Sign in to follow this  
Abarth

1970 Honda CB250k Super Sport

Recommended Posts

New box of Honda bits arrived, installed new air filters, new rubber carb mounts, battery strap and clutch cable.
 
zotbvjba.jv4.jpg
 
Old ones were fairly rooted
 
uoo4rrx4.tn0.jpg
 
Popped open the clutch cover to see this mess, 45+ years of grease mixed with dirt. Cleaned in up and banged the new cable in. Adjusted the clutch bite and took it for a ride. Totally changed the feel of the bike! Clutch is smooth and gear changes are direct. Stoked, simile on dial achieved. 
 
/ cool exhaust baffle, i'll replace this soon. 
 
xxgvz33i.iwr.jpg
 
Thanks for looking!

 

 
  • Like 2

Share this post


Link to post
Share on other sites

Been riding this as my daily, everything was running good except the battery kept going flat.

Found these specs on the net: 

CB250 = 110W output (~8A)
1156 bulb draw - 27.3 watts EACH (1.93A)
1157 bulb draw - 26.9 watts full (1.92A), 8.3 watts running (.6A)
Headlight - OEM - 25W/35W (1.7A/2.5A)
coil charging (assuming 5 ohm primary resistance, 14.5 volts) - 42 watts (2.9A)
neutral/indicator bulbs - 3 watts (.2A)

So the charging system wasn't up to the task of keeping the battery charged while riding round with the headlights on 100% of the time. To fix this I upgraded to LED bulbs which use about 1/8 the power; brake light, park lights and gauge lights. Way brighter now and the battery stays topped up.

 

IMG_3171.jpg

  • Like 1

Share this post


Link to post
Share on other sites

Next mission was to upgrade the way it went round corners, with blown front seals weeping milky fork oil and shocks on the rear which looked like the factory ones it was lose in the corners. Offered a lush ride over bumps but thats about it. 

Got some new rear shocks and painted the tops black to blend into the bike better.IMG_3676.JPG

 

 

Share this post


Link to post
Share on other sites

The tires on it also looked about the same age as the shocks so they were binned for new ones, I liked the ribbed vintage look so I got some new Chen Sheng and Maxxis tires.

IMG_3698.JPG

Then had a massive day at the workshop;

Installed new rear shocks

New tires, inner tubes and rim tape

Stripped and rebuilt the front forks, new genuine Honda seals and fork oil.

New brake shoes, lubed the brake drum mechanisms.

Tided up some rough as guts wiring around the points.

IMG_3708.jpg

 

Rides well now, handles solid round corners and the brakes actually work. Stoked!

  • Like 4

Share this post


Link to post
Share on other sites

Added a new chain, front and rear sprockets, what a difference! Since this is my first bike and all my previous two wheel rides were Vespas I had no idea the old chain had so much slop in it. Also banged in a genuine Honda oil seal behind the engine sprocket just for future piece of mind.

After a lot of work she seems to be running good mechanically now so the focus is on to tidying this up externally. I'm torn on keeping that big chrome, stock fenders classic look or cut everything down to create a cafe racer. 

In the mean time I brought new mufflers to replace the old rusted out pieces. They came with the thinnest sound baffle already (yellow) so I added an extra sound baffle kit (white) to reduce the noise. Goes well now, although I need to have a fiddle with the carbs again to balance them out, one header pipe had a baffle jammed in it and the other side didn't.

Who knows why but I removed it so both cylinders flow at the same rate. 

 

 

IMG_4439.JPG

IMG_4443.JPG

  • Like 2

Share this post


Link to post
Share on other sites

Was pining over tire stickers on some instagram cafe racers so decided to get some for the Honda. Loads of different types on tirestickers.com but settled on Yokohama Advan being a Japanese  bike and all.

I have the Advan stickers to add on the opposite side of the tire, so far so good.

IMG_4475.JPG

  • Like 2

Share this post


Link to post
Share on other sites

I decided I like the factory chrome look so I added genuine Honda indicators to replace the old rusted out ones. I painted the triple tree and handle bar mounts in VHT Epoxy satin black. Slowly getting this bike tidier.

Now these bikes are know for their charging systems being weak, a common mod on these is to remove the old regulator and the rectifier and replace it with a modern 2 in 1 regulator/recifiter unit.

Got started pulling out the wiring and noticed it was pretty rusty round the battery holder so that all came out for a freshen up. Can see the factory regulator tucked under the bottom of the battery tray.

 

IMG_5482.JPG

All removed

IMG_5496.JPG

The original regulator wiring is left disconnected in the loom. The original rectifier (orange fins) is removed and the wiring for this is used for the new regulator/rectifier unit. 

Yellow and Pink wires are from the alternator, green is earth and red is positive. 

