Author Topic: Oppy 42 ci head: flow optimization / grinding issues  (Read 14976 times)

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Offline Jim Knutson

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #15 on: December 08, 2016, 05:16:25 pm »
Cam timing only affects valve event timing.
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Offline flatlanderfornow

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #16 on: December 08, 2016, 10:45:02 pm »
You have to advance the flywheel to do the ignition timing.  Clean the crank and bore of the flywheel real good then
turn it ahead 3 or 4 teeth on the ring gear from stock ( no need for the key). Tighten the nut to spec 140 ft lb I think
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Offline DeereRacer

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #17 on: December 08, 2016, 10:55:48 pm »
Changing cam timing on most small engines including the opposed has no effect on ignition timing. Ignition is triggered by the crank not the cam.
Great post so far lots of good information.
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Offline GermanFred

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #18 on: December 09, 2016, 03:20:26 am »
Alright, now I got it:
* Advance the cam by 1 tooth (-> to change timing of valves opening/ closing)
   AND
* Advance the timing of the ignition by turinng the flywheel some degrees, e.g. 10-12  deg. earlier (by timing key or without).
Cheers!


Does anybody has a "valve timing chart" for the 'model 404007' oppy?
I mean something like this:


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Offline GermanFred

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #19 on: December 09, 2016, 03:27:51 am »



No on the red circle,it does nothing for intake flow,these heads flow plenty on the exhaust side as is


Any suggestions regarding the intake side of the head? Should be grinded to look the same as the exhaust side?
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Offline GermanFred

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #20 on: December 09, 2016, 03:32:19 am »
Oppy mechanics manual says:



However, do you think, re-facing the valves and seats both to 30° is advantageous? Because of:




Do you think re-facing the valves and seats both to 30° is advantageous to flow for an oppy?    
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Offline GermanFred

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #21 on: December 09, 2016, 03:39:02 am »
Sorry guys, three questions in a row...  :doh:
But for better citing options I kept each question to one post  :P
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Offline GermanFred

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #22 on: December 09, 2016, 05:07:34 am »
You have to advance the flywheel to do the ignition timing.  Clean the crank and bore of the flywheel real good then
turn it ahead 3 or 4 teeth on the ring gear from stock ( no need for the key). Tighten the nut to spec 140 ft lb I think

Service Manual says:
Description..........Wrench/Socket Size............ Torque
Flywheel . .  . . . .  . . 1-1/4” . . . . . . . . . . .  150 ft. lbs. (203.0 Nm)
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Offline PJG56

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #23 on: December 09, 2016, 06:34:00 am »

Do you think re-facing the valves and seats both to 30° is advantageous to flow for an oppy?

Leave the exhaust seat @45 deg
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Offline GermanFred

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #24 on: December 12, 2016, 03:42:43 am »
Hey guys,
a new week - a new question.


Reagrding intake manifold and carb. bolted to it:

What the heck does this spacer-thingy do? Shall it create turbulance, direct flow to somewhere, ...? Could I cut out the fins or does this do something negative?
In my eyes, the fins restrict the Diameter. The fins not even have ponty tops but extent blunt into the open diameter. I cannot understand how this shall be of any good use to free flow.



Unfortunately, this topic does not really give any sbstantial answers: http://www.heymow.com/index.php/topic,10359.0.html
It only says: Let the fins in, they are supposed to keep the air-fuel mixture atomized.
 :confused: How?
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Offline Jim Knutson

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #25 on: December 12, 2016, 08:56:34 am »
Remove the fins, but leave the spacer tapered as it is now.
If you quit when you're behind, you will never win.

Offline GermanFred

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #26 on: December 15, 2016, 03:02:06 am »
Thank you, guys.

Wish you all a Merry Christmas!

Jan
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Offline GermanFred

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Re: Oppy 42 ci head: flow optimization / grinding issues
« Reply #27 on: February 14, 2017, 08:16:13 am »
Dear Sirs,

maybe someone is interested in seeing what I did to my Oppy so far.

      --> http://wp.me/p7g7mv-Du

Happy Browsing,
Ferd
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we race on fields, no ovals