1971 Honda SL70 Barber Small Bore Bike

[Hurco550]

A while back I picked up this 1971 SL70 for next to nothing. I didn't have any immediate plans for it, and it had kinda got shoe horned into a display piece in the basement until its place in the project list came up. Down the road, I was hoping my son would end up with it as his first "big" bike, but he is currently only 1 and a few months old, so we have some time before that plan goes into action.

Its number came sooner than planned, as talk of a group of DTT miscreants descending upon the Barber Small Bore event seems to be coming to fruition. I don't have much money to throw at this thing, so it'll be a budget build. I found a used Lifan 125cc manual clutch 4 speed about an hour north of me with the carb, ignition and wiring with it. I will swap that in, refurbish the rest of what I can, and possibly build a set of earles forks and a side hack for it down the road.

These little things were originally street legal as well, so it could be a neat little round town bopper too.

 

[Tim]

That is sweet. Extend the swingarm - there’s going to be a hill climb event

but they seem to be big on the idea of “use the wrong tool” - they’d rather see Vespas doing hill trials kind of thing.

 

[Maritime]

Ha, signing up. I was hoping to bring the Hyosung to this but will have to be next year as I am out of vacation time until after it's over.

 

[Hurco550]

That is sweet. Extend the swingarm - there’s going to be a hill climb event

but they seem to be big on the idea of “use the wrong tool” - they’d rather see Vespas doing hill trials kind of thing.

I'm still unsure on the actual rules and regulations, but i'm guessing that this will be considered a dirbike and get lumped into that class. Don't think I wont still full send this thing up any hill or down any path I come across though

 

[Tim]

There's next to nothing in terms of 'rules' it seems. Just bring something stupid and race I figure.

 

[whynot]

Are CB100s consider small bore?

 

[irk miller]

Are CB100s consider small bore?

200cc or less

 

[Hurco550]

I was really wanting to find a yamaha sr185 exciter to run the creek bottom on, but haven't found one cheap enough. A little weazy tacky cruiser with ape hangers would been funny to see on the offroad course.

 

[Hurco550]

I went and picked up the lifan 125 after work Friday. It looks to have very little hours on it. The guy I bought it from races pit bikes and swapped it out for a 140cc piranha. Another "issue" he had with it is that it comes with a manual lockout that keeps you from kickstarting it if it isn't in neutral, even with the clutch in. I understand that being an issue when racing. Here it is next to the stock 70cc mill. The mounting points are identical, though the 125 is definitely wider and longer.

It was a real chore getting this thing in the frame due to the longer cylinder. The sl70 is one of the only bikes using this engine design that still had a full cradle frame. I really though I was going to have to pull the top end to fit it, but by squinting just, doing an ancient gregorian chant while simultaneously performing an interpretive dance, I got it in. Im glad I hadn't just painted the frame and im leaving it sweaty, because it also required a few sacrifices of frame paint on the way in.

Clearance is clearance...

I need to build an exhaust. I could likely modify the stock one to work, but I'm guessing the tiny tube would be a bit choked up for the 125cc lump. I will also make a new simple lighting harness with a reg/rec for a non battery system. Since it's street legal, I'll need to retain a headlight and tail/ brake light. It came factory without turn signals, and will remain that way.

 

[Deviant1]

Hell yeah man!

 

[Maritime]

Woot! Looks good. that should be a fun little bugger. Make a rack for beer runs!

 

[Hurco550]

Haven't forgotten about this little booger, I've just been distracted. Not sure if Barber Small Bore will happen, being as the end of the world is occurring, but I figured i need to get this thing ripping up sod none the less.

I pulled most of the stock harness off. All of the stock parts are going into a box in the case that i ever want to restore this thing some day.

I want to also put as much of the new stuff in place as nicely as possible without cutting on the frame. The coil mount was first. I made a simple little aluminum bracket up in order to put it in place of the new one.

I got everything wired up enough for the ignition and kill switch to work + get spark.

Ive still gotta fab up the exhaust and clean out the tank before i can fire it up, but progress is progress none the less lol

 

[Hurco550]

Hey, it hasn't even been a whole year since updates. I feel accomplished.
I spent a bit of time the last few days over Christmas break on cleaning out the tank since. It was bad. I know a lot of people have covered their method of tank cleaning, but I'll tell you mine anyhow. Like most things that I do, I am sure that there are better ways.

Step 1. Remove petcock and make block off plate. I used an aluminum plate with a gasket made of parts store gasket sheet.

