When using aftermarket camshafts and upgraded valvesprings in a k-series motor, the tensioner often begins to develop problems. The exact nature of this problem is related to additional harmonic vibrations induced in the chain by the lobe profile of the more aggressive cams. Not all aftermarket cams will result in these additional harmonic vibrations, but there are a few problem setups. The primary problem that develops due to these additional vibrations is failure of the ratchet mechanism on the stock timing chain tensioner. Below is a partially disassembled stock timing chain tensioner.

There are three main components, the tensioner body, the tensioner spring, and the tensioner piston, left to right respectively. On a failed tensioner, the ratchet mechanism wears out prematurely due to the added vibrations in the chain resulting in the possibility of the tensioner piston fully retracting into the tensioner body. This allows the cam gears to skip teeth resulting in catastrophic engine failure. Typically, this won't happen when there is oil pressure within the tensioner, but in low oil pressure situations, like engine startup, the possibility of the cams jumping teeth is very high when the ratchet mechanism has worn out. The signs of a worn out ratchet are shown below.

In the final picture, a worn ratchet is shown on the left and a new ratchet is shown on the right. It is clear to see how badly the teeth become worn. This wear occurred within 3000 miles. The intake cam jumped teeth, and several valves were bent on startup.

An existing solution to this possibility of failure on startup and low oil pressure has been to use a sleeve inserted into the tensioner body to prevent the tensioner piston from fully retracting. This approach prevents the cams from jumping teeth however it introduces a new problem, chain breakage. The vibrations in the chain cause the tensioner piston to strike the sleeve insert which will cause very large impulse forces in the tensioner and chain. I do not recommend that anyone use a sleeve modified tensioner due to the risk of chain breakage.

To address the issue, I have developed a dual spring system that will increase the resistance as the tensioner compresses to prevent the chain from jumping teeth under low oil pressure situations. The spring still allows natural movement of the tensioner piston, thus avoiding the situation that leads to chain breakage. Pictured below is the dual spring setup that replaces the stock single spring unit.

The dual spring system will not prevent ratchet wear. However, it will function as a failsafe for low oil pressure conditions without increasing the risk of chain breakage.

update: 11/24/2007

During the testing of the dual spring tensioner, further insight was gained into the specific cause of additional chain vibrations. The video below demonstrates the loading and unloading of the timing chain between the two cam gears.

In this video, only the primary lobes of the VTEC system are engaged. This chain slap results due to the tendency of the exhaust camshaft to rotate clockwise (towards the intake camshaft) resulting in slack between the gears and greater stress on the chain tensioner. Further experimentation showed that the vibrations were worse as the overlap between the intake and exhaust cams was increased. Because the Hondata K-Pro engine management allows full control over the VTC, the overlap between the intake and exhaust cam can be controlled to some degree. Using the ECU controls, the intake camshaft was retarded as much as possible to minimize the occurence of harmful harmonics that result in excessive chain tensioner wear. A screen shot of the modified cam angle map is shown below.

Using a dual spring modified chain tensioner and minimizing the overlap between the cams during low rpm and low load conditions restores reliable operation of the chain tensioner system.

Dual spring modified tensioners are available for $100 + shipping. Please contact me via email if you are interested in purchasing one.
copyright 2008