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adding weight to piston?
I've got 5 new P&Cs with pistons matched weight group and pin/piston all within 1 gm. I have a 6th new P/C which is 9gm lighter than the rest. Is there any way to add 9gm weight to the one piston/(pin) or do I have to find a way to take 9gm off the other 5.
Thanks Alan |
Or, can I reduce 1 piston/pin by 9gm and place them at the fan end (1&4).
Alan |
Find the lightest and match it .
Thats what most do afaik , and what I always do. It will not be hard to get rid of 9 gms. I always shoot for zero, I sleep better. |
I got 5 'heavy' ones and one light one. The light one is the one I just received - at the bottom end of the lightest weight group. So do i have to lighten the other 5, or can I add weight to the light one?
Alan |
Reread post # 3.
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Go lighter is what would do in a heartbeat.
I made a mistake ( Imagine that LOL) -One time and took off weight on the lightest one. My engine thankfully. I had to rematch all of them to a EXTREAM light number. It came out SUPER light . I shaved from every known spot to man. This engine has over 30K miles of Spirited driving on it and still purrs. |
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regards Alan |
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Do it nice or do it twice! |
OK, guess I better get my grinding gear out. Curse. Yes a rebuild is a bit cumbersome to rid an oil consumption issue - but I had just fitted a used set of P/Cs to replace my worn out set - beyond wear limit, but still working OK. But the rings on the 2nd set don't appear to have bedded in. I could have just gone thru the process again, hoping for better results with a new set of rings. But I had a part set (5) of new P/Cs - so decided to 'do it nice or do it twice'.
Regards Alan |
With a 3 beam scale you will have it done inside 2 hours. EZ
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Alan |
There is really no magic involved .
Just make sure you leave NO burrs! I have not ever had a piston comeback because I took too much weight off. Like I said, I screwed my own up one time really bad. It came out with pistons that were lighter than RSR stuff. It would SCREAM! I talk to the guy that bought it from time to time. No problems . We shoot for pirrrfection.......that makes at least hit the target. |
What weight difference actually matters? There must be a point where it doesn't make any difference as things such as friction etc override any minimal weight differences?
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Wait until you start removing material from the piston. It's slow going when removing 9g. You keep milling material away, weigh it, remove some more, weight it again, still not even close, remove more, STILL a long way to go............ etc.
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You can take some off the pin too.
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I planned to start on the pins - figured that was where the bulk surplus weight was (and I have a lathe which may/or may not help). Was going to see how far I could get with the pins, then finish on pistons.
Alan |
You will do just fine.
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Waynes book says 'the machinist will remove weight from the pin' as per pic. How would they do this? I have spent about an hour with dremel and stone, and have not removed a gm. I still got 45gm to go. It is too hard for my lathe tools.
Regards Alan |
Alan, here is how Jim did his by hand - looks pretty sweet (post #4 for pistons/pins) -
http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/800923-connecting-rods-balanced.html |
Hi there Ron. That is mainly about balancing the rods. Jim had another post - which I read, on doing the pistons and pins. He said he used a die grinder bit on the pins. I'm not sure exactly what sort of bit he used - but I have tried a metal fluted bit I used on my intake manifold and I tried a grinding stone. Both suggest i will be here til Xmas before I can reassemble. There must be a more effective way to remove 45 gm of tough metal. Ideally I would like to use the lathe - since I got one.
Thanks Alan |
I cannot for the life of me see how I can remove 9gm of material off this piston. I can see maybe a gm. So I think I am stuck with working the pins.
The other reason for posting the pic - note the ring gap positions. This is how they came out of the new cylinder. I guess it may be debatable whether to bother orienting them. The ones I pulled after 2 or 3 track sessions had the compression rings moving quite a bit - the gaps converging a bit like this one. The oil ring was still where I put it. Regards Alan http://forums.pelicanparts.com/uploa...1455238899.jpg |
Send them over to me
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Thanks for the offer. But I just spent $200 freighting 1 P&C here. The cost of getting 6 pistons to and from US won't be cheap. If I have to I will hunt out a shop here. But hopefully I can find the right cutting tool. I should have enough gear - as long as I know what I need.
Thanks Alan |
I had 4g difference on my 3.6 pistons. I remember that was quite easy to remove from the pins with a stone on a Dremel.
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My handy dandy Dremel would find all sorts of places .
