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RB26 cams in RB20 didnt work :-(

jnr32r

By jnr32r,
in Engines & Forced Induction

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jnr32r Proficient

jnr32r

Posted
Posted

I tried the swap on sunday unseccesfully....

Changed them without any problems, checked everything was the right way, i even had a copy of the GTR manual to guide me thru.

But when it came to starting it would start up and idle very bad.

It was very lumpy and it wouldn hold idle at all. I played with the PFC ign/inj adjustments, but it didnt make much difference.

At one stage it stayed idling but it was very rough. I also noticed that the boost gauge was only showing very little vacuum about -5mmHg.

After alot of frustration we started thinking it could be the valves are already opening as the RB26 cams are 0.1mm thicker than the RB20s at the lobe. Which in turn will push the the valves 0.05mm open.

I still dont really understand the hydraulic lifters concept and how they work. As i understand it when the lobe is pushing down the lifter it is solid as the oil cant escape and when it comes up it fills up with oil untill it gets pushed down again.

So i suspect what might be hapenning is that putting the RB26 cams straight in without taking the oil out of the lifters will make solid and thus opening the valves, and then never fully closing as the oil cannot escape fully.

If thats correct that would mean that before putting the RB26 cams in one should empty the oil out of the lifters.

Im not sure if thats right, but if someone can clarify the lifter operation that would be great.

RB20 cams are back in and everything is fine again....

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bbenny Mentor

bbenny

Posted
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Sorry to hear it didnt work!

you have had the exact same problem as 4 of us who have tried it. has anyone here bolted in some HKS or Tomie items into their RB20 yet? i dont understand why they should work as a bolt in, yet the GTR ones cause so many problems...

Roy Grand Master

Roy

Posted
Posted
After alot of frustration we started thinking it could be the valves are already opening as the RB26 cams are 0.1mm thicker than the RB20s at the lobe. Which in turn will push the the valves 0.05mm open.

How did you come to measure / identify they are 0.1mm thicker? What / where is that a measure of?

Ahh32 Proficient

Ahh32

Posted
Posted

They work for me. i made sure to soak the lifters in oil for a few hours before i installed them.

are u guys sure that you don't have any vaccum leaks, as i have just rebuilt my engine all hoses with new hose clamps and all, the went to tune it and it wouldn't idle. ended up being that nearly all the hoses on the intake manifold where leaking. (yes they were tight)

jnr32r Proficient

jnr32r

Posted
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Posted

Roy: It is measured at the heel of the lobe the flat section with no lift.

Ahh32: Why did you soak them in oil??

WazR32GTST: Can you confirm that your mechanic actually bled them before he put them in?

Im still not convinced thats the reason why they havent worked. Maybe Sydneykid can help here ...

WazR32GTSt Grand Master

WazR32GTSt

Posted
Posted

i can confirm that my mechanic bled them

when i picked the car up he said to me that he bled the lifters. not sure if he did it because they were noisy with the old cams or that this is a standard protocol for a cam change. either way i am 100% positive that this was done.

Waz.

lukevl Collaborator

lukevl

Posted
Posted

I dont' want to sound like a spoil sport - but whoever put GTR cams in their car and had it idle didn't use GTR cams. You got ripped.

The reason that GTR cams don't work without going into too much detail is that mechanical cams (all GTR and R34 GTT) have a linear lift ramp which in a GTR is app. 0.55mm high and takes something like 50 degrees to reach that point. In a mechanical cammed motor the clearance should be set at the point where the ramps meet the cam lift. (at hot running) So in a GTR, the tappets should be set at about 0.5mm, but Nissan recommend a smaller clearance which not only makes the car sound tough as (as GTRs do) but allows for a lot of valve growth (which GTRs do).

IF you run the GTR cams in a hydraulic cammed motor, you end up with cams that have about 360 degree duration on the seat instead of about 240! This is utter stupidity and should not be done. I am not taking a slash at the people who have done it, but at the people who say it is good and can be done. If it does not make complete sense to you, don't worry it takes a while to get your head around, and I can draw you a picture one day if you want.

Luke

lukevl Collaborator

lukevl

Posted
Posted

Sorry I phrased it wrong. GTRs have a lot of valve growth and this is characterised by their larger than normal ramp sizes. Honestly I think they specify their clearances to be so tight purely to make the GTRS sound tough. And man does it work! If you run the 'right' clearance in the GTRs it would sound a lot more sedate on idle and low speed running but still make the same HP.

ylwgtr2 Grand Master

ylwgtr2

Posted
Posted

hmmmm dunno bout that.....your meant to run them as tight as you can get them....well this is the case in motorcycle racing,but they get pulled apart every race so i guess that wouldnt work in an everyday situation....i have also noticed that the inlet valve has a larger clearance than the exhaust(which is opposite to the way it normally works)one would assume that this would be due to the sodium filled exhaust valves that RB26s have....

lukevl Collaborator

lukevl

Posted
Posted

i have never seen Nissan clearances. I know what they are meant to be because I have cam doctored GTR camshafts, plotted them and found out what clearances are needed to run them at. Noramlly you put 0.05mm more clearacne on the exhaust to accomodate growth. Anything half decent runs Inkinel (spelling) or sodium filled exhaust valves. At the end of the day who gives a toss? GTRs have big ramps and need larger than expected lash settings. Nissan set them closer than they need to be. I bet they didn't set them at this setting for emissions testing but...

If you are a hard core racer, you set the tappets wider than usual and you eat valve springs, but thats the price you pay for HP.

Do not run Solid camshafts in your hydraulic car. Its not fair to people like jnr32r who take your word and end up wasting their time and money trying it. Try to keep the BS to a minimum and this will be a nicer place.

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