ardiesse wrote: ↑Mon Nov 21, 2022 10:44 am
I'm commenting without reading (as usual) . . .
The last time I rebuilt an "early" grey I couldn't get the 48-FJ front engine plate gasket, so I made my own out of gasket paper. It got me thinking - the timing gears are helical, so as a result, the valve timing is directly affected by the thickness of the front engine plate gasket. This was the case. I needed to use two home-made gaskets to get the valve timing close to spec. If your front engine plate gasket's too thin, the valve timing is retarded.
So here's a hint: if you need to advance your grey's valve timing, put shims between the camshaft thrust washer and the front engine plate. The reverse step - retarding valve timing - is trickier. You have to use a thinner front engine plate gasket. Either that, or "enthinnen" the camshaft thrust washer.
Rob
The helical gear bit got me curious. How big is the effect?
CAUTION: The following text contains maths (mefs). Viewer discretion is advised.
In a grey motor, the crank gear (labelled 1 in the image below) is pressed onto the crankshaft as far as it can go (until it bottoms out on the crank snout, labelled 2 in the image).
- exploded diagram.png (82.09 KiB) Viewed 494 times
The crankshaft is fixed into position in the block by it’s bearings. This means that the crank gear can be located in only one position in or out of the block (in the direction of the green arrow in the image). The camshaft gear (labelled 3 in the image) however has a few more variables. The camshaft retaining plate (labelled 5 in the image) mounts onto the camshaft (labelled 4 in the image) as far as it can go (until it bottoms out on the cam snout). When the gear is pressed on to the camshaft, an amount of end float is allowed between the gear and the retainer (as shown by the red arrow in the image). The specification given by GMH is 4-6 thou, allowing for some variance.
- camshaft end float.png (119.02 KiB) Viewed 494 times
There is also a steel engine plate (labelled 6) between the retainer and block. This steel plate is not likely to vary much in thickness. The gasket (labelled 7) that goes between the block and the engine plate however could vary in thickness. Because there is the variability in end float and gasket thickness the cam gear can be in different positions in or out of the block. This means that the cam and crank gears can be meshed together by varying amounts.
For straight cut gears, it does not matter how far engaged the two gears are – as long as the teeth are meshing, the two gears are rotationally aligned to each other. The cam and crank gears however have helical cut gears. As helical gears mesh, the two gears move relative to each other. This is obvious when putting a distributor into an engine block – as you stab in the dizzy, the helical dizzy gear moves the dizzy shaft and the rotor moves around to point at a different cylinder (acceptable practice is to then swear at the dizzy, and have another go). For our cam and crank gears, if the cam is moved in or out of the block a different amount then the cam and crank gears spin relative to each other. This effects camshaft timing.
So how much difference does this make? By measuring the camshaft diameter, width and tooth length (D, W and L on the diagram below) then the angle that the camshaft rotates as the gear engages can be calculated.
- mefs.png (33.59 KiB) Viewed 494 times
From some measurements, W=0.875”, D=0.5455” and L=0.930”. Working on the sums, = 6.622° With a little more mefs (and bearing in mind that crank and cam angles are different beasts), for every 66 thou of extra clearance a the snout the cam timing changes by 1° (crank degrees).
To put this into perspective, an unused aftermarket engine plate gasket measured at 16 thou, and the engine plate at 140 thou.
Out of curiosity (if I was doing a little mefs, I may as well do some more) the backlash between the timing and crank gears (either from manufacturing or wear) can also adjust camshaft timing if it is excessive (should be 0.003-0.004” for a grey motor). Backlash is measured as per the image below, by inserting feeler gauges between the gear teeth.
- backlash.png (128.32 KiB) Viewed 494 times
Assuming that the backlash is present at the tooth root, for every 0.022” of backlash the camshaft timing changes by 1º at the crank.
Cheers,
Harv