collapse

www.cognitomoto.com

www.dimecitycycles.com

https://www.townmoto.com/collections/vanson-leathers


www.restocycle.com

www.CITYLIMITMOTO.com

www.jadusmotorcycleparts.com

www.bisonmotorsports.com

www.speedmotoco.com

www.lostapostlejewelry.com

www.sparckmoto.com

www.pistonsociety.com

www.steeltowngarage.com


Author Topic: saving a 1980 KZ750 twin  (Read 69553 times)

Offline Nebr_Rex

  • DTT SUPPORTER
  • *
  • Posts: 875
Re: saving a 1980 KZ750 twin
« Reply #520 on: Dec 02, 2018, 20:16:08 »
looks like the exhaust is set at 110 BTDC from the factory. but since my head was decked i will have to check it.

Bingo!


.

Offline doc_rot

  • DTT BOTM WINNER
  • *
  • DTT SUPPORTER
  • *
  • Posts: 1169
  • Oh the usual... I bowl, I drive around...
Re: saving a 1980 KZ750 twin
« Reply #521 on: Dec 10, 2018, 04:41:16 »
I had a chance to degrees the cams. When I set the intake to 110* lobe center I'm showing that its "closing" at 42* ABC @0 .050"
using the calculator i found  that puts me at 8.933/1 which i believe is too high. To get me under 8.5 i need to retard it 7 degrees further putting the lobe center at 117ATC 
this will change the lobe separation from 110 to 113.5.

 does this seem correct?
« Last Edit: Dec 10, 2018, 05:02:10 by doc_rot »

Offline teazer

  • DTT SUPPORTER
  • *
  • DTT BOTM WINNER
  • *
  • Posts: 8821
Re: saving a 1980 KZ750 twin
« Reply #522 on: Dec 10, 2018, 11:18:15 »
I would set the cams where you want them to be for valve timing events.  Don't change cam timing to achieve a preconceived CR number.  What is the static CR and are you OK with that number?  If so, you are good to go at 108-110 degrees. 

Later inlet valve events will in theory allow the motor to peak at higher revs but that's not really what you are trying to achieve with this motor.  You want as much low end compression as practical to get more low speed torque.


Offline Nebr_Rex

  • DTT SUPPORTER
  • *
  • Posts: 875
Re: saving a 1980 KZ750 twin
« Reply #523 on: Dec 10, 2018, 22:03:08 »
What is your cranking compression?
While knowing what your dynamic compression is nice to know.
I am more old school and prefer a compression gauge.
How do people come up with these dynamic compression ratio limits?
There are different combustion chambers, ignition systems, grades and blends of fuel.
I have a 10.1/1 cr V8 that pumps 185 p.s.i. and a 464cc KZ440 with 10.2/1 that pumps 195p.s.i.
and they both run fine on 91 octain.


.

Offline doc_rot

  • DTT BOTM WINNER
  • *
  • DTT SUPPORTER
  • *
  • Posts: 1169
  • Oh the usual... I bowl, I drive around...
Re: saving a 1980 KZ750 twin
« Reply #524 on: Dec 11, 2018, 01:29:51 »
hmm it never occurred to me to try cranking it to see what compression it was making on the bench. I will have to finish fixing up my starter clutch.

Offline doc_rot

  • DTT BOTM WINNER
  • *
  • DTT SUPPORTER
  • *
  • Posts: 1169
  • Oh the usual... I bowl, I drive around...
Re: saving a 1980 KZ750 twin
« Reply #525 on: Jan 13, 2019, 19:07:17 »
Some info of interest to KZ750 twin owners. guy used Ducati 750 2 valve pistons (88mm) for 948cc twin

https://translate.google.com/translate?sl=auto&tl=en&u=www.z750twin.de%2FManfreds_LTD.htm

Offline Nebr_Rex

  • DTT SUPPORTER
  • *
  • Posts: 875
Re: saving a 1980 KZ750 twin
« Reply #526 on: Jan 13, 2019, 19:19:33 »
not bad 84 h.p. and 72 ft.lbs.  .




Edited; spelling

.
« Last Edit: Jan 16, 2019, 20:42:44 by Nebr_Rex »

Offline datadavid

  • Posts: 1411
Re: saving a 1980 KZ750 twin
« Reply #527 on: Jan 16, 2019, 06:24:04 »
I Hope you are aware that with a piston stop you need to note where the piston stops when rotating both cw an ccw, then you have true tdc exactly in between your markings.
I dremeled out the valve pockets and there is plenty of room now. I also cut the tach gear off an extra exhaust cam so I can use that cam on the intake.

intake base circle is 33.1mm with 8.1mm lift the exhaust has a 32.3 base and 9.84mm lift

my stock intake cam was shimmed at the very end of the shim range at 340. once i put in the exhaust cam i needed another .4 mm to make up the difference so I had to disassemble the head to put in some different vavles to get me in the shim range. I had the new valve faces ground and lapped them before reassembly. I realized i never took an photos the port and polish my buddy helped me with. We didn't go too crazy, just removed the casting flash and smoothed out the ridge where the valve seats were cut.

I measured the stock intake lobe center and found it to be at 79.5 BBDC, the manual states it is 80 BBDC. I plan on timing the exhaust cam on the intake the same as stock.

Interesting to note that the TDC mark on the advancer was 2 degrees off actual TDC which I found with a piston stop.

Offline doc_rot

  • DTT BOTM WINNER
  • *
  • DTT SUPPORTER
  • *
  • Posts: 1169
  • Oh the usual... I bowl, I drive around...
Re: saving a 1980 KZ750 twin
« Reply #528 on: Jan 16, 2019, 06:30:07 »
.