Balancing Piston, Rods, etc.

So as part of the refresh I am doing on my engine (more on this later in another thread) I decided that I would try to balance the pistons, rods, wrist pins etc with the goal of getting each component/assembly within .5 grams as many article on this process set as a goal. Well it turns out that these components in my engine were not this balance from the factory. ORIGINAL WEIGHT IN GRAMS FROM FACTORY Cylinder 1 2 3 4 5 6 MAXIMUM VARIANCE Piston 410.5 411.8 409.8 411.5 411.5 415.1 5.7 Wrist Pin 111.7 111.7 111.8 111.8 111.7 111.7 .1 Rod 547.9 546.3 546.5 547.3 545.8 546.0 1.9 Assembly 1070.1 1070.0 1069.0 1070.8 1070.8 1069.2 1.8 Note that the totals of each component shown don't add up to the total as I weighed each complement and then all of them together. Also the rod bolts all weighed at 30.1 and the rings are within .3 grams for each set, the bearings are within .1 grams and the circlips are within .1 grams or each other so I did not show them. My original goal was to have each component within .1 grams or so of each other but this was not the case from the factory on either the pistons or the rods. And the pistons have a variant of up to 5 grams. But the assemblies are with 1 or two grams would could be compensated by remving weight form components. I have to replace one piston so in using a replacement piston and rod without removing weight here are the figures I would have. Cylinder 1 2 3 4 5 6 MAXIMUM VARIANCE Piston 410.5 411.8 402.8 411.5 411.5 415.1 12.3 Wrist Pin 111.7 111.7 111.8 111.8 111.7 111.7 .1 Rod 547.9 546.3 553.4 547.3 545.8 546.0 7.4 Assembly 1070.1 1070.0 1068.0 1070.8 1070.8 1069.2 2.8 You can see that the assemblies are still with 3 grams but the variance of the components is higher, with the replacement piston much lights with a variance between the heaviest and the lights of approx. 12.3 grams. But the replacement rod is approx. 7.4 grams heavier.. I am reluctant to try to lighten the other pistons in an amount of up to 12.3 grams as this seems like a lot of material to be removed. In these calculations I have not "balanced the rods", i.e. setting the small ends and big ends in balance to equalize the reciprocating weights. So my basic question is how critical is it to have each component equal in weight vs having the assemblies equal? I am hoping that some of you will have insights on this. Over the years I have rebuilt several engines, MG's, Alfa's, Harley's, etc. but never tried to balance these components.

Sorry i cant help with the balance but hopefully u upgraded the rod bolts while its apart.

Very nice! I have no experience building engines so take this with as much salt as you like. It makes sense to me to treat the weight of the assembly as a whole rather than each component since the assembly is a fixed collection of parts. You move the components around between assemblies to balance the rotational mass.

You want to rig up something to weigh each end of the connecting rods separately. Then you're trying to balance the rotating (big rod end and bolts) and reciprocating (small rod end, piston, wrist pin, and rings) components. https://rennlist.com/forums/996-foru...rebuild-6.html I think I recall Skip or Jake mentioning somewhere that factory engines could be up to 3 oz (not grams!) out of balance.

I see 3 oz/ inch of radius commonly for dynamic assemblies that include the crank, front accessory drive, flywheel, and pressure plate all spun together on my CWT550 dynamic balancer. It commonly takes 3-4 hours to correct the balance of each part individually, then as a dynamic assembly as each component is added to the mass. When balancing rods I always balance end to end to move the imbalance point to the centermost part of the rod. My balance tolerance per set of 6 pistons is 1.2 gram for intermediate level and .5 gram for race level balance. If you have a deviation of this great per set of 6 pistons, you'll compromise structural integrity before you attain an acceptable level of balance. In this case, you must compromise balance, for integrity. Never compromise strength, for balance. If I have a bigger deviation than 4 grams per set of pistons out of the box, I send the pistons back, as they fail my QC. We check the pistons as soon as they arrive for balance, concentricity, skirt dimensions, ring groove width, and depth, as well as a host of other things. I never use stock pistons, but a deviation this great per set of 6 stock pistons is very far out from what I remember in the old days. That said, pairing things up is used when balancing V8 engines. Don't do that with a flat plane application. Balance all the rods as tight as you can, and all the pistons as tight as you can. Don't forget to weigh the rings, and clips, too.. I can see a 1gr difference in a ring pack and two pin clips. the rod that weighs 553 gr needs a lot of work on both ends. If you can make a jig like I show below you can do the small and big end balancing, or a local race shop may be able to balance the rod set for you the proper way. Don't just try to pair up light pistons with heavy rods/ etc, as that won't work with the level of deviation that you have. Don't try to remove material from the heavy rod without a jig, else you'll shift the imbalance to the opposite end of the rod. Balancing jig for performing end-to-end balancing. Fairly light for a 101mm diameter piston Not the before(initial spin) and after (final spin). Before is the dynamic assembly only, had we not corrected the balance. After is after the dynamic assembly was corrected. This one saw intermediate level balance, not race balance.

Amazing feedback, Jake. I know you could be spending your time doing a million other things. Your contributions to this forum are greatly appreciated.

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Sure.. Yeah, I am actually on vacation this week.. Ava and I went fishing today after I made this post :-)

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A well deserved vacation!!

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I have made a balancing Jig for the rods. Not quite as fancy as those you can by or as Jake's but it seems to work pretty well.

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I am replacing the rod bolts with stock Porsche bolts. This engine will not be used for high performance or track time.

Thanks for everyone's comments, especially Jake's. I agree that the components, particularly the pistons should be much closer. trying to take 12+ grams of a piston is too much. I decided to go back to the source that I got the one piston from and get the other 5 from that engine. Then I will have a total of 12 pistons a(with 11 that should be useable) and 12 rods to choose from for weights to get them much closer before I start any weight adjustments. It would have been nice to due Nickies with new pistons but it just was not in my budget. Back in 2008/2009 when I had my cracked head/intermix most everyone, the dealer, my indy and Jake said that I would need a new engine (not many were repairing the heads then) and even back then the price from Porsche for a remanufactured engine was over $10,000 (imagine how many they could sell at that price now) so the cost would have been $13,000+++. Now as we all know the cost would be $24,000 +++. I ended up having the head fixed and a valve job on that side for $500 by Costa Mesa R&D which is closed now as the owner passed away in 2018, spent another $1,000 or so on parts including some that were not directly linked to the problem, spent a week or two of my time and ended up getting 11 years and 50,000 mile before the latest problem. If I can get another 5-10 years and 50,000 mile I will be very happy. After I received the other pistons and rods I will update what I am doing. Once I get closer to weights I am having the small end rod bushings replace before final balancing.

Im making an end table out of my old block and need 3 more pistons and rods. If u r gonna trash the extras ill pay 4 the shipping for a few. Good luck with the assembly

Porsche run different batch weights when making a set of pistons , the one you have that is quite far away from the others will be a different batch weight , you need one matching your other pistons

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I am getting the five from the set the one light one I got came from. We will see how they weigh out. but from the original set in my car the variance from lightest to heaviest was 5.3 grams. I will let you know what I have left.