quad making tapping sound

i have a 93 quad dohc. i recently changed the head gasket and everything was good for about 2000 miles, but then a tapping noise started coming from the motor. no noiuse at idle but as soon as i give it a little gas it taps repeatedly in relation to rpms until back to idle. any ideas would be appreciated.

Unfortunatly Im pretty sure I have bad news for you, the antifreeze that got into the motor oil wore the rod bearing(s) and you now have a piston hitting the head (usually #3). Why am I jumping to this conclusion, same thing happened to me, bought a car with a bad head, changed the head and gasket, made it 70 miles before mine started tapping. Sounds kinda like a sewing machine right? Sorry to give you the bad news, I didn't believe my buddy when he said thats what was wrong, I tore it down and found out he was right.

In my case the rod, crank, and rod bearing needed replaced, so I did a complete rebuild and am back on the road again. Its alot of work to verify im right, either you have to pull the head and see the marks on the piston & head, or you have to pull the oil pan, oil pump, and rod bearings.

sounds like a good possibility that you are correct, the only thing is after I noticed water in my oil before I changed the head gasket, I drained the water and oil, added new oil and ran it without water for just long enough to lubricate the bearings. the only other things that i suspect are lifter tap, or incorrect cam-crank timing(which i doubt because i spent awhile making sure the chain was back in correctly and tight)... If i decide to go into the bottom through the oil pan, how difficult will it be to replace the bearings(and are the rod bearings the only ones to replace or are there crank main bearings), also if this is whats causing my problem, will i be able to see the problem(how do you tell if a rod bearing is bad)....... thanks for all the help

I doubt its the timing off, I accidently had my exhast cam off one tooth after re-assembly, the valves didn't hit the piston, the only way i knew it was off was at an idle the motor would shake, once I got about 1000 rpms it would go away. I also suspected the lifters were bad, then my mechanic buddy listened to it and gave me the bad news.

In my case the piston was barely hitting the head, giving a tapping noise, no damage to the head, basically only took the carbon off the top of the piston, so as I said it was barely hitting the head. The rod bearing on #3 was gone, it was in the oil pan, the crank was so worn down that it had to be replaced, and I had to get a new rod. Without seeing or hearing the car i'd guess that yours in the same shape mine was, or real close.

How I knew mine was bad was when my buddy hooked his oil pressure gage up to it and the oil pressure was all over the place. I tried rigging up an oil pressure gage of my own, but I kept breaking them when the pressure would spike. The pressure would be at 10 lbs then jump to 80+lbs. That should give you an indication if im leading you in the right direction or not.