Broken frame plus déjà vu

[alwyn]

Talk about déjà vu  - way back c 1950 when kickstarting my near new Mark III for the return journey to home in the Adelaide Hills after work, my attention was drawn by a bystander to the fact that the motor appeared to be swinging up and down within the frame with eack kick of the starter - I of course said, "you're dreamin'," but on checking I found that both down tubes of the frame had broken at the junction with the steering head - I recall breaking out immediately in cold sweat as I realised my good fortune, for I had raced to work that morning at full pelt down the mountainous road from the hills running a trifle more late than usual!

Yep! It's happened again! Yesterday, whilst servicing my T35 ready for the Bay to Birdwood Rally coming up in a couple of weeks, I just happened to spot some lateral movement at the junction of the near side bottom frame tube at its junction with the casting which connects it to the frame down tube and carries the torsion bar anchorage bracket. I have no idea for how long it's been in this state - the offset at the joint can be seen quite clearly in the photo below - I guess the torsion bar within has probably saved me from a calamitous fall this time rather than being saved by sheer providence as was the case years ago with the Mark III!

I am of course looking for the best suggestion for a quick repair - has anyone out there experienced the same problem? At the moment I'm thinking engine out and complete replacement of the bottom frame tube! Can't think of any shortcuts!

Alwyn



Larger view

[eddie]

Alwyn,
I have done several repairs when the bottom tube has broken by the rear lug. The biggest problem is that the break occurs flush with the end of the lug. I find it easier if the bike is stripped down to the bare frame and the torsion bar removed from that side. Start by making a cut around the lug with a hacksaw (about 5/16" from the break), carefully continue sawing until down to the braze between the lug and the tube, then cut in from the end of the lug. Heat the lug with a welding torch until it is possible to peel the sawn end of the lug away from the tube (this should also burn away any greasy deposits). Leave the frame to cool naturally. Next file away ALL traces of braze from the exposed tube (brass inclusion in the repair will seriously weaken the joint). Next 'V' out the joint (the tube is quite heavy gauge - about .120" thick). Now you will need to keep the two tube ends in line - I prefer to use a short piece of 1" angle iron as a crude 'V' block clamped to the side of the tube. The frame should now be heated until the ends of the tubes turn light brown in colour. It is now ready for the break to be MIG or TIG welded. The original contour of the lug can be restored by building up the cut end with silicon bronze. You can even extend the lug a bit to give the repair a little more support. After fettling and a coat of paint, the repair is almost invisible. You may need to clean out the bore of the tube as the ends of the torsion bar are quite a close fit in the tube.

Good luck with the repairs, if you need any more details, get in touch.

Regards,
Eddie.

[Doug]

Alwyn,

That is a nasty job to put right. As outlined already, you need to weld the tube, free of the presence of the brass spelter used to braze the tube to the lug. If you have any residual brass in the vicinity, two things will happen. One, you will boil the zinc out of the brass, contaminating the weld and making a hell of a stink. Two, the remaining copper will penetrated the surface of the steel, inter-granular attack I think it is called, embrittling and weakening the steel.

Besides the method already outline, here is another to consider. Cut the frame tube midway between the lug and the front motor mount. Replace the front few inched with a new frame tube. This gets the weld joint well away from the lug, and you have good access all the way around to get a good welding job. But what you say of the bit of frame tube still in the frame lug? Well do not think that you will be able to heat the front lug up and drive it out, this is almost certain to fail. By the time you get it hot enough to free the spelter all the way around, you will have loosened the joint to the front down tube as well. You may find also, that they pinned to joint to hold the alignment while brazing. Probably you will only end up over-heating the joint in an attempt to free it, and boiling the brass as mentioned above.

So I would suggest then boring out the tube. I have been giving this some thought, and I think it could be do with a piloted counter boring tool such as shown:


Larger view

The pilot would be a free fit in the tube and would guide it two-thirds of the way through the lug. The diameter behind the cutting tool would then provide guidance for the last little bit. Since the fracture is already displaced, I do not think the rest of the lower frame tube can be trusted to provide proper alignment, indeed it may deflect the tool out of alignment when the pilot passes into it. So I think it would be best if the tube were first cut back to midway between the lug and the motor mount, out of the way.

