MTTB: The Restoration of a Track Bike

[toratora]

Sticky Sava track tires for Mike's bike were the project for today. We employed Greg's bead breaker again--I was too busy getting a work out to take photos of that action, but here are a handful of nice ones, and one of the Brembo RCS14 Master.

We also did a carb swap to see if the bike would run better. It ran a little bit better, but still suffered major bogging with the throttle open.

To start things off we used Mike's tire warmers. We got the new tires nice, and warm, but as it turned out we needed to heat up the old tires to get them off. They were really stuck on the rim--probably from having been warmed up previously. It was so much easier having help to mount the tires on the wheels. Didn't take hardly any time at all, and I'm not nearly as sore as I've been from previous tire outings.

Front tire on the bike. I should have taken a photo of the rear one too. Have to get that later I suppose.

And the pretty Brembo action. Before heading over to meet up at Ed's for dyno day I unboxed Mike's new RCS14 that he picked up from KurveyGirl. It's really sweet. That titanium banjo bolt weighs so little that you can't even tell it is in your hand. Kurvey throws that, some tubing, and a bunch of crush washer in with the RCS. Is's that cool, or what? I put it on the bike, but didn't have a chance to take photos yet. The reservoir for it has yet to show up--so I used one from a GPR rear brake for now. This is becoming a very nice bike.

[toratora]

I finally had opportunity to put the All Balls KTM SX65 seals into the Derbi forks today. Ed granted me access to his bench so that we could use the pneumatic action to loosen up the bolt on the hydraulic tube. I've not yet figured out a way to loosen this bolt with hand tools.

Now these SX65 seals aren't an exact match to the stock seals. So far the forks looks to be well sealed, but I wont know for sure until I mount these on the track bike, and do some testing. I really hope these work, because then we have a very nice solution for these bikes. I also intend to play around with the fork oil weights, and quantities. Those of you with a sharp eye will notice that I'm using 5 wt, rather than 7.5 wt. Yup, trying out a little experiment.

The Forks: These are the 2003-2004 GPR Sebac forks. The require slightly different seals than the older ones. The 2002 forks do share the same seals, but those are anodized gold rather than silver.

I think I already showed how to disassemble these forks earlier in this thread so this is just the assembly section. Lube up the seal, and place it into the fork tube. It wont go in all the way, but it will slide down to the seat. With the new seal in the fork tube used the top cap to seat the seal. It doesn't take much force, but you want to apply it evenly. You will know it's in place because you'll be able to see the ring for the retaining clip.

Once the inner seal is in place insert the retaining clip.

Then insert the dust seal. You should be able to put this one in place with just your hands. It doesn't take much force, just a little bit of finesse.

Then slide the stationary tube onto the sliding tube. Insert the spring. Reach in and pull out the hydraulic tube. Add the nylon spring cap. Now it's time for the secret tip on how to do this. It's nearly impossible to hold the hydraulic tube to insert the bolt. So take a small screw driver, and insert it into the small hole in the top of the hydraulic tube. Rotate the spring so that the tube reaches high enough that you can thread in the bolt. Then torque the bolt.

These forks take 120ml of 10 wt fork oil. You can change the wt, and amount to change the dynamics of the fork damping. Lower weights will decrease the damping. More fluid will stiffen the forks. Grab your graduated cylinder (you can get these off eBay for less than $3), mark with a Sharpe where you want to measure to, and pour in the desired amount. Pour this into the fork. Insert and torque the top cap.

[toratora]

It turns out that the Sabac forks found on the 2002-2004 GPRs use 120mm of 10 weight! The inner top bolts should be torqued to 17Nm.

I'll go back and update the previous post...

[toratora]

Lots of Action on Mike's bike today. I've been wanting to do this work for quite a while, but things like cold and rain keep causing delays. When we took his bike to the Dyno we were unable to get it to rev up. We finally had to give in and not test the bike. Which was a real shame because knowing its power curve would be quite interesting, and nice to compare to our other bikes. Just have to wait for the Next Nor*Cal Dyno day.

Today I just plodded through things. First I did an inspection of the reeds. They looked great, and they hold succession too.

I then did a visual inspection of the cylinder, and piston from the exhaust port--this is pretty easy you just pull the exhaust off and look in the port. It didn't look brand new but it looked okay. Nothing to indicate why the engine wouldn't rev. Hard to get photos of this part!

Next was the leak down test. Again it worked great.

Next up compression. Here it produced around 6 bar (more than in the photo)—which is actually a bit on the low side, and I'm going to probably have to do more investigation on this one.

Then on to spark, because well maybe it was the ignition, but again I found it had good spark. The plug looked a little bit rich, but nothing horrible, and it produces a strong spark.

I did notice that the fuel filter wasn't filling up as fast as it should. So I think it might be the petcock. I'll have to go to Treats and source a good one.

I did check the carb previously. I cleaned out the carb on the bike, a Mikuni TM24, and it was unhappy even still. So I grabbed the TM24 from the Monza (which I already had off the bike), and tested it on Mike's bike. This carb works great on the Monza so I should at the very least be able to get the bike to rev. But nope.

[toratora]

After chatting with Ed we decided to get a new top end for Mike's bike. We ended up going with the Gila kit. Mostly because it was what Benji had in stock. It's a good kit. I've installed them for people previously with good results. I also picked up an OMG hi flow petcock, a new Top wrist pin bearing, high flow fuel line, and some new super soft Domino grips. This bike is getting some nice action.

[toratora]

Ordinarily I'd take like a week to get the exhaust port all polished up, but I don't have the luxury with this one since we want to go to the track this weekend. So I worked on it for most of the day, and night. I was able to remove most of the casting lines. Would have liked to drop down a few grits to get it highly polished. For not it's at least smooth. It's not bad—much better than stock.

