On Mar 26, 7:07am, Dean Mericas wrote:
> I'm hoping to get some clear technical guidance from the group on the
> installation of a new/used cam in my TR4.
I'll do what I can.
> Through the list I have located a mild street cam, but I'm told it must
> be "timed in" as part of the installation process.
That is correct.
> The only specs I have on the cam are the following:
>
> Intake = 22 - 70 degrees
> Valve lift = 0.415
> Valve lash = 0.012
> Full lift @ 112 degrees
> Lift @ TDC = 0.390
>
> Exhaust = 62 - 28 degrees
> Valve lift = 0.400
> Valve lash = 0.014
> Full lift @106 degrees
> Lift @ TDC = 0.405
>
> The Bentley manual has instructions for aligning an unmarked camshaft that
> involves finding the "point of balance" on the camshaft and setting the
> crank to TDC. Is this same process used for any camshaft?
Basically, yes. You'll need to substitute the values above for the
stock values, though.
> Can anyone give me a clear step-by-step explanation of the process
> of timing in a cam, or direct me to a suitable reference?
This is the abbreviated version (from memory, since I haven't
done it to the new engine yet...). First you need to set up a
dial indicator on the block to determine TDC. Then set up
some sort of pointer on the front of the block to point to the
TDC mark on your cam degree wheel (available from your friendly
neighborhood parts store, if you don't already have a degree
wheel). Turn the motor in the direction of normal rotation until
you reach 22 degrees before TDC. You'll have to make up a tool
of some sort to indicate off the cam lobe (there's a nice drawing
of a very convenient tool in the competition prep manual).
Turn the cam in the normal direction of rotation until the
intake valve for the first cylinder reaches the measuring
value (say 0.050" lift). Then assemble the timing chain, and cam
sprocket to the cam. There should be a set of bolt holes that will
work; on the TR-2/3/4, there are two sets of holes that are a half
tooth on the chain apart. If you flip the sprocket over, you'll
get a slightly different alignment (at the 1/4 and 3/4 tooth
positions); that is, these holes are assymetric with respect
to the chain (although, see note below). After you've done a
test assembly, rotate the engine through a complete revolution
and check your work - it'll probably be off a bit, so you'll
have to remove the cam sprocket and pick another set of holes
or move the chain by a tooth or something. Continue this
iteration until its right.
> Do I have enough data on the cam to complete the process?
Almost, you'll also need to find the lift value at which the
valve opening and closing values are measured (usually 0.050"
see above).
> Finally, does it seem strange that exhaust "Valve Lift" is less than "Lift
> @ TDC"?
No, because the "valve lift" will be the "lift @TDC" (of the cam
lobe) multiplied by the rocker arm ratio. It should be about
1.5 times as much, in other words.
Note 1: Make sure that you do all your measuring off the intake
valve (which is the number 2 valve). The first time I did this,
I measured off the exhaust valve - it's very frustrating to get
it spot on, and then have to start all over again...
Note 2: Apparently the cam sprockets currently available from
all of the vendors are drilled incorrectly. When you flip the
gear over you get the same set of values (ie. full and half tooth,
instead of the 1/4 and 3/4 tooth positions as described above).
I'm not sure what the best way to deal with this is. Assuming that
you need to replace the gear (I always repalce the gear when I
put on a new timing chain), you can either gamble that this
combination will work - or at least be close enough. Another
option is try and find a good used gear. The third option is
to throw money at it and get one of the venier adjustable cam
sprockets that Cambridge Motorsports in England are selling.
I just bought one, and its very pretty, and should be easily
adjustable. I just hope that it doesn't slip during use!
sorry this was so long, but I hope its useful,
John Lye
rjl6n@virginia.EDU
http://avery.med.virginia.edu/~rjl6n/homepage.htm
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