Author Topic: Need help in choosing pstons  (Read 510 times)

0 Members and 1 Guest are viewing this topic.

Offline per

  • Full Member
  • *
  • Posts: 15
Need help in choosing pstons
« on: August 23, 2020, 06:27:24 am »
Hello all you of great knowledge!

As some of you know I am pretty new to this board and I am giving my cb 550 cafe racer some tlc.
I have a nice cb 650 head, 750 carbs, a couple of cams. I am thinking of staying with 61 mm bore becuase it is less complicated that going 65mm. Now, I am thinking of using cb 750 pistons from a cb 750 F2 wich is suppoed to have a nice dome of some 5mm. Of course they would need some maching to fit and not hit the head. Just flat 61mm pistons would create a very low copression ratio.

Would that be a good  way to get a decent compression ratio? Maybe somone on here has tried that combo?
Dynoman has a set of 11,5:1 61 mm especially for a 550 with 650 heads, but that would cost me twice the asking price Before I got it home, with shipping, sales tax and cutsom fees.

Any info is appreciated.

Cheers...........................Per
"Of course they are faster than me. They are young, fit and fearless, I am old, fat and scared!"

Offline Sano

  • Full Member
  • *
  • Posts: 54
Re: Need help in choosing pstons
« Reply #1 on: November 01, 2020, 06:10:42 pm »
Hi, Consider decking for .032” squish and using regular old cast flat top pistons and a ported head with a cb650r cam.  I am very happy with this set up, inexpensive and straight forward machine work.  I would consider next step to be a more aggressive cam and 1mm larger intake valves.  Included in the top end build would be HD studs and a laminated head gasket for reliability.  Good Luck

Offline per

  • Full Member
  • *
  • Posts: 15
Re: Need help in choosing pstons
« Reply #2 on: November 15, 2020, 11:48:33 am »
Hi Sano
Thanx for your answer but I have decided to go with the Dynoman 11,5 to 1 pistons made for cb 550 motors with 650 head. They are in the mail.
Cheers.......Per
"Of course they are faster than me. They are young, fit and fearless, I am old, fat and scared!"