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Tech Q and A November 2013

Dec 15, 2013

Chain Slap

Q I’m looking to put some bigger cams in my Civic Si’s K20 but keep hearing about chain slap. After reading the forums, now I’m starting to think I should just avoid doing cams altogether. What do you guys think? Does this problem only happen with certain cams or should I just keep what I’ve got?
Chico, CA

A Some camshaft makers would have you believe otherwise, but timing chain slap is indicative of a poor camshaft profile. By design, K-series exhaust valves close rapidly—quicker than older B-series or D-series engines. Some higher-lift, longer-duration camshaft profiles that feature steeper and improperly designed closing ramps only accelerate all of this, causing the exhaust valves to slam shut against their respective seats. Each time they slam shut, the chain builds slack, and each time they slam shut, the timing chain tensioner’s internal piston bashes against its ratcheting mechanism. All of this leads to premature tensioner wear, which can lead to excessive chain slack and some pretty serious engine damage. Worst of all, you’ll never know any of this is happening until it’s too late since you can’t easily monitor the tensioner and, even if you could, all of this happens way too quickly. Despite all of this, though, there are several aftermarket K-series cams for you to choose from that work exactly as Honda intended without muddling up your engine. We suggest having a look on your favorite Honda forum and see how your fellow K-series brethren have fared with what’s currently available.

Bolts vs. Studs

Q I’ll be assembling my 240’s KA24DE turbo engine later this year and am trying to prepare myself ahead of time. First off, I know I need to use head studs instead of the factory bolts, but I don’t know why. Second, how important is it that I use a stretch gauge on my rod bolts? I only have a torque wrench.
Raleigh, NC

A Depending on how much power you plan on making—and, in turn, how much cylinder pressure you’ll end up with—head studs may not be necessary. In many cases, a set of new OEM head bolts is fine. But nobody’s ever regretted upgrading to head studs, especially if you’re dealing with forced induction. Aftermarket head studs, like those from ARP, are significantly stronger than whatever bolts Nissan supplied you with, which were designed to do nothing more than fasten your stock cylinder head to your stock engine block without whatever cylinder pressure your turbocharger’s about to add. But head studs do more, like provide more accurate and more consistent clamping loads. When tightening a bolt, it’s got to be twisted into the block at the same time. Here, vertical and radial forces are being applied to the fastener simultaneously. Since studs are installed into the block in a relaxed state before tightening down whatever nuts they use, only vertical stress is applied to them during the tightening process, which yields more accurate results. As far as using a stretch gauge, it’s a valuable tool to have if you plan on assembling engines for a living. If not, you can ask your machine shop to pre-stretch your rod bolts. You might not think so, but every single bolt and stud on your engine is elastic and was designed to stretch. Once it stretches to its predetermined amount, it can do its job. Generally, tightening a fastener based on a specified torque value is sufficient—like what most factory service manuals call for—but in cases where a higher level of precision is required, like with rod bolts, stretching is generally the preferred method.

Hybrid racing fuel rail Photo 2/2   |   Tech Q and A November 2013

Valve Spring Q&A

Q I’ll get right to the point, guys: How important are stiffer valve springs and do I need them on my boosted B-series? I wasn’t planning on getting into the valvetrain just yet, but I’m worried about valve float, so if it’s something that I need to upgrade, then I just may do so.
Reno, NV

A It’s the valve springs’ job to close your engine’s valves half the time and keep the camshafts’ lobes in contact with their rocker arms the rest of the time. When executed properly, a positive seal is made against the cylinder head and bad things like valve float and valve bounce don’t happen. As engine speeds increase and the camshafts spin faster, greater amounts of force are applied to the valvetrain; all of this makes it more difficult for the valves to stop when you want them to. Once the valve springs are no longer able to withstand these forces, valve float occurs and the rocker arms briefly lose contact with their camshaft lobes. Meanwhile, the camshafts keep spinning while the valves have temporarily missed a beat. The results can hurt valve timing, resulting in major power losses, or worse, damaged camshaft lobes or rocker arms. Over-revving is a common cause of valve float but weak valve springs are also to blame. You’ve also got to be concerned with valve bounce, which isn’t much better. Here, the valves hit their seats so hard they bounce right off of them. Like valve float, valve bounce happens when the acceleration of the camshafts’ lobes exceed whatever the valve springs are capable of handling. Stiffer valve springs are the solution to all of this, but there’s more than one way to go about increasing valve spring pressure. Common methods include using thicker or larger-diameter coils, multiple coils, or stronger materials. Before settling on any valve springs though, you’ve got to consider what sort of clearance you’ve got in order to avoid coil bind, which is every bit as bad as it sounds. A multiple valve spring where one or two additional springs are placed inside of a main spring, increasing overall stiffness without being made up of thicker, bulkier wire that’s prone to binding, is the most common solution. Generally, the inner spring is inversely wound inside of its outer spring to avoid them tangling up with one another. Finally, it’s important to mention that stiffer isn’t always better. Too stiff of a valve spring will make your engine work harder, resulting in a potential power loss from increased resistance. Camshaft lobes and rocker arm pads may also wear faster from excessive loads so be sure to choose springs from a reputable manufacturer whose track record for not bungling up B-series engines is proven.

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