Setting compression after CC'ing heads.

[Buglet]

  When you check the weight 100 %. You should check the pistons complete with all the rings, wrist pin and clips.   

[billbuilds]

      Somehow I thought that the number on the CP spec sheet was that for the bare piston so that's why I removed the rings and wrist pin. I really don't have an accurate gram scale for anything over 300. I have an 11lb spring scale and it looks like these bare stock 88" TC pistons weight about 415 grams. Adding on thw wrist pin and the rings they look to weight about 655 grams.

[Ohio HD]

Bill, the weight shown on the CP spec sheet is piston weight only. You do need to weigh the rings, wrist pin, and rails if included. Anything that mounts to the piston is needed x 2 to balance the crank assembly.

Someone on this site has to have weighted these 98" CP pistons with rings and pin before. Maybe someone will post. Or maybe someone local to you cab weigh them.

[billbuilds]

Bill, the weight shown on the CP spec sheet is piston weight only. You do need to weigh the rings, wrist pin, and rails if included. Anything that mounts to the piston is needed x 2 to balance the crank assembly.

Someone on this site has to have weighted these 98" CP pistons with rings and pin before. Maybe someone will post. Or maybe someone local to you cab weigh them.

     Thanks Brian, I see what you mean now, really do need totals since pin weight can vary as I've learned from HD Street Performance. The pistons are enroute to Fuel Moto. Pins and rings are still here so maybe I can weigh them on my 300 gram scale and add that figure to the piston weight. I will need to pick up a couple of 2032's later today.

[Ohio HD]

Bill, I can't speak to all piston manufactures in regards to wrist pin changes in weight. The CP Bullet series pistons that I've been using for 117" and 124" motors, this is not the case. The wrist pins always weigh the same. Example is below.


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As expected the pistons with a higher (thicker) dome weight more. The wrist pains always weigh the same. I would expect the same with the 98" CP bullet series pistons.

CP would need a lot of wrist pin part numbers (different size / weights) to cover all of the options a customer might want with a given piston bore size.

[Don D]

Brian, weights still are missing rings and clips, which are fixed across all the pistons of course. Then I assume from your other posts the cranks are balanced for the exact weight of your parts.

For reference to achieve the factories intended balance the gross piston weights must be 1200 grams piston reciprocating weight for the early twin cam engines. Guys juggle piston weights and don't seem to notice the "sweet spot" so to speak actually the balance factor is changing unless they change things pretty radically. The shops that balance the flywheels get gross weight of the pistons and actually correct the balance based on their decided balance factor which varies between shops.

[Ohio HD]

Yes the rings and wrist pin retaining rings are missing because they are the same weights. These pistons I indeed used with custom built crankshafts and balanced with weights of the piston assemblies in mind. I would not use these 4.125" CP pistons with an off the shelf S&S crank unless I were to have the crank rebalanced. For that matter or an OEM HD 4.375 crank in regards to a 117" motor without rebalancing.

My only point to Bill is the four pistons CP offers for the 98" motor most likely has the same wrist pin. I'm trying to keep the info relevant to what he is working with.

[billbuilds]

     The most accurate scale I was able to use today to weigh my stock 88" piston rings, pin and clips only went to the tenth of an ounce and no switch for gram weight. The 1 pound 4.9 ounces it read equals around 593 grams. Seeing as a tench of an ounce is 2.83 grams there's sure room for the actual figure to be closer to the 600 grams that HD Street Performance mentoned as being required for the early TC cranks.
     The 300 gram scale that I have shows down to tenths of a gram. The CP pin alone weighs 106.9 gramss. Add the two clips and full ring set I and I get 138 grams even. With the piston weighing 421 grams that's a total of 559 grams. So there's 80 grams of reciprocating weight less With thr forged CP's over the stock cast pistons. I can see where this would change the balance some but how much I've no clue. Thanks, Bill

[Don D]

So you will drop another 50 grams or so with a dome cut. A little lighter piston won't change the factor percentage significantly. The cranks are balanced with a higher percentage to achieve low rpm smoothness and a lower percentage to achieve smoothness at a higher rpm. If I understand this correctly installing a lighter piston will increase the balance factor percentage. How much and how significant or important a certain number grams equals a certain number increase of the balance factor and what the rpm the "sweet spot" changes to I do not know.
S&S does follow the stock scheme and weights. They used to balance flywheels to weights the customer specified but then lean manufacturing took over.

[Ohio HD]

Bill, rather than clog up your post with all of this flywheel balance estimation I started a new post in regards to that in General. Sorry for clogging up the post.

Crankshaft Balancing


I "think" the piston weight changes moves a 60% crank balance to 64%.

I think it's a good idea to weigh the pistons that came from the motor and compare them to the new CP values. Then you can see what if any differences there may be.

[billbuilds]

     Thanks Brian. I could well have misinterpreted the spec sheet concerning the weight of these pistons. I'll continue over in general. Bill 

[Don D]

CP pin is 927-2250-15CP1C, see if 927-2250-20CP1C will make up the weight. Might be the simple solution.

