Topic: Lighter Pistons

[kpier883]

I have a basic question and I hope some of the engine builders can answer.

If I use a piston that is lighter than the OEM piston, lets say by 10%, does anything else in the engine have to be adjusted or lightened in order to keep the engine balanced?

Can I run higher rpm (assuming the valve train is up to it) since the forces to start and stop the piston would be lower?

Inquiring minds want to know...

[jkotsi]

Good question.  IMHO, I don't think you have to do anything further to the engine, but once you start $$$ decide where you stop.

Knife edge the crank, I have seen lightened rods, don't know if I would try it on OEM rods, lighten rocker arms, alum/titanium valve retainer, lighter rotor.

The engine will spin up quicker but I don't know that you will see any HP gain.


How much weight can be dropped from stock pistons?

Jim

[kpier883]

Well, actually I haven't weighed the pistons yet.  And in this particular case the bike in question is a KZ, not a sohc.  But I figure this question is pretty general and would apply to either one - Honda or Kawasaki.  And I trust the knowledge on this board to have a better answer than most other resources.

The pistons in question came from a 90's era Zephyr 1100 and i wanted to use them in an old KZ 1000 if possible.  I noticed the newer Zeph piston has smaller skirts and other features that indicate it might be lighter.  

Newer piston on right, older on left.  Piston on the left yields 998 cc while piston on the right would yield 1120 cc.  The Zeph was more oversquare and thus had a larger piston.

[kpier883]

bump.  Still interested in people's thoughts on lighter pistons.  Do they throw off the engine's balance?

[MRieck]

bump.  Still interested in people's thoughts on lighter pistons.  Do they throw off the engine's balance?

You will be fine using lighter pistons. Lighter is better....look at F1 pistons. You can run into problems using pistons a lot heavier than stock.

[kpier883]

Thanks Mike.  Does the lighter piston allow higher RPM if the valve train is capable?

[MRieck]

Thanks Mike.  Does the lighter piston allow higher RPM if the valve train is capable?

Yes. Absolutely

[Big Jay]

Inline four cylinder cranks ( Yamaha cross plane excluded ) are self canceling. As long as all the components weigh the same, it is in balance.

Jay ( Master crank balancer  )

[754]

Since I had my scales out today..
 Yodhi Aluminum superrod, with shells, and bolts ....260 gr

stock 736cc piston, C/W  ringset, pin,  &1 clip, ..
219.9 gr

MTC 970cc forged piston with tapered pin, rings, 2 buttons.. 273.3 gr

Cast 1080 piston with ringset, 1 pin, 1 clip....
295.8 GR

 Have NOS Wiseco 836 and Arais 970cc here , will add weights later..

[jkotsi]

Is it possible to lighten stock 550 pistons?  How many grams and where?

[Rod]

Is it possible to lighten stock 550 pistons?  How many grams and where?

I've been wondering the same, there seems to be plenty of skirt material that might be removed.

[CB500Four]

Is it possible to lighten stock 550 pistons?  How many grams and where?

Hi!

In my opinion and also experience it´s possible.
In my thread http://forums.sohc4.net/index.php?topic=63938.25 i gave an example for
mods on a CB750 DOHC piston. In a similar way you can do it on a CB550 piston.
I estimate you can lighten the piston in a range of 15g-20g, perhaps 25g if you taper
the wrist pin a little bit.


Regards,

[bwaller]

550 piston/rings/clips & pin = 173.7g  The pin alone is 36g.

To remove 20 grams would be a light combination.

[kos]

Here is a little secret....If you don't have desire to go "bigger" with your CB750 SOHC engine. Use the die cast Honda CB750 F2 pistons. they have a nice dome on them and in smaller cc, non F2 heads have a nice compression ratio.  Go 4th over (762cc) and you have a nice combination.   You will need to know a machinist as you will need to cut or "mill in" some larger valve pockets. I have specs here, if needed. Nothing lighter than OEM die cast Honda pistons!

BTW....762cc engines in our M3 CR750 racers went 155.556 MPH, hold Daytona Classic track record at 2:06 and won Daytona 6 times F750 class.

KOS

[bwaller]

It's a good option I'm planning Mark. One problem is finding rings for those 410's.

[voxonda]

Here is a little secret....If you don't have desire to go "bigger" with your CB750 SOHC engine. Use the die cast Honda CB750 F2 pistons. they have a nice dome on them and in smaller cc, non F2 heads have a nice compression ratio.  Go 4th over (762cc) and you have a nice combination.   You will need to know a machinist as you will need to cut or "mill in" some larger valve pockets. I have specs here, if needed. Nothing lighter than OEM die cast Honda pistons!

BTW....762cc engines in our M3 CR750 racers went 155.556 MPH, hold Daytona Classic track record at 2:06 and won Daytona 6 times F750 class.

KOS

Send you a PM, Mark.

[turboguzzi]

Is it possible to lighten stock 550 pistons?  How many grams and where?

I run a season and half with shortened 500/56.5mm stock pistons, simply shortened them on a lathe, no problems.

Can weight them if you really want to know though 550's should be heavier.

tg

[jkotsi]

TG, Do you remember how much did you shorten the stock pistons?

Jim

[turboguzzi]

there should be a picture of three different pistons i've used so far in a thread,

i basically cut the skirt till the I eliminated all the bottom arched cut, very close to the internal flat machined surface,

let me see if i find the pic,

[turboguzzi]

TG, Do you remember how much did you shorten the stock pistons?

Jim

Found it jim, the psiton on the right is the stock machined one

http://forums.sohc4.net/index.php?topic=55162.0