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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Cracked FF3 Lower Link?
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<blockquote data-quote="Elanman39" data-source="post: 163106" data-attributes="member: 5453"><p>Well, I've done a bit of digging around on the internet and a few quick sums and the answers are surprising.. According to several different manufacturers websites hand held pistol grip grease guns can generate up to 17,500psi (!). Some claim 20,000psi which I find amazing. I measured my cracked FF3 link and the bore of the front pivot is not particularly central to the forging. As a result the wall thickness at the extreme front of the link is just 1/8" in the central region. Assuming the link is mild steel as it is described and taking mid-range values for yield strength and ultimate tensile strength for mild steel of 50,000 and 64,000 psi respectively the burst pressure for a seamless mild steel tube with 1/8" wall thickness and 1" overall diameter which replicates the central section of the front of my link comes in at 16,000 psi using Barlow's burst pressure equations. So given the age of the parts, the probably poor quality of the steel and the significant offset of the machining it is well within the realms of possibility that I could have cracked the link with my little hand held grease gun. If I didn't it's quite possible someone else has at some stage in the past.... </p><p>The good news is I have repaired my link as discussed, grinding the crack out to a wide vee and then using mild steel filler rod and an argon arc to weld it back up, taklng the opportunity to increase the thickness of the material locally by bringing the crown of the weld to a peak and then grinding and polishing it back to a nice stress raiser free ridge along the leading edge where it was thinnest. The really good news is there was no measureable distortion and with nice shiny new bushes fitted and jig-reamed the link is perfectly square.</p><p>I'll put it all back together tomorrow evening....</p><p>In the meantime, please go carefully with those grease guns!</p><p>Nick[ATTACH=full]53495[/ATTACH]</p></blockquote><p></p>
[QUOTE="Elanman39, post: 163106, member: 5453"] Well, I've done a bit of digging around on the internet and a few quick sums and the answers are surprising.. According to several different manufacturers websites hand held pistol grip grease guns can generate up to 17,500psi (!). Some claim 20,000psi which I find amazing. I measured my cracked FF3 link and the bore of the front pivot is not particularly central to the forging. As a result the wall thickness at the extreme front of the link is just 1/8" in the central region. Assuming the link is mild steel as it is described and taking mid-range values for yield strength and ultimate tensile strength for mild steel of 50,000 and 64,000 psi respectively the burst pressure for a seamless mild steel tube with 1/8" wall thickness and 1" overall diameter which replicates the central section of the front of my link comes in at 16,000 psi using Barlow's burst pressure equations. So given the age of the parts, the probably poor quality of the steel and the significant offset of the machining it is well within the realms of possibility that I could have cracked the link with my little hand held grease gun. If I didn't it's quite possible someone else has at some stage in the past.... The good news is I have repaired my link as discussed, grinding the crack out to a wide vee and then using mild steel filler rod and an argon arc to weld it back up, taklng the opportunity to increase the thickness of the material locally by bringing the crown of the weld to a peak and then grinding and polishing it back to a nice stress raiser free ridge along the leading edge where it was thinnest. The really good news is there was no measureable distortion and with nice shiny new bushes fitted and jig-reamed the link is perfectly square. I'll put it all back together tomorrow evening.... In the meantime, please go carefully with those grease guns! Nick[ATTACH type="full"]53495[/ATTACH] [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Cracked FF3 Lower Link?
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