Topic: '78 CB750k conversion to cafe racer (yes, more issues)

[Elan]

looks like you have a harley 17" drop center rim? Going back to 18" would definately help. Is that your plan? Could that be a 19" in the back of that pic?

Yeah I want to go back to stock 18"

Not sure what you mean by "in back of that pic"?

whoops, i meant in the 2nd pic. I guess its just the perspective of the pic that makes it look so big

[Stev-o]

Looks like a 16" HD rear rim?  If the tires are over six years old,they should be changed regardless of how the tread looks. 
I really like the Bridgestones I have on my K4.

[deafcaferacer]

Yeah I am going to switch the rear tire out.

Would a 2.15 x 18 rear rim work okay on the cb750k? 

For a 2.15 x 18 rim, the acceptable range of tire size is from 100-120/4.0-4.75 x 18" right?

[deafcaferacer]

Got my gas tank back from the sandblaster- final price was around $80.

I guess the next step is a lot of elbow grease with either a scotchbrite pad or could I run emory paper or 1000-1500 grit sandpaper on a hand sander I have and just go over everything?

Also I assume the pink stuff is bondo? I'm reading up on removing bondo using a heat gun.

You can see in the picture that the bondo on the right side of the tank help defines the bend in the gas tank which is making me nervous- I do want a bare steel industrial look with the occasional dent or scuff mark, but no serious dent. I guess we'll see what happens.

[sinister902]

Detached the gas tank and brought it to the sandblaster (General Sandblasting in East Bridgewater).

Removed the petcock with a big ass wrench and some choice cuss words, and capped with a galvanized pipe cap, a tip I picked up on this forum.

they make galvanized pipe caps that are the correct threads?

[deafcaferacer]

Detached the gas tank and brought it to the sandblaster (General Sandblasting in East Bridgewater).

Removed the petcock with a big ass wrench and some choice cuss words, and capped with a galvanized pipe cap, a tip I picked up on this forum.

they make galvanized pipe caps that are the correct threads?

Apparently. When I screwed it on, I took extreme care not to force it on so as not to ruin the thread.

[Elan]

you can also just have them plug it with a silicone plug and powder coat masking tape.

Are you planning on putting the emblems back on? thats looks tedious to get all that bondo out!

[deafcaferacer]

you can also just have them plug it with a silicone plug and powder coat masking tape.

Are you planning on putting the emblems back on? thats looks tedious to get all that bondo out!

What I'd like to do is do the same thing that's shown on the bike in my avatar- a custom CB750 plaque.

Any tips/tricks on sanding/removing bondo? Or just elbow grease all the way?

[Elan]

you can also just have them plug it with a silicone plug and powder coat masking tape.

Are you planning on putting the emblems back on? thats looks tedious to get all that bondo out!

What I'd like to do is do the same thing that's shown on the bike in my avatar- a custom CB750 plaque.

Any tips/tricks on sanding/removing bondo? Or just elbow grease all the way?

I would think a wire brush on a grinder, but i havent done it. I havent heard of any chemical processes. sorry, thats all I got...

[knowsnothing]

I know this is a little bit late, but it does look like you have a 16 inch harley on the back.  One of my 78's had one as well, pretty ugly.  Also know that stock rears for both 77 and 78 were 17 inchs, not 18 like the earlier years. 

Good luck with the bondo...that stuff sucks

[stewonepot]

It has been mentioned on here that using heat with a torch will help to soften the bondo for removal regards Stew
ps hope the dents underneath arn't too deep.

[deafcaferacer]

Thanks everyone for the input.

Well, after using a combination of hand sander with 80 grit, then 150 grit emory paper, then 800 grit fine, and a mini wire brush wheel on a dremel, to dig out the bondo in the depression around the emblem mounts, I'm pretty much there.

Got ready to use very fine wet sandpaper and the scotchpad, but had to stop because of the rain. 

But it's looking pretty good. No serious dents or deep scratches. It's said that every 40 year old tank has a nasty surprise if you sand down to bare metal, but I seemed to have escaped unscathed, for the most part.

Pics to follow as soon as I finish, tomorrow.

[deafcaferacer]

All done with the tank.. all that's left is to now to clean out the inside, rinse it out with an anti-rust formula. Still reading up on that.

It really fits the industrial look I am going for, with minor dents and scuff marks (visible in the 2nd photo). After I sanded down to 1000 grain wet, I wiped it down with a good coat of WD40.

It occured to me that I should have sprayed the underside with a primer/first coat before sanding down to bare metal.    and I didn't do that.. so I'll have to either mask it off or sand again. I wonder if an anti-rust primer is good enough for the underside? Or do I follow primer with an anti-rust coat of paint?

[Elan]

Nice job! you dont waste any time huh?

I dont think it would be very hard to mask. I would probably use an epoxy sealer on the underside, but theres no 1 answer to that either.

[deafcaferacer]

Well after a lot of cleaning and de-rusting of the bottom side, I uncovered a pinhole leak near the petcock.  Of course a lot of opinions out there on how to fix that- from welding to using epoxy, to bond. Curious what you guys would suggest.

[Elan]

Well after a lot of cleaning and de-rusting of the bottom side, I uncovered a pinhole leak near the petcock.  Of course a lot of opinions out there on how to fix that- from welding to using epoxy, to bond. Curious what you guys would suggest.

That happened to me and I used solder. that was 2 years ago and no problems. I would have welded, but didn't have the resouces at the time

[deafcaferacer]

Thanks Elan..

Temporarily sealed the leak and filled the tank with white Vinegar.. already starting to see flakes come off and the steel showing underneath.

While I was at auto zone, I saw this interesting product; could it be used on the inside of a gas tank?:

[Vinhead1957]

Price for a gal?   Looks promising

[deafcaferacer]

Price for a gal?   Looks promising

It's not cheap- $32 for a gallon. I also saw a pint of Evapo-rust for $8.

One gallon of Vinegar = $2.99 can't beat that 

[Vinhead1957]

I got evaporust for 22. A gal

[deafcaferacer]

Well the replacement 18" rear wheel came today, looks to be in good condition. No rust, no dry rot in wheel. Thread is good, minor wear. Dunlop T100 front tire mounted backwards (correct?)

One of the mounting bolts is missing- I have sent the ebay seller an email about that.

[Stev-o]

Front tire?   I wouldn't ride on that mounted on the rear. 

[Retro Rocket]

Front tire?   I wouldn't ride on that mounted on the rear.

Me either, wrong profile and shape for the rear...

[deafcaferacer]

What would you guys suggest?

[Retro Rocket]

What would you guys suggest?

A rear tire       Sorry i just couldn't resist...   What size is that TT100 ?, use it on the front {if its the right size and you have a front 18 inch rim } and buy the matching rear Dunlop to suit...