Just installed a motor in my 98 Prelude. Its making like a tapping noise but along with the noise there seems to be a miss. Whats weird is that when the car gets up to temp and runs for a while its stops and sometimes it comes back. A buddy of mine who installed the motor says its coming for the cylinder head. He said it might be a collapsed lifter, a bent valve or a bad rocker. Any ideas. Thanks

 

I would pull the valve cover off and see if you are getting oil up to the valve train.
If you have a good coating of oil on everything then you can put the cover back on and start figuring where the noise is exactly coming from.
You can take an ratchet extension or heavy screw driver and touch it at various places along the valve cove then listen at the other end of the tool to find where it is the loudest.
Or pick up a mechanics stethoscope to try and find the noise.

 

We did that with the screw driver and we did not hear any difference. Today I started it up this morning and it was cold out. I heard the noise at start up but it stopped. I let the car warmup for a while and the noise did not come back.

 

Any chance that this is the sound?: http://www.preludepower.com/forums/s...d.php?t=304996

 

Does it idle evenly? A compression test would give some indication of the valve seating integrity.

Absolutely take the cover off and thoroughly check the condition of everything especially look for maring on the cam lobes.

Its a bit combersome but check the valve lash when the engine is stone cold, before you have started it up at all that day. If it ticks in the morning when its cold, check the lash in the morning when its cold. If its a sticking valve, you'll be able to catch it dead in its tracks checking the lash (if it sticks when its COLD).

All you do is slide a 7-8 thousands feeler gauge between the cam lob and the rider on the rocker. You do have to turn the engine over progressivly to fixed points for each cylinder, as indicated by marks on the cam gear - this so you are checking the slack at the lowest (when the valve is closed) spot of cam lob.

If you find substancially "loose" lash, then it's because the valve is binding in the head.

The lash gets tighter in these engines over time (through valve/head-seat ware) not more loose. If the valve clearence has never been adjusted you may have no lash at all, which can cause a burt valve over time.

I can walk you through the complete procedure and also how to make the necessary $100 valve lash set-screw-nut-holder for this car for about $12 if bucks if you want

The ol' spare vacuum hose in the ear works great to isolate sounds. much cheaper than a stethoscope and more precise than feeling through a screw driver

 

Now later in the day I started the car up let ran for an hour. I then reved the car and the noise came back and when I let off the gas the noise stopped. So the noise is there for a second then stops. I did replace the knock sensor, oil pump, water pump, all new hoses and belts including timing belt, cap, rotor, plugs, wires, rebuilt trans, gaskets.


As of the sound clip from the other reply it does sound a little like that but nots as long.

 

I wonder if one of the mid rockers is just flapping around because one of the 'lost motion' springs is damaged? The lost motion spring keeps the mid rocker pushed onto the mid cam lobe when vtec isnt engaged. If a lost motion spring was damaged the mid rocker could be flaping against the cam lob intermittently whenever the harmonics were right.

 

Been thinking about this problem this is the only other scenario i can think of. Theres only a few things in the head that could possible tap like that. Obviously two metal things are hitting each other and in normal operation all the parts work in close tolerances of each other.

The rocker is under constant tension between the cam lobe and the tip of the valve accept for when the valve is all the way closed and the rocker is riding the lobe base circle and maybe there's a few thousands slack.

If the valve intermittently is binding and not closing all the way then the rocker-to-valve tip slack would increase from a few thousands tolerance, to whatever height the valve stuck open at. The rocker has upward momentum as the valve is closing but when the valve stops short, the rocker lifts off the valve tip. When the cam lobe comes back around and pushes the rocker back down, as to open the valve, the rocker impacts the valve tip and clicks.

The only other thing i can think of is the mid rocker/lost motion spring thing.