A Heart Transplant for the old '81 XT500!

[Number Two]

I have a diagnosis of the engine condition that led to its failure, but comments are certainly welcomed.

The ultimate death of the XT was cause by two primary conditions.  Number one, wear.  It was old, and somebody used it too much when it was new.  The cylinder was a little oblong, lost its crosshatch, the rings were worn, the piston was worn,.. you get the idea.  Second, the bike was running too lean.  In the pictures above, the stuff on the valve that I thought was casting, was in fact really hard carbon deposit.  I'm thinking a lean condition caused excess heat in the cylinder, and combined with the wear, caused some type of minor ring failure.  The engine started to burn a lot of oil, which sooted up the valves and cylinder, and may have led to poor seating of the exhaust valve and the heavy coking on the intake.  The oil buring masked some of the lean mixture indicators, but after the exhaust valve got blasted clean at the machine shop, it shows clear signs of pitting.  My recomendation is to of course richen up the mixture a la jetting or newer more adjustible friendly carb.  As an air-cooled single, any additional oil capacity or cooling could help, as would hosing the mud and gravel out from between the fins to encourage cooling.  Finally, a sharp eye should be kept on the valve adjustment.  Every 2000 mi or less on the old iron?  That's all for tonight.  Tune in next time for another episode of 'This Old House Bike.'

[Crazy Uncle Larry]

Dude! YOU DA MAN!!!

THANKS FOR HEADING THIS UP!!!

That is looking nice. As for the taping job, remember...I ain't a painter either!!! And, all we're going for is coverage and ride-ability. She's for GO! not for SHOW!

Seriously, hope this hasn't taken too much of your time away from your own projects, work or most important-the family! I really do appreciate what you've done. Hope to see you this weekend and then we can confer on carbs.-Dad

[Number Two]

Got some paint sprayed last night.  2 tack coats and one medium coat of high temp semi-gloss black.  One coat of clear.  I had a couple runs where I got heavy handed, but I'm otherwise happy with the results.  The pics came out poorly, sorry bout that (cell phone).  I'll try sanding the fins out tonight, then maybe apply some clear there if the paint's not still too gooey.

[Hank]

Looks like fun.   Your head looks like it's brand new!

[Number Two]

ok, got the last coat of clear on after the sanding on Monday:







I like how it turned out, even though it's a little rough, but it just makes the rest of the bike look old and dirty.  hmmm.

[Number Two]

Checking my ring end gap.

[Number Two]

Tuesday night before the fall rally, I'm getting started on the assembly.  Everything looks good, until.....

NOOOOOOOO!!!!!!!!

[Number Two]

Yep, I made about the biggest newb mistake and busted the second ring while trying to use an automotive ring compressor.  That was extremely frustrating, as it seemed that I would now have a hard time getting it ready to go by  Friday afternoon.  I go directly to the internet (where else does one go in times of trouble), and got a new ring set coming overnight directly from Wiseco.  UPS to the rescue.  This time, I just used the chamfer on the bottom of the cylinder and a little screwdriver.  Worked like a charm.

[Number Two]

I replaced the cam chain, tensioner, and guides on a whim.  The chain is not stretched at all - oh well, at least I don't have to wonder.

[Number Two]

I did drill out the jets in the stock carb.  I knew Crazy Uncle Larry was getting a new one, so I figured I couldn't tear it up too bad.  I just went the next size up in number drills on the main jet and pilot jet/emulsion tube.

[Number Two]

Well it's all back together this afternoon, since the local dealership happened to have a Vmax exhaust doughnut that fit just right.  There was only one thing left to do...



Woohoo!!!!

[Number Two]

Took it for a short little jaunt to get a fresh load of premium gasoline this evening.  The biggest differences are the smoothness of the power and crispness of throttle response.  The XT went from 499cc to 502cc, 9:1 to 10:1, but mostly it went from old and busted to new hotness.  I'm impressed.... but mostly, I'm impressed that it runs after sitting in a heap in my garage.

Coming up in the next episode, watch as we release the XT back into the wild - it's natural habitat in the Black Hills of South Dakota.

[Number Two]

Checked for leaks, checked the cam chain tensioner again.  It is shaken down and ready for break-in.  I saw over on the rally thread someone suggested the moto-man method.  Crazy Unlce Larry, it's your bike and you're certainly welcome to break it in as you see fit.

I think the method is sound.  There's a little too much hype on the website for my liking, however.

...and I think I'm done for tonight - what a satisfying update.    

[Hank]

:thumbsup

Always a satisfying feeling.

[fringefan]

Wow I think he owes you a 12 pack and a back rub.