Engine Rattle from 2500 to 3000 RPM

[1969911T]

Looking for ideas where this rattle comes from. Kind of sounds like valves that are not adjusted right.

Happens on hot or cold engine
Does not happen when accelerating very slow
Happens is all gears when accelerating fast
Does not happen when idling, nor when transmission is in neutral
Just started doing this about a month ago.
Sounds like it’s on the left side of the engine, but not sure

Adjusted valves, they were fine
All accelerator nozzles have what looks like plenty of gas coming through them.
Thought I got some bad gas(always use 87 octane), but 91 octane made no difference.

Engine is stock 69T, rebuilt 150,000 miles ago with mechanical chain tensioners, original chains(270,000 miles old!), original webers(with air leakage through the butterfly shafts), new Marelli distributor, MSD ignition, never checked accelerator pump quantity, but have never adjusted it either.
Power is no different, that I can tell. Revs to redline just fine. Have pressure regulator on fuel pump and adjusted floats on webers about 2 years ago.

Any suggestions what to check?

My guess at this is an accelerator pump issue since it goes away at 3000 rpm when I think the main jets take over and I need to get a measuring vial for the fuel amount.

Thanks in advance for any ideas
Steve

[edmayo]

If you have that much mileage on mechanical chain tensioners that would be the place I'd go. They are now out of adjustment!

[1969911T]

If you have that much mileage on mechanical chain tensioners that would be the place I'd go. They are now out of adjustment!

Is there a rule or measurement about how tight to to adjust? I just do “snug” which is very subjective! The left tensioner had the nut come loose about 7 or 8 years ago with major rattling. Went back with loctite

[edmayo]

There is no published procedure for adjusting mechanical tensioners since they were never used excrpt maybe by the race department. Which nut are you talking about, the 8 mm tensioner nut or the 42mm cam nut?

[1969911T]

There is no published procedure for adjusting mechanical tensioners since they were never used excrpt maybe by the race department. Which nut are you talking about, the 8 mm tensioner nut or the 42mm cam nut?

Ed,
My tensioner is made from the original by threading the cylinder and inserting a bolt with a nut under the bolt head(Not Porsche design!!). I adjust the bolt against the sprocket to get the chain "snug" then use the nut as a lock nut to hold the bolt in place. Lasted for over 150,000 miles.

I think this works because the 69T is the lowest HP engine made, so the heat is less. I figured the steel chain thermal stretch is less than the magnesium case and aluminum parts, did not want the cold chain to be very tight. I am now suspecting the right side tensioner is loosening since the left did this a few years back.

Ever had a chain break in an engine? I figure I will get new ones whenever I rebuild this again.
Steve

[RSTarga]

You live a charmed life.

[66S]

I use a screwdriver to push on the idler pulley, using the pin as the fulcrum, to a point where the chain slack is gone and look at the clearance between the mechanical tensioner and the idler pulley arm, should be about 1/4”, they give that clearance and provide a little block to check it against with the tensioner kit but I’ve forgotten it and just go by feel. Mechanical tensioners are the cheapest and most fail-proof tensioners but the y should be checked and adjusted every 10,000 miles. How about $500 930 tensioners? Pure profit. And with solid tensioners your 911 can roll backwards in a forward gear with the motor off on a hill and not retract the tensioner like hydraulic tensioners. The motor sounds like hell when it starts up after that. And while I’m at it how about those microscopic c clips on the new timing chain master links, don’t like those at all.

[1969911T]

Thank you Ed! It was a loose chain because the jam nut got “unjammed”on the right side, about 0.1” more on the chain tensioner and the problem went away. Used shims instead of depending on a jam nut. Changed the main seal and found a leaking oil cam line, while I was in the area.

[edmayo]

Happy to hear you got it fixed, and you seem to like the solid tensioners, I would never use them, but as long you're happy with them and keep up with adjustments keep doing what you're doing.