I thought I'd bring to light something that you guys should realy be checking when installing camshafts into your engine. Since the QR25 doesn't have hydraulic lash adjusters (like the SR20DE does), it is necessary to manually set the clearance between the base circle of the camshaft's lobes, and the bucket that sits on top of the valve/spring. Too much clearance, and it will make noise as the cam's ramp starts to act on the bucket. What we mean by "ramp", is the part of the cam that starts to curve as you first start coming up on the lobe that opens the valve. With too much clearance, it will "slap" the ramp, and you will get a rattling noise. This will also wear the cam out very quickly. The clearance must be set between .010" and .013". Any looser than .013" and you will get some noise. Any tighter than about .0095" and you will get rough idle, because the valve won't fully close on the base circle. The Nismo and JWT billets are ground on factory base circles, but it's still a wise idea to check this when putting the cams in. When I got my cams from JWT, I went back and checked them, because I'm just paranoid like that, and I was surprised to find 6 valves out of spec. They were between .014" and .017"!! This would have certainly been noisy. So, here's how to fix this problem.



The buckets that the camshaft's lobes engage are all custom fit to the base circle of each lobe. There are 16 lobes on both sets.. (8 lobes per side- intake and exhaust). The buckets are measured from the little nipple under the bucket that engages the valvestem, and the top of the bucket that the lobe acts on. This thickness can be checked with a micrometer, or you can look on the bottom of the bucket and there is a laser etched number inside. This number will be in millimeters.. and will be in the range of "644 - 748" or somewhere around there.. Don't remember exactly. Take that 3 digit number.. and add a decimal to it to get the right number.. For instance.. if you had 728 on one.. It's 7.28mm thick. Now.. here's what you do..



1. Install the camshafts and TQ them down to spec.

2. Install the timing chain and make sure it's all lined up like it's supposed to be (engine at TDC, exhaust cam's dowel pin at 12 o'clock, intake cam dowel pin at 9 o'clock). You don't have to TQ down the sprockets.. just tighten them down sufficiently

3. Get a piece of paper and write down numbers 1-16.

4. Start at the intake cam's furthest end, rotate the crankshaft until that furthest lobe's base circle is directly over the bucket on top of the valve. With a feeler guage, measure the clearance between the base circle and bucket.. You do this by sliding the feeler guage between the two. If it fits loosely, go up a size until it fits snuggly and the next size up will not fit. When you find that feeler guage that does fit.. write it's thickness down on paper for number 1.

5. Go down the cam doing this for every lobe until you get to the end. Then, start on the exhaust cam and do the same thing. Remember to draw the head up on the paper, so you can remember which number corresponds to what lobe.



After getting all of your clearances.. If any are out of the spec (.010" - .013"), you will need to get different buckets from Nissan. Here's how you determine which bucket you need.



Take for instance.. one of your clearances measured .017". We need to get that clearance down to at least .013. But, for safety's sake, let's get it down to .012", just to make sure we're in spec. Ok, so we know that we have .005" too much clearance between .the .017" we're at now.. and the .012" we want to be at. Take that bucket out from the lobe in question, and look at the number underneath. Let's say it reads "728". That means it's 7.28mm thick. Now, to take up the slack of .005", we need to get a bucket that's .005" thicker. But, we first need to convert the .005" to millimeters, since our bucket's measurement is in millimeters.... .005" comes out to .127mm. Now do this..



7.28mm (bucket thickness) + .127mm (slack we need to take out) = 7.407



Since the buckets available from Nissan are in .02mm increments, we need to round this down. From a choice of 7.40 to 7.42, we will round down to 7.40. Now, you know which bucket you need to order. The number under the new bucket will read 740, instead of the old 728 that you had before. Write that number down next to the number of the lobe you were on, and then move on. Do this for all lobes that are out of spec. Go to Nissan and tell them the 3 digit number from the lobe that you need and they can order them.



Make sure to double check them again once you get them installed.. Hope this helps.. and I realy would be checking this guys.. Like I said.. I had some cams that were ground on stock base circles, and they were off. It might be a pain.. but it's worth it!



Travis (Forced Induction Racing)