stuff under the right side cover.  All looks good.  I miked the clutch pack and it is hardly worn.  But, the balancer chain tensioner system didn't look like any in the manual, and the spring that is supposed to be used for tensioning was missing.  I couldn't find any sign of spring debris in the bottom of the crankcase.  The bolt that is used to tighten the adjuster was tight, and about 3/4 of the way towards tight chain.  Once the bolt was loosened, it was easy to move all the way tight, with no hint of the chain getting too tight.  As I moved it, I could see the slack reduce, but not go away completely.  My judgement is that for now that will be fine.  Another discrepancy between my actual machine and the manual was that supposedly, if the adjustment was out of room to adjust, you could remove the adjuster and move it over a tooth to get more slack out.  Mine is not built that way.  The adjuster arm fits to the adjuster cam with three splined teeth, and will only go on in one position.  Any comments on what I found would be welcome.

On to the manual.  I don't remember where exactly I got the manual, but since it is supposed to include my bike's year in the range it supposedly covers, I don't have any confidence that buying something else will be any better.  Oh yeah, it has the pro link swing arm, 17" rear, and 21" front wheels.  Some sources don't agree with that equipment in 1981.  Folks do change things around, though.  Title says 1981.

I do like this machine so far.  I've ridden everything from 650 BSA to Trail 90 in the dirt.  It starts in one or two kicks cold, has plenty of power for the hills, and compared to the older bikes, the suspension is way easier on my 68 year old butt.  I want to keep the headlight, but I'll be ripping off everything I can to reduce weight, but there isn't much that isn't functional to get rid of.  Oh well, it still beats the weight of my stripped down BSA by about 100 pounds.

tom

Edited by geezer99

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'81 should have a gear driven balancer, and a 6speed gearbox.so probably your engine is not original. Post the engine number, and pics of your balancer

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Muzz67, thanks for the reply.  I've already buttoned up the right side, so no pictures.  Your suggestion is well taken, though, because anytime I'm into something, I should just take plenty of pictures for future reference.  Old-timers disease seems to be getting me.  Any way, the engine serial number is:

ME01E5201796

Also when I got it back together, it started on the first kick, but gear shift was stuck in neutral.  It wouldn't shift up or down.  What???  I didn't mess with the left side of the machine at all.  Looking closer, I found that the shift shaft, or spindle, was sticking out about 10 mm farther than the wear marks where the seal rubs.  Fiddling with it, I could easily move it in and out with my fingers.  Worked fine if pushed in.  Jammed if out.  So I took off the left cover and discovered that the two snap rings on the shaft were out of their grooves.  Slid them into place and measured the distance between thrust washers and the space in the case to be a good match.  I guess the external shift lever must have been smacked at some time to jump the snap ring.  Weird.  Funny that in the few hours I've put on the bike it never happened before.

Seemed the two thrust washers were a very sloppy fit on the shaft.  That may be why the snap rings were out of place?  Partzilla does not show any washers at all.

By the way, I searched the web a bit to see what folks had done with gear shift shafts, and found that some folks are welding broken shafts because the web "conventional wisdom" is that the shaft requires splitting the crankcase to remove.  Not true.  The shaft will come right out if the left case is removed.  A 6mm bolt on the end of the shift drum needs to be loosened, but otherwise it would be straight forward to remove the shaft for replacement or welding. 

While I had the left cover off, looking around in all the cracks and crannies, all looked well.  There was a very light "dusting" of fine aluminum particles on the bottom of the crankcase.  Considering it's age, not unusual.  A buddy that repairs aircraft engines says he's not worried as long as the particles are too small for a serial number. 

thanks again,

tom

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Your engine is 1981, so probably original. Sounds like they used the last of the 5speed motors in the first Prolink frames.

    The shift-shaft circlips are  easily dis-lodged when bike falls to the left, bit of a nuisance but like you discovered, its not a hard fix.

A short length of pipe slipped over the shaft (against shift-lever to washer to protect seal) will stop it being pushed in.

   Either that, or learn to fall the other way.......

The spring on the balancer adjuster is commonly removed so it doesn't fall of and do damage.

      Magnetic sump bung a good idea too.

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Thanks again for your reply.  My bike does have the six speed transmission.  And gear driven front balancer.  Sounds like many manufacturers will use up all stock, making some oddly equipped outliers.

I like the idea of a magnet on the drain plug. 

tom

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The 6peed is a single gear-driven balancer,, ie no chain like the 5speed.

  adjuster is to set the backlash of the gear. There is an exact measurement but cant remember, if in doubt dont do it too tight.

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That is good to know.  As I adjusted it, I was turning the balancing shaft back and forth.  I could see how much slack there was quite easily.  All the way tight was still allowing a little backlash, so that's where I left it.  Thanks again.  Now I'm off to run some favorite trails.

tom

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I had a piece of aluminum the size of a grain of sand jam the xr250 tranny in first gear.  How many aircraft engines share their sump with a gear box and wet clutch?

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That's a joke, son.  Most aircraft engines do not have clutches or transmissions.  Almost all use gear driven camshafts.

But there are a few that share a gear reduction and crankshaft protecting clutch.  The Austrian built Rotax 912 series is one.  Because of the clutch, they recommended motorcycle oil.  I've flown 50,000 miles behind a 100hp Rotax.  It is an 83 cubic inch engine with water cooled heads and air cooled cylinders.  Bare engine weighs about 135 pounds.  They have a full flow oil filter and cooler.  The time between overhauls is listed as 2000 hours.

Personally, I take contamination seriously in any engine.  Debris in crankcase, particles caught in the filter or screen, smell, all point to potential problems.

tom

 

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