R34 neo problems

[Eire34neo]

Hi lads, r34 rb25det neo owner from Ireland .

Im having problems with intake valve clearance on stock rb25det been to low of a clearance in some cyinlders on intake side only . The engine idles at 800 and doesnt go up or down but the engine has bad vibration and incomplete combustion and trying to pass emissions test My co levels are 5.18% low idle and high idle is 8.95%. .

Head gasket has been changed to stock head gasket and head got skimmed (wasnt blown or anything just bought a whole gasket kit and did everything)

I have attached compression test and valve clearance test results . I dont have a leak down tester i must buy one this week.

I have no issues with Cam timing or ignition timing just so thats clear.

Hope someonecan shed some light on this for me as i know the aussies have serious rb knowledge as i spent a few yeads over there. thanks

 

Edited July 10, 2022 by Eire34neo

[Eire34neo]

Sorry for double post but what i mean by haveing no issues with cam timing i just mean the cams and crank correlation with timing belt on is correct.

 

I obviously had the cams out and back in but i wound the crank back so all pistons were even and then installed cams . 

 

I was thinking i bent valves or something when i checkes valve clearance and found intake valves to tight but then i realised they should be lose if the valves were bent and not tight like mine are

[GTSBoy]

I've copied in my reply from PM below. The first bit about a "bad cam" relates to a question in the PM. I think the lack of a clear sequence in the OP above is the same as in the PM question, so my reply works here equally well. Let's see if we can clarify that and get into it from there.
 

Quote

 

Won't be a bad cam unless that engine has been abused with no oil changes. If it had been, you would have seen the damage when you had it apart.

Your story above doesn't make it clear what order things have been done. Why was the head off? To fix this misfire/noise problem? For other reasons? If the head was off to solve this problem, how come you suspect something in the head's condition, instead of having it checked out while it was off, etc etc?

It's more likely to be electrical. A misfire, either from fuel or spark. Is the ECU throwing any codes? Have you checked engine earths, etc, all the usual shit?

 

 

[Duncan]

On 11/07/2022 at 9:01 AM, GTSBoy said:

I've copied in my reply from PM below. The first bit about a "bad cam" relates to a question in the PM. I think the lack of a clear sequence in the OP above is the same as in the PM question, so my reply works here equally well. Let's see if we can clarify that and get into it from there.
 

 

And also, did the problem only start after the cam was removed or was there an issue (same or different) previously

[GTSBoy]

I've had some further back and forth with our Irish friend. Car was fine before head came off. Head only came off for pre-emptive/reparative replacement of many gaskets to correct oil leaks, etc. Valve stem seals were put in by a shop. Close inlet clearances and rough running only became apparent after reassembly. There's no information on whether the clearances were tight before the engine was pulled apart.

I'm out of ideas beyond taking the head back off, taking it (with the cams) to the head shop, and perhaps testing for teh head having gone soft, leading to valve seat recession.

[Duncan]

hmmm...I'd still do the leakdown test that he mentioned first, some head issue is suspicious but better to rule out other issues. And cams should always go with the head for any work with solid lifters, they can set everything in the shop

[Eire34neo]

Hi lads. Thanks for the help cant beat the aussies to be fair always helpful even to a paddy irishman😃

Here is the full story just so we are on the same page . I rushed the original post and my message to Gtsboy

Its a 2000 r34 4door gtt rb25det neo auto(for now) with 236thou kilometers all stock apart from mid section to back box is aftermarket exhaust still has cat and original downpipe and 02 sensor .

I got the car from japan back in october last year drove it for a few days because it was winter here and i didnt want to drive it without it been undercoated properly. The car is mint to be fair not a spec of rust apart from one or 2 small surface not even worth talking about. Rust is a big thing in Ireland especially in winter as we salt the roads. I put it in the shed and totally stripped it all suspension out engine and fuel tank out etc.  

The car was runing grand apart from the turbo squealing like a supercharger at 5k rpm.

 

So i went and cleaned the underside and epoxy primed it and then brushed and sprayed seam sealer everywhere , some stone chip and then a coat of white paint. Turned out well better than engine😅

I bought a full gasket kit,sprak plugs,oil and filter and went ahead and stripped the engine to the block. Sent the head away without the cams as the machine shop asked me if they were out already.

Got the head skimmed and valves cleaned/lapped and valve stem seals changed. Went to collect it and he said everything was really carbed up and the stem seals were bad but now everything was perfect he said. I didnt ask about a leak down on it at the time and i wasnt thinking about the valve clearances atall as i thought nothing would of changed.

