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Tank mounting misalignment

Oldhaven

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VOC Member
The B Rapide I am working on has not run since at least 1966 and probably much earlier. I am pretty sure it has the original tank and UFM. I have had the tank sitting on the UFM, but had never tried to fit the front mounting bolts. Yesterday I tried to assemble the tank to the front mounts with the FT80's and could not get both bolts in. This is almost always not an easy thing to do anyway, from my past experience with a C Rapide, but this was just about impossible. Since the UFM is bare right now I put some rods in the front and rear engine mounts , the sidecar holes, and through the tank mounts. as the picture below shows, the hole for the tank mount is quite misaligned. Looking at the ends of the bosses for this, (not shown here)it is apparent that the right hole is not centered in the boss, but is forward of center. Further more, the entire front of the head lug casting/forging is rotated clockwise relative to the cylinder head mounting holes. It is hard to see, but the steering stops are not in the same position side to side, and there is less steering travel on the left than the right. The off center tank mount through hole on the right side does attempt to correct the casting/forging misalignment, but does not go far enough, so their respective misalignment's are not equal. (I hope that makes sense). No wonder I am having trouble. There is no problem with the alignment front to back on the UFM, and all the critical holes are perpendicular to the UFM and parallel to each other, and I see no crash damage. So the questions I have are:
Are there other B's out there with this problem? This is an early 1948 UFM and I can't imagine it is a one off thing. (Head lug is one of the ones with square bottom edge and rib, for those familiar with the three types of them I know about.)
Other than re-machining the tank mounts, has anyone had to make or modify FT 80's with enlarged or slotted hole so the bolts can go in at all without stressing the tank flanges. I see this as my only good option unless someone has dealt with this before in a better way.

Ron

head lug  1.JPG
 

Bill Thomas

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VOC Member
Hello Ron, They say you should not take the the Head Lug off the oil tank, But I think I would because to me that looks like Crash damage, Try putting your long studding though the bolt holes in the oil tank, After taking the head lug off, All The Best, Bill.
 

Oldhaven

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VOC Member
Correction to my first post, the headlug is round bottomed, hollow and has a rib, shown as type 1 in the Vince Farrell article in MPH 733.

Bill, I may remove one or two lug to oil tank bolts and try this, but I just measured distances of the tank mounting holes from the edge of the bosses on both sides and they vary from 1/8 to 3/16 of an inch from front to back and top to bottom measured at the appropriate points relative to the steering axis, and they are not the same on both sides, contributing to the problem. They are way off in the casting. I just can't see this much misalignment in that casting from a crash without some visible sign of damage.

I was in the process of getting the UFM and petrol tank ready for shipping to get some bad Kreem tank liner put in about 25 years ago taken out, and now I am in a funk about possible expensive crash damage. I may have to reassemble the front end and check alignment of the front axle, or at least put some sort of device down the steering axis to check it.

Ron
 

davidd

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VOC Member
Ron,
I spent most of my life trying to avoid exploring details that would have made my life appreciably better, so others like Norman and Trevor, who have years of in depth experience, may have better answers.

The bad news is that your FT4 is bent. The good news is that it may not cause too many problems.

I spent the winter making two FT4's and I had 5 originals to choose from in order to make the pattern. They were all bent. I chose the least bent and it was .25" off to the right in two feet. I was able to machine the casting so that this deviation disappeared. I concluded that most of the bends were due to sidecar work. The casting just is not designed to take the loads imposed by a sidecar without bending. All were bent between the head lug mount and the steering stem. All of these bikes were US bike and probably should not have done sidecar work, but it could also be minor crash damage. However, if they are all bent, or mostly bent, then it seems that we are not all suffering from disastrous consequences. So, I would not be too upset.

I would remove the steering head (the warranty has lapsed, just don't tell Bill) and do some measurements. Your bend looks quite different than what I was seeing. It looks like the twisting was clockwise along the rake axis. The ones I looked at were on a horizontal axis, namely, put the steering stem part in a vice and put a bar through the sidecar lug and jump on it. You may have some of both.

You can do some rough measurements on the milling table. I assume you have an "Outy" UFM, that is, the steering lug grips the head lug from the outside and you use the solid head lug. You will have to space the FT4 so that neither the head lug mounts or the gas tank mounts are touching the table. The machined surface you want is the five oil tank mounts, or three mounts with five holes. You will have to take out the bearings. Make some washers to go in the bearing pockets and put a hole in the center to match your ground drill rod. I used 7/8". I used a stop in the chuck and moved the table from one end of the drill rod to the other to see the variation on the quill.

I think once you overcome the disappointment you will see that you can do some repairs and get the steering axis somewhere close to the centerline of the five holes. I think this is all you need. you may have to weld and tap an new hole for the gas tank mount, but you will have fixed the geometry already and this would be a cosmetic fix.