Broken center drills make good boring cutter bits, and it simplifies things by having the cross-hole cylindrical. The alternative would be to broach a square hole to take a small lathe tool bit. A flat and a set screw from the end will hole it in place and keep it oriented. The cutting edge should be about 0.003" proud of the conical step shoulder of the pilot. This is rather important, as it sets the "feed rate" of the pilot. While it may be impossible to feed the pilot too fast, in practice you will be driving this with (I hope) a gear reduced electric pistol drill, preferable variable speed with plenty of torque. So in order to avoid having the pilot race, then bog down and stall, only to free up and race again, it is important to set conditions where the feed rate is more uniform than you may be able to achieve by solely feeding by hand. The rate of cut is determined by many things, but mostly by the relief angles ground on the tip of the tool. These can be hyper critical, small variations determining if the bit does not bite into the metal, or tries to bite too well and dig in. You will have enough trouble adjusting the bit, not to have to worry about that also. So grind the bit to be aggressive so you know it will cut freely, and use the "lead", the 0.003" proud dimension, to limit how much it can dig in. Then you can just lean into it as hard as you can and know it is only going to advance at a steady 0.003" per turn and the speed will be much more uniform.

The other setting of the tool that will be a bit tricky is the tip must bore a hole just a little larger than the shank of the pilot to follow. You can not have a large clearance, as you will rely on the shank for guidance when most of the way through the lug and the lead pilot diameter has been all but machined away. Of course, this resulting diameter should be the size required to leave a gap between the lug and the replacement tube to braze a new joint. I think 0.005" gap or 0.010" on the diameter is about right. Bore a hole in a block of steel the size of the tubing i.d. to try it out and fine tune the pilot cutter. I have not shown and provisions for the swarf. I think flats for such are more likely just to encourage the chips to pack and jam, so it might just be best to pull the pilot out every five turns to brush off the chips and apply some more cutting oil. Flats might work if a second person were available to provide a blast of compressed air to blow the chips through.

I think a butt weld would be sufficiently strong to splice the tube without the need to have a reinforcing sleeve. Due to the torsion bar, there is no room for such inside the tube anyway. You could put one on the outside, but that would be unsightly, and I do not think necessary. If you are worried about the butt weld, then you could cut both ends of the tube at a 45º and scarf the joint, which would be stronger than a joint perpendicular to the axis of the tube. I think the reason it broke the tube where it did is the joint may have been overheated slightly when originally assembled, causing some spelter to penetrate the steel tube. The rest of the joint is backed up by the lug, so no matter if the tube was weakened. But right where the lug ends, it is no longer reinforced. Not only that, there is a stress concentration transitioning from the relatively stiff lug, to the more flexible tubing. So you want to avoid having you weld joint right there, but a few inches away it should be fine. While it is not unknown for Mark frame to break at the front lug, most do not, and it is more common that they break at the rear. My Mark 3 was hit in the front so hard it bent the front down tubes just below the front head stock, and while the frame was cracked in other locations, it did not break at the front lower lugs. So if it just "went", I think some other extenuating circumstances were at play, and not just that the basic design is just too weak. Granted, the Mark frames are a bit flexible, but they usually break at the rear.

Use a piece of aluminum bar turned to be a light drive fit in the i.d. of the tube, to align the ends. Leave this in place to tack the joint, but then drive it out. Use aluminum rather than steel. There is a risk with steel that your tack weld might penetrate through and weld the alignment pin fast. And after all, you do want full penetration of the weld. If this happens with the aluminum, you can at least take a stout rod and drive the aluminum pin back out, even if it means tearing the aluminum past the blobs of weld that penetrated into the i.d. of the tube. If you left the alignment pin in place for the duration of welding, it may be keyed into the weld to such an extent that you might not be able to drive it out. Second, molten aluminum has an affinity for molten steel, the mixing of the two will cause the steel to form a coarse (and weakened) grain structure on solidification. Three or four tacks around the tube will not matter much, but its presence around the entire inner perimeter of the weld is not desired. An alternative, is to use a short length of angle iron as a v-block to align the tubes externally, as related by Eddie above. If the splice is mid-way between the lug and the motor mount, there will be a sufficient length of tube either side of the joint to allow a good alignment.

Then once that is fixed, braze the tube to the lug. Or better yet, use silver-braze (silver solder, hard solder.) Getting the proper free running spelter to wick through the joint may be difficult, but most silver braze alloys excel at this, provided you do leave a gap for capillary action. There are some gap filling silver braze alloys out there, so you can not just use anything to hand. The other advantage to silver-braze is it melts at a much lower temperature (1100-1200ºF) than brass spelter, so boiling off of the zinc (when present) or inter granular penetration of the copper alloying constituents is not a problem. Not that this means immunity, as once you overheat and "burn" the silver-braze flux, you are up the creek without a paddle. The lower temperature will enable you to braze the repair joint without loosening the adjacent joint for the front down tube.  

