7.3 engine knock
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New User
Joined: Apr 2004
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7.3 engine knock
I recently purchased an '88 F350 with a 7.3 that had attempted to put the #7 exhaust valve thru the cylinder head. I replaced the piston and the head. After getting it fired up (it had set for 4 years) it knocks on number 7. If you crack the injector line it goes away. I have changed the injector 3 times and still have the noise. I have checked the pump timing, it's right. Compression is 400 lbs. and the taper and OOR on 7 was less than .003". I am wondering if anyone here has encountered this and if so what was the fix...
Thank you for your input...
Thank you for your input...
Posting Guru
Joined: Sep 2002
Posts: 1,897
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From: Northeastern Pa - USA
Is the noise coming from the top or the bottom ? Did you use the valves that were in the old head ? Maybe they are bent. Maybe the pushrods in that cylinder are wrong and moving the valves too far ? You said that you have changed injectors to validate the problem there . I believe if it were the pump, you would have problems in other cylinders. Are the pushrods in the right direction? I think the copper top should be up. Where the hell is malcolm when ya need him ?? I hope I shed some light on the subject for you. Good luck and keep us posted.
Junior User
Joined: Jun 2002
Posts: 54
Likes: 0
From: Covington,TN
Did, you replace the rod and bearing too? I would almost think with that stress the rod may be stressed and slightly bent which could cause the concern. I would pull the pan and look at the rod bearing and see if there is abnormal wear. Also did you measure the piston clearance in the bore, I have seen differences. The service manual shows clearance for #7 & 8 is 0.0060-0.0085. The rod length is 7.128-7.132 center to center.I hope this helps.
Posting Guru
Joined: Oct 2003
Posts: 2,438
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From: Monroe, WA
I'm right here Bilder. This is a tough one to do by message board. Is that a new piston you put in there or a used one? I would say the injector was the problem, but not after you tried 3 of them. Sounds like piston slap or the rod bearing is loose. You say there was .003" taper, but what's the piston clearance? Sorry, no miracle cure here, but I'll be thinking about it all day at work. 
