camshafts and springs swap : last upgrade, promissed...

[nmauduit]

For those who may be interested, here is a quick description of my recent upgrade : for convenience to get going I got a rebuilt engine for my S4se while the original one is stored awaiting TLC, and was told at the time it was equipped with CPL2 cams, a Sprint equivalent. Having had some spare camshafts reground to Q420, I decided to know for sure where I was going and to replace the cams and springs/platforms. This was done without removing anything from the bay, radiator still bolted in place.

Original lift was confirmed at 0.35". Camshaft bearings were changed as well to save the other camshaft set complete with their plateforms, and clearance checked with plastigauge (right in the middle of the range).

CPL2 cams on standard platforms/springs initially

A quick photo of actual sprockets location before dismantling, for quick reassembly later : all went well for a while, then at some point the chain slipped a tooth or two, probably at the crank, and I had to reset everything eventually. No big deal, though one needs to go easy when rotating the crank for a safety turn until sure that there is no valve clash inside.

snapshot of sprockets position at TDC before dismantling

A timing disk is attached to a spare crankshaft pulley bolt, while the crank can still be rotated using a 5/8" opened end spanner. A tin finger is attached to a convenient nearby block bolt. It can be read with a mirror from the top, or directly through the radiator opening to double check.

timing disc on spare threaded pulley bolt

I was planning to reset accurately the TDC at the distributor on this occasion, too, so the jackshaft losing its initial location was not a big time waster. I found out eventually that the pulley was fast 4 degrees.

accurate TDC location (pulley was fast 4 degrees)

Springs and platforms were changed using compressed air and a short hand lever tool (cheap, but adequate for this job). Some collets can be stuck to the platform, and I found that a quick tap with a light hammer as the lever is under tension would help. Q55 springs are a bit stiffer than the stock ones, and I would rather not reinstall race springs in the car, since putting the collets back can be fiddly and I could only hold the lever compressed with one hand for so long. I first tried out the compressed air on all cylinders just in case, and realized that the pressure was sufficient to turn the crank, so later I engaged a speed and blocked the wheels, to prevent moving from TDC while swapping the springs. I initially started with 6 Bars for the two cylinders with pistons at the bottom (which would not move), then reduced to 4 Bars for the last two, but the crank stayed.

springs removal under compressed air

Once everything was apart, I first assessed if I would have to order shims, to minimize down time. The valves remaining the same and platform tolerances being rather good (within 2/100 mm for the new ones, better than 1/100mm for the stock ones), calculation from previous shims based on cam base circle difference proved good enough. So one set of cams was selected among the two at hand, and 3 shims ordered to my favorite engine parts supplier.

shim measurements to the hundredth mm

A dial is attached for timing the camshafts from the Cylinder 1 platform motion, exhaust first.

dialing in the camshafts exhaust first

Vernier sprockets were already installed, but these are very convenient and I will probably buy some for my next engine. This is the photo before timing, 110.5? BTDC

EX before 110.5 deg

A first round helped assess the relationship motion/angle, as this gave 108? BTDC

EX after first round 108 degree crank

Intial Intake was 96? ATDC

IN before 96

I had read with interest various threads on cam timing, yet I could not really grasp the motivations supporting a timing different than the specs for the Q420 profile as discussed in lotus-twincam-f39/q420-cams-t16004.html, so I kept with standard 106 Ex / 100 In for now. As for valve clearance though, I opted for a more conservative 8 thou In / 10 thou Ex as target to get started, esp. as some of the shims available at hand were a bit marked. I will check again this engine later (or when I eventually swap it), it will be easy to reset the shims to a desired range then.

This work was quite pleasant actually, even though the room behind the radiator is not huge to hold the spanner when rotating the crank. I eventually plugged the spanner into a ratchet to get the leverage required for stopping precisely within one degree. Then since nothing has been taken out try out is very quick when timing is done.

The car started very easily, idled a bit high thanks to the extra lift and possibly more accurate timing: I will jet the carbs up a bit before trying it out.