Twin Rat Restoration

efkruger · Post by **efkruger** » Sat Dec 23, 2017 5:26 pm

I used to design and build welding fixtures and jigs for an earth moving manufacturer in McAllen, Texas for years. I have wondered what the welding fixture looked like for a Hodaka motorcycle frame. No doubt all bolt holes were located with precision with this welding fixture but quite often in weldments (welded structures) there is some variance in the positioning of structural members. Especially if they are not really important to fixture exactly in position such as a frame tube. After looking at how this frame member is coming into close contact with the tank, its clear maybe it was not positioned quite where it should have been. It appears to have been fitted by tacking it in place and then heating and tapping the end of the tubing down to make it come in contact with the tube it gets welded too. Also, the fact that there was more clearance at the front makes me think this.
When designing and building welding fixtures its always a challenge to make the weldment exactly as the engineering drawing specifies and also to be able to remove the weldment from the fixture after it has been assembled. Thanks Gentlemen.

Bullfrog · Post by **Bullfrog** » Sat Dec 23, 2017 5:53 pm

EF, thanks for creating some "room" for me to wander around in. Um, none of my Hodies are that tight on the fit between the tank tunnel and the frame. Since yours is, it makes sense to provide a "cushion". Though I have to wonder whether the "ears" on the tank are where the tolerance variation resides.

Merry Christmas! (and Happy New Year!)
Ed

efkruger · Post by **efkruger** » Sat Dec 23, 2017 5:59 pm

There you go, that could very well be also, absolutely!, Thanks Ed, Bless you and yours

efkruger · Post by **efkruger** » Sun Dec 24, 2017 3:13 pm

W.A.R. on a 93A seat pan. That's it gentlemen, I am going to show how to weld and repair a seat pan in case anybody would like to try it themselves some time. The bottom pic is before starting. First, I removed the cover and foam and discovered it was all rusted between the pan and foam. Need to get all the rust from around areas to weld repair. Very important, rust and weld do not mix good, Brass rod especially. That's what I will use to do this weld and repair. Brass flows on very nicely and you can use it to build up damaged areas. I then removed the old ears by drilling out the spot welds. I did this because I am going to put a reinforcement plate on the bottom of the pan where the ears were before. I am also going to weld the ears on to this plate. Also, lets straighten out all bends, dents, and damage on the pan now before we weld it up. Once its welded its hard to straighten.

efkruger · Post by **efkruger** » Sun Dec 24, 2017 3:28 pm

Ok now here I have clamped a small piece of rectangular tubing underneath the front of the pan to get that front edge nice and straight while we weld it up good. Notice how its clamped very good just giving me space to weld it. I will weld it up on both sides. Then I will wash it in water to get off the brazing flux and give it a sandblasting to clean it up. That's looking much better now. Tomorrow I will fabricate the reinforcement plate with some ears welded to it and fasten it on to the pan. I will post details on this tomorrow. If you zoom on the pics you can see the pan is loaded with cracks. All of these will be welded up. Going to do it the right way, yeah man. Thanks gentlemen!

efkruger · Post by **efkruger** » Sun Dec 24, 2017 3:39 pm

Along the edge of the pan its thin sheet metal and I have bought some edging for this gauge of sheet metal that I will use all around the edges of this pan. This is to protect the new cover from the sharp edge of the metal. Now, this edging I will use on my Bultaco Sherpa S 100cc that I have started restoring also. Its pan I have repaired all ready. This edging also I will use on some on my air cleaner screens. I think from the factory the screen originally had some edging but it has long since rotted off. Take a look. The edging I found on Ebay. Dad Gum Ebay has everything! I buy all kinds of things I need there. Its the best place to by from.

efkruger · Post by **efkruger** » Mon Dec 25, 2017 2:43 pm

Merry Christmas! Today I finished the W.A.R. on my seat pan. Leaving off from yesterday I needed to put the rear bolting ears back on and finish welding the seat up. And that's what I did today. The ears were broken and had been welded in the past. I welded them some more after removing some of the old weld and made sure they were welded good. Then I positioned them back on the seat pan exactly where they were before and welded them back on using brass brazing rod. Then I inspected for anymore cracks in the sheet metal and repaired them as well. There were cracks everywhere. Also, the rust was so bad that the pan was getting holes rusted through. In these areas I also put a layer of brass over these area to strengthen them. Everything came out real nice. I did not end
up using a reinforcement plate like I stated yesterday. It would not be original if I did. Now that I am done with W.A.R. on my seat pan. I will sand blast it good, paint it, and then recover it. I need to order a new foam and cover asap tomorrow. Anyway take a look

efkruger · Post by **efkruger** » Mon Dec 25, 2017 2:53 pm

I have ordered another pan from Bruce Young in Idaho and I will repair it the same way. I like using brass on that sheet metal, flows on real nice and is strong. Its easy to do, just takes some equipment. Nothing like doing things yourself. Sure saves a buck also. Welding those ears on like I did is much stronger than those five spot welds that it came with from the factory with. After painting I will put that edging on that sheet metal edge and recover it. Thanks for looking Gentlemen.

