Wednesday 27 April 2022

Dre-XT-Stück - Pannier power FTW!

There's mods, which improve the looks of a bike. Then there's my favourite ones, which improve the performance and sometimes you find some mods to improve the reliability of your (not so?) trusty steed. But the ones, which pay the biggest dividends are the ones, which improve usability. Having a set of sturdy and (more or less) water proof panniers are a perfect match for this category.

NATO-standard, 40mm anti-aircraft gun ammo box, also known as ammo box size 7. Heavy, sturdy and usually not very expensive at the army surplus shop of choice. I mainly used 15x15x1.5mm box section and a bit of 40x3 flat material, all stainless steel and all TIG welded for my pannier rack and given the weight of the boxes themselves, I was not very much concerned with the overall weight, but rather favoured sturdyness over excessive weight savings.

First step was to make two frames, approx 300x220mm to mount the panniers to.

They were previously used on my old XT500A and the TR1, so some mounting hardware was in place.

The actual mounting was rather straight forward.

The big trick was to make them look symmetrical.

All of this is probably relatively easy, if you have someone, who can give you that elusive third every now and then. But C-clamps do a fairly good job too and some off-cuts can really help with aligning parts.

As might have been obvious, initially the boxes still sported the reinforcing ribs on the in- and outside. They were in the way on the inside and didn't quite look the part on the outside, so a bit of removal was due. With them being only spot-welded, an autobody chissel and a lumpy hammer make short work of them. Unfortunately sometimes they leave some (not so) small holes. What's more the old mounting holes weren't "exactly" identical left and right. So quite a few holes had to be filled in with the old MIG.

These small holes could probably be closed with just a small squirt of the old hot-metal gun, aka. the MIG.

The bigger 8mm holes, definitely needed a bit of back with a small copper off-cut. Aside from some slight warping this went waaaaay smoother than I imagined.

As hinted before, looks were of a somewhat secondary urgency in this exercise. To be honest, the whole lot came out so ugly only a mother could love it. Guess you can call me mum now. 

The first testride revealed that even though the frames and the struts were well stiff enough, the 3mm strong tabs I used to bolt everything to the frame allowed for some or more precisely too much flex. As the whole lot allowed for about half a meter of leverage to the front-most mounting point the boxes could be shifted as much as 10mm to the left or right. This did absolutely NOT help with handling to put it mildly. The additional set of struts cured that issue pretty reliably. Now it's maybe 2-3mm, if you really lean into it.

A bit of casually "thrown in roughly the right direction" paint was applied to the outside of the panniers and then it was time to do, what you do:

... and transport all the junk. All of it.

 ... and a backpack, because on some days close to 80L of storage space might not be enough. (The other pannier was still empty at this point.)

Sunday 24 April 2022

Dre-XT-Stück - Easter is resurrection time

What do you mean, you didn't even know the old girl. I mean some of the last pictures were on the "very pretty" side of things. Guess I may have deliberately omitted a few things... 

Let's start off with two beauty shots of the old girl:

Next thing wasn't very drama either: Made a pair of knurled nuts to be able to remove the seat without tools.

Still not quite drama-land - even less so, when I scored a lovely Arrow Paris Dakar in stainless steel for a good price. And yes, there was a friend (made for an XR600) already waiting on the shelf... Definitely could be modified to fit an XT. 

And on this lovely day full of sunshine and loud braaaaaap noises, I decided that it would be really a good idea to finally to do the oil-change as the old girl was nearing the 3000km mark and I had planned quite a few more in the coming days with the sidecar being sold and the TR1s jetting not fully sorted at this point the old Dre-XT-Stück was my main transport... and then it happened: The oil-drain bolt just snapped. So off with the oil tank, get the bit of bolt out and then chase the M8 thread of the oil-drain. 

Not quite the amount of drama one would expect? Well, I guess for some reason I didn't tighten the oil-return properly (i.e. to 11 and a bit). On the same day, the old TR1 had started leaking from oil-drain as well, which would turn out to be a partially stripped thread... perfect timing I tell thee.

