RB26 cams in RB20 didnt work :-(

[browny]

Is it pertinant to ask how much a RB20 follower can be depressed before it is moved away from the oil gallery and therefore becomes solid?

If this distance is very small then wouldn't the ramps of the solid cam mean the valve would open earlier and close later (albeit a small amount), therefore giving a longer duration.

So relating to lukevl's diagram the inlet cam might start to open at -250 and close at 50 giving a duration of 300 degrees. The hydraulic cam on the other hand might open at -225 and close at 25 giving a duration of 250 degrees.

Would this matter?

Obviously I don't really know what i'm talking about so I might be right off track.

[Sydneykid]

Is it pertinant to ask how much a RB20 follower can be depressed before it is moved away from the oil gallery and therefore becomes solid?

Yep that's the right question, but it is only relevant if the base diameters are different. Then I will compare the difference in base diameters with the oil flow ports overlap. If the base diameter is larger than the ports allow then that's a problem. But if the base diameters are the same its irrelevant.

If this distance is very small then wouldn't the ramps of the solid cam mean the valve would open earlier and close later (albeit a small amount), therefore giving a longer duration.

Yep, but it is a very very small amount. Maybe enough to make the idle a little lumpy but not enough to kill it.

So relating to lukevl's diagram the inlet cam might start to open at -250 and close at 50 giving a duration of 300 degrees. The hydraulic cam on the other hand might open at -225 and close at 25 giving a duration of 250 degrees.

More like 250 (hydraulic cam) versus 260 degrees (solid cam).

Would this matter?

If it is 50 degees then yes it would, if it is 10 degrees then no it wouldn't.

Obviously I don't really know what i'm talking about so I might be right off track.

As lukevl will tell you, cams are not my specialty. But despite what the cam doctors of the world tell you, they are really only a stick with bumps on it. They simply go round and round, turning rotation into up and down. Like a girl I knew once :headspin:

[lukevl]

I give up. I have done all that I can on this topic. The one thing I didn't mention is that hydraulic lifters have a running cleearance of between 0.1 - 0.15mm as stated by the SAE. Ask any camshaft 'specialist' they will not recommend runnning solid camshafts in your hydraulic motor.

BTW Sydney Kid - sorry I didn't read your extra long post because I don't have time, but I'm sure it had some truths in it.

I am literally exhausted with this arguement. Good luck.

[lukevl]

Oh crap, I'm back already- but only briefly

I glanced past and noticed your base circle query. Base circle is the same on all models of RB twin cams (32mm). R34s have a larger shaft diameter which makes them easy to pick. Not to mention different drives in the front of the camshafts.

[Dump_Pipe]

oh poor luke you just can't win can ya.

[Cubes]

Its a good discussion.. I'm unsure why luke is getting shirty about it all?!?!?!

[RPMGTR]

maybe Luke is getting shirty because he is correct...............

[Roy]

maybe Luke is getting shirty because he is correct...............

LOL...and thats fine. I know there are right and wrong ways of doing things, and the solids in the hydraulic head isnt exactly 100%, but if it works better then the std RB20 cams wheres the harm?

That said, if i can get my engine running again im going to bite the bullet and pay the $1,000 for cams, would good old Luke be able to hook me up with some cams that would work well on an RB20?!?!?!?!

[ylwgtr2]

Oh crap, I'm back already- but only briefly

I glanced past and noticed your base circle query. Base circle is the same on all models of RB twin cams (32mm). R34s have a larger shaft diameter which makes them easy to pick. Not to mention different drives in the front of the camshafts.

where are they larger?

[DoughBoy]

where are they larger?

R34 = more expensive car= larger.... camshaft? Or do you call it a bumpstick still?

[Sydneykid]

maybe Luke is getting shirty because he is correct...............

So, let's assume Luke is correct about the camshafts, the extra (anti rattle) ramp on solid cams makes the cams longer in duration when used with zero clearance. The longer duration creates excessive overlap, lowers the vacuum and the engine won't idle. All quite logical.

But (there is always a but) whilst it might be true to say RB20's have hydraulic followers and therefore have zero clearance, that does not mean that the valve opens as soon as the follower hits the (anti rattlle) ramp. The follower is in contact with the camshaft lobe all the time and held there at the engine's oil pressure, at idle say around 30 psi. The oil to feed the follower is supplied through the gallery in the cylinder head with the port designed to line up with the matching hole in the lifter at zero lift. The ports are around 2 mm in ID. This means for ~0.7 mm of camshaft lift the ports have enough overlap for the oil to freely flow between the follower and the head.

The engine oil pressure is at 30 psi, so as long as the pressure from the valve springs is lower than 30 psi, oil will flow from the cylinder head to the follower. But as soon as the valve spring pushes back at more than 30 psi the oil will flow from the lifter back into the cylinder head. That's how hydraulic followers work, they cycle to keep the clearance at zero, so no rattle and maximum valve opening.

RB20 valve springs have about 80 lbs per inch at the seat, so as soon as the (anti ratttle) ramp tries to lift the valve off the seat, the valve spring pushes back at greater than oil pressure. As long as the ports and the holes line up, the oil will flow from the follower back into the cylinder head. This means the valves won't open for around the first ~0.7 mm of lift. That's more than enough to get past the (anti rattle) ramp.

Luke posted

Base circle is the same on all models of RB twin cams (32mm).

This means that the hole in the follower and the port in the cylinder head line up at zero lift and things happen (oil flows) as per the standard RB20 cams and therefore as per the description above.

Bottom line, I have no idea why some people have success and others don't. But I am going to stick those R34 GTR cams into the RB20 as soon as they arrive.

