Puzzled: sparkplugs re-gapping themselves tighter during tuning
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From: Cincinnati, OH, USA
Puzzled: sparkplugs re-gapping themselves tighter during tuning
Motor: built B18C5, block NOT decked, ~12.5:1 CP shelf pistons (big *** dome), Portflow ITR head milled slightly, stock ITR rods, ARP rodbolts, OEM headgasket
ZFR6F-11 Plugs (don't flame - it's all we had around for now. 7E+8Es coming tomrrow) gapped by me using feeler guages to ~0.032"
Took car out for some street tuning. Pulled plugs to check timing. Noticed they were gapped unevenly - tighter than I gapped them. Re-gapped them and went out for more tuning. Car taken up to ~9000 RPM several times. Came back in, plugs are gapped tighter again! Difference is 0.012" - 0.018" depending on plug.
Plugs are obviously at least one (if not two) heat ranges too hot due to mark on strap.
All 4 plugs have a slight mark on the electrode on the side facing the piston. Looks like abrasion.
Compared plugs to BKR6Es from another car. Compared plugs to BKR7Es from another car. Both sets of plugs are NOTICEABLY shorter from the base of the plug to the tip of the electrode.
What the hell is going on? Are the clearances tight enough that piston-electrode contract could be a concern? Anyone know how much of a concern rod stretch is with ITR rods? I'll try to post pictures tomorrow.
ZFR6F-11 Plugs (don't flame - it's all we had around for now. 7E+8Es coming tomrrow) gapped by me using feeler guages to ~0.032"
Took car out for some street tuning. Pulled plugs to check timing. Noticed they were gapped unevenly - tighter than I gapped them. Re-gapped them and went out for more tuning. Car taken up to ~9000 RPM several times. Came back in, plugs are gapped tighter again! Difference is 0.012" - 0.018" depending on plug.
Plugs are obviously at least one (if not two) heat ranges too hot due to mark on strap.
All 4 plugs have a slight mark on the electrode on the side facing the piston. Looks like abrasion.
Compared plugs to BKR6Es from another car. Compared plugs to BKR7Es from another car. Both sets of plugs are NOTICEABLY shorter from the base of the plug to the tip of the electrode.
What the hell is going on? Are the clearances tight enough that piston-electrode contract could be a concern? Anyone know how much of a concern rod stretch is with ITR rods? I'll try to post pictures tomorrow.
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Re: Puzzled: sparkplugs re-gapping themselves tighter during tuning (blundar)
At high RPMs the piston has to be contacting the electrode causing the abrasion your seeing. Shine a light down in the spark plug hole with each piston at TDC and look for marks on the piston. Check the plug length and don't run it until it's corrected!! The stock rods are probably stretching at high RPM's.
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From: albany, ny, usa
Re: Puzzled: sparkplugs re-gapping themselves tighter during tuning (blundar)
wrong plugs, the reach is to long, you need to use bkr7e11's, my buddy had the same prob on an lsvtec with ctr pistons, milled head and the zfr plugs
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Re: (blundar)
Your pistons are without a doubt hitting your electrodes.
Considering nothing broke, you are lucky.
I wouldn't drive the car until you get a colder range plug - as you stated, the colder plugs electrodes will sit substantially further away from the top of your pistons.
When I clayed my motor (CTR pistons), I had less piston to electrode clearance than I did piston to valve clearance.
Good luck.
Considering nothing broke, you are lucky.
I wouldn't drive the car until you get a colder range plug - as you stated, the colder plugs electrodes will sit substantially further away from the top of your pistons.
When I clayed my motor (CTR pistons), I had less piston to electrode clearance than I did piston to valve clearance.
Good luck.
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