IMG_5487.JPG

Cleaned up the battery holder, stripped to bare metal and gave it a couple of coats of epoxy paint. Luckily the new regulator/rectifier bolt holes almost lined up to the original regulator holes on the bottom of the battery holder. A quick file to slot the holes and bam fits mint. Added some super seal connectors for reliability and bolted it all back together.

IMG_5503.JPG

Gave it a polish, as it stands now:

IMG_5450.JPG

  • Like 4

Share this post


Link to post
Share on other sites

Been working on a couple of my mates bikes over the past year too. Massive amount of effort went into getting this 1971 Triumph running again. 

Started off life with looking alright with chrome, metallic blue and white scallops. But yikes underneath was a different story, fuel tank was so rusty it leaked fuel on one ride ruining the factory blue paint, cooked no less that two Pazon electronic ignitions before we completely replaced the wiring loom. Positive earth wiring really? 

New carbs, cables, shocks, tires, etc....

IMG_1402.jpg

Boom, cafe spec.... runs good now! 650cc 4 speed, but my, such a brut to ride with so much torque on tap. 

IMG_4712.jpg

 

Also did some work on a 250 Honda Superdream, I really like this bike, sits low and has those sweet Comstar wheels. 

IMG_4686 2.jpg

 

  • Like 6

Share this post


Link to post
Share on other sites

Summer is finally here in London, been mint cruising round decent weather. She's been running good, super reliable.

She's getting a bit noisy in the top end so I'll get the cam chain and tensioner replaced for some peace of mind shortly. These motors apparently are notorious for their  chewing out their rubber tensioner wheels over time.

Got some sweet 78 Sprint glove for summer rides too, they have a lot of cool summer riding gear on this site, check it out: https://www.78motorco.com

IMG_4949.JPG

  • Like 4

Share this post


Link to post
Share on other sites

Added new low rise handle bars, hid all the wiring inside and vintage styled grips. 

oiejaa2o.23m.jpg
 

The engine has been suffering from a bit of blowby, white smoke blowing out the crank case breather and generally been down on power. 

So rebuild time! +1mm oversized pistons to add a little bit more displacement, I think it adds something like 9cc lol. I'll dyno it before and after to see what extra HPs have its making after the freshen up. 

Got a few other bits and piece to add while I have it apart like cam chain tensioner, cam chain, some new chrome pieces.

Looking forward to the rebuild!!

q2xtmtks.axb.jpg

  • Like 4

Share this post


Link to post
Share on other sites

Strapped this onto the dyno and did a couple of runs to see what power its making pre engine rebuild. 

Only made 15HP and puked a huge puddle of oil from breather pipe at about 10k rpms, far cry from the factory 25 - 30HP. Power delivery is nice and linear with the air/fuel mixtures being spot on, so happy about that.

After this we checked compression which was 80psi on the left and 170psi on the right.

Also did a leak down test with 40% loss on the left, which again meant oil spewing out the oil breather and making a huge mess. 

Good basis to start the engine rebuild, we'll get it back on the dyno again after the rebuild. If it does make 25 HP after the freshen up then its going to feel like a rocket ship compared to how it had been running.

Just waiting on some cam tensioner parts to arrive then next weekend we'll start pulling this engine down and sending bits off to get machined. Exciting.

 

Honda - Dyno.jpg

Honda Dyno Chart.jpg

  • Like 2

Share this post


Link to post
Share on other sites

In prep for the rebuild I got measuring some numbers.

The digital scales came out to measure the weight of the pistons, rings and pin. Amazingly they all were perfectly equal in weight to the nearest gram, stoked. 

Next piston to cylinder clearance; its only 0.0008 ~ 0.0019 inch as apparently these ART Honda pistons don't expand much. I'll keep these numbers for the machinist. 

Lastly these motors run a 9.5:1 compression ratio so there is a bit of room to remove a bit of meat from the head/cylinders. Been reading online guys removing up to 0.02 inch before running into clearance issues, this also increases compression to around 10.3:1ish. Nice to know as I'm 99% sure the head isn't flat anymore.

 

Pistons.jpg

  • Like 3

Share this post


Link to post
Share on other sites

Got the motor out, pulled it down, unsurprisingly the rings were broken.

What was surprising was how broken the rings were. Still good for 10k rpm on the dyno haha! There was also a huge amount of slop between the cylinder and piston.

Checked over the rest of the engine and everything else looks in good nic. Crank is perfect and the head looks good. So just a case of really worn pistons and rings. 

Cylinder and head are at the machinists now getting machined to accept the +1mm pistons.

 

AFB20F81-CF00-4618-AD80-F1C58DC43A34.jpeg

48F97669-261A-4A1A-AF0B-1F257896C82C.jpeg

03051C8B-5378-4797-9E94-4030FEF6133C.jpeg

  • Like 3

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

Sign in to follow this