In case you're wondering: from the point where the hose came undone to where the engine died it was 1.6km or about 3-4 minutes. The old girl died peacefully with no nasty noises.

Stash the bike away out of sight, borrow a trailer and get the bike home to the workshop and ignore the old girl for a few days.

The assessment of what parts where still available on the shelves was somewhat comforting. As long as I hadn't ruined the crank, pretty much everything else was available. A new 95.25 cast piston of dubious quality (I later found out it was one of the better ones out of the cheapest knock offs), a complete head (albeit the one with the smaller valves) and a good camshaft. So really all I was missing was a well worn 95.00 cylinder as I had the current cylinder taken out to 97mm. 

Obviously there was a reason why it was so cheap - it had a stripped thread in one of the head bolt threads.

As the budget ABSOLUTELY did not allow for someone else doing the machining and also I hadn't exactly made the best possible experience with the one shop that actually works with private customers, I decided to tackle the whole job myself. 

And shockingly enough, that cylinder would have been a straight up pass with a quick deglazing and a 95.00 piston that would on the upper end of the tolerance field. (The subito has to be read in reverse, the bore is at 95.08mm, so with a straight up 95.00 up to 95.04mm piston jobs would have been a good un'...)

And so starts what would become an incredibly long Thursday morning: First hone close to size of about 95.18mm with an 80 grit stone.

Do a sanity check with a vernier caliper, just to make sure I don't make mistakes reading the micrometer or subito. 

Then a final hone to size to 95.25 with a 120 grit stone.


And then ultimately wash the bore with diesel and clean the liner with a WHITE cotton cloth. Once the diesel on the rag is still yellow after going through the bore multiple times, the hone job is finished. And if you do a proper job, you can get top and bottom to within less than 1/2 a 1/100th of a mm and yes, I obviously went with the tightest clearance Yamaha allows for the old XT600, which is +0.045mm over piston size.

All of the above results in a fit like this:

At this point it was all or nothing and get cracking. Put the old girl on my lift and started to dig into the engine. 

And the first (very) good sign: Head and cam look like new.

Yup, that's a nice seizure. Most of the burnt oil on top of the piston came from the initial run in as the cylinder technically was vastly over the max. wear limit, when I installed the piston. But then again, when the old girl was cold, she smoked and rattled quite a bit...

My professional verdict: It's f*cked.

Or to quote Star Trek: It's dead, Jim. As a matter of fact after the engine had cooled off, I could still kick it over. Tough little bugger.

Conrod wasn't blued and neither where the crankshaft webs, so when the gudgeon pin fit without unusual play, I declared the crankshaft fit for service.

Installed the piston, slapped the cylinder on...

... and then the other head bolt thread stripped.

Helicoiled it to the moon and back and tore the base gasket. On a Saturday afternoon. Decided to say f*ck it and got it on with some gasket paper. To be honest, I am not great with scissors, so this wasn't exactly a master piece but good gasket paper with lots of grease can work wonders.

Test fit on the old cylinder.

At this point I wasn't even shocked anymore when one of my M6 helicoils gave up and I had to install a time-sert.

As Mr. Postman also dropped off a set of new tyres (Mefo MFE99s, thanks for asking), I installed them the following day.

Oh the engine? 

As a matter of fact a couple of things became instantly apparent: First, there's a good reason, why Yamaha finished the cylinders on XT600 engines on the upper end of the tolerance spectrum. The old girl almost seized (luckily she only cut out) multiple times on the first two or three runs and it would take almost 70-80km of run-in time until she would hold an idle both cold and hot. But the two most notable changes were first the engine noise, the newly built engine makes almost no undue noises at all, neither hot or cold and second the amount of extra power about two full points of extra compression give you. Don't get me wrong, she ain't exactly slow and I am sure a few extra ponies will find its way into the stable once the engine is properly run in at 200-300km, but when in the past the engine would happily pull to 140kph, now the engine will pull to 110kph and that'll be the feel-well speed for this engine. Maybe once she's run in that'll increase to 120 or thereabouts, but the difference is notable.