#21 - Life Saving Failure
As many know, I was on the way home from a nice ride down the coast and snapped my cam chain.
While this would normally be a horrible thing, in this case, I got lucky and no major damage from the chain break occured. On the other hand, I did find a shim had eaten nearly completely through one of the Ti Retainers and was ready to be spat out. I also found the intake valve clearances had shrunk considerably from .008" down to .001" on the worst valve. It appears the cam chain snapped just before other things started to cause carnage!
As a result I am changing Cams, Springs, Retainers, tensioner, cam chain, and tensioner blades to different parts, not just replacing them with parts that will fail again.
This gets to the design philosophy of the original Carpenter 265 kit. While it makes good power and it runs pretty well, in my opinion it has some fundamental flaws, all of these changes should fix those issues.
Springs will be a good bit lower rate than the 100lb seat pressure and 220lb open pressure springs that were installed. No need for such strong springs when the valve+tappet+shim+retainer+collets only weight 70 grams combined.
The cams going in are both higher lift and longer duration, yet have more gentle ramp rates and won't be as violent with the valve train, allowing for lighter springs to have better valve control. They're also not regrinds, they're billet, so should flex less at high RPM as well as have the OEM base circle, making for shorter shim use, all good things.
Here's a visual comparison new cam at top:
While researching the cam chain I found there was a change in 2010 from a full strength chain with 4 then 5 plates per link alternating to a waisted chain using 4 full them 3 full and 2 shortened plates per link. I'll be using the older, stronger design coupled with the better blade design from the Roadster to hopefully achieve the best system possible, strongest chain paired with most gentle blade curvature.
Finally, the graph below is the prediction from enginesim on what the torque curve will look like with all this done, numbers are flywheel:
Hopefully this shows up and is realized once assembly is complete. This chart doesn't account for significantly lighter valve springs, and it's set using 92 octane pump gas, so there should be around 7% more than this available with the right fuel. To normalize the above to wheel values use 0.875 multiplication factor.
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