Timing chain rattle?

[Lazyeye]

Vehicle: 1979 280zx, stock N/A engine

 

Symptoms:

When the car is cold there is a rattling sound and it runs very rich. After running for 5-10 minutes the rattle clears up and the engine stops running rich. If I stop the engine and wait a few minutes then start up again, the rattle is there for a few miles again.

While it is rattling and running rich, the engine idle is low, about 400rpm and it hesitates and tries to die when I come to a stop. After 10 minutes or so the richness clears up and the idle comes up to 1400 (I have a lightweight flywheel and haven't adjusted the idle yet).

 

I adjusted the valves very carefully using the fit/no fit method (thanks to KammyZ's photo tutorial), there was no change to the sound.

 

I stethoscoped the engine with a driver extension rod and the sound seems to be coming from the block and or the valve cover.

Link to short video I shot with my blackberry: http://www.youtube.com/watch?v=e6MAzNcwmS8

 

I've been searching a lot around HBZ and youtube and it seems this could be a timing chain rattle. What do y'all think? If I take the valve cover off, can I check the chain tension? How loose/tight should the chain be?

[bjhines]

Is your oil pressure OK? The tensioner is oil-fed and a failing oil pump pushing cold oil may be too little pressure to get the tensioner tight.

[Lazyeye]

The oil pressure shows in the low-middle of the gauge (I don't recall numbers) and then about the time the rattle goes away it moves up to 2/3 to 3/4 position.

[S30TRBO]

I'll play. I say timing chain guides. Take your scope and listen near the front cover.

[Dtsnlvrs]

Is your oil pressure OK? The tensioner is oil-fed and a failing oil pump pushing cold oil may be too little pressure to get the tensioner tight.

 

You state that the idle is about 400rpm. If you are not making much oil press, and at 400rpm you are not, then the chain tensioner shoe will not extend enough, leading to.......

 

 

I'll play. I say timing chain guides. Take your scope and listen near the front cover.

 

 

The timing chain guides being worn erratically, which causes the rattle when the oil press is low.

 

Short term fix, is to get the idle stable at 800-1000rpm when warm, and double check your oil level.

 

Long term fix.....replace the timing set (chain, guides, tensioner, etc.)

[Zmanco]

My own experience is that oil pressure drops as the oil warm up. Not sure what could cause it increase with temperature like you are seeing.

 

Also, you should put a mechanical gauge on, at least temporarily, to determine what the oil pressure really is. My stock gauge with the original 38 year old sender appeared to be working properly. It read about 15-20 psi at idle and about 80 psi at high revs. Turned out I really had less than 10 psi at idle and only 50 psi at 7k. The stock senders are notoriously inaccurate, and as they age it appears they get worse.

 

Here's a thread where I initially thought my pressure was too high, and after using a mechanical gauge found it was too low: http://forums.hybridz.org/index.php?/topic/84776-oil-pressure-too-high/page__p__807432__hl__oil%20pressure__fromsearch__1&&do=findComment&comment=807432

[Zmanco]

FYI, here's how I finally solved the oil pressure gauge problem. It's not perfect, but it's close enough now that I've verified with another gauge.

 

http://forums.hybridz.org/index.php?/topic/86624-s30-oil-pressure-gauge-improvement/page__p__821848__hl__oil%20pressure__fromsearch__1&&do=findComment&comment=821848

[Lazyeye]

Thanks for the advice, I'll be checking it out this weekend.