No matter how you go about it, it is a major and difficult repair to do.

-Doug

[alwyn]

Thank you Eddie and Doug for your respective well considered inputs toward solving my frame problem - it's great to be able to lean on the technical expertise so often displayed by each of you within this forum.

I do not have the means nor the ability to do the repair myself but have facilities and skilled help nearby that I will employ - I will however do the disassembly and reassembly of the bike myself.

Without having yet consulted my preferred local engineers, I am leaning toward Doug's suggestion of reaming out the broken off section of bottom tube from the lug and brazing in to the lug a new tube of length to join (by butt welding) to the existing tube at or just forward of the forward engine mounting bracket (it is only about 45 mm from the face of the lug to the engine mounting bracket).

I think this method has the benefit of ensuring the absence of brass inclusion in the weld which both of you emphasise as being critical to the success of the weld and it avoids the risk of damaging the joint between the lug and the frame downtube by excessive heating and rigorous working - also, having regard to the appearance of the repair, if the butt weld is located at the engine mount bracket it should be well nigh indistinguishable by virtue of a fillet weld (as presently exists and which I will saw away) at the bracket/tube interface and a full penetration V-butt weld to the remainder of the circumferential joint beyond the limits of the bracket/tube interface. I'd like your further comments please.

On the drawing below, I have merely annotated Doug's drawing with the object of conveying my understanding of it and have noted the diameters of the tool relative to the lug and frame tube diameters. Where I have noted '- clearance', I envisage just sufficient clearance on the diameters to allow free rotation of the tool within both the lug and the existing tube. Would you please tell me Doug, have I understood the principle of your reaming tool correctly?



I am expecting that my 'engineers' will turn up a length of tube out of solid shafting rather than search availability of matching tube from local stockists - what grade of steel do you fellows consider suitable for this?

Alwyn

[eddie]

Alwyn,
Just a couple of points to consider if you go about the repair by Doug's method. The boring bar Doug has sketched will need to be modified slightly by machining a flute along it's larger diameter, because at the moment there is no passage for release of the swarf generated. I would suggest that the flute should be just above the toolbit as this gives the easiest passage for the swarf as it leaves the cutting edge, and is on the side where no thrust is applied. Regarding getting the replacement stub of tube machined from solid - I would prefer to get hold of a short piece of solid drawn tube as this should be stronger than a piece of machined bar (any machining marks that go around the tube could create a weakness from which the next crack/break generates).
Regards,
Eddie

[TGETINMAN]

Alwyn
I hope you get her all together! I am looking foreward to the bay to birdwood. armed with my Digital camera i will be there!
Gook luck
Dave

[Doug]

Alwyn,

Would you please tell me Doug, have I understood the principle of your reaming tool correctly?

Yes, you have interpreted it correctly.

...what grade of steel do you fellows consider suitable for this?

I do not think Douglas used anything particularly special in the way of tubing for their postwar frames. Any cold drawn seamless tube should do, or low carbon round bar should your shop drill out a short piece from solid. If you can only find welded seam tube, place the seam at the top or bottom, not the sides. As Eddie mentioned, if the o.d. is turned (it is Ø1") then you will want to sand out the turning marks. Unfortunately, there is not much you are going to do about the drill/boring marks of the i.d. if you machine from solid.

Actually I would not place the joint against the engine mount. You are placing the weld right at the point of a transition in section, which would put a stress concentration directly on the weld seam. This is much like welding the crack by the frame lug, without the brass contamination. The other disadvantage is for the welder, he now has to weld a joint with the thickness of the tube on one side, and a mass nearly double that on the other (the tube plus the thickness of the engine mount clip.) No, put the joint midway between the lug and the engine mount, where the welder can hold the torch (hopefully TIG) square to the joint and do the best possible job. As for hiding the joint, I see no reason why you can not dress the weld flush with the adjacent tubing. If it is a good welding job, it will be strong enough. If you are worried about it, as I mentioned you can scarf the joint. 

-Doug

[alwyn]

Hi all,
Thanks for all the friendly help and advice. I am happy to relate that the frame repair has been finished and the frame and some other ancillary parts that were looking a bit daggy have gone off to the paint shop to be grit blasted and repainted - a very dark shade of black has been requested

I have prepared an account of the repair abundantly illustrated with photographs too numerous to be posted here. If you would like to read the account and view the photographs all is available here.