[toratora]

I was all set to hear this engine spark to life today when I discovered something really cool, and yet it meant I wasn't going to be able to button it all up today. Popping the tope end off showed me that it was a 50cc kit. Pulling the piston showed me that it had a Metrakit crank. That's awesome news, but the Metrakit crank uses a bigger bearing on the little end. This is a desirable mod to be sure, and a great thing for this little engine. But it meant I had to race down to Treats to get a proper wrist pin bearing. First world problems I know! I did make it, and tomorrow I hope to hear some beautiful two stroke music.

This hose was a bugger to remove. I had to use all my tricks! Okay I didn't put the heat gun on it, but I was close.

Inside everything looked pretty good. I'm really surprised that it had such low compression. Maybe with a proper ring it will do better, but then again as a 50cc barrel Mike would want to replace it anyway.

I didn't get a photo of the crank yet. Once I realized what it was I had to pack everything up and jump on the Silver bike. I'll probably get a nice photo tomorrow.

For now here are some comparison photos.

Now check this out. These are the instructions that come with the Gila kit. Do people really do this? Crazy!!!

Derbi Motor Plaag, To install the conversion kit Derbi-Piaggio engines must check that the piston does not touch the lower crankcase, if so must be lowered in front of the crankcase, a diameter of 50 meters and a depth of 9 mm, with a special cutter for aluminum without disassembling the motor. Protect the stork blow and wash the crankcase to remove all the chips and check before riding.

[toratora]

Wisdom from Xero

Now check this out. These are the instructions that come with the Gila kit. Do people really do this? Crazy!!!

Here's a technique I have employed in the past when in a pinch ...


Yes, Barbasol !!!

The foam keeps the little metal shavings of death from getting into every little nook and cranny.
You can then go and ShopVac out the metal shavings that have been magically suspended in the foam.
Of course, you will still need to thoroughly rinse out your work area.

This isn't a "silver bullet," and by no means the "proper" way to do the job, but in a pinch.

[toratora]

Wow today was a hard one. It was suppose to be a simple put the kit on, do some heat cycles, attend a few other things on MT Mike's bike, and wrap it up. Nope not even close. Xero I'm so happy you posted that hint. Some folks are totally against what I call Pickup Truck Mechanics, but when you don't have what you need you've got to Macgyver.

Here's the super nice Gila kit.

Proper bearing for the Metrakit crank.

Slipping the puppy on.

Quick look inside.

I actually then put the head on, torqued the nuts on the studs, and when to check the squish when klink. What? No way the crank would not turn around because the piston was hitting the bridge they put in there to stop the kids from putting kits on their street bikes.

Okay this meant a trip to the dollar store to get supplies. It also meant that I had to pack up everything to go to the store. Life without a garage in the big city. ¯ \_(ツ)_/¯

So first I installed the nice new high flow petcock and fuel line.

Well the dollar store had extension cables to get power for the rotary tool and shop vac to the bike--I bought five of them. But they didn't have any shaving foam. I knew I had some at home so I figured I just have to give it a better look see. When I finally figured out in which container they were stored I realize there was no way I would be able to dig it out. So off to get some. At the Walgreens I saw this:

The setup—a rag to keep particles from going everywhere. Q-Tips placed in the bearing lube holes. The hose from the shop vac that I would have running the whole time. Paper towel stuck into the cases (this worked really well when I put some foam in first). Then I would fill it up with foam.

It's pretty amazing how well it worked. When the rotary tool would catch the paper towel it would rip it to shreds spewing it everywhere. This actually happened a bunch. The first bit I use was way to dull, and didn't work too well. The second bit was nice and sharp, and things went pretty swimmingly afterwards. It's much harder to do this stuff with the studs in place. Well it's much harder to do this stuff with the engine in the bike. Damn. But it came out pretty nice all things considered.

Then a quick test to make sure there was enough room.

Putting the puppy in place.

Then a quick inspection, and what the hell? That's way too much gap.

And way too low for the BDC check too. What the hell?

I then realized this must be a Metrakit 43mm stroked crank. This top end wasn't going to work with this crank. And it was getting dark. I use to have one of these cranks. I gave it to someone that I thought would appreciate it (he didn't by the way). Some time later I happened upon a Parmakit 43mm kit. It's a monster kit and totally brand new. Well dig dig dig through the containers. Found it.

A quick check of BDC, and TDC, and it looked pretty good. This might actually work.

[toratora]

Put it all together, torque it down and check the squish. It just barely had a usable squish. So I had to test it. I didn't bother with the pipe, water, or anything. Just had to see if it was going to run. Sure enough it started right up! Cool!

Then it was time to attend things like the pipe. Only to find that one of the exhaust bolt holes was buggered. Time for the thread chaser. These are kind of like taps, but they wont weaken threads already in play, which a tap would actual do. This was a bit of a painful process as my hands were already totally worn out from today's activities. I've still not really recovered from the crash, and the pain while always present gets pretty bad when doing work. And by this time I'm in some serious ouchy land.

Once the exhaust manifold was in place it was time to do the leak test. Well it wasn't holding so I got out the bubbles. Up sure enough right at the exhaust. I was going to have to get aggressive with some sealant.

Once that was happening, and the water all together, it was time for a heat cycle. The bike started right up. Smoked like crazy from all the building grease I used all over the place. But it sounded great. Revved very nicely, and seems to be doing well. I've since done a second heat cycle, things look pretty good. It's too late to do a proper revving of the bike now so the third heat cycle will have to wait until morning.