Justinp551 Posted January 30, 2012 Share Posted January 30, 2012 I completely rebuilt a n42 combo few years ago but rarely driven. I had the machine shop bore block, new pistons, resize the crank bearings, and balance the whole rotating assembly. However beings how this was my first car engine I re-used the rod bolts. Now the engine is out to switch to a nicer body s30. Read a few posts about putting new rod bolts in and have ordered apr bolt and popped the oil pan off the other day to install. I purchased a digital scale and wanted to make sure what was going in matched what was coming out. Well the rod bolts old and apr are all 40grams +-1g. I am happy with that but the nuts are a different story. The stock nuts are 14mm/8-9grams and the apr are 13mm/6grams. With the apr nut/bolt combo I am a total of 4-7grams lighter than what it was balanced for. Is this critical on a street engine with occasional spirited driving? I have considered using the apr bolts and stock beefier nuts to get back to balance weight and look stronger but figure apr wouldn't sell the smaller ones if they were weak. Also the apr combo is taking roughly 36 grams off the total rotating weight. So would it upset the balance to go with the lighter apr set up? Or should I put the stock nuts on the apr bolts to get the balance weight back? Some input on what direction to go would be great. Thanks. Quote Link to comment Share on other sites More sharing options...
inline6 Posted January 31, 2012 Share Posted January 31, 2012 With the apr nut/bolt combo I am a total of 4-7grams lighter than what it was balanced for. When balancing is done, the crank is typically balanced by itself. Then the flywheel may be bolted on and the balance is checked and adjusted as necessary, next, the pressure plate... The disc is balanced by itself instead of while on the crank assembly because its relative position changes all the time relative to the other parts which are "fixed" in their position. Rods are not assembled onto the crank when it is balanced. The rods are typically weighed and each one is brought to within a certain range of the others. As long as there isn't any substantial difference in the weight of the new rod bolts and nuts from one rod to the next across the rods (1 to 2, 2 to 3, etc.) you won't harm any of the balance just by putting in slightly lighter hardware. Only if say, you ran the stock hardware in 1 of the rods and the new stuff in each of the others would you mess anything up. Make sense? Quote Link to comment Share on other sites More sharing options...
Tony D Posted January 31, 2012 Share Posted January 31, 2012 As long as your cylinder to cylinder is consistent you will be O.K. On a V8 (bobweighted crank) it would be a different matter. And if you had your counterweights cut down to minimum to match recip weight it would make some difference... but not in this instance. I would not mismatch the nuts. Keep the ARP Hardware. Quote Link to comment Share on other sites More sharing options...
Justinp551 Posted January 31, 2012 Author Share Posted January 31, 2012 Thanks for the quick answers. I did not know how things were balanced and it makes sense. I appreciate the info. Apr it will be! Quote Link to comment Share on other sites More sharing options...
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