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Crank build for racing engine
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<blockquote data-quote="greg brillus" data-source="post: 179166" data-attributes="member: 597"><p>It could be a degenerative condition......It has to do with the side play and rocking of the rod little end, coupled with having a piston whereby the little end rod to piston clearance is too much......That is the gap that you can move the piston sideways on the rod with the pin in place.......If the rod supported by its big end does not rock too much from side to side, then the issue is not so bad.......If this condition worsens due to wear, or more clearance given due to racing specs (verses a road engine).......In service, the rod can and will favor rocking to one side.......This in effect jams the pin in the little end......This then causes the friction to go skyward.......Thus the pin and little end of the rod get hot and turn blue.......With our new pistons we had made (at a huge cost) by CP in the USA......we had them make the inside of the pin boss on each side much narrower.......so we now have a side to side clearance of about 30 thou total......we also got them to move the pin to the rear towards the thrust face.......we also got them to move the pin much higher up towards the crown to offset the normal huge "Top heavy" pistons you end up with when running high compression......All these features should hopefully stop the "Also very common" issue of these pistons suffering from bad scuff marks on the front and rear skirt faces......I have ran the engine for about 1 1/2 hours total with this new piston and so far it all looks very promising.......My earlier hand finished piston suffered major cracks around the pin boss on both sides.......16.5:1 Comp will do that.......Too high, so back down to a better 14.8:1 now.......It is my belief that this excess side clearance between the rod and the pin boss on the underside of the piston causes this excessive heat build up.......And you should not run too tight a fit of the pin in the little end bush as well.........Especially on a race engine.</p></blockquote><p></p>
[QUOTE="greg brillus, post: 179166, member: 597"] It could be a degenerative condition......It has to do with the side play and rocking of the rod little end, coupled with having a piston whereby the little end rod to piston clearance is too much......That is the gap that you can move the piston sideways on the rod with the pin in place.......If the rod supported by its big end does not rock too much from side to side, then the issue is not so bad.......If this condition worsens due to wear, or more clearance given due to racing specs (verses a road engine).......In service, the rod can and will favor rocking to one side.......This in effect jams the pin in the little end......This then causes the friction to go skyward.......Thus the pin and little end of the rod get hot and turn blue.......With our new pistons we had made (at a huge cost) by CP in the USA......we had them make the inside of the pin boss on each side much narrower.......so we now have a side to side clearance of about 30 thou total......we also got them to move the pin to the rear towards the thrust face.......we also got them to move the pin much higher up towards the crown to offset the normal huge "Top heavy" pistons you end up with when running high compression......All these features should hopefully stop the "Also very common" issue of these pistons suffering from bad scuff marks on the front and rear skirt faces......I have ran the engine for about 1 1/2 hours total with this new piston and so far it all looks very promising.......My earlier hand finished piston suffered major cracks around the pin boss on both sides.......16.5:1 Comp will do that.......Too high, so back down to a better 14.8:1 now.......It is my belief that this excess side clearance between the rod and the pin boss on the underside of the piston causes this excessive heat build up.......And you should not run too tight a fit of the pin in the little end bush as well.........Especially on a race engine. [/QUOTE]
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Crank build for racing engine
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