Throttlebuddies

Hey guys,

just built a B6 Engine for a NB miata. Block has H beam rods, king bearings etc. Head was rebuilt witth new seats, Valves, Valve guides, cat cams springs etc. but still stock cams for now.
Problem is, that i have very loud valvetrain noise, as if the valve lash was way off, which it unfortunately is not, sinc thet would have been an easy fix. All of the lash was adjusted by a reputable shop in my area. Checked clearence and was within spec.
This is the head noise im talking about, at lower idle there is none, starts at about 1800 and is really present at 2500 and very loud at higher rpms.

Already done several checks:
- Pulled bottom end apart, measured everything from bearing clearance to piston to wall clearance. obviously nothing, since the noise is from the head (but hey, still tried)
- Checked compression. 12.5-13 Bar on every cylinder so 180-190 psi
- Engine drives well and has power
- Everything clears in the head, nothing is hitting anything as far as i can see
- No major metal shavings in the oil, except for normal break in stuff
- timing is on point, belt tension is also fine.
- Tried running without accessory belts, still the same
- Changed the clutch release bearing
- oil flow in the head also good.
- Bolt torque also fine (cams, cam gears, head studs etc.)

im all out of ideas, maybe somebody knows whats up... the only time i heard a sound like this was on an engine with too much valve lash. but not nearly as loud as this.

sixshooter

iTrader: (12)

If the valve lash was set with the head not torqued to the block it will often change once torqued.

Buy a cheap mechanic's stethoscope and pinpoint the origin of the noise.

Throttlebuddies

i have checked valve lash with the engine warm and in the car again and was in spec. was about 0.25-0.3mm . at that point engine had about an hour runtime on it.

thats a good idea might get around to that. but does come from the head, im certain.

HarryB

That should be cold lash; if it is warm, it is too loose.

Throttlebuddies

i can check cold again on the weekend but i doubt that it will be much different. as the lash was not really hot but when he enihgine was at operating temp but has already been off for 30min.

Turbomack

Which direction does it change after the head gets torqued down?

Throttlebuddies

it gets smaller. id say. hence the spec my engine builder was using required for more clearance than 0.25mm when cold.
but i think it doesnt have to do anything with valve lash because on a standard engine the clearance when cold starting is higher and the noise is almost not audable. never had any NB head sound nearly as bad as this even at -5 celsius.