gx200 open motor

JRW31526

Member
Okay i got a genuine gx200 block and head

14cc head milled .060 (.045 fire ring hg)
ported/polished
28.5/25mm ss valves
spring pocket cut
dual 60lb springs
aluminum retainer/keepers
lash caps
1.3:1 billet rockers
cm pushrods
isky lifters
isky 315 (260 duration)
honda flat top piston (.010 in the hole)
arc rod (std leingth)
bsp max stroke crank (2.133)
arc flywheel (32* timing)

Running a tilly 304wx on race gas
and a j pipe with a .990 id
how much do you think i will have to index the plug?
 

Kart43

Member
What is the question

You will have to explain what you mean by "how much will I have to index the plug"
 
Just put the piston at TDC and measure from the top of the plug hole to the piston, and compare with the plug. that's what I do anyway.
 
Go gapless you will never go back lol.Also keep in mind with your temp
lead on the plug it will raise it some too.jmo but .060 on a 14cc head
is a lot.I do .040 on mine and .080 on the 22 other opinion may vary.
but I also use the .010 gasket along with high temp copper sealer
 
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Kart43

Member
When you refer to indexing a spark plug you are speaking of the orientation of the grounding strap, so the open side is pointing toward your preferred direction. As the plug manufacturer does not care where the strap is welded on in relation to the threads every plug is different.

Simply put a mark on the insulator(felt marker) where the gap is open install and tighten plug see where gap ends up, keep trying dofferent washers until it points where you prefer.
 

Kart43

Member
Quite often the spark plug electrode has to be indexed to provide clearance for the piston at TDC no voodoo in that just good sound building practice to prevent catastrophic failure, or the plug closing up.
 

clone king

New member
Voo doo. yep, to the unknowing.. no bad ju ju in doing things correctly.
voo doo & bad ju ju comes from not correctly doing things.
Boogy Woogy..Trick or Treat...lol
 

Devil-D-Dawg

New member
Quite often the spark plug electrode has to be indexed to provide clearance for the piston at TDC no voodoo in that just good sound building practice to prevent catastrophic failure, or the plug closing up.
Yeah I get that, but is that indexing or clearance-ing?
 
Indexing was more of a flat head thing because of the valves
you wanted it turned away from the ex side because the
valve would come up and slam it closed.this is also
why you could buy washers thin or thick too.
Now on the ohv wont matter because your over
the piston and the valve are facing down.you just
don't want the piston hitting the plug.The more
you take off the head the closer it will get so
the higher in the head it will need to go
 
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Flash06

New member
I like the autolite 3935 for alky much better than the 3910x, it burns hotter. As far as indexing there is no need to do so on an ohv only flatheads, as mentioned above you do need to clearance the plug when the head mad been milled a lot. You shouldn't have to do it since you only have .015 cut off the head when you add that .045 gasket. Put the 3935 in, it is a much better alcohol plug than a 3910x which is run on a stock motor on gasoline. Jmho
 

Kart43

Member
As far as indexing the plug goes it would make very little difference in these engines, but it is not VooDoo nor is it incorrect information. There are volumes of data indicating it's effectiveness, and relevance. It is not only applicable to flatheads it is utilized in the latest 4 valve, hemispherical chambers, it's effect can be seen when using an oscilloscope diagnostic tuning center, of which many current mechanics would have no experience with.
 
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