All of the above is based on the assumption that the gas tank is not strong enough to move that mount hole by itself even in an accident and that the casting has been bent. Once you have it out you can examine it more closely and hope for an easier answer.

David
 

Oldhaven

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VOC Member
Hi David,

On closer examination I have found what may be some indication of a prang. One of the steering stops is bent on the correct side to produce this twist. I will post some pictures later. In the meantime, thanks for the encouragement. I am sure it can be salvaged. Before I do too much I have a lead on the correct matching UFM for my engine. It is number 3144 and was on ebay in 2008 listed by a cycle shop in Ontario. It has not turned up on a club registered machine since then, so it may be on someones shelf. I will talk to the shop owner tomorrow. If any of our Ontario or Canadian section members has a line on it it could be my best solution, though from what you say, it may be bent too.

Ron
 

Bill Thomas

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VOC Member
Hello Ron, Another thing to check, If you think it had a crash, Is the roundness where the steering head bearing cups go, I know a bloke who went too fast on the race track and the lock stops got a right bashing, It stretched the holes where the cups go, Ok, It was me !! Cheers Bill.
 

Oldhaven

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VOC Member
Bill, I was right in the middle of a tapered roller bearing conversion, so I had a chance to look at the roundness. Nothing noticeable in the bores. since the new Patzke outer bearing races fit fine. I have attached another picture showing the steering stop, which, as you say, got a right bashing. It is hard to believe the headlug could bend between the steering head and the tank mount, which is why I was so skeptical at first, but the evidence is right there, and David confirms how common slight bending is. This still does not explain why the tank mounting holes are so far off center in the bosses, but I think I can assume that the through hole was drilled on the same setup as the other machined surfaces, or using the machined flats for the tank mounting bolts, so the small rod shown through the tank mounts should be parallel to all the other ones. this in itself is a good indication of the correction needed. I won't be able to do the testing David suggests until the end of next week, but that is the next plan.

IMG_0356r.jpg
 

Bill Thomas

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VOC Member
Hello Ron, Yes I thought David had been Drinking !! Or is it made of Malable iron ? Sorry David , Just a bit of fun, I would have thought the weak spot would be where the 5 bolts are, I am expecting you to take them out and find them bent or something, David, Is there any slack, ie Adjustment on the five bolts ? I have never seen one apart, I always thought that is why we were told not to take them apart, One of my bikes had a full blown Tank slapper, ie Me over the top, + my race mistake I have already told you about, I had put two allan bolts to make smaller lock to lock and they were smashed to bits, But the only sign of damage was the stretched cup holes, Will be good to see what you find, All The Best, Bill.
 

davidd

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VOC Member
Hello Ron, Yes I thought David had been Drinking !! Or is it made of Malable iron ? Sorry David , Just a bit of fun, I would have thought the weak spot would be where the 5 bolts are, I am expecting you to take them out and find them bent or something, David, Is there any slack, ie Adjustment on the five bolts ? I have never seen one apart, I always thought that is why we were told not to take them apart....

Bill,

Well, you are correct. What I was finding was the portion in the head lug and the portion that contained the side car lug mount were not in line with the portion that contained the steering stem. If you put the steering head in a vice and clamped on the gas tank mounts you could see that the tail was twisted.
003.JPG


You can see that the last two oil tank mount holes are directly over the side car mount.

The fit of the FT4 in the oil tank is pretty close. The oil tank, being sheet metal, may vary somewhat, but it it is a little wide it just closes down when bolted. The oil tank mount holes appear to be reamed to size and I suspect the factory did not want you fooling around with the fit. Smaller bolts could be quite exciting.

The one in the photo is an inny. If I remember correctly there are two types of outies. There is one with a boxy cross section, which I think Ron has and one with a recessed cross section like the one above, but with the motor mount cast in as an outy. I think Tim has one ons his GFR. The inny is much easier to machine the one in the photo as it is compact and the other side of the motor mount is in the same plane as oil tank mounting holes.

What I did was put a 7/8 X 3' ground rod through the steering stem. I then laid the ground rods on two V-blocks, on on each side of the steering head. As the axis of the steering head was parallel to the milling table I put a spacer under the the rear most oil mount hole and took a skim cut off the top. I then flipped the steering head over in the V-blocks and did the same to the other side. I did this a few times until I could use the same spacer under either side and the mounting surface was parallel on both sides. I could then mill it to dimension. Ron has the problem that he is already at dimension and he has the giant claw on the back to grab the head lug, but there are solutions.
001.JPG


David
 

Bill Thomas

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VOC Member
Hello David, Wish I had use of those kind of tools, Always wanted a Mill', Not that I would know what to do with it !!, What is the Standard Headstock made of ?, Cheers Bill.
 
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