Dialling-in (degreeing) a grey motor cam

Includes fuel system, cooling system and exhaust.

Moderators: reidy, Blacky

Post Reply
User avatar
Harv
Posts: 4648
Joined: Mon Oct 08, 2007 2:00 pm
State: NSW
Location: Sydney, Australia

Dialling-in (degreeing) a grey motor cam

Post by Harv »

A query over on the FX/FJ forum got me curious - just how would I dial-in a grey motor cam? One thing led to another and next thing you know I'm buying stepped woodruff keys to see if/how they work. :oops: I really got to work on that attention span thing.

Results from the small research project attached below as a PDF file document (if you can't read it on your 'puter or eyephone, PM me and I'll send you a Word version).

Dialling in a grey motor cam.pdf
(331.87 KiB) Downloaded 34 times

Cheers,
Harv
327 Chev EK wagon, original EK ute for Number 1 Daughter, an FB sedan meth monster project and a grey motored FED.
In the Shed
Posts: 1622
Joined: Wed May 16, 2012 10:18 pm
State: SA
Location: South Australia

Re: Dialling-in (degreeing) a grey motor cam

Post by In the Shed »

An interesting read Harv. Thanks for taking the time to write that up and post for all to access. Hope this didn’t side track you for too long!

Regards
Stephen
A day in the shed beats a day at work!
FbSTDwagon
Posts: 744
Joined: Thu Jul 02, 2020 3:04 am
State: SA

Re: Dialling-in (degreeing) a grey motor cam

Post by FbSTDwagon »

Nice document Harv.

Only last week I was curious about my cam and I dialed it up and it’s somewhere near the specs Clive sent for the 82, but I figured it’s not adjustable so I just need to send it.

As for the timing gear backlash… with the steel timing gear my backlash is .012 - .015 but my memory tells me the FB book space was .004 -.007… but my memory has holes in it.

Will check that out next time I have the book open.
Drew
ardiesse
Posts: 1001
Joined: Thu Jan 19, 2017 9:57 am
State: NSW
Location: Sydney

Re: Dialling-in (degreeing) a grey motor cam

Post by ardiesse »

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
EK283
Posts: 2153
Joined: Thu Mar 16, 2006 9:51 pm
State: NSW
Location: SYDNEY NSW

Re: Dialling-in (degreeing) a grey motor cam

Post by EK283 »

How does it affect performance?
Advancing or retarding the cam will move the Torque curve higher or lower in the rpm range.

General Effect

Advance
Improves low-end power and throttle response
Intake Valve Opening Event Happens sooner
Piston to Valve Clearance, Decreases intake valve clearance
Moving 4° Causes...Peak torque about 200 rpm sooner

Retard
Improves power at higher rpm's
Intake Valve Opening Happens later
Piston to Valve Clearance, Increases intake valve clearance
Moving 4° Causes...Peak torque about 200 rpm later

Regards Greg
So many cars so little time!
User avatar
Harv
Posts: 4648
Joined: Mon Oct 08, 2007 2:00 pm
State: NSW
Location: Sydney, Australia

Re: Dialling-in (degreeing) a grey motor cam

Post by Harv »

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
exploded diagram.png (82.09 KiB) Viewed 155 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
camshaft end float.png (119.02 KiB) Viewed 155 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
mefs.png (33.59 KiB) Viewed 155 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
backlash.png (128.32 KiB) Viewed 155 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
327 Chev EK wagon, original EK ute for Number 1 Daughter, an FB sedan meth monster project and a grey motored FED.
User avatar
Errol62
Posts: 8653
Joined: Sat Dec 06, 2014 2:44 pm
State: SA
Location: Adelaide

Re: Dialling-in (degreeing) a grey motor cam

Post by Errol62 »

So any effect on timing due to variation in tolerances is negligible. Assuming things are half serviceable. But due to the cam being driven any lash will result in slight retardation, whereas variation in combined gasket and engine plate thickness can go either way.


FB ute fixer upper, EK van on rotisserie
getting my FB ute on the road
EK van on rotisserie
ardiesse
Posts: 1001
Joined: Thu Jan 19, 2017 9:57 am
State: NSW
Location: Sydney

Re: Dialling-in (degreeing) a grey motor cam

Post by ardiesse »

Now you've made me curious. So I found a camshaft, with timing gear attached. The gear has 48 teeth and is about 0.900" thick. The helical gear angle is such that there's almost exactly one tooth's difference between the front and rear faces of the camshaft gear.

360/48 is 15/2 (dividing by 24), hence 7.5 camshaft degrees in 0.900" of axial gear movement. Double that for the crankshaft, and you get 15 degrees in 900 thou axial movement, 1 crankshaft degree for 60 thou axial movement. Now let me compare your numbers gained using proper trigonometry.

One degree for 66 thou. Good enough.

I seem to remember making a measurable difference in valve timing by using a second (home-made) front engine plate gasket out of 0.008" gasket paper. I might have to re-consider the effect it actually had. But it reminded me how difficult it is to measure valve timing to anything better than about 3 degrees - I was using the "spin-the-pushrod" method to determine when all the lash was taken out of the valvetrain.

Rob
Post Reply