Alwyn

[Ian]

That is great Alwyn - I am sure you would have tidied it up before the rally anyway 

[Doug]

Alwyn,

A monumental repair, and a major undertaking that I am sure you are relived to be on the downhill side of. You will have the satisfaction of a thourough job well done that will outlast the next six successive owners! About two hundred years from now when it is undergoing a molecular recombination restoration (sort of like how they make chicken patties today) some future owner will be puzzled as to why the tubing changed from seamed to seamless! More in the present time, I do not think you will need to worry about the right front corner of the frame anymore.

Lucky break with the lightweight drillpress!

-Doug

[alwyn]

Hi all,
Getting close to completing the reassembly now - a few dramas along the way - one step forward and two or three backwards a couple of times (I warn, don't take as gospel all of the directions in the manual! - and yes! - of course I kept photos! - but not of the bits that I got ballsed up with

Anyway, a pre-existing fault lay in the fact that the dynamo had ceased to dyna, or to clarify that, it had ceased to charge - as of this afternoon the patient is still very sick and is undergoing further surgery but the prognosis is pretty grave - I have therefore appealed in the parts needed section here to anyone who has a spare serviceable armature that they would be prepared to part with for a reasonable sum - the MO says the regulator is also in rather a poor state of repair but at the moment is, or was alive pre-disassembly and seems likely to survive at least in the short term but I have appealed also to any one who has a spare one of these also to make me an offer.

Alwyn

[Eero]

Hi Alwyn and All

I am from Finland
Sorry, I write and spoken English is not grammatically

I have the Douglas T35 model, year 1947
The frame number is T35S811.
The engine and gearbox number is T35S922
Its frame broke the same place as you Douglas.

This spring I will drive me Douglas 320 km, until I noticed a fracture. Fortunately, torsion bars gave the hull size.

Do you have more photos in the fracture site and its repair.
Fracture of the tube section is not circular, and I would say that the rectangle with the jacket which will continue the fracture of the engine mounting bolt  up. Is this a pipe around the mantle?. 

I have carefully examined all of your messages to the repair and I will pay it to the same method used.

Regards

Eero

[Doug]

Eero,

Alwyn passed away January 2009.

I do not know if you spotted it, but in one of Alwyn's posts there was a link to a fuller article on the frame repair process with many more photos. The full path of the link is here-

https://www.douglasmotorcycles.net/aa-files/html/Alwyn/2006/framerepair-webpage/index.html

-Doug

[Eero]

Hi All

I have read and printed Alwyn Frame Repair - November 2006 Account Photographs & text.
My wheel is the backbone angle pipe fittings different from those of Douglas Alwyn or David's MK 1 1947 Douglas. (compare my T35 photos). Can anyone explain the differences?   

Eero

[David H]

Hi Eero

I think by the look of your photos that the difference is due to an earlier repair to the frame.  I replaced the whole bottom tubes in the end as the welded repair was Knocked back when I tried to register my Mk1. I also used 4130 Cr-mo tubing to add significant strength to the bottom of the frame.

All the best David H

[Eero]

Hi David

Thank you for your previous.
I find a CrMo 4130 tubes Ø 1" and a wall thickness is 0.083" (2,1 mm)
Use the same kind of tube, or did you have the thicker wall of CrMo tubing?
From Finland I can not find CrMo tubing 4130 with a wall thickness of 0.120 "(3.048 mm)
What Tig Welding filler material are you using?. I thought that using ER80S-D2, ER70S-2 or ER70S-6 filler. http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp

Regars
Eero

[Doug]

Source of supply for 4230 one inch tube with 0.120 inch wall-

http://www.mcmaster.com/#89955k89/=2a5hvd

-Doug

[David H]

Hi Eero

I got the tubing from Performance metals in Melbourne (WWW.performancemetalsaustralia.com.au) they dident  have any problems supplying it. Because the whole lower tubes were replaced we could not Tig in the new tubes. the front lugs are cast iron/ steel and the rear lug is bronze so the only option was to machine out the old tube and bronze in new ones. I didn't do the job as it had to be done by a Victorian Roads department approved engineer. It's a long story but I had the frame repaired and the people who did the job put the front lugs on the wrong sides. Then had them cut off and re welded on the correct side only to have the job rejected by Vic roads department. There is a regulation in Victoria that prevents the use of welded frame repairs on the road. So after a lot of negotiations they allowed me to use the frame only if I had the lower tubes replaced again and it was done by an approved engineer. so the details of how he done this I don't know sept to say it was a beautifully neat job.
Hope this helps a little
Cheers
David H