# 95 Nissan HB truck - engine knock when cold



## zootal (Sep 27, 2007)

My 95 NIssan truck has developed an engine knock at ~3000 rpm and above, when cold. It's a very pronounced knocking noise - sounds like very rapid hammer blows. It seems to come from the upper engine area, but not 100% certain. It goes away after 10 or 15 minutes of engine operation. Is this enough information for anyone to take a guess as to the cause?


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## marc780 (Sep 6, 2007)

Sounds like piston slap or bad piston pin or pins


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## zootal (Sep 27, 2007)

marc780 said:


> Sounds like piston slap or bad piston pin or pins


I doubt it's the wrist pins - wouldn't they make noise at low speed? Piston slap I could believe - it's made a noise when cold under certain circumstances since I bought it with 14k miles. I hope not - I really don't want to have to pull the engine until next summer, when I'll have the time and money to do something about it.


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## marc780 (Sep 6, 2007)

I hope i am wrong about your engine cause there's no cheap fix - without hearing the engine im just guessing at the likely causes. But lower engine noise is almost always serious though; so unfortunately I'm not sure you'd make it to next summer with this engine. I'd find a good mechanic to listen to your engine and find out what he thinks it is -


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## zootal (Sep 27, 2007)

I'm not sure it's lower engine noise - IE bearings, wrist pins. That type of problem, when that loud when cold, doesn't go away when the engine is hot. I'm voting for piston slap, as the pistons expand quite a bit when the engine warms up, and are capable for making quite a bit of racket when cold and no noise when hot. It's almost academic - with over 100,000 miles on the engine, if I have to pull it out for any reason, I'm going to do everything - bore, new pistons, surface head, valve job, etc. No sense in doing the job half way, just to have it blow in 20k or 30k miles. <sigh>

Any words of wisdom about going through this motor? Would I be better off finding a short block from the local engine shop instead of doing it myself? I used to work as a mechanic, still have my tools, have (successfully) been through several engines but 1) I did electrical and carburetors (remember those? I can go through hitachi carbs with my eyes closed, and never misplace a ball or spring) mostly, 2) I retired my tools over 20 years ago


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