efkruger · Post by **efkruger** » Mon Dec 25, 2017 3:04 pm

When I get the new foam and cover I will post the installation of those items onto the seat pan also. I have never done a Hodaka seat before. I have only done Bultaco seats. On the Bultaco seats I used aluminum pop rivets and adhesive to secure the cover to the fiberglass pan. Slightly different than on this all metal pan. But we will see.

matt glascock · Post by **matt glascock** » Mon Dec 25, 2017 4:02 pm

Merry Christmas!! Say, could you comment your torch set-up and your approach to brazing on this severely compromised metal? I have a couple really chewed seat pans that I'd like to attempt to rally for future projects. I have basic rudimentary welding skills. Thanks ef! Looks great!!

efkruger · Post by **efkruger** » Mon Dec 25, 2017 4:40 pm

Yes Matt, I would be glad to, thanks for asking, I will do it in the next day or two.

matt glascock · Post by **matt glascock** » Mon Dec 25, 2017 5:23 pm

Many thanks, ef!

efkruger · Post by **efkruger** » Mon Dec 25, 2017 10:41 pm

I am going to start on some instructions for welding using brass welding rod and an oxy-acetylene torch. The most important thing in order to do a good weld is to prepare the metal. It should be absolutely clean of all rust, paint, dirt etc. The best way to do this on a rusty pan is to sand blast it. I you don't have a blast cabinet take it to a commercial sand blast shop and have them do it. I take most of my frames, exhaust pipes, swingarms, chain guards, etc. to a shop and they can do it in just a few minutes. They will have compressors and equiptment that are industrial capacity. This seat pan would take 10 seconds at the most to blast. Its imperative for the metal to be down to silver base metal for a good weld.
Next, I use a 3/32 inch dia. flux covered brass rod for the filler metal. I also have some powdered flux in a can incase flux becomes missing from the rod. Just stick the rod into the powdered flux when the rod is still hot and it will adhere to the rod.
Next, the flame of the torch tip is very important to adjust correctly. Look at the pics I will post that show the correct flame. You adjust your oxygen to get the desired flame. The acetylene you adjust for the size of the flame you want. Also I used a Victor torch tip size O-W-1 This tip works good for this gauge sheet metal we are using. You do not want to get too much heat or you will melt through the sheet metal. Refer to my pics for flame type and the color of the metal when its heated and ready to apply the brass. You must have the metal glowing orange or the brass will not adhere to the metal! Very important. Preheat the metal until its glowing orange and then put the end of the brass rod touching the heated area and into the flame and it will melt.The brass will flow towards the heat. You will see this when you do it yourself. Then you move along with the torch tip heating the metal and melting your rod at the same time. You can move the flame around and smooth the brass out nicely. You can go over the area again to build it up. You should also practice on some sheet metal of similar gauge to become confident before you try your new skills on your pan. That's what you need to do.
When you are welding cracks on your pan use a dissimilar metal such as aluminum to back up and support the cracked area. You must do this or the metal will move and become distorted from the heat. Also, the backing plate keeps molten brass from flowing through and onto the ground. Back up and clamp the aluminum piece to the underside of the area you are going to repair and clamp the cracks down and together. Then you preheat and weld over the cracks. The dissimilar aluminum will not adhere to the brass when the brass flows through the cracks when its molten. Very important to keep the sheet metal clamped down.
Wash the welds with water to remove the flux after welding and also chip away any flux that remains on the welds. Be very carefull with the torch, its very, very hot! Don't touch things with your bare hands and right after you just welded, its hot! Wear eye protection!

efkruger · Post by **efkruger** » Mon Dec 25, 2017 10:53 pm

Tomorrow I will post some pics and more concerning W.A.R. on seat pans

hodakamax · Post by **hodakamax** » Tue Dec 26, 2017 3:19 am

I do like these how-to posts. Seat pans are a popular item to repair on vintage bikes. Don't forget to put this in the Resonator!

