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Guru Needed, New 25/30 Engine Startup Problems!

Black_R33

By Black_R33,
in Engines & Forced Induction

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Black_R33 Enthusiast

Black_R33

Posted
Posted

Brand new RB25/30 long motor built by RB specialist, installed it last night and it has no comp on cycl 5! Holy shite. Very confident nothing got in it during installation and don't doubt the builders skills but what could it be? If I had to guess I assume it must be stuck valve but how? How does the hydraulic set-up work? Could they be not yet pumped up? After getting oil pressure up (took the inj fuse out and cranked) I started it for about 1-2 mins thinking the plugs where fouled and it would fire up on all 6 after a bit but no good... I don't want to run it anymore as all the fuel in the cylinder will be washing the bores clean and that would be bad.....Any ideas before I have to pull the rocker covers off and start to investigatagtion the top end first?

:)

Mesmer Enthusiast

Mesmer

Posted
Posted

This happened to my 25 when i rebuilt it. We got a little careless at the end of the rebuild and didn't check the lifters as they where fine when i pulled the engine down.

At least 5 or so where locked up and not letting the valve close all the way. Replaced them and its been running fine until now.

So that may be your problem too.

John

  • 2 weeks later...
Black_R33 Enthusiast

Black_R33

Posted
  • Author
Posted

Important Update!!!!!

Did a leak down test and found exhaust valves open on cyl 5 ! AHA! Pulled the cams out and wacked 2 new lifters in it (OW!$100 each from nissan). Put it back together and cranked it.........Beautiful-No 5 no probs.... but now no comp in 1 and 4.....WHAT THE? We chopped one of the old lifters in half and found some carbon in it so we think that the lifters must be sucking that crap into them when they pump up and can't bleed down thus holding the valves open. Looks like I need to replace them all!! We have been bleeding them down before assembling the head, this is the right procedure yeah? If we have to replace the lifters does anyone know of a cheaper supplier than oem? Anyone rebuilt heads with similar probs got any stories or techniques to share? Would love to hear your thoughts!

Cheers

P.S Still pretty happy its not terminal though....phew! :)

Cubes Grand Master

Cubes

Posted
Posted

It has been suggested to me that this 'may' be the cause of my valve float, as occasionally on startup i get the lifter pump up miss. :)

I'd be interested if there is a cheaper than nissan way out of it.

Similiar year VG30 lifters are the same part number so that may be a start, well for myself with the R32 head anyway, possibly the US may have something aftermarket.

Cubes Grand Master

Cubes

Posted
Posted

No idea...

Black_R33 has experienced a bad lifter holding valves open and now I'm being told that my problem may be partially my lifters due to a couple of symptoms; the all of a sudden valve float and lifter pump up i'm experiencing and the occasional same valve float lifter pump up miss.

No idea.. Will find out when the head comes off. I had planned to pull it off this mid term break, it won't be happeneing as I'd prefer to have a little extra money stashed away just incase it gets expensive. :S

Lifter pump up miss cannot be mistaken, its a different sound to an ignition or fuel miss.

I'm sure black_r33 agrees. :domokun:

Mc. Stocky... believe me I have fantasized about a nice solid lifter conversion + a set of gtr high lift cams... high lift = lots and lots of mid range. >_<:ph34r::)

darkstar Contributor

darkstar

Posted
Posted

Try a Wrecker.....

Could also be something trival like swarf (tiny filings) either on the valve seat or in the valve guide causing them to stay slightly open.

The head should have been pressure/vaccum tested before assembly - this would have detected it before you installed.

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