Datsun Roadster Forum-311s.org

Greetings, my engine makes rattling noises at certain rpms, mainly lower. I'm pretty sure it's the timing chains, but I don't know why they are noisy. I don't think it's a rod knock. The engine is fairly new (under 20k), new bearings under 20k, newer chains and gears, cut upper chain guide (for years), shimmed original upper tensioner (always), lower chain guide in place, original lower tensioner. Checked valve lash hot (all fine), the vent in the valve cover is fine and not vibrating... it really sounds like the chains. The upper chain guide and tensioner are original and have typical groves worn into them but nothing to where it appeared to need replacement (they come with "tracks" don't they?). It's loud enough that it bothers me when poking along slowly (2000rpms) in 2nd/3rd gear on quiet forest or neighborhood road. 20/50 oil. I think my other engines have made similar noises, but I'm not sure it was this loud. Thoughts/suggested tests welcome!

Tensioner oil feed blocked/clogged maybe?

Lol … I’m sure you have gone through every possible/potential cause in your mind already Greg. That being said, I would think if it was the timing chain itself, the rattle would be most noticeable right at start-up and low idle before oil pressure has a chance to build up . Especially when you’re starting it cold running 20w-50.

I once had a heat shield that came a bit loose and caused a rattle similar to a timing chain but only at a certain rpm range …
Drove me nuts trying to locate that rattle.

Are you positive that it’s not from some ancillary components, Alt bearing, WP, or even valve train? No overadvanced timing? Disconnect fan belt?

Thanks all. Timing is good, definitely a mechanical noise. Good idea to remove the water pump and alternator from the equation so I'll try that. Another possibility is the crank scraper I installed. I know it had some clearance issues before that I fixed last time, but I think it was Redroadster that commented I could be adding a "vibration source" when I was posting about trying it. Perhaps something I should have considered, but honestly I think the motor made noises like this before too? I thought it was the dip stick rattling against the scraper (for some reason before and after the scraper my dip stick has been difficult to use... resists coming out, seems to need to bend some to go in and out). I wiggled it and it didn't change, but I'll check that again too.

I get the typical taptap rattle on start up before oil hits that quickly goes away, but this is different. No obvious issues with valves (lash is good, springs in place, rockers wearing normally) and the tensioner is shimmed just fine. The closer I look, the more it seems to come from the front of the engine. I sure hope it's something external.

My money's on the crank oil slinging cutoff thingy
Take the 20-60w 0ut put in 5-30, see what's what it may have little flow to the tensioner

Greg, have you tried listening with a stethoscope? They work very well at amplifying and isolating noise.

theunz wrote: Thu Sep 01, 2022 10:16 pm Greg, have you tried listening with a stethoscope? They work very well at amplifying and isolating noise.

I used a large, thick wood dowel and listened to the entire engine (much safer than the stethoscope I had which long ago BLASTED my ears)... Works great. I feel a lot better, as all sounds fine... mechanical but not slappy. I repositioned the dip stick and all but eliminated the sound when I replaced it... pretty sure that's the culprit! Thanks!

Are you sure that it isn't pinging?

LOL your right about getting blasted by the stethoscope! Best to approach any metallic noise gingerly with it.

spl310 wrote: Fri Sep 02, 2022 7:59 am Are you sure that it isn't pinging?

Yes, it's a rattle at low load or free reving.

Try using a piece of garden hose won't blow your ears out and will id the noisy spot.