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Post by boanerges on Dec 7, 2008 12:48:36 GMT -5
Hey guys I am in the process of cleaning up my frame -- 1978 SR500 E US model. Currently taking off the passenger peg mounts so I can install my alloy swingarm. Ground off the tubes holding the pegs but have a question about the area around where the tubes weld to the frame. There appears to be a second skin of steel wrapped about half way round the frame tubes -- this region is circles in red as shown in the picture  My first instinct is to have at it and grind off the welds and remove this second skin around the frame tubes. Anyone try this? Advice? Thanks Bill-- |
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Post by solo2racr on Dec 7, 2008 15:05:00 GMT -5
I did a similar thing with the TT frame I use for my SR. Not passenger pegs but for the top shock mounts (single shock conversion). What I did was to use a cut-off wheel on a 4" side grinder and cut through the weld. You need to be rather careful doing this to not cut into the main tube. Once the piece was off, I swapped out the cut-off wheel for a sanding disc and cleaned it all up. If done right, you can't tell that anything was ever there. Taking your time on this one will really show in the end. I did nick a couple places when I did mine and just welded a bit over top to fill and cleaned it up as I went.
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Post by boanerges on Dec 7, 2008 18:13:00 GMT -5
Thanks Solo:
Do you think the metal sheathing was put there for any function?
Bill--
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Post by solo2racr on Dec 7, 2008 18:30:11 GMT -5
Just bracing to strengthen the area. But, not having passenger pegs anymore (or in my case, two shocks) no need for the extra bracing to be there.
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Post by boanerges on Dec 7, 2008 18:41:24 GMT -5
Your probably right, what's strange to me is that the other side of the frame doesn't have any. Getting down to smooth tubes on that side will be a snap.
Of course the frames were designed in the days before CAD and easy computer stress analysis. The engineers probably just felt that when in doubt ......
So, thanks for the advice Solo, think I will have at the frame shortly with my cutoff disk (carefully) on my mini-grinder.
Bill--
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THUMPS
Junior Member
THUMPS, ridden by Dave
Posts: 92
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Post by THUMPS on Dec 7, 2008 21:32:48 GMT -5
Perhaps it was reinforced because it was on the drive side.
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Post by curly001 on Dec 8, 2008 5:11:44 GMT -5
Bill, I prepared Rick's(wizz954) frame that he races in post classic and it didn't have the second skin for the passenger pegs. They were just welded straight onto the main tube. It was a 81/82 model frame. Curly
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Post by aero on Dec 8, 2008 7:05:26 GMT -5
Solo2racr is bang on the money here. As he says- Do most to the heavy cutting with a grinding wheel. The real trick is to clean up with a SANDING wheel on your angle grinder. That piece does absolutely cock all in terms of bracing the frame. I can't see any reason for it being there. It just isn't doing anything. What I am doing on my frame is cutting the foot rest a little longer and welding on a lug. One it means I don't have to spend all day cleaning off that gusset and secondly if I ever want to have footrests again you can make something up to bolt on  |
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Post by boanerges on Dec 8, 2008 10:29:43 GMT -5
Thanks for the help everyone.
Curly:
Nice to know that the later models did not have this second skin. Makes me think that there was a perceived structural benefit on the drive side as Thumps pointed out. My guess is that Yamaha eventually removed it to reduce weight and manufacturing costs when they came to their senses.
Aero and Solo:
Great advice, will be sure to follow up my grinding efforts with a sanding disk. I think it will make for a much cleaner look, take off a few ounces too I guess.
I am thinking of taking off the rear master cylinder bracket on the exhaust side and the small gusset at the base of the triangle on the LHS too. Both visible in the picture. Probably just weld in a horizontal tube as a cleaner substitute. Maybe could triangulate these space frames too with another tube-- anyone see anything like this? (will try to post a picture later)
Bill--
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Post by aero on Dec 9, 2008 7:23:32 GMT -5
You have to be very careful. Bracing a frame really is not as simple as welding on some extra bits. You have to understand that those extra bits will just shift the loads about. I don't see a problem with replacing the mounts with a tube, I'm doing a similiar thing. But I'm not taking it any further as that would mean I'd have to get my thinking cap out. And that hurts my head. Have a look under the 'articles' tab then go to 'stiffening a frame, kawa 750' example. I can't link it direct to the article. www.tonyfoale.com/For those who don't want to read all that article the closing paragraph..... Now just a word of caution. Frame stiffening as discussed will in most cases significantly reduce the stress levels in frame members as well as stiffening the whole structure, but there are occasions where the stiffening of one part of the frame may lead to increased risk of failure in another unstiffened area. A flexible frame acts as a spring and can absorb and reduce the effects of some types of loading, if only parts of the frame are stiffened then we may pass more load through to the unstiffened areas which may deform locally more than before even though the whole frame deforms less. Well, now you have a rigid frame to work from, but that's all it is at the moment. Handling will probably have improved somewhat already but to get first class results you must start the fine tuning process. That is, selecting spring rates, matching tyres, changing geometry by moving the fork sliders in their yokes, etc. the list is endless. But that is all another story. _ _ Tony Foale from www.tonyfoale.com. with permission. |
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Post by StewRoss on Dec 10, 2008 3:02:45 GMT -5
Yes, use a 4" angle grinder and go carefully. Pain staking but worth the effort. This frame is the same as one of my E model frames I have here...I have now seen three different versions of the E model frame. They differ in this area and also in the gusseting in the area between the tubes above the swing arm pivot. That one is the one with the most gusseting with the extra in between the peg support tubes...it'd be interesting to hear their reason for it as (...has already been said) the later ones have basically no gusseting in the peg areas. Butted up welds straight onto the tubes. Easier to modify... The '85 - '95 models even had rear set pegs standard! Wonder why they went away from that? Some even had bolt-on pillion peg brackets as well... SR  |
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THUMPS
Junior Member
THUMPS, ridden by Dave
Posts: 92
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Post by THUMPS on Dec 10, 2008 11:28:54 GMT -5
What methods are acceptable to reinforce the frame. Welding, brazing? I am a hobbiest mig welder but at this point wonder if the welding might make the steel more brittle. I am guessing that gas or Tig might be better.
I would like to reinforce my swing arm as I am under the impression that it might be the most flexy area along with the forks. I have a set of 38 mm forks and trees that have the same bearing race size as the SR.
Thanks
Too much work, not enough time, too cold.
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Post by solo2racr on Dec 10, 2008 12:05:56 GMT -5
Both are fine as long as each are done properly. Welding is quick, cheap, and easy. But, the welded areas should be normalized afterward. This is tricky in that not enough heat won't do anything and leave the stress in the frame (due to shrinkage from the weld) and to much heat destroys the strength. Brazing is the traditional British method. If done properly, it's just as strong as welding. But, that is the key, "If done properly". I personally like to braze. There more to it that just melting the brazing rod onto the metal. The joint fitment has to be near perfect with brazing where as with welding, it doesn't have to be as good. For you, I would pick which ever method your more comfortable with or better at. If each are done correctly, the end results are the same.
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