Piston question

[K-Dub]

Ok Im getting ready to do a top end on my 04 R. Im thinking I want to raise the comp to 12 to 1. But have read that the aftermarket high comp pistons wiegh less than the stock piston and messes up the harmonic balance of this engine. Which hurts the crank and crank bearings, if Im understanding this correctly. I have read in another thread that the Wiseco piston wieghs more than a JE, now does the Wiseco wiegh the same or closer to the stock piston, or an I not understanding this whole harmonic balancing thing between the piston and the crank?

Also do I need to change the cam evertime I do a top end? I have the shop manuel and it gives the wear limits for the stock cam but not the HRC cam.
This is my first 4 stroke rebuild, been riding and rebuilding 2 strokes for 22 years.

[370kingR]

Ill hit you up on this K-Dub....

Anytime you can lighten the piston and or piston connecting rod, you will do your crank bearings (main and rod) a HUGE favor.....period.

Your not going to gain power, your just going to gain longevity on the parts responsible for keeping the crankshaft rotating smooth.

No harmonic balance issues...none of that...total nonesense who ever told you that.

The lighter the piston the better, that is without compromising its structure. For example, you would'nt risk lightening the piston around the wrist pin bosses too much because it would likley cause it to fracture in that area.

The manufacturers know their limits of where and how much material can be removed.

Think of the force of a piston traveling in one direction, then it has to stop all that momentum and start it up again in the opposite direction and vise versa. The more weight, the more it will want to keep going in that direction, thus making it jerk the bearings around.

People talk about removing weight from the counter balancer but in the end, its not being done by anyone i know to compansate for weight, stroke, big bore.....

IME, Wiseco's have weighed the most and CP's have weighed the least. CP pistons have alot more inovative stuff you can build into them. Not that Wiseco or JE doesnt have the means to do what CP does, its just CP offers more.

Hope that helps a little.

[GPracer2500]

I think the best of both worlds would be the lightest piston possible AND a dynamically balanced, blueprinted engine.

Various crank service companies can dynamically balance a crankshaft for the reciprocating weight. A full blueprint would require the skill of a builder/machinest. I don't think either step would be necessary for acceptably smooth running engine though.



AFAIK, the way it works is the crankshaft weights balance out the (vertical) movement of the piston. But in doing so, the side to side movements of crankshaft create another imbalance (horizontal). That's where the counterbalancer comes in--it balances out the movement of the crank that is 90 degrees from the up/down movement of the piston.

[K-Dub]

Ok thanks for the help. I read about the aftermarket pistons messing up the harmonic balancing on here, I believe in the sticky about crank bearings. (not 100% sure though it was on this site) I thought that the less rotating mass the better but after reading what I did I dont want to mess up my crank. But let me make sure I got this straight. If I go aftermarket piston that is lighter it should not hurt the crank, but help take some jerkyness from it.

Ok also how much life will I lose off the life of the engine if I go to a 12:1 piston in your opinion? And who makes a good piston for the money? Not going to race this R just want a little more go power, at my wieght I could use a little more in tight spots. I rode a friends that was all stock except the piston and it was a 12.5:1 and it was way more snappy off bottom.
Who is CP?

[chad502ex]

anytime you install an aftermarket piston pack on a crankshaft that was spec'd by HONDA for a stock recipicating weight,..

you aught to consider the harmonics generated from the imbalance from OEM..

In other words, if the ultra-light piston you installed on a stock crankcraft is not re-balanced in x and y axis using bob weights, then you stand a better chance of increasing the amplitude of the harmonics generated by the imbalance. Those forces are what destroy crankshaft radial bearings.

The lighter the new piston pack is away from the stock piston pack originally 'balanced' for, the greater the amplitude of the harmonics the new piston will cause.

There is an acceptable piston assembly weight range the new piston pack can deviate from stock piston weight, I am not to say, but again, the lighter the new piston from stock, the greater the deviation, the greater the amplitude, the shorter the life the crank bearing have with the increase in harmonic amplitude....


