[QUOTE=davepk,Nov 10 2004, 04:37 PM] A stretched chain would indicate an increase in the inter link distance.

 

Thanks... I'll try that.... I was just hoping there was a way I could "eyeball it" and see if the chain had stretched.

gernby: I don't know how much of an impact 1 degree of play would make... or even 3 degrees, and I'm not sure how much of a "stretch" would be required before I could just look at it and tell that it was off. But you know the tribulations I've been through, so I'm willing to check anything at this point.

davepk: That's exactly my reasoning behind trying to troubleshoot this issue. If the cam chain is stretched, it will basically throw off the timing.

all: The reason I'm wondering if my chain might be stretched is because I'm putting down particularly poor dyno numbers. With the stock cams, I'm putting down only 208rwhp... I baselined at 201. See my mods list and you'll understand why this doesn't seem right. With the Toda cams, I make about the same peak hp, but I have even worse low-end. I suspect that the power loss is due to the timing being off, and the Toda cams are probably impacted more severely because of their increased overlap and duration.

If it turns out that the chain actually is stretched, one of the culprits of the possible stretching of the cam chain could be the Toda valvesprings. They are considerably stiffer than stock springs, and could put additional strain on the chain.

I dunno. I've been chasing my "power issues" for months now, and I haven't found a solution. This just seemed to be another plausible culprit.

Edit: BTW... that 208rwhp may not sound too terribly bad, but keep in mind that I previously put down 212rwhp (on the same dyno) with just the Toda cams and AEM CAI. Since then, I've added the Toda header and Amuse R1000 exhaust. There's no reason that I should be making anything less than 220-225 now.

 

The play is taken up by the tensioner. There are 2 sides to the timing chain. The fixed length side and the auto tensioner side. The problem is the physical distance between a cam sprocket tooth and a crank sprocket tooth doesnt stretch. But, the chain on the fixed length side that is meant to maintain that fixed distance can stretch.

 

No stretched chains don't usually cause play so much as they cause accelerated wear on the cogs.

 

Oh... one more notable tidbit: I've already replaced the autotensioner to address noise from the tensioner/chain. It resolved the noise, but the power loss remains. However, I did notice the power loss before I noticed the noise.

 

There are TDC/angle sensors on both the crank and the cams. My bet is that the ecu would know if the chain is stretched too much because it could see it in the signals it recieves.

To measure the chain stretch all you need do is remove the valve cover.
Align the cam sprockets to TDC and then observe the crank pulley TDC indicator mark. A stretched chain should show the pulley mark further CW than the indicator arrow on the block.

 

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I agree... but how far off would the cams have to be before the ECU decided there was a problem. The sensor type is "inductive", I believe, and just looking at the setup of it, I wouldn't expect that it could detect a change of less than 3-5 degrees. The sensor itself is pretty wide, and the "tooth" that it picks up on is also pretty wide. Seems like that would allow a lot of room for error... but I could be wrong.
I'm assuming that if it did detect a problem, it would throw a code immediately (since a problem there could lead to valve-to-piston contact). I definitely haven't seen any codes.

You're idea for measuring the chain stretch is along the same lines that I was thinking, but as gernby stated... it may be possible that the chain isn't stretched enough to be visibly noticeable, but it still might be enough to impact performance.

 

yogi:
A quick pic to illustrate what would happen. The arrow on the left is the autotensioner that takes up the slack when the chain stretches. However, since the chain is stretched, it allows the angle of the cam gear vs. the crank gear to change as indicated by the other two arrows.

 

The sensors, tho inductive and wide rely on edge detection. It is the edge of the sensor tooth that is detected not the tooth in whole.

I do agree however that its likely that chain stretch alone would rarely be enough to be a factor in engine performance. But in combination with tooth wear and tensioner performance the resulting variations in timing should be detectable by the ecu. This is only a guess on my part. That variation might occupy all of a degree or two of rotation and would likely be swamped by the ecu's ability to manipulate ignition timing.