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  1. #1
    GAV's Avatar
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    Octane bends spark plugs

    just finshed building my new octane engine which has
    new crank and cases
    new MSX barrells and pistons
    single carb manifold
    new billet head off a 700 polaris snow mobile (had the squish machined out to 85mm to clear piston)
    ski pumps up 195psi on both cylinders

    but when i take it for a ride it will bend the plug in the front cyl closed
    so i pulled the head off and there is no damage at all in the cyl
    i reassembled it and ran it again, did the same thing so i checked the clearance between the piston and plug and i have 9mm so the piston is not hitting it
    any idea what whould cause this


  2. #2
    john zigler's Avatar
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    somthing has to be hitting it. are you "sure" you truly have 9mm clearance at TDC?

    what head are you running, from what snowmobile, and what plugs does that machine call for. waht plugs are you running? you may need to switch to a non projected tip plug.

    either that, or you have some parts bouncing around in there.

  3. #3

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    Detonation

  4. #4
    GAV's Avatar
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    i have had the head off 2 times and there is no marks on the piston or head
    i have 1.5 mm squish clearance so the piston even if it was to hit the plug it will hit the squish 1st
    the plugs i am running are NGK BR9ES when it bends the end they have no marks on them. Using a set of verniers measuring down the plug hole to top of piston on tdc i have a distance of 27mm. The measuremnt from the spark plug washer (i realise it will crush down) to the tip of plug is approx 20.7mm so i have approx 6.3mm of clearance...

    the head is off a rmk 700 snow mobile & i machined the squish out to 85mm for the msx pistons and machined up to make my 1.5mm squish and bring the comp down to 195psi ish

    can detonation cause this i have never seen it before?

    attached is a pic of the engine
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  5. #5
    I like Boobs. wetwolf's Avatar
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    You ar running too lean. I have had snowmobiles on the dyno close a plug gap before with no signs of anything going thru the cylinder. It was getting the electrode hot enough that the combustion was enough to deform the heated metal and close the gap. Back off the timing, increase the cooling, or the jetting and you should be OK. What timing are you running at WOT?

  6. #6
    GAV's Avatar
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    Thanks mr wolf
    i will throw sum moor fuel in it and see how i go
    ignition is a baxter limeted curv

  7. #7
    bowsniper's Avatar
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    what octane fuel? 195 psi needs more than 93.

  8. #8
    TEAM BRONX TECH FAT BOY's Avatar
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    I would say sunoco 110 octane or vp 109

  9. #9
    I like Boobs. wetwolf's Avatar
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    Quote Originally Posted by GAV View Post
    Thanks mr wolf
    i will throw sum moor fuel in it and see how i go
    ignition is a baxter limeted curv
    Whats the advance set to at WOT?

  10. #10
    GAV's Avatar
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    fuel is 98 pump gas (australia) with polaris ves racing synthedic oil at 40:1
    have no idea what end timing is the limeter is 9500rpm
    i think i will put moor fuel in and take it for a ride and see how i go

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