Thread: slotted rocker arm shims?

I am in the process of putting a motor together and heard of someone taking the smooth shim out and putting in another slotted shim in. is this to keep rockers on better? any info on this would be great. thanks

in my experience, dont fuck with factory unless there is a major flaw... worked well with my hondas. just my 2 cents

The rocker arm shim slots are different widths, if you place a slotted shim on the nonslotted side you'll see that it does not sit flush at the bottom of the rocker and there is a gap there, the shim will split as soon as the cam rotates over and creates a pressure, and you'll have a nasty mess when the rocker arm shifts. You have to machine the rocker arms to the same tolerance on the fork portion where the slotted shims fit. It is better for high RPM, but you have to do a complete valve job since the shims are actually different thicknesses that are not slotted, but the slotted shims are all the same thickness. Kind of a lot of work to do, but if you take the head apart a lot for racing applications, it would help incase you loose a shim or something. If I were a machine shop it'd be at least $240 to get this done, since I would have to make sure all the valve stem heights needed to be equal for each cam lobe. If you're not spinning the engine at high RPM 8,500+ then I would not worry about the valve shim. I would actually like to do an experiement one day on a regular low port engine and do the conversion and see how high it can go before it spits a rocker arm... anyone have a donor engine?

Well I was scrathin my head and eating my banana but that explains things. Dont let someone else rebuild your engine that doesnt put sh*t back from where they got it...

^^^^Yep...just like that...^^^^

Its a simple mistake, just make sure you can move the rocker arm around once everything is installed, if the rocker arm is stuck in place and can't move around a little, then it's probably pinned with the slotted shim on the wrong side.

k thanks for the info i will leave it alone then

I've thrown rocker arms and lost shims down in the oil pan before. Re-shimming everything correctly was such a PITA I never want to go through that again.

I had my rocker arms machined when I had my W11 head rebuilt. The machine shop ground down the rocker arms so now I have a keeper on each side. Each valve stem was measured and ground to the correct height. The underside of each rocker was engraved I(intake) or E(exhaust) 1,2,3...

Now if I throw a rocker arm I never have to worry about measuring valve shim height. If a keeper rolls down the garage drain, I won't care because I can walk into any Nissan dealership for another one, they are all the same size.

Had other custom work done to the head, over kill really, but labor was only 369.00. On the other hand the head should be good for 8800 to 9000RPM. Now I just need to work on making enough power to reach that RPM range.

How much of a difference in height are the slotted pucks vs the flat? When I pulled my engine apart I measured both and IIRC the slotted was something like 2.945mm while the not slotted was 2.943 or some where in that area all the flats were within .001-.002 of a mm. I was measuring at the part where the rocker contacts on the top and the stem contacts on the bottom. Will that much of a difference really cause an issue?

If your flat shims are all that close you're lucky. Mine were all over on my DE head.

I understand where you'r going. I started to modify mine just because I didn't want to throw any more rocker arms and I wanted it to be easy to replace the shims if I did. It wasn't about high RPM. What you want to do is not at all unreasonable and has been done before.

After I posted here yesterday I started a thread on the mods I did to my DET head here :

http://www.sr20-forum.com/general-sr20/53864-overkill-my-head-modifications.html

That thread also contains a link to another thread where Andreas Miko discusses modifying the rocker arms. It was my guideline.

If your shims and slotted keepers are truly that close in thickness you may be able to use all slotted keepers after just modifying the rocker arms.The HLA (lifters) can handle a small amount of difference.

The machine shop only changed me 5.00 dollars apiece to modify each rocker arm, but of course I had other work done at the same time. Someone more mechanical than I am could probably do it themselves.

I dont see what your guys issues with the shims are. The broken grooved shim in that picture looks like you had the grooved shim on the wrong leg of the rocker to the point it put pressure and split it like that.

The grooved shim normally goes on the left leg of the rocker. I did the dual groove shim mod on my DE head and reved it to 9k several times, then set my rev limiter to 8700 and had no issues pounding off it all day long. You have to shave the outer edge of the right side leg until the leg sits completely down onto the flat surface of the grooved shim. Pretty simple. I shaved it down just enough to where it fit nice and snug and was all the way flush. Never had a problem. I checked my valve lash clearance on both the left and right side of the rocker pad to the cam lobe and it was even across and within specs on the lash. Its soo little of a difference between shim thicknesses that it really wont matter. Ive had my shims all out of wack and order and put them back in however and ran my s4 cams to 8k rev limiter all the time, Matter fact had the motor spin to 12k+ on several occasions when i broke a gearstack right at redline under full boost and never spit a rocker out or anything.

The dual groove shim mod is easy and doesnt require all this valve job and so on that David mentioned. Just shave down the outer edge of the right leg until it fits snug and the bottom pad is flush on the flat part of the shim throw em in and make sure your clearances from left to right are fairly close. As long as they are within .002" of each other you should have no issues. The hydraulic lifters will take care of the rest.

Granted i was running a VE oil pump that has higher pressures and volume so it helps but even on the de oil pump you shouldnt have any issues.

If you want pictures. Go into my initial build thread and you can see all the pics of the dual groove shim mod. Andreas Miko has been doing this modification for a long time and doesnt go through all this valve job nonsense and measuring shims and so on. Just throw em in. Unless the head has had a valvejob done to it in the past that would have changed valve height, your clearances from side to side should be almost identical and so on. Your talking these shim differences go in like .0005" increments.

Any more questions feel free to ask. Again ive been there done it with great success. C2 cams, BC springs and retainers, and VE oil pump, dual groove shims 8700-9100 all day long.