timing chain frustration

at 75000kms my buddies 1980 400i was making a fairly pronounced chain rattle and upon inspection i found the adjuster screw level with the jam nut. we decided to pull the motor and replace the worn components and reseal it. the cam gears,idler gears,tension and fixed shoes and chain all showed considerable wear so all were replaced as well as the small bearings(idler,water pump etc). the only parts i reused were the tension pads on the upper covers and the tension spring as they looked fine.after days of scraping 40 year old gaskets and a complete clean up every thing was reinstalled and adjusted. after initial start up i was pleased with the way it ran so a good road test and final adjustments were next. when he returned from a 20 mile drive i could hear a noise at or above idle ... a familiar chain rattle. the only initial adjustment recommendation i could find was 20lbs of force between the cam gears should deflect the chain by 1mm. up on the hoist with the motor running i backed out the screw until she rattled continuously and adjusted in a 1/4 turn increments until it was quiet. at least it was at idle(1000rpm), at 1100rpms it rattles and at 1200rpms its quiet.it you snap the throttle it will rattle briefly and once it returns to idle its quiet.i figured that the tension spring was the culprit so i ordered one up and replaced it in frame (no easy feat). still the noise remains,only when at operating temp and only at or near 1100rpms. i have tried the adjustment tighter and looser with no change in the noise or speed at which it occurs. i only used the best parts on this job and was very careful with assembly. i know its the chain making the noise as i can hear/feel it while adjusting the screw so what gives? im ready to shoot this horse.

 

thank you for your responses. I did run the engine without the vacuum pump. the noise only occurs when hot, quite when cold. I have some other projects on the hoist and had to walk away from the 400i for a minute. yes the motor expands with heat ,shouldn't that make the chain tighter? thanks for the link raemin , I have read it before when researching the initial replacement but will reread it again to see if I missed something......