Topic: Rotten rusted CB750 aka The Red Rider OUT OF HIBERNATION

[MoMo]

[/i]Figured I'd finally get around to starting a build thread. I found the site a bit over a year ago.  At that time I was redoing 2 or 3 bikes, working full time and doing bike work for several customers.  A couple weeks ago I bought this 750 from forum member mrjack55.  Here is a link for the original post http://forums.sohc4.net/index.php?topic=98780.0  Here are two photos taken by Jack, I neglected to take any photos before the tear down.



As you can see the bike is cosmetically excellent (considering it has 75000 miles ) but suffers from severe frame rot.  My theory is the bike was ridden year round, pressure washed, parked on the side stand so the water wouldn't drain out the drain hole.  I was a mechanic for 14 years back in the heyday of the sohc, probably worked on 1000's of bikes but never saw anything like this.




[img][http://i705.photobucket.com/albums/ww51/photolar/red%20black%20750/swingarmouter-1.jpg/img]

My plan is to leave the bike the same color, swap the frame and install a low mileage 1975 Cb750F motor that I recently acquired.  Motor only has 6000 miles.  The cost to restore to stock would outweigh the future sale price.  Figure at least 500 for paint and new side covers, at least a 100  for new foam and seat cover, 50 to 100 for good chrome fork ears.  What with the 1000 I paid for the bike plus another 1000 or so, I'd have 2000 into a high mileage 1975 Cb750.  Now if it were a 71 or earlier I'd do it.  Bike will not be a cafe racer, it will look very similar to above photos but the red and black theme will be continued-the frame will be red, and the seat may have red piping.  all for now...Larry

[brandEn]

Wow that is some serious rot. Did you know it was like that when you bought it? Looking forward to seeing updates.

[MoMo]

Wow that is some serious rot. Did you know it was like that when you bought it? Looking forward to seeing updates.

The thread mrjack55 created when he first got it showed some of the damage.  I put the link to it in this thread.  I thought the damage was just to the lower frame rail, but after removing the motor and all other parts the extent of it was revealed. What makes it even more ironic is the rest of the bike is pretty much rust free.  The chrome is very good to excellent.  This is the drain hole that I believe was clogged, probably would not be a bad idea to drill one on the other side.  This is the right side of the crossmember, since most people use the sidestand it seems the drain should be to the left.



I removed a half cup of dirt and rust from the area between the swing arm gusset and sidestand mount ...Larry

[Terry in Australia]

G'Day Larry, I suspect that old chain lube and road grit has caused more damage to CB750's than just about anything else. Rotting exhaust pipes is another example of muck blocking drains and causing extensive rot. Cheers, Terry.

[MoMo]

G'Day Larry, I suspect that old chain lube and road grit has caused more damage to CB750's than just about anything else. Rotting exhaust pipes is another example of muck blocking drains and causing extensive rot. Cheers, Terry.

Yea,  it probably blocked the hole and prevented water from draining out.  Still baffles me though why the area around the gusset is left open for water, grease and dirt to enter. I remember reading an article a long time ago that gave a reason but I sure cannot recall it. (barely remember yesterday sometimes ).

 I received a spare set of very good condition 341 pipes with the bike.  OO took off the exhaust after a year and put the Jardine on. Stored them in his attic, so they are in very good condition ...Larry

[ekpent]

I was going to ask Larry if you got that minty set of pipes with the deal. You lucky dog you---

[Stev-o]

So is the plan to repair the frame or use a different one?

[MoMo]

I was going to ask Larry if you got that minty set of pipes with the deal. You lucky dog you---

Yes, pipes were included , Eric

So is the plan to repair the frame or use a different one?

Steve-O,  There are a bunch of options as I got a spare frame with serial numbers that are two digits off.  What I plan to do is probably technically illegal (that is if a scribe or pharisee saw it) but is by far the safest option. Here is a photo of the donor frame




 I spent yesterday sanding, priming and painting. Weather was warm enough to paint outside . Tentative plan is to make a two tone red and black 750...Larry

[ekpent]

Some crazy weather for sure,over 40 here today in Michigan and no snow on the ground.Glad I don't have the snowmobile bug yet. Sure we will pay the price though here sooner or later,maybe next week a little.

[Mcwilliams570]

Looking good Larry..What color red is that?

Matt

[MoMo]

Looking good Larry..What color red is that?

Matt

It is a Rustoleum sunrise red that is very close to the color the tank is painted.

Some crazy weather for sure,over 40 here today in Michigan and no snow on the ground.Glad I don't have the snowmobile bug yet. Sure we will pay the price though here sooner or later,maybe next week a little.

It was in the 50's here-I pulled the Silverwing out and went for quick 100 mile ride.  I am sure you are right about paying later.

[lucky]

What causes the frame to rust is a variety of factors.
If the holes in the frame were completely closed off you would have less corrosion because there would be almost no oxygen
Was the frame of the bike near the coast?  Salted roads?

[lucky]

G'Day Larry, I suspect that old chain lube and road grit has caused more damage to CB750's than just about anything else. Rotting exhaust pipes is another example of muck blocking drains and causing extensive rot. Cheers, Terry.

Yea,  it probably blocked the hole and prevented water from draining out.  Still baffles me though why the area around the gusset is left open for water, grease and dirt to enter. I remember reading an article a long time ago that gave a reason but I sure cannot recall it. (barely remember yesterday sometimes ).

