Jim, another piston idea for 6.25" rod length. Derek got me thinking about the 4.8/5.3 LS motor pistons like Fred is using on BritishV8. They are .007 shorter compression height than the ones above. 1.328 Probably around 10 to 1. 3.78 bore standard and slightly larger pin size than the Buick at .945 instead of .940. https://www.ebay.com/itm/5-3L-4-8L-...745170&hash=item36024bdaf4:g:KhcAAOSwtJZXUbQ6
Jim, can you weigh the rods from the 340 you tore down? We have the weights for the 300 rods and the cap screw 350 rods, so it might be nice to complete the information gap...
I'll see what I can do tomorrow. Looks to me like the oil slinger on the 340 crank doesn't need to be touched, as there appears to be plenty of room for it in the groove. About .400 larger in the groove than the 340 slinger. Jim
Jim, the 350 one Chris has needed to be machined. Makes sense the 340 one would be similar to the 300. Have you checked the seal area differences? I know the 300 uses a different rear seal than the 340 and 350.
Yes, the seal is roughly 1/2" larger in diameter also. As is the slinger, but I see no real need to turn that down since there will be .200" all around it in the gap (on the diameter). The bottom is cut out and there's a hole at the top. Any oil that comes out the back of the bearing is going to be flung out pretty quickly, and it seems to me a larger diameter slinger is going to work better than a smaller one. I'll compare the slot in the 340.
Got some component weights for you guys, on the 340: Rod with inserts, bolts and nuts: 681 grams Piston with rings: 597.5 g Wrist pin: 168.5 g Jim
So with the parts I used in my 340 build, I removed 75 grams on the rods, 89.3 grams on the pistons, and 97 grams on the wrist pins, for a total of 261.3 grams removed from each piston/rod assembly. That's about 9-1/4 ounces or better than half a pound. And I feel bad about the heavy wrist pin locks. Jim
The cap screw 350 rods averaged just over 657 grams. That was with the rod, cap, and bolts. That's interesting if the 340 rods weigh more, but good news if its true because it means there aren't any disadvantages to going with the cap screws.
The insert is the bearing shell. 41.6 g per rod. So it looks like the 350 rods are a little heavier. Jim
Oh ok. So we are talking 15-20 grams per rod, which works out to about 1/3 of a pound added to the rotating assembly. Is that significant? It looks like the numbers are: 300 rods- 589 340/early 350 rods- 640 Late 350 rods-657 Thanks for weighing those Jim. When I weigh the 2bbl iron manifold does it need to be stripped or is it ok to have the water neck, etc on?
The cap screw rods I have weighed were between 660 to 690 grams, the one in the pic was in the middle of the weights. And yeah, they were all from the same engine! Brought my scale over to Mart's and he had a sbb 350 nut and bolt rod there in his basement that weighed 618 grams but it has polished beams so that might of removed 5 or 10 grams from factory weight? So probably around 630 grams factory.
Well if you aren't going to include the insert weight, which after all is a part of the rotating assembly, then the 340 rod is 681-41.6= 639.4 grams. Your math is wrong. 27 grams per ounce, 16 ounces per pound. Your phone calculator should have a conversion function. 340 rod: 640 grsms. So yeah, 30+ grams lighter, over an ounce. Jim
Ohh I just used the Google grams to lbs calculator and just used 20 grams per rod as my figure. Claims a gram=.0022 lbs. Don't know if that works out to be the same as you said or not. That seems to be a wide variation between factory rods, but then again I'm not GM. Perhaps since I ordered my rods reconditioned they were weight matched and lost a tiny bit during reconditioning?
OK, let's be clear about whether we are talking about weight per rod/piston assembly or weight per engine. What I was talking about was 1/2lb per rod/piston or 4lbs per engine. 9 ounces is a lot of weight to take out of a rod/piston assembly and really makes a difference in how the engine responds to the throttle. The difference between 340 and 350 rods is not that great so if your pistons are light enough to offset that extra weight the rebalance job may be easier as Derek said. Production tolerances in 1970 were a lot looser than they are today and factory balancing was the minimum that had to be done. Jim
Oh ok, that all makes sense now. Good things to know, have you decided what route your going with the current build?
Not entirely but I do know I'm not putting cast iron rods in the engine. I'll probably just keep looking until I find a deal on some seconds. Ideal would be about 6.3-6.375 long with about a 13/16 to 7/8" pin, 2" journal of course, and not too much to take off the width of the big end. H-beam preferred. Probably go back to Venolia for the slugs, I'm pretty happy with the last set. I know it's more money up front but over the life of the engine it's peanuts, and I get to specify everything about them. That makes it a lot easier to choose rods as I can make adjustments in the pistons, and savings on the rods can go towards the pistons. I can stretch out the cost over a few months so it doesn't have as big of an impact and I don't have a deadline. I think it makes more sense than starting with a particular piston and then trying to get a rod to match, as the piston is the more complex part. Jim
I gotcha. Man, those rods Derek posted would have been about perfect then huh? I had suspected/hoped you had hopped on them but I guess someone else got them.
They did, I made offers up to $200 and then was barred. I should have just bought them but too late now. Jim
