Plugs bent over and engine running rough and hot.

[xymox]

Wierd situation happening. Engine started running hot so did the usual adjustments to the needle and noticed no real difference. Decided to reinstall the stainess needle and still ran like crap. Noticed number 4 egt was running real hot on climb out 1450s but under idle it was cooler than the number 3 egt. Both egts are in the rear by the way.

Was doing some static wot pulls to see if I could reach the normal 3200 rpm I would expect... Bogged down at 2800 ish and could hear what sounds like detonation and backfiring.

Finally pulled valve covers and noticed valve clearanse was way off( sloppy) so tightened them all down to .006 per the manual. Also pulled plugs and noticed number 2 and 3 bottom plugs we're bent over so that ground strap was touching electrode. Put new plugs in and Ran engine and was running fine after some high speed taxis. Pulled bottom plugs again and the same 2 and 3 we're bent over. Regaped and added an extra crush washer to the problem plugs. Still runs fine.

Pulled head and jugs... Noticed some lead buildup which I scraped off but sure wasn't thick enough to cause any interference. No lateral play in the piston and connecting rods. Top of Pistons showed no signs of impact with anything . Kind of at a loss as to what would cause the plugs to fold over.

[xymox]

After I ' looked a bit more' I realized that it was in fact making contact with the piston head. See attached picture. So now the question is, why would the clearances move enough to cause interference after over 150 hours?

[Brett]

MoFoCo heads I assume?

[xymox]

Sure are. I guess it's luck of the draw.
Anyone know of a shorter plugs that can be used?

[Onex107]

There are two places that could allow that to happen. The shims on the cylinder barrel and the thickness of the fire ring. Have you re-torqued the head and seen a lot of change? New heads with new fire rings? They come in different thicknesses. Did you use silicone to seal the cylinder shims? Physically the compression ratio had to change to allow that to happen.

[Onex107]

I have been know to put a head back on and did not know the fire ring had dropped out until I found one left over.

[Brett]

I use the NGK plugs DR8EA, they are just shorter than the Autolite ones and have clearance in my circumstance.

[xymox]

That's exactly the plugs I picked up this morning. Thanks!

[sonex1374]

Looking at the photo of the valves, the coloration on the exhaust valve is a bit uneven, and it looks like the valve seat may have changed position slightly. If the clearance on the rocker arm adjuster has opened up, that might suggest the valve seat has shifted. It might be time to send the head off to a bug shop for a valve job, including a new guide and seat on the exhaust valve. Might not be anything to worry about, but worth investigating perhaps.

Jeff

[xymox]

There are two places that could allow that to happen. The shims on the cylinder barrel and the thickness of the fire ring. Have you re-torqued the head and seen a lot of change? New heads with new fire rings? They come in different thicknesses. Did you use silicone to seal the cylinder shims? Physically the compression ratio had to change to allow that to happen.

I disagree in part. The most probable scenario is reusing the same plugs and over torqing and using the same crush washer and the auto lite plugs. Results = too much penetration.