 I received a spare set of very good condition 341 pipes with the bike.  OO took off the exhaust after a year and put the Jardine on. Stored them in his attic, so they are in very good condition ...Larry

When a tubular frame is being welded A lot of heat builds up inside of a tube and that heat and gas must escape. Usually a small hole is drilled so the welder can finish welding the weldment and the gas can escape from the hole.
If there is no hole the welder will have trouble completing the welding because the molten metal wants to keep blowing out of the weld seam.

An tubular aircraft mounts the hole is plugged with a small special rivet upon completion.

[MoMo]

When a tubular frame is being welded A lot of heat builds up inside of a tube and that heat and gas must escape. Usually a small hole is drilled so the welder can finish welding the weldment and the gas can escape from the hole.
If there is no hole the welder will have trouble completing the welding because the molten metal wants to keep blowing out of the weld seam.

An tubular aircraft mounts the hole is plugged with a small special rivet upon completion.
[/quote]

That makes sense, but why wasn't the opening filled after the frame cooled down-probably cost too much time (which translates to money) to fill that in farther down the assembly line.  Here is a photo of the opening, which is open on either side of each swing arm gusset...Larry



and this is the opening in the lower brace, which may not even be open to the downtube

[lucky]

You are right. Often the motivation for doing or not doing something is money.

But many of the Honda CB750 frames have lasted over 30 years! That one that you have with that much corrosion is one of the worst that I have seen.
They were only about 1/16 (.062) thickness to start with.

I am wondering if some of that corrosion could have been from battery acid.
Looks possible .

That is how you can get a 40 lb., frame.

[MoMo]

You are right. Often the motivation for doing or not doing something is money.

But many of the Honda CB750 frames have lasted over 30 years! That one that you have with that much corrosion is one of the worst that I have seen.
They were only about 1/16 (.062) thickness to start with.

I am wondering if some of that corrosion could have been from battery acid.
Looks possible .

That is how you can get a 40 lb., frame.

Battery acid is a possbile contributor,  but the rest of the bike is so clean it seems the OO would have washed off the residue of acid.  I have worked on hundreds, if not thousands of 750's back in the day but never saw anything close to this...Larry

[MoMo]

Worked on cleaning up the fuse box and battery box yesterday.  Used vinegar and baking soda to remove the oxidation on the fuse box.  Primed the battery box with rusty metal primer after glass beading it in my little HF bead box.

Before


After


battery box finished


Last day of vacation ...Larry

[Greggo]

It is unfreakinbelievable that bike looked so good, and had so much ROT!  I like the red on the donor frame.

[MoMo]

It is unfreakinbelievable that bike looked so good, and had so much ROT!  I like the red on the donor frame.

thanks, Greggo.  Every time I pass the original frame in my shop I shake my head in disbelief. 

I'd never seen that quote from Terry that you use, it is hilarious...Larry

[Terry in Australia]

Looking good Larry, hey the vinegar and baking soda thing looks interesting, I've got some K1 carbs with brass floats that are pretty badly corroded (not chewed out, just covered in white #$%*) I wonder if the vinegar/soda mix would clean them up? Cheers, Terry.

[MoMo]

Looking good Larry, hey the vinegar and baking soda thing looks interesting, I've got some K1 carbs with brass floats that are pretty badly corroded (not chewed out, just covered in white #$%*) I wonder if the vinegar/soda mix would clean them up? Cheers, Terry.

Terry,  vinegar and baking soda is what was always used to clean corroded car battery terminals.  All that corrosion inside the plugs is pretty much that type of corrosion.  Not sure about the crap in carbs-if you try it let us know how it fairs. 

I just saw your quote on manliness that Greggo uses-that is hilarious...Larry

[Terry in Australia]

Thanks Larry, I'll try it and post a couple of pics. I enjoyed that manliness thread, it was great for me to see folks not being too serious. Cheers, Terry.

[lucky]

Vinegar will cause it to rust much faster.
Sculptors use it to make new metal have a rusted look.
Baking soda is put on batteries to neutralize the acid on the top of the battery.
If you mix vinegar 50% with water the steel will rust even faster.

Phosphoric acid is what you need . It turns iron oxide into iron phosphate.
It stops the corrosion process.

Then rinse with water and dry....paint within 4 hours.

Aluminum gets a white powder (aluminum hydrochloride) and again phosphoric acid is best for the corrosion, and then coat with alodine. You can get Alodine from Aircraft Spruce company.

[Terry in Australia]

Vinegar will cause it to rust much faster.
Sculptors use it to make new metal have a rusted look.
Baking soda is put on batteries to neutralize the acid on the top of the battery.
If you mix vinegar 50% with water the steel will rust even faster.

Phosphoric acid is what you need . It turns iron oxide into iron phosphate.
It stops the corrosion process.

Then rinse with water and dry....paint within 4 hours.

Aluminum gets a white powder (aluminum hydrochloride) and again phosphoric acid is best for the corrosion, and then coat with alodine. You can get Alodine from Aircraft Spruce company.

Thanks mate, but I tried Phosphoric acid on the floats and it did nothing. Cheers, Terry.

[Greggo]

Thanks Larry, I'll try it and post a couple of pics. I enjoyed that manliness thread, it was great for me to see folks not being too serious. Cheers, Terry.

I laughed so hard when I read through those posts my stomach hurt, and I had tears coming down my face 

Still makes me laugh when I look at my posts!