383 Noise - Name that tune

[Lunatic]

1986 GMC Jimmy / 383-700R4-NP208

PLEASE do not bash on the builder – It won’t accomplish anything.

383 stroker built 05-03-2014 - Currently has 610 miles as of 6-29-14 to current date – It is not being driven at this time.



Two road trips:
*1 hr one way, 1 hour back (approx 120 miles total)
*2hr30m one way, 2hr30m back (approx 330 miles total)
Downtime between arrivals and departures (First was to work, second was to family residence).
160 miles local travel (errands, etc)

Noise began after return from second road trip

Minimal oil contaminants (metal) upon initial oil drain (610 miles). Although present, the amount noted was to be expected from the break-in period. Using Royal Purple 15W40 Full Syn oil with WIX 51061R oil filter.



Known info from use of mechanic stethoscope and/or other methods:

*No noise from heads (per valve locations, checked from valve cover to head overlap, on head surface)
*No noise sourced from headers (per cylinder locations, checked along head surface)
*No noise from cylinders (under heads, external check)
*No noise from cylinders (under side, external check)
*No noise from rocker arms (per locations, checked from valve cover surface)
*No noise from intake manifold, entire surface area
*No noise from mechanical fuel pump (rod, arm, etc)
*No noise from crank seal area on timing cover
*No noise sourced from distributor stem
*No noise from new PS pump - belt removed
*No noise from alternator - belt removed
*No noise from new water pump - belt removed
*No noise from new oil pressure sender

*Rear main crank seal has minor leak (1 drop on seal housing, 1 drop on flywheel cover – No drips to ground)



Oil pressure remains above 60 psi until engine is driven at operating temp and fan-cooled (not idled in driveway). The ending noise remains regardless. Drive to the store without noise, park and shut the engine off - The ending noise is heard.

If the engine is throttled heavily under load (steep incline, etc), the noise returns briefly, then disappears.

I cannot locate the noise source, even though it sounds loudest by distributor area on top side. It is even louder below, at the rear of the engine.

The ending noise leads me to believe it is pressure or vacuum related being that once the crank stops spinning, the noise remains and then bleeds off.

I have been hunting this issue for about two weeks now as time allows. At this time, I am focused on the oil pump. The noise is right for it, the gauge indicates an issue, and the approx location of the noise leads me to it. So it seems. I will provide updates as discoveries are made.

This vehicle is not abused in any manner. Tires have never lost traction on pavement. Oil changes are kept up and any leaks are dealt with immediately. This vehicle is kept in running condition for weekend driving and road trips.


Any ideas or questions leading to a solution are appreciated.




Troy B
Ft Hood, TX



383 Noise YouTube video

[youtube]https://www.youtube.com/watch?v=nsG_SGmwjZw&feature=youtu.be[/youtube]

[bd]

One-at-a-time, disconnect the vacuum hoses and cap the ports evacuating the power brake booster, the A/C vacuum reservoir, and the cruise control system.

[bd]

Incidentally, IMHO the engine should be broken in using a conventional mineral oil containing ZDDP, regardless of whether running a roller or flat tappet camshaft.  Full synthetic oil inhibits initial ring seating as well as proper lifter/lobe break-in in flat tappet engines.

[Lunatic]

Thanks for the response, bd, I actually found the source tonight - The oil pump.

What you mentioned is news to me - A person can never stop learning new things.  Thanks for that info.

Being that the engine was dyno'd before I received it, I 'd like to think all will be fine. I'll still be switching back to conventional with the additive though.

If you like, you can read up on everything I did to reach the conclusion and what further actions will be taken from this point on another board.  Feel free to jump in as well.


Thanks again !



Troy B
Ft Hood, TX

[bd]

Please keep us apprised as the diagnosis develops....

[Lunatic]

Sure thing, bd

This problem is resolved.

So, short version - The engine wasn't breathing properly. Because I didn't have a breather on either valve cover, it was basically a sealed engine, with a vacuum that had to inhale from the weakest point - The one-drop-leak-rear main oil seal, to be precise.

The solid squeal was from air passing the sealing surface at the crank, which, because it was spinning, kept the seal seated and "rigid" - So the squealing was actually whistling. When the engine was shut down, the seal rubber basically flapped/vibrated as the vacuum pushed past it, producing the elk mating call.

I did call the builder this morning, and he suggested I pop the pcv and oil fill cap, and fire it up - So I did.

Noise was gone. I put the pcv back in, still no noise. I then put the oil fill cap back in - And within 5 seconds, the initial noise returned. When I pulled the oil fill cap back off, the action produced a loud gasp from the hole I just opened, like popping the top on a carbonated drink can.

So, I went to my box of goodies, grabbed a breather and it is now in place of the oil cap.

Insanely-stupid-simple fix.

I'm just glad its no longer an issue.


Thanks for jumping in, bd



Troy B
Ft Hood, TX

[bd]

Great explanation, Troy!  And, very well done on the diagnosis!  Thanks!