eshack93 Posted March 13, 2022 Share Posted March 13, 2022 Alright I’m at a loss here. Parked the truck because I heard a slight knock at higher rpm’s. Determined it to be fuel knock as 2 injectors were straight dumping fuel. Had them rebuilt, put a new air compressor, while I waited on the injectors, because the old one was tired. Ran the truck moving some dirt at the place just to see and once it got up to temp the knock came back but way harder. Pulled the pan, cylinder 2’s bearing was in bad shape. Full Inframed the truck as it’s been on my mind because the truck has had excessive blowby in my opinion for a month or two. Put it all back together yesterday and drove it this morning to “break it in” and no sooner did I get to the gate the hard knocking came back. New rods and mains, pistons, liners, rings, adjusted the valves, checked the heads for warpage. What am I missing here? All the valve springs, rocker arms, push rods appear to be just fine. The trucks is an rs686 with the two valve endt 676. ANY help is appreciated. Quote Link to comment Share on other sites More sharing options...
mrgumby Posted March 13, 2022 Share Posted March 13, 2022 E6 flat tappet cam did you check the cam and lifters? Quote Link to comment Share on other sites More sharing options...
eshack93 Posted March 13, 2022 Author Share Posted March 13, 2022 i have not. guess that will be next on my list. i glanced at the camshaft but did not do a thorough check Quote Link to comment Share on other sites More sharing options...
JoeH Posted March 13, 2022 Share Posted March 13, 2022 We had one of our endt676 engines drop a valve seat out on one cylinder once. Hell of a sound. It was fine when I shut the truck off one day, but when I started it up the seat must have dropped in while it was shut off. I kept the piston, it has chunks embedded in the crown. Too cool of a paper weight to pass up! Quote Link to comment Share on other sites More sharing options...
JoeH Posted March 13, 2022 Share Posted March 13, 2022 Oil pan and valve covers show you pretty much everything you need to see on an engine. Pull valve covers and check your pushrods and rocker arm, look for a cylinder way out on adjustment. Pull your oil pan to see the condition of the bottom end, look up at the camshaft and check to see if you wiped a lobe off with a broken lifter face. Quote Link to comment Share on other sites More sharing options...
JoeH Posted March 13, 2022 Share Posted March 13, 2022 Mack doesn't make cams for these engines anymore, don't know if PAI does. I think there's a cam shop in the Midwest (berry cams maybe?) That can weld and regrind a bad lobe. Quote Link to comment Share on other sites More sharing options...
eshack93 Posted March 13, 2022 Author Share Posted March 13, 2022 Definitely leaning towards the valves. Gonna pull the heads in the morning and send them off to be completely redone. I had the valves in adjustment and ran the engine, with the knock, and now the intake on number one and 4 are both loose. Gonna drop the pan and inspect the cam. I’ll let yall know tomorrow 1 Quote Link to comment Share on other sites More sharing options...
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