RB20 cam base circle diameter

[Funnygas]

I am looking for the base circle diameter of a stock RB20 cam. I know the RB26 cam is 32mm. Need to know the measurement of the RB20 cam.

[DrMango]

If you have nothing by the morning on this then I can throw a caliper on one of my cams as my engine is still apart. Your looking for the diameter of where the bearing rides on the cam?

Kyle

[Funnygas]

no, its the round portion of the cam lobe. It's where the lifter rides while the valve is closed.

[DrMango]

i can do that tomorrow for you in the morning

Kyle

[Funnygas]

sweet dude, thanks

[j-ran]

re-opening this can of worms again charles?

[mcfly]

29.5mm

[DrMango]

HAHA. There you go. Pretend like I did that measurement


Its 29.5 mm man. Just measured it lol(I didnt;)

Kyle

[mcfly]

still measure if you can, two heads are better then one

[DrMango]

Okies I will

Kyle

[Funnygas]

im pretty sure its 29.5mm just need to make sure.
like i said on gtrc. "i dont work on pretty sure. this isnt a brianV8 build"
"pretty sure" never works more than 10% of the time for me.

[rb-racer]

"haha thats true, BrianV8 would have been more clever lol "

why would he talk about himself in third person, is he retarded?

[DrMango]

Im very sorry but it was a very long day of running around for parts and trying to fit in some time on actually putting pistons and accessories on the block today. I forgot to do the simple tast of throwing a caliper set on the cam. I will do it in the morning tomorrow for sure. I hope I havent held you up to much

Kyle

[Funnygas]

Im very sorry but it was a very long day of running around for parts and trying to fit in some time on actually putting pistons and accessories on the block today. I forgot to do the simple tast of throwing a caliper set on the cam. I will do it in the morning tomorrow for sure. I hope I havent held you up to much

Kyle

hahano worries man. im just talking with a machine shop.. they want to know how much material they are taking off

[DrMango]

I will make it my first thing of the day to take care of.

Kyle

[DrMango]

Dude im measuring the round part where the lobe is. Its comming up as 32 mm on the round part where its on a closed valve..

Kyle

[DrMango]

either I have GTR cams(not likely) or they are both 32mm
Is there a marking somewhere I can look for to see if its a RB20 cam?

Kyle

[mcfly]

Well that makes things neat. Measure the lobe now from the base :p

[DrMango]

base to lobe 39.75 mm

Kyle

[mcfly]

so 7.75 lift, seeing as 7.8 is the factory lift for rb20 these appear to be oem rb20det cams with a 32mm base circle.

I don't know why I had 29.5 in my head

[DrMango]

So for the record RB20 and RB26 base cam circle is 32 mm

Kyle

[j-ran]

that throws things off a little, doesn't it Charles

[mcfly]

So why did it not work the first time, If you ever go to do this again i have some nice calipers we can measure with. Maybe there is more then one rb20 cam size?

[j-ran]

Ya, thats possible, I have my old motor apart, we should throw the calipers on there and see sometime. Not 100% sure why it didn't work the first time... Maybe lifters need to bleed. Charlie can tell you more, but from what i remember we weren't making good compression because the valves weren't properly closing on compression stroke. We thought we eliminated valve timing as the root cause of this, but who knows. I think it's worth another try, I'm here to help Charles, anytime bud.

[Funnygas]

i played around with valve timing alot. best compression i got was 90 psi. my understanding, through extensive research, was that the base circle was larger and the valves did not seal 100%
further questioning found that bleeding the lifters is risky business.
hrmm...
if only i had the 20 and 26 cams side by side to compare...
some have got it running and working well. others have not. there has yet to be an explanation as to why or why not, the ones who did it havent said anything, the rest gave up without much inquiry..

[Funnygas]

Well shit. I wish I had found this thread before...
RB26 cams in RB20 didn't work :-( (http://www.skylinesaustralia.com/forums/RB26-cams-RB20-didnt-wor-t50069.html)
alot of discussion on why they will or will not work. sydneykid claims to have done it a few times and that it works.
this post should help...

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.

[j-ran]

Good find Charles, when are we gonna try this again? I have re-gained motivation on this subject because i don't think we did any of those things lol

[Funnygas]

we didnt. I tried... I re-did them 3 times that week (twice on monday night, once on tuesday night. reverted back to stock on wednesday so i could goto skymeet on friday).
let me order up some cam gears then you and damien can come over and we will get it figured out...

[j-ran]

Sounds like a plan, where are you living now? Didn't you and Einer part ways?

[Funnygas]

Yah.. after I went over to his house (next door) to ask what was going on (he changed his mind daily.. we were kicked out.. then we could stay) and the fucker attacked me.. I left... Im living on columbia now.. and I have a garage :D

[mcfly]

This would all make sense if there were rb20's with 32mm cams and some with 29.5mm cams or near that.

[DrMango]

I measured mine in an 89 Type M so maybe later years came with smaller base circle cams.

Kyle

[Funnygas]

that could explain why some work and some dont.

hey jordan..
what year was your car?
those cams in your old motor.. pull them, we can compare them with my gtr cams.

[mcfly]

take pictures of the cylinders on your old engine Jordan. I want to know how bad it blew up too.

[j-ran]

that could explain why some work and some dont.

hey jordan..
what year was your car?
those cams in your old motor.. pull them, we can compare them with my gtr cams.

I've got a 1990, and the cam covers are off right now. I don't have a micrometer or anything, but i have an old vernier caliper i think. Maybe I'll go check it out.

take pictures of the cylinders on your old engine Jordan. I want to know how bad it blew up too.

lol, I will for sure... maybe do it this weekend. What size allan key socket do I need for the headstuds?

[j-ran]

Ok, Checked it out

http://i939.photobucket.com/albums/ad234/j-ran/IMG00169.jpg

Definately 32mm for the portion of the lobe that touches when valve is closed.

[mcfly]

not sure exactly. Never pulled a rb20 head stud actually.

The rb26 is m10 hex. if you need some tools just let me know.

[DrMango]

I checked the manual and they come up as M12 1.5 under RB26 and Im pretty sure thats what they were when I got my new studs for RB20

Kyle

[mcfly]

I checked the manual and they come up as M12 1.5 under RB26 and Im pretty sure thats what they were when I got my new studs for RB20

Kyle

m12 is the thread size for a rb26 bolt. The head itself is a m10 hex.

rb20 is a m10 thread bolt.

[DrMango]

Thats my mistake, I should have figured that out lol

Kyle

[mcfly]

Common error so not a big problem ;)

[Zacho]

it will be a 10mm hex as stated, and your cams when #1 is at TDC have "grooves" in them for the socket. Longer the hex on the socket is the better, I ran into issues with a short 10mm hex.

[j-ran]

I hope you don't need that socket back immediately damien, I didn't pull my head today because it was raining.

[Funnygas]

something is coming back to me. something about the drive for the CAS on the exh cam being different between the 20 and 26 cams when lined up with the timing marks on the cam gears... i will have to check into this.
JORDAN! (or anyone) can you take a pic of the cam exh cam gear with the cas off and post it?

[DrMango]

Sorry. If you had asked yesterday I could have done it for you. Its too late now and hope someone else will be able to assist you

Kyle