[nv033]

Bottom line, I have no idea why some people have success and others don't.

U referred to some possible install problems on a previous post....it may sound like a stupid question but what sort of things could cause these sort of problems on install.....

the fact that the vaccum drops to -5 and does not idle?? what is causing this? ive noticed on my car that if u give it more fuel it can idle....i pm'd u a question before regarding idle issues... i think this install of camshaft is the possible cause of my idle issues but mine are with aftermarket r25det camshafts into a rb25det.....how would advancing the intake cam gear affect this? :confused:

replies would be mostly appreciated :headspin: :headspin:

[Angry]

interesting discussion. few valid. but some more arguementative than fact.

but "i give up"

I'm still going to go thru with my swap. So bugger whats happend. can;t argue with results.

Thanks for the posts SK . fair bit of a read . and all makes sence to me (for the most part)

I look forward to seeing pics of your install and hopefully we'll see more guys busting out with GTR cams there after.

Also SK : u mention one setup u had being converted to solid followers with GTR valve springs. I have a set to accompanying my cams on the way at a later date, is this a better way to go about it? i am i doing the right thing and doing that as well with my cam swap?

Thanks again

Matt

[N I B]

80lb seat pressure eh? NSW springs must be like WA Dynos.

[Ahh32]

i still say vaccum leaks.

nv033- if you add fuel and it runs then more than likely there is that is not getting metered being sucked into the intake. i.e vaccum leak

[nv033]

i still say vaccum leaks.

nv033- if you add fuel and it runs then more than likely there is that is not getting metered being sucked into the intake. i.e vaccum leak

if there is a vacumm leak ive noticed idle goes up.....when i give it fuel it idles but it doesnt drive cause it stalls all the time :headspin: :headspin:

[Sydneykid]

80lb seat pressure eh? NSW springs must be like WA Dynos.

That's a good point Steve, I can't remember actually measuring an RB20 valve spring. It is written in the data book at the machine shop, but they may not have been standard valve springs. Have you measured a standard set?

I don't think it matters though , if there is enough valve spring tension with the standard RB20 cam to control the clearances then there will be enough with RB26 cams.

You have worked on more RB's than I have, what do you think the problem is?

[Sydneykid]

Also SK : u mention one setup u had being converted to solid followers with GTR valve springs. I have a set to accompanying my cams on the way at a later date, is this a better way to go about it? i am i doing the right thing and doing that as well with my cam swap?

Thanks again

Matt

Hi Matt, it's not quite as simple as just changing the followers to solid, you also have to change valve springs, valve guides, followers and the valves themselves. There is also machining to the cylinder head to get the valve spring tension correct. It's a fairly expensive proposition.

[Sydneykid]

U referred to some possible install problems on a previous post....it may sound like a stupid question but what sort of things could cause these sort of problems on install.....

the fact that the vaccum drops to -5 and does not idle?? what is causing this? ive noticed on my car that if u give it more fuel it can idle....i pm'd u a question before regarding idle issues... i think this install of camshaft is the possible cause of my idle issues but mine are with aftermarket r25det camshafts into a rb25det.....how would advancing the intake cam gear affect this?  :confused:  

replies would be mostly appreciated  :headspin:  :headspin:

The most common problem is cam timimg. It is sooooo easy to get wrong. When you are bolting down the camshafts, a number of the valves have to be opened by their respective camshaft lobes. This has the effect of turning the camshafts to the point of least resistance (by the valve springs). If you are not watching, it happens unnoticed while you are tensioning the cam bearing retaining bolts. Or when you are bolting on the pulleys. Or when you are tensioning the cambelt etc

I have seen this a number of times, the easy pick for exhaust cam timing is the CAS. It ends up all the way in the adj slots to get the ignition timing right. Or you get the reverse, guys mark the CAS and put it back in the same place. But the cam timing is say one tooth (7.5 degrees) out. They don't check it with a timing light, so they never know that both the camshaft and ignition timing are both wrong.

If you mark the CAS and put it back in the same place and check the ignition timing with a timing light and make sure it is in the same place, then you know the exhaust camshaft is in the right place.

The inlet camshaft is little easier to check as you only have to worry about the camshaft timing itself. What I do is mark TDC on the inlet camshaft with a white paint pen and mark the cam bearing correspondingly. I just make sure the white marks line up at all times when I am assembling. You can of course do the same with the exhaust camshaft, it adds another dimension of checking.

When I talk to guys who have had trouble, I ask 3 questions;

1. Did you mark TDC on the camshafts before assembly and check it after assembly?

2. Did you mark the CAS before you removed it and did you put it back in exactly the same place?

3. Did you check the igntion timing with a timing light before you started and did you make sure it was back in exactly the same place when you finished?

If I don't get all three positive responese (and I can see the marks), then that's where I start looking.

Next is other problems with the engine, quite often you find people try to do three or four things at once. Fix a problem, add a new part and swap the cams all at the same time. My suggestion is always, get the engine running perfectly before you start. Do any other maintenance and servicing and make sure the engine is running perfectly before you start playing with camshafts.

I have run out of time, so I will make another post later. Hope this was of some help.

[N I B]

Or use a tomie kit for $770 but by the time you have good 2nd hand 26 cams and updated springs from the factory jobs that are around 45lb if the engine is very fresh you have well overspent on an RB20 that is then held up by tiny valves that are shrouded by their tiny cylinder bores.Just buy mild replacment cams but if you are talking a wild 25 then the effort becomes worth while if you want to loose the vct but SST is working on modifying aftermarket performance 26cams for vct.This is why we are testing on Pauls GTS using stock 26 cams,Cheaper than stuffing new HKS jobs if it dont work.