Cam Installation on ’92 ZX7R
Q. If I’ve removed my cams from my 92 ZX7 and spun the crank with the cams out, with the timing mark on the pick-up lined up at 1, 4 TDC and the cams installed according to the manual – which leaves #4 up on the lobes, how do I know the engine is correctly positioned? because #1 and #4 are TDC at the same time, I’m confused where the engine should be as there is no indication that I can tell that lets you know which piston is @ compression and which is @ exhaust.
A. This is one of the BEST questions on this site in a while. The answer is, the spark plugs fire also on the exhaust stroke.
If you have the crank set at 1/4 TDC, which piston is on the exhaust and which is on the compression is determined by how you install the cams. If you install them with the lobes UP on #4, that cylinder is then on compression and #1 is on exhaust. Or if you install them opposite, then number 4 is on exhaust and #1 is on compression. Then rotate the crank 360 degrees and you are back where you started as the cams turn 1/2 the speed of the crankshaft.
I have found that if you try to line up the tick marks on the cams to the cylinder head exactly the way the shop manual shows, and it seems to be a hair off……., and doesn’t exactly look like the picture, remove the cams, rotate the crank 360 degrees and try again. This may not make sense, but it has some influence on where the links of the chain wind up even though the crank is right back where it was before. Though rotating the crank 360 degrees is the same, the links of the chain match up to the cylinder head position.
So, to answer your question, even though it appears that there is only 1 correct spot for 1/4 TDC, you may have to rotate the crank 1 complete turn in order to get the cam marks and the chain to line up exactly as it shows in the picture.
I hope this makes sense as to why you would have to rotate the crank 1 complete turn back exactly as it was in order to get the cam chain to line up exactly with the tick marks and the cylinder head. If you don’t have this right, your timing will be a few degrees off and you will lose power.
I first discovered this when a customer brought a bike to my shop and had removed his cams and could not figure out why the tick marks were not matching up perfectly.
We unbolted the cams, removed the chain, rotated the crank 1 complete turn, and everything feel back into spot perfectly!