Maxie

efkruger · Post by **efkruger** » Tue Dec 26, 2017 3:27 am

Good Idea! I keep forgetting about the resonator. Thank you brother!

Yeah that's right, all these old bikes have a rusty cracked seat pan on them right. They could be made heavier duty but then they would have been heavier. The seat pan on my Bultaco Sherpa S 100cc weighs a ton and a half. Know wonder those 100mx yamahas' gave me a good run on the track back in the day. I used to race flat track and I should have taken that seat pan off and made one from aluminum. The OEM pan is hell for heavy.

efkruger · Post by **efkruger** » Tue Dec 26, 2017 4:35 am

In a while I will post some more pics concerning W.A.R. on old seat pans. I would just like to say that before anyone tries this on your seat pan that you should practice first on some scrap sheet metal rather than on your seat pan. Practice by welding two pieces of sheet metal together that are the same gauge as your seat pan. The Hodaka seat pan is approximately an 18 gauge or about .050 thousandths of an inch thick. Practice thoroughly so you will learn how the metal reacts to the heat and how the brass melts and flows toward the heat. Don't practice on your pan or you will just make a mess possibly. Practice and get the hang of it. Another thing I want to stress is cleanliness of your metal. A must, any dirt, rust causes poor welds. Also, when you weld thicker pieces it is imperative to heat them properly or the brass will not adhere too them. The bolting ears I welded on to my pan, I preheated them along the edge of them were I was going to weld them first, so they would be orange in color in this area. Very important, you do not want to glob a bunch of brass on and have it come off when you just landed after a jump. Try welding some scrap together and then try to bend them apart, you will know what kind of weld you have by doing this.

efkruger · Post by **efkruger** » Tue Dec 26, 2017 7:23 am

Ok gentlemen here are some more pics to go with my post. Note the white rod in the necessary equipment pic, that's you flux covered 3/32 inch dia. brass rod. They come in three foot lengths.
Make sure to get the correct flame configuration before you start.
Look at the bright orange color of the metal after I preheated it, bright orange, you are ready to touch your brass rod to that area. Then use the flame to melt the rod.
Look at the laying down brass pic. See how nice it goes on.
Then you have it cooled down, it looks good.
Zoom up on the pics. This Forum website really does good on zooming pics up for clarity and detail. Yeah man

efkruger · Post by **efkruger** » Tue Dec 26, 2017 7:30 am

Just a few notes, Remember to clean every thing down to bare metal, either grinding, sand blasting, etc. Use a dissimilar metal such as aluminum to back up the area where you want to repair. It keeps the molten brass from falling through and helps to keep the metal from warping from the heat when its clamped. The brass should not stick to aluminum either. Don't use steel because it can get welded to your seat pan also. Using an aluminum back up piece is how I filled in the holes on the bolting ears with. I had it underneath the holes and filled them up from the top. I hope this was informative to my brothers in Hodaka. If you have questions just asked. One last thing, be extremely carefull with the flame of your torch. Its super, super hot. You do not want to get burned by that. I have been a welder since I was 15 years old and I have never been burned to where I needed medical attention and I do not want to ever.

matt glascock · Post by **matt glascock** » Tue Dec 26, 2017 8:28 am

This is an excellent tutorial, ef. I'm most appreciative. Great illustrations too. I had a portable DIY-quality oxyacetylene rig that was stolen out of the back of my truck awhile back and have not replaced it yet. I intend to some day with a lightly better set-up. All I have now is an oxyMAPP torch (basically a MAPP gas torch with an oxygen bleed-in). Do you think this set-up has the juice to make these repairs? Thanks ef, and again, this is a really nice and thorough instruction set you've prepared. Thanks for taking the time for a welder wannabe like myself.

efkruger · Post by **efkruger** » Tue Dec 26, 2017 9:16 am

You are very welcome Matt. On the MAPP set up I don't know if its hot enough to melt brass, just have to try it. With Oxygen it might be. Dad Gum thieves, sorry about that.

matt glascock · Post by **matt glascock** » Tue Dec 26, 2017 9:47 am

Yep. Left it in my truck for about an hour and PRESTO! Gone. At its hottest, oxymapp is probably a good 400-500 degrees F colder than acetylene and with a much smaller flame, so probably not adequate. I'm going to have to bite the bullet and replace my oxyacetylene rig. Time for an upgrade anyway, but it still makes me mad.