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Old 02-14-2008, 12:19 AM   #1 (permalink)
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103 cid pistons

I ran into a problem with my parts choice on my build. I have my engine cases back together with my stroker Jim's' SE crank, I had bought a set of 103 SE cast pistons 21966-07 and have a set of big bore cylinders to match. I assumed the 07 pistons were the right dimensions pin to deck and to bottom of skirt. I overlooked the width of the rod. The 07 crank has a narrower small end rod. The only SE Pistons for the earlier engines seem to be forged which I have a set but mine are .010 over which means boring another set of jugs, or just wondering about opening the piston pin boss up to accept the wide rod? I have a mill but is this a bad idea? I also have a gram scale to match the weight of the pistons to each other.
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Old 02-14-2008, 05:41 AM   #2 (permalink)
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Piston mods

I can't think of any reason that would not be an acceptable procedure.
Make sure the vise(assuming you are using a piston fixture) is indicated in square, and make sure the wrist pin bosses are parallel to that. Find the center of the piston, zero out, and gently with a 1/2" ball-end cutter,take even amounts on material from each side. Gently, slowly, take your time, measure, use good common sense, and you can do it.
As far as a balance factor getting out of whack, the amount on aluminum you will remove, will only be a few grams. No harm.
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Old 02-14-2008, 07:06 AM   #3 (permalink)
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I ran into a problem with my parts choice on my build. I have my engine cases back together with my stroker Jim's' SE crank, I had bought a set of 103 SE cast pistons 21966-07 and have a set of big bore cylinders to match. I assumed the 07 pistons were the right dimensions pin to deck and to bottom of skirt. I overlooked the width of the rod. The 07 crank has a narrower small end rod. The only SE Pistons for the earlier engines seem to be forged which I have a set but mine are .010 over which means boring another set of jugs, or just wondering about opening the piston pin boss up to accept the wide rod? I have a mill but is this a bad idea? I also have a gram scale to match the weight of the pistons to each other.
The whole idea of that design (tapered rod end and piston matched to the rod) was to lighten the reciprocating weight. The rod end is lighter and it allowed more surface for the pin in the piston so they took advantage of that and made the pin much shorter than earlier piston pins. This made the piston lighter too....I said that to say this, if you mill the taper out of the pin boss you are making the piston weak in that pin area. Since Harley shortened the pin the pin to piston surface was reduced and if you reduce it more by milling out the taper how weak is that piston getting. I know Harley says you can use a earlier piston with the new style rod but I would be careful going the other way.
The rest of the changes to the 07 and later rods (beside the lighter rod end and Piston pin) is....the crank pin side of the rod was made larger and heavier, this allowed Harley to make the balance weights MUCH smaller and lighter in the ''B'' motor. Less weight in the Balancers lets rpm rev faster and less stress on the balance drive train and less chance the balancers will come out of harmonics.
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Old 02-14-2008, 09:43 AM   #4 (permalink)
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In a earlier post I was advised not to use forged pistons for a street machine (warm up time issues ) I have not been successful in finding part numbers for cast pistons that will fit the pre 07 103 config. Any links to who might?
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Old 02-14-2008, 10:41 AM   #5 (permalink)
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In a earlier post I was advised not to use forged pistons for a street machine (warm up time issues ) I have not been successful in finding part numbers for cast pistons that will fit the pre 07 103 config. Any links to who might?
Thats a good one..... Forged pistons are just over kill if your compression is low, your not exceeding 6200 rpms, and they are spendy....warm up time issues...BULL !!!
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Old 02-14-2008, 12:10 PM   #6 (permalink)
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I am not trying to be funny just trying to do this build right. I have looked for Keith Black cast pistons and have not found any reference to 103 s. And your point on weakening the piston by modifying the pin boss was also my concern. So since I have a set of oversized forged flat top pistons I will just bore out another set of jugs. Any recommendations on clearances.
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Old 02-14-2008, 02:42 PM   #7 (permalink)
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I am not trying to be funny just trying to do this build right. I have looked for Keith Black cast pistons and have not found any reference to 103 s. And your point on weakening the piston by modifying the pin boss was also my concern. So since I have a set of oversized forged flat top pistons I will just bore out another set of jugs. Any recommendations on clearances.
The clearances vary with the metal used, the best advice there would be call Keith Black if you use his pistons. If I remember correctly they run very close tolerances like under a .001. Wiesco uses .0020~.0025, Harley uses .002, etc.