Step 2. Flush the tank THOROUGHLY with hot soapy water. I probably flushed it 5 times with soapy water, then 5 times with clean water until it came out pretty "clean" and clear with as little flake and residue as possible. I had a length of chain in the tank as I sloshed the water around to help knock off the flakey rust and varnish mixture. The chemical I use doesn't eat through varnish well, so you have to get that outta the way so that it'll work on rust.

Step 3. Fill the tank up with the rust remover solution. I use "Sunnyside Rust Remover Bath". This particular gallon I've had for several years and this is probably the 3rd tank I've used it on. When I first bought this stuff, back round-abouts 2016 or 2017, when looking up the MSDS, the page header was actually for Metal Rescue or Evaporust. I cannot remember which now. It has since been changed to a "Sunnyside" header on the MSDS. It currently sells for $22 a gallon at Menards in Central Ohio. Its expensive, especially compared to some of the phosphoric options, but it works well and at least there's no acids to neutralize. Also, I was plenty careless and it didn't hurt the paint at all.

Step 4. Let it soak. The label says do not exceed 48 hours. Following instructions is for idiots. I left it for 4 days. Oops. Good news is a whole didn't tear in the universe at 48:01... or maybe it did? is Rona my fault? Am I why were getting a $600 stimulus check instead of $2000? Am I why "Baby Shark" has more YouTube views than any other videos on the platform??

I Digress.

Step 5. Poor it out. I put it back in the O.G. container to be used again. I'll strain it before using it again, as I did last time.

Step 6. Flush with lots of hot water, until it comes out clean and without bubbles. I didn't use soap, just water. (note, I don't have a hot water spigot in my basement where this went down. If so, id have just run hot water outta the tap through the tank. Instead I got a free workout carrying gallons of hot water from the kitchen sink. I used a 5 gallon bucket to dump everything into.)

Step 7. After getting all the water shook out as possible, IMMEDIATELY pour some acetone in the tank and slosh around. Its probably not the best practice, but I just covered the filler with my hand. This helps to dry the water outta the tank.

Step 8. Pour out as much acetone as you can, then insert a shop vac hose in the filler neck on "blow" to dry up any remaining acetone.

Step 9. IMMEDIATELY pour in something to stop flash rusting. I personally used a splash of acetone mixed with WD40. Enough to fill the tank about a half inch on the bottom, then sloshed it around. This tank is going to be sitting on the bench for a while as this project slowly progresses.

Step 9 Alternate. If you are a more organized and faster bike builder/mechanic than I (which you prolly are), you can replace the petcock and IMMEDIATELY fill full of gasoline in order to stop the flash rusting.

For your enjoyment, here are some pics. (Warning, first pic is graphic, viewer discretion advised)

Before Pic of the Inside of the tank. (No, that's not a close up photo of Mars....)

I like to sit the tank over a 5 gallon bucket, in case it springs a leak or the petcock block off fails. (note: this pic was actually taken before the petcock was removed and blocked off, but you get the gist)

Here is the rust Remover bath solution that I used.

This is after the acetone and shop vac "dry" but before the anti rust treatment. As you can see, if you work quickly, there will be minimal flash rust.

This is after a slosh of WD40 / Acetone mix.

Now I have a nice piece of moto art on my home office desk until I get the rest of this thing done...

 

[irk miller]

I would line that tank, if I were you.

 

[iatethepeach]

This is almost exactly the procedure I follow, too, though I mix it up a little by using a leaf blower and kerosene/2-stroke oil at the end. Nice write-up.

 

[Hurco550]

I would line that tank, if I were you.

Is that due to thinking that there'll be thin spots? Just curious as I've never lined a tank before, but have dealt with issues with poorly installed liners from P.O. 's. Usually Kreem, which I would NEVER use.

 

[Hurco550]

This is almost exactly the procedure I follow, too, though I mix it up a little by using a leaf blower and kerosene/2-stroke oil at the end. Nice write-up.

Thanks. I often use 2t premix, but since this will sit in my basement for a bit, I went for something a bit more aromatic like WD-40 lol.

 

[Jimbonaut]

Man this thing's cool

 

[ridesolo]

Looking good.

 

[irk miller]

Is that due to thinking that there'll be thin spots? Just curious as I've never lined a tank before, but have dealt with issues with poorly installed liners from P.O. 's. Usually Kreem, which I would NEVER use.

Because it is a Honda tank, which is thin from the factory, then it got rusted to shit making it even thinner. You lost a lot of metal. Can't say you leak now, but remember a certain DR370 on the trails in Ohio? It hadn't leaked in two years before we took it on those trails. I wouldn't wish Kreem on Eric Clapton's worst enemies, but Caswell is legit and the best, IMO. I've also had good luck with Por 15.