joes mack Posted August 26, 2010 Share Posted August 26, 2010 a friend of mine just bought a 84 rd with a 400 cummins in it and it has a knock in the engine he pulled the heads off and had them checked and a valvejob done on them and the engine still knocks we took a hose and placed aginst the heads/block and found that its coming from the aircompressor mounting point on the block. my questions are is there timing gears under the cover. and could there be a broke tooth on one of the gears making the noise??? i dont know a whole lot about cummins engines and im just guessing about the problem with this engine. but other than the knock the engine runs fine revs up good and sounds good. he drove the truck about 40 miles to his shop and it never missed a beat. he dont want to work the truck until it is fixed any info will be a great help. i allmost forgot it is a big cam 3 ..joe Quote Link to comment Share on other sites More sharing options...
rhasler Posted August 26, 2010 Share Posted August 26, 2010 a friend of mine just bought a 84 rd with a 400 cummins in it and it has a knock in the engine he pulled the heads off and had them checked and a valvejob done on them and the engine still knocks we took a hose and placed aginst the heads/block and found that its coming from the aircompressor mounting point on the block. my questions are is there timing gears under the cover. and could there be a broke tooth on one of the gears making the noise??? i dont know a whole lot about cummins engines and im just guessing about the problem with this engine. but other than the knock the engine runs fine revs up good and sounds good. he drove the truck about 40 miles to his shop and it never missed a beat. he dont want to work the truck until it is fixed any info will be a great help. i allmost forgot it is a big cam 3 ..joeDoes it only knock when the air compressor is unloaded? Quote "Mebbe I'm too ugly and stupid to give up!" Link to comment Share on other sites More sharing options...
joes mack Posted August 27, 2010 Author Share Posted August 27, 2010 it does it all the time thats why he pulled the heads thinking it was a valve or a seat. you can put the hose on the block, air compressor, and the heads and you cant hardly hear it but when you put it on the front of the engine where the compressor bolts its real loud. joe Quote Link to comment Share on other sites More sharing options...
rhasler Posted August 27, 2010 Share Posted August 27, 2010 I haven't worked on alot of Cummins engines either. There were timing marks on the accessory drive/air compressor. It's been awhile since I messed with one, but I think the noise was only there during the air compressors unloaded stage when the compressor was out of time. I'll see if I can find that information when I'm closer to a manual. Quote "Mebbe I'm too ugly and stupid to give up!" Link to comment Share on other sites More sharing options...
rhasler Posted August 27, 2010 Share Posted August 27, 2010 I think on the Big Cam III the accessory drive pulley should be at the "A" mark, the crankshaft on the air copmpressor should be rotated so that it's timing mark is at the 9:30 position. Manual also says the two cylinder air compressor does not need to be timed. Quote "Mebbe I'm too ugly and stupid to give up!" Link to comment Share on other sites More sharing options...
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