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Rb25/30: Bad Lifter?

ST240

By ST240,
in Engines & Forced Induction

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ST240 Enthusiast

ST240

Posted
Posted

Hey guys.

I'm hearing a strange sound that i at first thought was spark knock due to a poor tune or even rod knock or worse, but I'm leaning towards a bad lifter due to the high consistency/repeatablity of the sound (and not to mention I've added a ton of fuel and killed timing to make sure). These are the details of the sound:

-Sounds like a rapping similar to spark knock

-Only occurs under medium/high load acceleration AND

-Only occurs above 3k rpm OR around atmospheric on the boost gauge

-Does not occur under very light acceleration up to redline

-Does not occur when revving in neutral

-Does not seem to be heard at engine RPM

-Just started occuring within the last 50 km on a new RB25/30 build

I had to spin the cams around several times when the engine was dry to put the timing belt on. Is it possible there's air in the lifters now? Is there anything I can try before i proceed to pull the damn thing apart? Any other ideas?

Thanks.

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DVS JEZ Grand Master

DVS JEZ

Posted
Posted

definately has a bearing type knock not a pinging sound and is wierd how it only does it under load,

how rich is it when it ramps up and makes the sound?

my 2 cents is bearing knock but in early stages and needs load to be evident

T04GTR Grand Master

T04GTR

Posted
Posted

drain your oil into a clean container and sit it in the sun. you will be able to see if there is any bearing material in it. if so, $60 worth of oil and $80 worth of new bigends is cheaper than a new bottom end....

better to be safe than sory.

GTScotT Grand Master

GTScotT

Posted
Posted

To test if its big ends, warm the motor up till its capable of making the sound when free revving, then disconnect 1 coilpack at a time until it doesnt make the sound anymore...

If one of the coilpacks being undone cuts the sound, you know youve got rod knock.

I am all for trying to slap in a new set of bearings too provided the crank isnt marked. Had one chew RIGHT OUT on me before and luckily didnt mark the crank. Motor is still going today :)

ST240 Enthusiast

ST240

Posted
  • Author
Posted (edited)

Thanks guys I'll try the thing with the oil.

The thing is it doesnt make that sound when free revving with no load. Thats the strange part. And it really doesn't seem like its at engine RPM which is why I'm thinking valvetrain... FML.

Edited by ST240
ST240 Enthusiast

ST240

Posted
  • Author
Posted (edited)

I understand that... But shouldnt you be able to hear rod knock just free revving the thing?

It definately isnt spark knock. Just logged a run, AFRs in the low 10s, timing was 10* (!) map was anywhere from vac to 4 psi. And it still makes the sound as loud and as consistent as ever. Please tell me that isnt spark knock, although i wish it was.

Edit:

Here it is free revving. No knock sound.

Edited by ST240
ST240 Enthusiast

ST240

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Posted (edited)

Well there was shiny particulates in the oil/filter. Quite a bit and smaller than grains of salt. The oil also had a silvery swirl to it. For comparisons sake i changed the oil in my dd 240sx beater with at least 2k+ km since last change and there wasnt nearly as much. Under half the amount. So for the RB to have double the f**king particulates on 200 km doesnt look good at all.

Is there any point in pursuing further? Are particles typical on a rebuild? I was going to try driving it while disconnecting one injector/coilpack at a time to see if i could isolate it. But i definately do not want to wreck the crank. FML. Serious.

Edited by ST240
Bliksem Veteran

Bliksem

Posted
Posted

Its not hard to remove the sump and take a look. If its a big end bearing you'll find a heap of copper particles sitting in the sump. You'll also be able to push on the rods to see which one has any signs of movement/wear.... as long as the crank is still ok you should be just looking at some new big end bearings...

DVS JEZ Grand Master

DVS JEZ

Posted
Posted

yeah id remove the sump, take the caps off the rods and check them out, see if its more than 1 failing, if you cant find anything wrong there then remove the main caps 1 at a time and check the bearings there too, refit it before removing the next one.

if you find a failed bearing you need to try determine what caused it, might need to measure the crank to see if its the correct size for the bearing used.

talk to your machinist that machined the engine for rebuild to see what they think caused it.

if nothing is found get some new bearings, what brand did you use? maybe try a different brand.

i wouldnt drive it anymore or the cost of a new gasket for the sump and some big end bearings might turn into and new crank

ST240 Enthusiast

ST240

Posted
  • Author
Posted (edited)

You guys are gonna hate me. But i have to post this up incase anyone else has the same problem:

The nuts holding the turbo to the exhaust manifold were loose. That sound was obviously the exhaust pulses escaping once there was back pressure on the turbo. I tightened them up and they were loose within 40 km! To solve this, I fabbed up some little "tabs" similar to the ones that come stock on our RBs, that you bend against the nuts to stop them from backing off.

Thanks guys :P .

Edited by ST240

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