I wasn't making fun of you, sorry you don't have a sense of humor when it comes to some of the advice thrown around on this forum by one time engine builders......I find it extremely funny and even entertaining at times.
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Old 02-14-2008, 04:35 PM   #8 (permalink)
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The clearances vary with the metal used, the best advice there would be call Keith Black if you use his pistons. If I remember correctly they run very close tolerances like under a .001. Wiesco uses .0020~.0025, Harley uses .002, etc.

I wasn't making fun of you, sorry you don't have a sense of humor when it comes to some of the advice thrown around on this forum by one time engine builders......I find it extremely funny and even entertaining at times.
Hi Doc,
What are your thoughts on the warm up issue? Not needed? Needed? Needed to a certain temp...etc. I too have heard (here) that warm up was necessary when using forged pistons.

Thanks,
NC
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Old 02-14-2008, 05:39 PM   #9 (permalink)
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Warmup should be a part of standard procedure before high rpm operation of ANY internal combustion engine no matter what type of pistons they have.
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Old 02-14-2008, 05:48 PM   #10 (permalink)
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Warmup should be a part of standard procedure before high rpm operation of ANY internal combustion engine no matter what type of pistons they have.

Sure, but how much? Forge or cast piston differences? etc...
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Old 02-14-2008, 06:40 PM   #11 (permalink)
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Sure, but how much? Forge or cast piston differences? etc...
Like Bob said it's important to warm up any motor before whacking the throttle, not so much for the pistons but expansion for the whole motor. The piston gets the heat first so it starts to expand first, then the cylinders start to grow, and the heads start to get soaked with heat. If you put your hand near the cylinder and feel heat your good to go down the road, when the engine reaches operating temps of 200* to 230* it's good to womp on then. Whether you have forged pistons or cast pistons it doesn't matter this warm-up process is necessary or your going to shorten the life of your engine.
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Old 02-14-2008, 07:48 PM   #12 (permalink)
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Old 02-14-2008, 09:04 PM   #13 (permalink)
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The pistons I do have are SE 22944-00 forged flat top. I have not at this time been able to find pre 07 103 cast pistons I checked with my local dealers mechanic about cast pistons for this application and he wasn't aware of any. I am sorry I seem thin skined, not at all I enjoy the knowledge found here I just was hoping to learn of some alternatives before leaving for work and returning the 07 cast pistons. I am guessing by the lack of input about cast pistons they may not exist.
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Old 02-17-2008, 02:17 PM   #14 (permalink)
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Don't know if this info is too late or if it will help, but the S.E. 103 stage 1 efi kit for '06 models had cast pistons. Supposed to be an upgrade to match the CVO 103 models. The kit is in the 2007 catalog, page 538, part 29877-06 for 06 EFI Touring models, 29842-04 for '04 & '05 models. Should be able to look up replacement pistons for the kits. This makes me think the '06 CVO 103 models had cast pistons. Should be able to get piston part numbers for a '06 103 CVO. This might not help, they may have changed to the tapered rods on the earlier CVO's but it might be worth checking out
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Old 02-17-2008, 04:47 PM   #15 (permalink)
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Originally Posted by milphillips View Post
Don't know if this info is too late or if it will help, but the S.E. 103 stage 1 efi kit for '06 models had cast pistons. Supposed to be an upgrade to match the CVO 103 models. The kit is in the 2007 catalog, page 538, part 29877-06 for 06 EFI Touring models, 29842-04 for '04 & '05 models. Should be able to look up replacement pistons for the kits. This makes me think the '06 CVO 103 models had cast pistons. Should be able to get piston part numbers for a '06 103 CVO. This might not help, they may have changed to the tapered rods on the earlier CVO's but it might be worth checking out

You are correct, the '06 and earlier CVO 103's had cast flat-top pistons. The part # escapes me, because I had a set of these pistons, but your local dealer should be able to hook you up with the correct part number.
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