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Crank build for racing engine
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<blockquote data-quote="oexing" data-source="post: 179169" data-attributes="member: 1493"><p>Basically when annealing steel parts you watch these colours for knowing the temperature you want to have for correct hardness. But to this purpose you´d degrease the parts first so you will get "true" colours. With conrods I´d think they will be a bit oily all the time so maybe it is not purely the annealing colour effect but some oil film discoloration too. I see same discoloration on my BMW wrist pins plus polished conrods but never care, just thrash the thing. I do extra close fits of piston pin in conrod bush as I believe when you got pistons with easy push fit pins the pins will float anyway in the piston once the engine has run half a minute. Lots of car engines got pins pressed into conrods for floating in the piston only.</p><p> I do not support the idea of excessive side clearance small end to piston faces inside for heating up the place. When there is a lot of sideways motions of conrod upper end you got some more serious flaws: The big end roller/needle bearing faces were not made dead parallel within microns - or the conrod is bent and twisted - most of them are . These flaws typically like to push pin securing clips out of the piston as you can feel ridges at both sides of the piston pin bores. I strongly suggest to restore side clearance of your conrod small end to piston insides. When having extra close fits you only mask over other defects in the crank assembly you´d better not want to have or even produce more lethal defects . In my photos one piston is from the old Jag and the smaller one from a Laverda 750. Both show brownish rings from discoloration and nice polished rest of piston pin , no contact onto piston inner faces obviously, else there would not be the brown rings remaining. And the Jag conrod even got a looong drilling from big end up to the small end for pin lube !</p><p> Coming back to those faked and modded classic racers - what is the attitude in this community down under and elsewhere: Is there openness and honesty about all mods done, especially about real capacity ? Seems to me many competitors are very tight about telling what they have done, possibly because they got their mechanic and don´t quite know what has been done. </p><p> In the racing business engines get checked for correct capacities else they get banned from participating. Not so in classic racing so my grumble about that fraternity is the cheating widely done it seems and that I find quite unfair for fellow competitors and spectators as well. When one keeps to original capacity it is obviously no match to overbored engines with 20-30 percent more capacity. So then this is no real contest about tuners´ skills about finding extra power from the original correct capacity. I do believe there is not much honesty about mods done to these engines - for ridiculous reasons like giving no advantage to competitors who may like to copy your ideas. Well, you only provide your ideas but it is a very different thing to really do the special mod and turn into a reliably working engine - that is the bigger challenge. </p><p> No, not my world, too much cheating and aggressiveness in an amateur sport .</p><p></p><p> Vic</p><p></p><p>BMW R 69 S with 734 cc :</p><p>[ATTACH=full]62097[/ATTACH]</p><p></p><p>[ATTACH=full]62098[/ATTACH]</p><p></p><p>[ATTACH=full]62099[/ATTACH]</p></blockquote><p></p>
[QUOTE="oexing, post: 179169, member: 1493"] Basically when annealing steel parts you watch these colours for knowing the temperature you want to have for correct hardness. But to this purpose you´d degrease the parts first so you will get "true" colours. With conrods I´d think they will be a bit oily all the time so maybe it is not purely the annealing colour effect but some oil film discoloration too. I see same discoloration on my BMW wrist pins plus polished conrods but never care, just thrash the thing. I do extra close fits of piston pin in conrod bush as I believe when you got pistons with easy push fit pins the pins will float anyway in the piston once the engine has run half a minute. Lots of car engines got pins pressed into conrods for floating in the piston only. I do not support the idea of excessive side clearance small end to piston faces inside for heating up the place. When there is a lot of sideways motions of conrod upper end you got some more serious flaws: The big end roller/needle bearing faces were not made dead parallel within microns - or the conrod is bent and twisted - most of them are . These flaws typically like to push pin securing clips out of the piston as you can feel ridges at both sides of the piston pin bores. I strongly suggest to restore side clearance of your conrod small end to piston insides. When having extra close fits you only mask over other defects in the crank assembly you´d better not want to have or even produce more lethal defects . In my photos one piston is from the old Jag and the smaller one from a Laverda 750. Both show brownish rings from discoloration and nice polished rest of piston pin , no contact onto piston inner faces obviously, else there would not be the brown rings remaining. And the Jag conrod even got a looong drilling from big end up to the small end for pin lube ! Coming back to those faked and modded classic racers - what is the attitude in this community down under and elsewhere: Is there openness and honesty about all mods done, especially about real capacity ? Seems to me many competitors are very tight about telling what they have done, possibly because they got their mechanic and don´t quite know what has been done. In the racing business engines get checked for correct capacities else they get banned from participating. Not so in classic racing so my grumble about that fraternity is the cheating widely done it seems and that I find quite unfair for fellow competitors and spectators as well. When one keeps to original capacity it is obviously no match to overbored engines with 20-30 percent more capacity. So then this is no real contest about tuners´ skills about finding extra power from the original correct capacity. I do believe there is not much honesty about mods done to these engines - for ridiculous reasons like giving no advantage to competitors who may like to copy your ideas. Well, you only provide your ideas but it is a very different thing to really do the special mod and turn into a reliably working engine - that is the bigger challenge. No, not my world, too much cheating and aggressiveness in an amateur sport . Vic BMW R 69 S with 734 cc : [ATTACH type="full"]62097[/ATTACH] [ATTACH type="full"]62098[/ATTACH] [ATTACH type="full"]62099[/ATTACH] [/QUOTE]
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Crank build for racing engine
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