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clubhousemotorsports
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« Reply #15 on: June 05, 2016, 04:32:00 PM » |
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I will be riding my 620/750 SS tomorrow at the track. I built it this winter to replace the 97 750 motors that keep cracking cases. It is a simple conversion with off the shelf parts but a few pitfalls and a few things that should be taken care of if you plan to keep it more 620 than 750.
The smaller bore does mean the angle cut on the pistons to heads do not match well. You could either machine the 620 heads or just bolt on a set of 750 heads. I was trying to just get back to 750 at this time so I simply set squish after finding the high points and will re-visit the heads this fall as I have a set of ported 750 heads if I decide I want "more"
I would have the heads re-cut as it should be a easy job for a machinist and then it is done. Cams are higher lift on the 620 but less duration so it may not be much better. I hope to swap to 750 cams just to find out at some point. The stock 750 pistons do NOT have room for any more lift unless you sink the valves in the heads.
You can find 750 heads that will bolt up but keep in mind you are also changing pistons weight which means you may change balance so keep that in mind as well. Sometimes for the better sometimes worse, you could always re-balance and be better than oem.
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koko64
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« Reply #16 on: June 06, 2016, 01:12:01 AM » |
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Interested to see the results of your 620/750 cam comparison down the track.
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2015 Scrambler 800
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clubhousemotorsports
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« Reply #17 on: June 08, 2016, 05:02:05 AM » |
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Me too, I am wondering if the bike will prefer high lift short duration vs low lift long duration. Sort of old school thought vs new.
The balance of the motor with the 750 pistons is not great as the motor is not as smooth as I would like. I would tear it down for a balance job if I did not have plans for different pistons at some point. Maybe I need to build another bike to play with and just balance this one to be my 60hp rain/training bike.
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koko64
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« Reply #18 on: June 08, 2016, 11:10:29 AM » |
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The soft motor rain bike  . Old school Vs new school cam comparison thread would be a beauty.  I have wondered how cams with 750 cam duration and carbed 900V cam lift would work in a hot 750 motor. So reground 750 cams for more lift. Alas I dont know who could grind that down here. I wish I knew who did Vee Two's cams. |
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« Last Edit: June 08, 2016, 11:25:06 AM by koko64 »
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2015 Scrambler 800
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DarkMonster620
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« Reply #19 on: June 08, 2016, 01:40:03 PM » |
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I "heard" someone once say "a 750 with 620 heads is better than a 620 with 750 heads". . . this was referring to EFI models . . . koko, have no idea how the 750 with 900 cams will react
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Carlos I said I was smart, never that I had my shit together Ducati is the pretty girl that can't walk in heels without stumbling. I still love her. "When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." |
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clubhousemotorsports
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« Reply #20 on: June 08, 2016, 01:56:54 PM » |
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If I get my hands on a set of stock 750 heads I will let you know.................. wait I might just have a set.
next up 750 cams in the 620 heads
or
750 stock heads
then
750 heads with 620 cams
750 heads with 900 carby cams
750 heads with 900ie cams
750 ported heads w/ 900 carby cams
620 heads and the 2 sets of 750 heads are different and it is a SS so i have to take the frame off everytime I do a head swap so I am not sure how quickly I will get this done as it is bike season here and I need to get to work.
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ducpainter
The Often Hated
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DILLIGAF
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« Reply #21 on: June 08, 2016, 02:08:07 PM » |
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If I get my hands on a set of stock 750 heads I will let you know.................. wait I might just have a set.
next up 750 cams in the 620 heads
or
750 stock heads
then
750 heads with 620 cams
750 heads with 900 carby cams
750 heads with 900ie cams
750 ported heads w/ 900 carby cams
620 heads and the 2 sets of 750 heads are different and it is a SS so i have to take the frame off everytime I do a head swap so I am not sure how quickly I will get this done as it is bike season here and I need to get to work.
This experiment should only take 4 or 5 seasons.  |
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"Once you accept that a child on the autistic spectrum experiences the world in
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is even more amazing than yours."
To realize the value of nine months:
Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent.”
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DarkMonster620
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« Reply #22 on: June 08, 2016, 02:09:38 PM » |
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cause what I want to do is the 750 FBF 11.1 conversion but keep my 620 heads . . and "some magic tot he bottom end". .. looking for "efficient/dependable" This experiment should only take 4 or 5 seasons.  |
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Carlos I said I was smart, never that I had my shit together Ducati is the pretty girl that can't walk in heels without stumbling. I still love her. "When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." |
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Speeddog
West Valley Flatlander
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« Reply #23 on: June 08, 2016, 03:50:41 PM » |
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~~~SNIP~~~
620 heads and the 2 sets of 750 heads are different and it is a SS so i have to take the frame off everytime I do a head swap so I am not sure how quickly I will get this done as it is bike season here and I need to get to work.
Just swap horizontal heads, and double whatever gains or losses show up on the dyno.  |
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koko64
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« Reply #24 on: June 08, 2016, 04:08:28 PM » |
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2015 Scrambler 800
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clubhousemotorsports
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« Reply #25 on: June 08, 2016, 05:08:29 PM » |
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You know Nick I just might try that, hey the harley 883 racers used to cheat by putting a 1200 piston and cylinder in the rear as tech never checked there. you know the vibrations cannot get worse.
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koko64
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« Reply #26 on: June 08, 2016, 05:10:50 PM » |
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Shifty brilliance that. |
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2015 Scrambler 800
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koko64
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« Reply #27 on: June 09, 2016, 01:48:05 AM » |
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I reckon 750 cams with about 2mm more lift for inlet and exhaust would be interesting.
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2015 Scrambler 800
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Duck-Stew
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« Reply #28 on: June 09, 2016, 07:54:26 AM » |
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I reckon that all 750 cams should be recycled for their steel...
If it were my motor, I'd put a set of 695 heads on it, some 11:1 (or 12:1) pistons in it and ride the piss out of it.
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Bike-less Portuguese immigrant enjoying life.
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koko64
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« Reply #29 on: June 09, 2016, 11:29:05 PM » |
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I wonder if people would feel the same way about these cams if they had about 2mm more lift. Seems to be more wrong with 750 heads than just the cams.
Swapping heads sounds like a great way to go.
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2015 Scrambler 800
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