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Ever since I rebuilt the NA motor (about) 2 years ago), it's had a VTC rattle, but it's not exactly the same as the knocking that happens to TTs running high lift camshafts with heavy duty valve springs. Symptoms:
- With the RPM above ~1500, lifting off the throttle results in a brief rattle that seem to come from the Intake cam gears.
- While racing the engine slightly (in the 1500-2000rpm range) and holding the rpm steady, the same rattle will occur intermittently
- Occasionally on hot days, the driver's side intake cam gear will exhibit a nasty knocking, which I assume is the same as the knocking that occurs on TTs with high lift cams and HD valve springs. This knocking completely dissapears after about a minute once the car warms up. Background info:
-1990 block, crank, pistons, girdle, etc
-1994 NA heads, upper & lower plenums, fuel rail, etc
-1990 cams & gears
-18k miles since rebuild
-Rebuild included rings, bearings, all gaskets and seals, 120k kit, etc
-The noise has been present since the rebuild
-The engine I took the cams and gears from had no such noise
-I've been using Mobil 1 10w30 ever since break in was complete (dino was used during break in). I took some time to diagnose the exact problem yesterday, and I found that unplugging both VTC solenoids completely eliminated the problem. Hooking either one back up caused the noise to come back on the respective side. Any ideas? My thoughts are as follows:
- Both VTC solenoids failing before 115k miles (which is when the engine was rebuilt) is unlikely.
- The intake cam gears made no noise on the engine the came from, so that should eliminate them as the problem.
- The only cause that makes a bit of sense to me would be that the VTC gears aren't getting enough oil pressure. They receive their oil pressure from the front cam journal iirc, so that would mean that either both front intake cam journals aren't receiving adequate oil pressure, or the passageways within the cams are obstructed. If low oil pressure at the cam journals was the issue, I think I would have had some serious mechanical issues by now. Also, since the car has good oil pressure, that would mean there would have to be obstructions within the head on both sides, which I find unlikely. I also find it just as unlikely that both cams would have obstructions in their passageways. Finally, were there any differences in VTC solenoids over the years? My only other thought was that perhaps there was a difference, and the newer VTC solenoids aren't compatible with the older cams. Thanks in advance for any help!
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