valve tap?

[SquamInboards]

My 2001 GT-40 that I just swapped for an '89 351 seems to be making a tap-tap-tap-tap-tap sound right when I start it up, seems like it's coming from a valve on one side... but it goes away at different RPMs... any ideas? Major? Minor? should I address it before running the engine again, at least before running it hard again?

[Hollywood]

RE: valve tap?

sure it's not an exhaust gas leak?

i'd atleast pop off the valve cover and take a look, could be a bent push rod.

[SquamInboards]

RE: valve tap?

I'll see if I can get the valve cover off and look... it's pretty crowded on that engine... I'm pretty sure it's a metallic click/tap, not an exhaust leak, plus wouldn't water come out if there was an exhaust leak? There doesn't appear to be any water coming out anywhere it shouldn't.

[TRBenj]

RE: valve tap?

If you havent heard one before, an exhaust leak sounds very much like a ticking/tapping noise.

Id pull off the valve cover and see if any of your rockers are loose. You'll need to pull the exhaust manifold to get the VC off. You might want to invest in new gaskets before pulling everything apart.

[surroundsound64]

RE: valve tap?

You might want to invest in new gaskets before pulling everything apart.

I'd second that.

[SquamInboards]

RE: valve tap?

I had the gaskets 'in stock' already, actually... so we pulled the valve cover and checked for loose rockers; couldn't find anything unusual.
If it helps, the sound is mostly right when the engine starts up, and also when backing off the throttle hard, as the engine slows down. The sound then goes away at idle, and cannot be heard during acceleration either. The engine is back together in the boat now, I'm driving it, but gently. I will keep a close ear on the sound to see if it changes. It does appear that we've ruled out the exhaust leak, having checked the old gasket (nothing unusual or visible) and cranked down the bolts on the re-install. Interesting note - the manifold bolts were not very tight in taking them off, however, the sound is exactly the same as before.
Thanks for the help so far, I'll post here again as the problem comes more to light.

[SquamInboards]

RE: valve tap?

Okay, so update: It's definitely a valve or related part making a tapping noise, however: It only happens when the engine is cold. I start it up, it idles fine, but has the tapping, same as above. 2 minutes later, above maybe 140-150 engine temp, it goes away. I never hear it again, as long as the engine stays warm. Revving, backing off, high speed, low idle, nothing. Any thoughts?

[core-rider]

RE: valve tap?

Two things to check... 1 - You checked for loose rockers, but did you check the pedestal under the rockers? They have a nasty habit of cracking in half if the bolt is tighened too much. 2 - Get out some feeler gauges and check the actuall valve lash. Since they are pedestal style rockers you have to get shims to change the lash.

My guess your lash is off on one or more rockers, but as the parts heat up they expand enough to make most of the noise go away. Also, the injectors can make a valve ticking noise, but since your noise goes away after awhile I would stick with looking at the rockers.

Good luck...

[Mikeski]

Sounds like a gunked up hydraulic lifter to me, run some STP though it for the next two oil changes. Sometimes that's enough to clean it up.