You will have to be brave and adventurous . I guarantee you will not hurt the piston if you pretty up the skirts ,( Radius ), counter sink the pin a little bit. Engineers tell me a radius is let prone to failure than sq edges . I have had pistons that I even shortened the pins . Do not let it scare ya . You should not ever install a piston without a deburr anyway. 9 gm is not difficult. Dont make it a religion. Just do it. |
To give you some reassurance, take a look at the last page of this pdf. It shows where JE removes material from their forgings to lighten the piston. You can easily remove it from under the crown and around the pin boss where it's REALLY fat.
http://www.jepistons.com/PDFs/TechCorner/SCPDrawings/JE_Piston_terminology_and_features.pdf I did this on a set of 3.3L turbo pistons and it was surprising how much material was removed to get the weight I needed out of it. |
Just for perspective, Porsche specifies 8 grams as the tolerance for replacement pistons. The weight classes themselves are 4 grams wide.
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If you can find a wrist pin that is 9 grams lighter than the others, you will not have to hack into your piston. That is the way I did when I had similar issue in my rebuild.
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You win, I want to see this .
I will go with the zero grams scenario (everytime ) and hope the Porsche fairy forgives all else. |
Nine grams is more than I would tackle but if you must, find a heavier wrist pin or 5 lighter pins.
Pins are inexpensive and vary greatly in weight. Send me the pins , your weight measurements and I'll work it out for you. |
I have 3 sets of pins. All the ones I have weighed weighs the same to the gm, (136gm) . Apparently the pistons all now come out in 1 gp weight too. So perhaps all the pins come out the same now too. No good having one gp weight pistons and varying pin weights. I will check some more pin weights - but I am not expecting any variance on 136 - if I could find lighter ones that would help.
9gm I am sure, would add up to a LOT of Aluminium dust. I am sure I need to pull as much as possible out of the pins. And that will add up to quite a lot of steel dust I am sure. Regards Alan |
Alan
You are over thinking this and working too hard. All of us have said we can whack 9 GM off for ya. LOL Lighter is better. If you were inept and took the whole 9 grams off one spot you might create a problem, but a smart guy ( Like you ) will be able to take some off everywhere under the piston , make a nice radius on the structure . ( 9 grams will be EZ ) |
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OK, I 'm going to have a crack at getting as much off the pins as possible, and then finish on the pistons. It would be useful if anyone has a pic of a piston that has had a decent amount removed.
I take the point that 9gm can probably come off the piston - after all I have 2 pistons that are 9gm different and I can't see where the xtra weight is. Odd that I read several threads and Waynes book about mixing pin weights to balance, and all my 18 pins i have to choose from are 136 gm. (my balance only goes to 1 gm). Thanks Alan |
I will side with, - this is not like unsprung weight, or the pin is, or is not part of the rod.
Smarter people than me will have to- ahem "weigh in" -on that. LOL I think you have broached F1 science. Focus on the job at hand. I bet if you make each piston with pin weigh as close to each other as you possibly can, you will be blessed by the Porsche gods. |
OK, progress. Started at a rate of about 1gm /hr with the dremel on the pins. At that rate it would take a week. Changed that approach to putting the stone in my power drill and the pin in the lathe with a slow counter rotation - to keep the grinding even. Should be finished tomorrow:-) I have taken 6gm out of the pins. That will leave me with 2-3 gm to take out of the pistons.
Two Q's; What is the best tool to lighten the pistons - I am guessing the grinding stone will clog up? I have marked my first targets in the 2nd pic - remove the ridge on the pin boss (#1), and take a chunk out of the boss corners (#2) and then start at the base of the crown (#3) if I need more? Thanks Alanhttp://forums.pelicanparts.com/uploa...1455514925.jpg http://forums.pelicanparts.com/uploa...1455514940.jpg |
I usually use a Dremel .
There are a 1000 types of stones, cutters, and wheels available . The round type sanding drums I use a lot. Radius your sharp edges , you will have it done EZ |
Oh, I got lotsa dremel tools :-). Had to buy 3 boxes of them to get the 1/2 doz stones I wanted for the pins. They weren't avail individually - not local anyway.
Alanhttp://forums.pelicanparts.com/uploa...1455571852.jpg |
The only difference between you and a professional is the so called professional gets paid.
However you will reap the dividends . Once you do this you will have the confidence to help others . |
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