Here's my advice: want a new piston, install it and have fun,.... If you are upgrading the bottom end somehow by splitting the cases,... rebalance the crankshaft to the exact weight of the piston assembly for a smoother rev.. Trust me it is smoother rev you can feel in the footpegs.

Hope this helps clarify.

[K-Dub]

Ok going by what Chad said does any aftermarket companies make a piston OEM weight? If not why? If harmonic balancing is a something that needs to be correct why doesnt someone make a high comp piston that wieghs the same as the stock piston so the people that want a little more performance with out spending the extra cash to get the crank and piston rebalanced and having to split the cases. If the OEM piston wieghs more than the aftermarket pistons then it should be easier to make a heavier piston without as much enginering to get the strength from the lighter wieght.

[chad502ex]

Originally posted by K-Dub
Ok going by what Chad said does any aftermarket companies make a piston OEM weight? If not why? If harmonic balancing is a something that needs to be correct why doesnt someone make a high comp piston that wieghs the same as the stock piston so the people that want a little more performance with out spending the extra cash to get the crank and piston rebalanced and having to split the cases. If the OEM piston wieghs more than the aftermarket pistons then it should be easier to make a heavier piston without as much enginering to get the strength from the lighter wieght.

most manufactures make lighter pistons because many think that lighter is better.. Is a lighter Titanium valve better than steel? If you concerns are for longevity, then your answer will be 'steel'. Same thing with a lighter piston,.. sure it may rev and feel faster, but it just depends on what you define is better. A lighter piston is preferred, especially if the lighter piston has more squish, more static compression, but if the 'lighter' piston to too light, then there is no way i would install before I rebalanced the crankshaft..

The opposite is true too. If the new piston is heavier than stock, the amplitude of the harmonics grow as the weight difference grows away from the balanced OEM recipicating weight. But who wants a heavier piston? LOL!

[K-Dub]

I think you missunderstood a little, I wasnt meaning heavier than stock, just the same weight as stock. Now I realalize if I was building a national motor I would want a light piston with the engine rebalanced and blue printed. Im not racing but would like a little more power with out sacrificing my reliability, so to me I need a high comp piston that real close to the same weight as stock. Now if I weigh my stock piston and then called the piston companys and asked the weight of thier pistons would I get laughed at?

[chad502ex]

Originally posted by K-Dub
I think you missunderstood a little, I wasnt meaning heavier than stock, just the same weight as stock. Now I realalize if I was building a national motor I would want a light piston with the engine rebalanced and blue printed. Im not racing but would like a little more power with out sacrificing my reliability, so to me I need a high comp piston that real close to the same weight as stock. Now if I weigh my stock piston and then called the piston companys and asked the weight of thier pistons would I get laughed at?

most engine builders who sell pistons have no problem of providing weights of the piston packs for this very reason, at least the ones I've dealt with over time..

good luck.

[czrider263]

What if its a DRG piston and is really light???:D :D :cool:

[chad502ex]

Originally posted by czrider263
What if its a DRG piston and is really light???:D :D :cool:

hopefully, the DRG piston will be everything we want in our piston... :)

[GPracer2500]

Originally posted by K-Dub
...Now if I weigh my stock piston and then called the piston companys and asked the weight of thier pistons would I get laughed at?

Absolutely not! Asking for piston weights is a completely legit question.

[K-Dub]

Does anyone know the weight of the stock piston?

Thanks for all the input guys! I learn alot from this site, they should teach this stuff in high school instead of english and speech.

[370kingR]

Originally posted by K-Dub
Does anyone know the weight of the stock piston?

Thanks for all the input guys! I learn alot from this site, they should teach this stuff in high school instead of english and speech.

Its like around 450 grams or so with the wrist pin and rings for the 04/05 i believe. I could go measure one but im too lazy :o

Venom CP pistons are 365 g's