# Engine Trouble - To fix (replace engine) or not...hmmm



## cbeatti2 (Dec 29, 2011)

Hi

My recently purchased 1986 300ZX (non-turbo) with about 190,000KM (118,000 miles) has what sounds like a rod knock, from what I can tell from youtube videos. This seems to mean that the main bearings are pooched and perhaps the previous owner ran low on oil and didn't notice until it was too late...the oil pressure sending unit is disconnected I see (grrrr). The car seems to be in good shape body wise and I really hate to start selling parts from her, being such a classic car, yet at the same time don't want to drop too much money into it for fear there are other expenses shortly down the road. I believe the clutch was changed not long ago but other than that I don't know a lot about the car other than what I can see...good glass all around, dash isn't cracked, tires are still in fine shape, not much body rust. Could use a paint job though...

So I trying to decide if i should go to the trouble of changing out the engine and risking having more engine trouble with the next one, or other issues, or just let her go. Obviously this isn't something that anyone can definitively answer on the forum, but what might be the consensus among 300ZX owners. Or maybe someone has some other ideas on the knock sound...initially I thought it might be a stuck lifter but it seems to be a deeper knock than that, and I have checked the timing belt to be sure it hasn't jumped a cog or two and a piston is hitting a valve.

Happy holidays


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## rogoman (Dec 16, 2004)

Reconnect the oil pressure sending unit and see if shows oil pressure. The reading at idle should be around 11 psi and at 3,000 rpm around 65 psi. If you're not getting anything, the sending unit may be bad; if you suspect a bad sending unit, remove it and install a temporary oil pressure gauge. If the pressures are extremely low, then there may be one or more wiped out rod/main bearings or the oil pump is bad or the oil pickup screen is plugged up.

If you've got a rod bearing knock, it can be easily narrowed down to the bad cylinder. While the engine is idling, pull one plug wire at a time; when the knock quiets down somewhat, that's your bad cylinder.


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## OriginalGinger (Apr 19, 2011)

Being an older car parts arent extremly hard to find. that VG was used in a bunch of cars like maximas and frontiers or exterras and the 300. If you like the car enough and its not all rusted out id say go for it. I just got done doing the same thing but i was looking for a project though  Heads are easy enough to dissassemble and clean and if you have an engine lift the oil pan isnt hard to get off to check the rods and crank. I get about 30 when i start the car and about 25ish after its been running for a minute in idle and about 50-60 when boosting.


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## cbeatti2 (Dec 29, 2011)

Thanks guys. 

Yeah, maybe I shouldn't write it off so quickly. I'll go through the list of things to try, and maybe do a compression check to see how the overall rings/valves are if nothing catastrophic is revealed during the first checks.

I've also been investigating the replacement engines (VG-30E's) to see if there was an easy swap type in my area...the Maxima might be a good candidate...looking for one that doesn't require much in the way of modifying the engine to fit the Z31. 

Cheers!


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## cbeatti2 (Dec 29, 2011)

Well it looks bad for the engine...basically it is running on three cylinders as the compression is so bad on the other three. As I contemplated the swap of the engine I decided to take a closer look at the underside of the vehicle to be sure all that effort would not be in vain. What I am now noticing is that the "suspension member stay" on each side is not very well attached to the body at all, due to the rusted body at this point. This seems like it might be fairly easy to reinforce and I suspect this is a common problem with the Z31's of this age. Do anyone know if this is can be repaired? Thanks, in advance.


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