Balancing piston weights
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Stellar HDF Member
Joined: Jun 2018
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From: WI
Balancing piston weights
Question one: if you have 7 1/2 gram difference in your piston set, would it be OK to run the piston set?
question two: if you need to balance the piston weights more closely, where do you take material out of a Cast piston to try and equal the piston weights with each other?
Knowledge is Power ..
question two: if you need to balance the piston weights more closely, where do you take material out of a Cast piston to try and equal the piston weights with each other?
Knowledge is Power ..
Stellar HDF Member
Joined: Apr 2016
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From: Masshole
Pretty big difference, that's almost 3 cubic centimeters of material! I don't see anywhere you could shave that much off of. I would contact the manufacturer and get a replacement for the one that's out of their spec.
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Stellar HDF Member
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From: WI
Agreed. However, according to Surdyke Harley, The piston falls within specs and they wont take it back and give me another one. The Screamin eagle big bore kit I received is not what they are cracked up to be. It seems that screaming eagle Harley Quality Control absolutely just sucks. Still waiting for a response from Surdyke harley its been two weeks, theyre waiting from the mother company for an answer. However, before I started conversing with them, they said the piston fell within specs, yet, when I pressed the issue they said they were waiting for an answer from the mother company. Confused! Is it Inspec or not? Upfront they seem to know the answer, but, when the issue was pressed now theyre waiting for an answer from the mother company. Confused once again. This is the last time I will buy Harley Davidson parts for a motor. Their quality control just sucks
Seasoned HDF Member
Joined: Jun 2017
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From: Granville New York
You should have went with suburban hd...they have a pretty decent speed department. I'm no expert but I wouldn't run them either. 7 grams seems like alot to have to take off but makes you wonder how many kits are out there racking up miles with pistons just like that. Im sure the hd tech isn't weighing parts before they throw them together. My se 117 pistons were a gram different and I took some off the sides of pin housing underneath it. I figured they get machined for connecting rods with a full top a the time so a gram more wouldn't hurt...knock on wood 6k so far this season.
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Stellar HDF Member
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From: WI
I did go to suburban Speed shop. They put the cylinders in torque plates, and had to hone the cylinders a little bit to correctly fit the cast Screamin eagle pistons.
If I ever build another topend again, I will be going with suburban speed shop. They use their proprietary Mahle piston design just for them. Between the piston set and having them bore your cylinders, its about the same price as buying a screaming eagle big bore kit and not having to go through all the damn headaches.
If I ever build another topend again, I will be going with suburban speed shop. They use their proprietary Mahle piston design just for them. Between the piston set and having them bore your cylinders, its about the same price as buying a screaming eagle big bore kit and not having to go through all the damn headaches.
Road Master
Joined: Mar 2013
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From: Central Ohio
Closer inspection of the piston would be nice, potentially some excess casting flash on the underside of the crown.
If you don't think there's enough material available for removal on the piston, you'll have to work on the pins... But how much this really matters when they share a common crank pin is up for debate. I for one would try to match them
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HDF Community Team
Joined: Jun 2006
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From: san antonio
I have dealt with crank balance as it is affected by piston weights on a couple of occassions, not the same as the OP with two pistons of different weights and found John Dahmer at Darkhorse a dependable source of information on how best to solve the problem. It would be interesting to hear what John would do faced with this situation. If equalizing piston weight is required, John would know best if 7.5g is a challenge to remove and, if not, where best to remove the material. John is busy, of course, but has always taken the time to talk on the phone and answer my emails.
3ccs does sound like a lot but that is .183 cu. in. Still a challenge but opening up the valve reliefs and attacking the other spots referenced in previous posts might work.
Not sure how to attack the pin.
3ccs does sound like a lot but that is .183 cu. in. Still a challenge but opening up the valve reliefs and attacking the other spots referenced in previous posts might work.
Not sure how to attack the pin.Last edited by djl; Jul 31, 2022 at 02:09 PM.
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Thread Starter
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Stellar HDF Member
Joined: Jun 2018
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From: WI
I think I safely removed enough material from both sides of the pin boss and the underside of the piston. Got them identical at 326.3 g each. Only thing left to do is throw it together and find out.
Knowledge is power…….
It really is a crying shame
that Harley Davidson‘s quality control
I find lacking,,,,,,,,
Knowledge is power…….
It really is a crying shame
that Harley Davidson‘s quality control
I find lacking,,,,,,,,
Last edited by Harley1004; Jul 31, 2022 at 07:02 PM.
Seasoned HDF Member
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From: poway
Are the rod end weights matched. Rear is typically heavier, which piston did you remove weight from?
Add,
Heck the the pistons are the same fitment. Put the heavy one on the front..
Add,
Heck the the pistons are the same fitment. Put the heavy one on the front..
Last edited by Max Headflow; Aug 1, 2022 at 12:34 PM.
