Rod balance

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Rod balance

Post  504T on August 21st 2015, 7:49 pm

A few years back I kicked a couple of rods out of my 600 ( SVO block, C head 15.2:1 injected methanol ) - I bought a couple of new ones ( through a forum vendor ) from Oliver - we tried to get as close to the same weight as we could and I had a machine shop balance them to match, along with re-balancing the rest of the rotating assy. I recently had another bearing issue and the machine shop ( different shop ) suggested I send the rods to Oliver to be checked out. I did that and Oliver said the rods checked out ok - were rebuildable - needed pin bushings and some needed re-sizing, but they checked the balance and found 4 grams difference in the rods - mostly in the big end. Oliver does not recommend taking more than 2 grams off of a rod - I know the newer ones were already a little heavier and had already some taken off them - and the older ones have a ton of runs on them, so when they offered me a deal on a new set I went for that. The most recent bearing failures were #2 and #7 rod bearings - the new rods were on #2 and #6. The rest of the bearings looked real good except for a small sort of half a football shaped shiny spot in the bottom rear of #4 main. There were some indications of a little cap walk on the mains. It wasn't real dry when I tore it down and that along with the pin bushings and cap walk had me thinking detonation might have been the cause of the bearing failures again. When I kicked the rods out a few years ago we attributed that wreck to detonation from having sucked the bottom out of the intake gaskets, I freshened it up about 180 runs ago and the bearings looked real good at that time - except for that shiny spot on #4 which was there then as well. I'm not sure what if any role the weight difference in the rods might have played in all of this. Just looking for a little input.
Thanks,
Kurt.
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504T

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Re: Rod balance

Post  DaveMcLain on August 24th 2015, 2:09 pm

A few grams one way or the other isn't going to make any significant difference or cause those sort of problems.


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Re: Rod balance

Post  gt350hr on August 27th 2015, 2:56 pm

An "above average" balancing person can adjust the placement of the rods in the engine ( usually more towrd the center) and compensate for the weight difference.

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