Preparing the motor home for a trip,(1996 460) I changed spark plugs. I noticed a slight miss and when I arrived at our destination (800 miles) I removed the plug and found about a quarter inch of the electrode missing. The plug had carbon build up at the top of the plug where it seats I must have missed one when I tightened them. A compression check revealed 120 on other cylinders and 0 on #6, the bad plug cylinder. I suspect I have a piston with a hole in it or a valve problem. Any insight would be appreciated, thank you.

 

Can you do a leak down test?

You would hear where the air is coming out.
(intake or exhaust if a stuck valve, oil fill if a holed piston)

 

Wow,800 miles from home with a dead cylinder.If it was me,I would pull the ign. wire and the rockers from the dead cylinder and continue with the vacation driving as little as possible until the trip home.You could take it to a service center to have them diagnose the problem,but then you'd have to find some place to sleep until it's diagnosed and or repaired.Huge repair bill if at the least they replace a head.You could buy a inspection camera/borescope and look in the cylinder yourself.I have one and it fits in the spark plug hole.It's a MTP Instruments and was about 150.00 up here in the land of double the price Canada.Tough call to make.Good luck.Maybe others will add to the idea list.

 

Thank you ArdWrknTrk for the information, I am going to test it this morning.

Thank you Big Vann, I have ordered a camera and will take a look inside, and then I will do what needs to be done. Thanks for the information on how to hobble home.

 

I found the problem—it was a burnt valve. I had the head reconditioned and will be putting it in next week. I should remove the other head to do a proper job but I am working in a gravel driveway 800 miles from home and don’t want to compound my problem with a broken head bolt or manifold bolt. I am doing a compression check as soon as I install the head. If there is a big difference in the compression of the two heads I will be compelled to recondition the other head. Please give me your thoughts on this. Thank you