RS Disposal Posted January 8 Share Posted January 8 I just recently had to do a major repair on my engine, a 1979 Mack ENDTB 675 which required replacing the turbo (previous topic was "Looking for 1979 Mack head"). Wasn't able to find a direct replacement but this rebuilder stated this one was speced out to be a replacement. The rebuilt turbo has a larger diameter compressor housing (cold side). I have noise in the intake. The truck seems to be running ok, doesn't appear to be missing, idles smooth. This truck never had a boost gauge before for a reference comparison, but the boost gauge will flutter depending how far I'm into the throttle. A quick question, pretty sure this turbo is producing more boost than the original. From what I have been able to find out, the original was around 15 - 17 lbs boost. This turbo looks like it will boost upwards of around 20 lbs boost. I don't let it run that high before I back out of it. Is there a possibility that this much boost for THIS engine might be cause some mechanical issues? I know my Cummins N14 runs around 20 lbs when going up the canyon where my trucks work, but that that is a totally different and much larger engine. I will try and upload a video/audio file in the morning with the noise. If this is the new normal after this engine repair, I'm good with that, because it was a major repair. Rear head rebuilt and #4 piston replaced. I just don't like noises that I don't remember from before the breakdown. Quote Link to comment Share on other sites More sharing options...
JoeH Posted January 9 Share Posted January 9 Considering the same year block can put out 25psi boost on the 283hp version I can't think of anything that'll get hurt at 20psi. That head you had rebuilt would make me nervous, it took a beating. Wouldn't be surprised if a valve seat worked itself loose... The fuel pump is what limits the truck on power. The turbo will only put out enough air to match the fuel pump needs. I think. Basically the fuel exhaust drives turbo, so when you run out of fuel potential you run out of turbo potential. 1 Quote Link to comment Share on other sites More sharing options...
fjh Posted January 9 Share Posted January 9 12 hours ago, JoeH said: Considering the same year block can put out 25psi boost on the 283hp version I can't think of anything that'll get hurt at 20psi. That head you had rebuilt would make me nervous, it took a beating. Wouldn't be surprised if a valve seat worked itself loose... The fuel pump is what limits the truck on power. The turbo will only put out enough air to match the fuel pump needs. I think. Basically the fuel exhaust drives turbo, so when you run out of fuel potential you run out of turbo potential. The older two valve V8 would make a popping sound when a valve seat came loose and could really be heard when shutting down the engine pop pop pop as it was being shut down! the seat was big enough it would not fall out un like the 4 valve V8 ! That said the six rarely had seat issues 2 or 4 valve! Just sayin! 2 Quote Link to comment Share on other sites More sharing options...
terry Posted January 9 Share Posted January 9 2 hours ago, fjh said: The older two valve V8 would make a popping sound when a valve seat came loose and could really be heard when shutting down the engine pop pop pop as it was being shut down! the seat was big enough it would not fall out un like the 4 valve V8 ! That said the six rarely had seat issues 2 or 4 valve! Just sayin! I had a 237 engine that had a loose exhaust seat, ran quite awhile that way, had the pop,pop when you let off it or coasted with it, when I pulled the head you could see where it was moving up and down in the carbon buildup. Terry 2 Quote Link to comment Share on other sites More sharing options...
RS Disposal Posted January 9 Author Share Posted January 9 If I had a loose valve seat wouldn't I get a mechanical sound rather that what sounds like a muffled pop pop? The sound only changes frequency with engine rpm, doesn't really get any louder or softer whether under load or coasting. Truck doesn't appear to have an engine miss and it pulls smooth. Going to, as I stated in my first post, get a clip of the noise and post. Going to do some trouble shooting, check exhaust temps with an infrared heat gun and also use a stethoscope and see what I can hear and find. Will pull rocker covers and double check valve lash and see if something there has changed. Just frustrated I can't seem to locate. Quote Link to comment Share on other sites More sharing options...
JoeH Posted January 9 Share Posted January 9 24 minutes ago, terry said: I had a 237 engine that had a loose exhaust seat, ran quite awhile that way, had the pop,pop when you let off it or coasted with it, when I pulled the head you could see where it was moving up and down in the carbon buildup. Terry My '79 makes this kind of a pop pop on throttle let off. Let us know what you find on valve lash. Quote Link to comment Share on other sites More sharing options...
Popular Post Joey Mack Posted January 9 Popular Post Share Posted January 9 Have you unhooked the air compressor intake pipe, to see if the noise is the compressor? 1 2 Quote Link to comment Share on other sites More sharing options...
Popular Post JoeH Posted January 10 Popular Post Share Posted January 10 Fair question, Joey. To elaborate on noises the air compressor can make: my '79 makes a ticking sound when the air compressor is building air pressure, and stops when the governor cuts off the air compressor. It's subtle, but maybe yours is behaving similarly? 3 Quote Link to comment Share on other sites More sharing options...
RS Disposal Posted January 10 Author Share Posted January 10 15 hours ago, Joey Mack said: Have you unhooked the air compressor intake pipe, to see if the noise is the compressor? I have thought of that but haven't done it. I wouldn't think that would cause the boost gauge to flutter Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted January 10 Share Posted January 10 Does your air compressor get it's air from the manifold? If so, it is taking in boosted air.. 1 Quote Link to comment Share on other sites More sharing options...
mechohaulic Posted January 10 Share Posted January 10 16 hours ago, JoeH said: Fair question, Joey. To elaborate on noises the air compressor can make: my '79 makes a ticking sound when the air compressor is building air pressure, and stops when the governor cuts off the air compressor. It's subtle, but maybe yours is behaving similarly? some have/had the sound similar to a shaking of spray paint rattle can, 1 Quote Link to comment Share on other sites More sharing options...
RS Disposal Posted January 10 Author Share Posted January 10 2 hours ago, Joey Mack said: Does your air compressor get it's air from the manifold? If so, it is taking in boosted air.. compressor intake is before turbo 1 Quote Link to comment Share on other sites More sharing options...
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