Odd noise at 3500 rpm under load

Austin

Austin

Daily Driver
Have been driving the 68 850 Spider a bit on weekends when traffic is slow enough to not feel like I'm risking too much. Have encountered an odd noise around 3500 RPM when under load (does not occur at 3500 RPM downhill, just under load). Sounds a bit like diesel clatter but I don't think it's pinging, as that's a different note. More of a clatter.

Is this a sign of an oil pump going bad? Transmission wear?
 
Might be the timing chain they can get loose and have a resonance slap at certain rpms

Check with Jeff he might have some input
 
kmead said:
Might be the timing chain they can get loose and have a resonance slap at certain rpms. Check with Jeff he might have some input
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If this is engine noise, my first thought would be "pinging", second would be timing chain slap as you noted. After that, I'd investigate valve adjustment, an exhaust leak (upper gasket), loose fan belt(s) or maybe a loose distributor cap or rotor. Hopefully not rod knock. :(

Is the sound intermittent, rhythmic or constant once at that rpm under load?
 
Jeff Stich said:
If this is engine noise, my first thought would be "pinging", second would be timing chain slap as you noted. After that, I'd investigate valve adjustment, an exhaust leak (upper gasket), loose fan belt(s) or maybe a loose distributor cap or rotor. Hopefully not rod knock. :(

Is the sound intermittent, rhythmic or constant once at that rpm under load?
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Seems to be constant while in sync with load, and will decrease with lower RPM or reduction in load but still at 3500 RPM. An example would be going up a hill near my house, it was not present on the high load/steeper part but was present on the longer slope/longer term load, and completely absent when going down the slope on return, though RPM was 3500 and above. I will have to listen again to evaluate the term "rhythmic" as that is possible.

I would think (read as: 'hope') that rod knock would be present at the same RPM whether under load or not, but I may be optimistically naive there.

Since there was some pinging, which was much higher in note/tone,for some reason it strikes me as possibly the gear box. It was a lower tone but still metallic (it's really hard to describe noises in print, ya know?) I haven't changed its oil yet, though it's in the plan.
 
I think it's probably the timing chain like Karl mentioned. I have the same thing on mine. I had it replaced and it's a lot better but it still comes up here and there but not as severe. I also have a long-ish hill by my place where I first noticed it. Seems to be less severe at higher RPMs so I tend to wind out the motor a bit when I'm on that hill now. I feel like 3500 is right where the power band starts on that little 903, I wonder if has something to do with that. Let me know what you end up finding.
 
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