[billbuilds]

CP pin is 927-2250-15CP1C, see if 927-2250-20CP1C will make up the weight. Might be the simple solution.

     That would sure be cool. Thanks

[billbuilds]

     I just called CP and was told that the .015 wall thickness wrist pin is 106 grams and the .020 wall thickness wrist pin is 131 grams. Will that be enough?

[Don D]

We are talking .15 vs .2 wall. You are taking off about 54 grams piston weight and adding 50 grams back pin weight. I would move forward. 

[billbuilds]

We are talking .15 vs .2 wall. You are taking off about 54 grams piston weight and adding 50 grams back pin weight. I would move forward. 

    Ya, I goofed on typing the wall thicknesses, doh!


Sounds real good. Your help is greatly appreciated. 

[Admiral Akbar]

I'm a little confused here.   

Early 88 ci TCs had about a 600 gram for 1 piston assy. balance factor.  OP has pistons that are 559 grams that need 10ccs cut off so they loose 27 grams. The new pin adds 25 so the piston assy weights 557.  Isn't the balance factor still off by 43 grams?

Don seems to mention that the balance factor for 88 ci TCs changed when HD went to cold forged cranks which is mid to late 2004 models.  Didn't it really change in 2007 when HD went to the 4 3/8 stroke?

[Ohio HD]

Bill, I agree with what Max has above. I placed some additional info in the balance post in General.

The .250 wall pins should get you really close. But I recommend weighing the OEM parts, just to see what they are.

[Admiral Akbar]

I have a set of early Wiseco 10.5 95 ci pistons that came out of my 02 RK and weighed them.. They weigh 554 grams. Ran them for 60K miles without issue. Motor wasn't balanced to the pistons. Did not seem to vibrate too bad.  IIRC it still had the original from motor mount when I sold it at 80K.   

Did the same thing for my 2000 fxdx. It did seem to vibrate a little more but then different motor mounts and weight.

If I crank out the numbers the piston change works out to 54.6% balance factor the Wiescos.

I guess it's really how anal you want to get.

I'm doing an all bore 107 for the DX and the piston assys weight 540.  I rebalanced since the crank was out of the cases.

[djl]

Seems the OP is on a path but I thought I would share my experience with piston weights and how the affect crank balance.  It has been years since I built an all bore 107 motor with an Axtell "Mountain Motor Kit". The cylinders would not hold a true bore and after a .010" overbore and new pistons at my expense, Axtell offered no help.  The final solution was a set of MTC cylinders/pistons. After assembling, the motor vibrated so bad it was unrideable. It finally dawned on me that the MTC pistons (weight) might be the problem.  So, I pulled the top end down and compared the MTC piston assy weight to the JE piston assy weight (crank was Hoban Brothers balanced to the JE pistons).  The MTC pistons were about 15% lighter than the JE pistons; problem found.  I called John Dahmer and he pointed out that anything more than 10% +/- weight differntial in piston assy weight would affect crank balance; balance being more sensitive to lighter than heavier.  I checked the .010" JE pistons and they were in spec so I intalled them with new rings; problem solved; quiet, smooth running motor.

Fast forward to two years back when I decided to rebuild the 95" motor in my Deuce to 98" which required new CP pistons with a 6cc dome.  I weighed the SE cast flat top 95" piston, rings, pin and locks and that assembly weighd in at 593.5g.  The scale I used was Mike Lozano's (Lozano's Brothers Porting) digital scale he uses for that purpose in his shop; very accurate.  The CP piston, rings, .150" wall pin and locks weighed in at 554.5g which was about 8% lighter but not close enough for me.  I called CP and orderd a .230" wall pin which put the CP piston assy weight at 599.5g; good to go.

I can't find all my notes from that build but I did find the CP .230" wall pin PN 927-2250-23CP3C which is different from the PN Don previoulsy posted 927-2250-15CP1C.  The difference is the wall thickness and the material. The PN Don posted is for a chrome moly 5100 pin (1C)and the pin (3C) I used is made of 9310 steel. I don't know if chrome moly is lighter than 9310 steel but the .230" wall pin I used added 45g to the CP piston assy weight.  I wish I could find my notes wherein I had recorded the indivivual weights of the piston, rings, pin and locks but I can't.

This doesn't add much to what has already been posted but I thought there might be something of interest to others reading the thread.

[Ohio HD]

It's very good real information. I can see where John said that a little heavier wasn't as bad as lighter. Good folks at DH for sure, that know what they're doing.

[billbuilds]

     djl,
     Thanks for posting your piston and pin balance experience. I found that .230 wall pin p/n in the CP catalog but it does not list the weight. I know that the .5 wall pins that came with the pistons are 106 grams. I found some on the Summit Racing website with a .250 wall thickness made of H-13 tool steel. They're p/n H9272250250C and they weigh 153 grams. I was thinking of going with them but maybe I'll check with CP to get a weight on their 927-2250-23CP3C first. Bill 

     Edit: just called CP and was told that the 927-2250-23CP3C pins are 144 grams. I really need to go with the 153 grams pins.