The vernier sprocket

Fitting the vernier sprocket

Shrigley Engineering

Thank you for purchasing your vernier sprocket. To get the best results from this product, please read the following guideline instructions.

This gear is suitable for all of the Imp engine range. It can be used on standard or Sport camshafts. To reset the cam timing back to factory settings, often lost due to skimming of the cylinder head face. It is also suitable for 'R' series competition camshaft. The vernier sprocket can be adjusted to alter the characteristics of the power band without the hassle of removing the gear / chain from the camshaft.

Fitting of the venier to a standard /L4/ Sport engine

1. Remove the battery earth terminal and distributor cap.
2. Remove the cam cover etc. to gain access to the cam.

1. Remove all four spark plugs.
   Select neutral.

2. Turn the cankshaft in a clockwise direction until the scribed line on the front of the standard cam gear is parallel with the top of the cylinder ehad. Place a blunt shaft of around 5 mm diameter (screwdriver) into number one spark plug hole and gently rotate the crank pulley back and forth watching the screwdriver rise and fall to gain an accurate top dead centre mark. Some Imps have a TDC pointer on the crank pulley, use tipex or white paint to highlight the correct TDC point.

3. Looking at the standard cam sprocket, the scrobed line should be close to parallel to the top of the cylinder head. If the cylinder head face, or block face, has had material removed from it, this will cause mislaignment of the camshaft's correct TDC position.

4. Now we have an accurate TDC mark for the crank, we need to attain the correct position for the camshaft. To do this, first undo the cam gear retaining bolt 9/16" AF and slide the gear off the end of the cam (be careful not to drop the location dowel into the engine). Unhook the chain from the gear, allow the chain to drop down temporarily. Turn the crank anti-clockwise about 30 degrees just to eliminate the chance of piston/ valve contact. Next, place the standard gear without the chain over the front of the cam and screw the bolt finger tight. To find the correct cam position, you will have to turn the gear until the scribed line is perfectly in line with the top of the head face. Once in line, mark the position of the cam relative to the carrier using a centre punch (I do this on the top of the first bearing cap). Remove the retaining bolt and gear; pull the chain up, using a magnet or hook.

5. Before fitting your new vernier gear, you must first bring the crank back to ||TDC position. Loosen the 3 cap head bolts on the vernier and check the free movement of the gear. Index the inner part of the gear to give an equal distance either side of the cap head bolt. Place the chain opver the new gear and offer up to the front of the cam; move the chain on link at a time, until the gear slots over the front of the cam and dowel. At this stage ther needs to be space in the slot either side of the cap head bolt for final adjustment.

6. Check whether the cam position is still correct; then hand-tighten the cam retaining bolt. Looking over the top of the chain tensioner, make sure the slider at the top of the band is sat properly in its guide. If so, check the crank TDC position and cam dots are still in line. Now tighten the 3 cap head retaining bolts, using a 5,, Allen key on the vernier and turn the engine by hand one revolution. The engine should feel smooth. Any resistenace should be invetigated. Do not force the engine round.

7. If your crank and cam positions are still in perfect alignment, torque the cam gear retaining bolt and reassemble the engine.

8. If your TDC and cam marks do not align, loosen the verniers cap head bolts and turn the cam independently of the gear to attain perfect alignment.

9. We recommend using loctite ratiner 601 on the camshaft retaining bolt.

10. Congratulations on fitting your vernier timing gear. You will now be able to feel the gains of increased compression ratio without the losses of inaccurate valve timing!
    Please note that Shrigley Engineering accepts no reponsibility for damage caused by incorrect fitting.