 

Stuck the head back on with original nissan gasket and nissan head bolts as the arp studs seem to be like golddust around these parts for rb25. I put the engine back from tdc to install the cams as to not hit valves so that should be ok. All cam timing and base timing is perfect all lines match and 15degrees before tdc is achieved with ease . Normal idle at 800rpm with no flucuating   . It just has bad vibration and pops as you hold the throttle, bad lifter tick and weird start when hot is another thing. Doesnt just fire up like nornal its weaker.

 

Only codes i ever got when driving it since all the work is done is code 21 for ignition singal so i bought 6 new nissan coil packs and checked harness with a meter. And code for the o2 sensor.I now had noticed the hot start was weird and the vibration and sort engine jolt came into it at idle and upto around 2.5k rpm. It pops 90% of the time under throttle . Anything over 3k seems to  start smoothing out. I pulled the coils and plugs after few days driving and they were white as. Range 7 so i changed to 6s with the new coils.

 

The car wont pass emissions test as the co levels are through the roof on her. I dont have any way of reading afr . Stock ecu with the nissan label still on it. Do people still do nistunes ive asked afew tuners around here half them dont even no what im saying haha. Also whats the cheapest option I have for scan tool software for the standard ecu system so i can check stuff as i wont be buying aftermarket ecu just yet. 

 

Now im here checking valve clearances and compression testing etc freaking out😆 

 

Its summer here now and all i want to do is drive the broad minded person😁 excuse my Irish I added a few pics of the build lads let me no what you think thanks for all your help

[Duncan]

Wow that is a big freshen up, hope you get to enjoy it for many years after that.

A couple of things. If you aren't happy with the valve clearances you need to get that sorted. Both too tight and too loose are a problem and going to cause damage. I've only ever had a machine show do it for me so I don't have any useful advice there other than I've heard of people using compressed air in a spark plug hole to hold the valves closed while changing springs with the head on

Secondly, as everything has been apart, more than likely there is just something wrong on re-assembly. I'd be re-checking all the connectors are well seated and the earths in particular are good, it sounds like you have a misfire from idle. coil pack and coil pack looms are a common failure

Also, since the plugs are white and it runs OK once you get a few revs on board it may be running very lean at idle, is the vacuum line to the fuel pressure regulator attached and not leaking? And, have you changed the fuel filter and/or the pump?

Finally, I believe Nissan Data Scan is the go to for monitoring the standard ECU

[Eire34neo]

Hi Duncan thanks for that. I have changed the coil packs for genuine nissan ones i replaced all 6 connectors on the coil harness as all clips were brittle and broken. Tested the harness for continuity all seems ok. 

 

The fuel vaccum line is connected. When i discconect it runs like shit you can hear it hunting. The fuel pump is standard.

 

Tonight i got to remove the cams just to have a look as i didnt get a leak down tester yet (order in) they dont stock shit here anymore. All seems ok with the cams and all caps clean as a whistle. 

 

I measured the valve protursion on both intake and exhaust valves stickng out top of the head. Obviously i didnt do that when i first took it of or take clearance values down which i should of. I wasnt thinking about the the skim and valve lap would cause that much clearance issues .

The inlet valve sticks out 5mm at top. Exhaust is 2mm. I dont think anyone will have a neo head lying around they could check. 

Question is do i need to get the valve tops cut or get the shims surfaced milled or grinded whatever they do. I really dont want to take the head of again she needs to be driven haha. So shims ? But is that allowed are they not hardened steel will i ruin them or take from life span 

Dont you think all my valves are out way out of spec and all to tight . Surely this would cause the weird start when hot becuase the clearance gets smaller when hot. I know Gtsboy thinks they wouldnt cause me this hassle either i just want to have everything to spec so i know the problem doesnt lie there and i can move on.

The machine shop should of known as i told them had solid lifters neo head etc. But i didnt give him the cams as he didnt ask for them just asked where they out already.

 

Thanks

[Duncan]

Like I said, I'm not a head guy, but there are separate shims under the buckets that you switch out for the desired clearance (assuming you have an endless collection of different sized ones handy). You've had 2 of the buckets out, just have a look underneath them, the shims generally stick to the bucket

EN-20 and EN-21 of the GTR service manual show specs and process for RB26, sorry I don't know specs for the 25 NEO

[Dasmbo]

Hi it sounds similar to a problem i helped a fellow skyline owner with the machine shop he had used to refreash his cylinder head had mixed a couple of valves up when putting it back together as intake and exhaust valves are different lengths once we changed that all was good but had to remove the head check to see if they are all at the same height inlet and exhaust by the way make sure you get the clearencs correct as your output power will suffer

Edited July 12, 2022 by Dasmbo