Dave:
Yes, it is possible to leave out the tensioner, or for it to be
in there but worn out. However, there are other sources of spark scatter
that should also be checked. Do not assume that it must be the
tensioner. Can you hear the chain rattling? Remember that the cam is a
significant source of drag and so the tendency is for that drag to
naturally keep the leading portion of the chain taught. It is the back
side of the chain that is slack, and that tends to rattle around.
Normally this will not make any difference in the timing, particularly
at idle.
Another source of spark scatter is the cam retainer. The is a
hardened piece of steel shaped like a parenthesis -> ( It bolts to the
front engine plate under the timing cover and engages a groove in the
cam. It prevents the cam from moving back and forth in the block as it
spins. If the cam is free to jump about, the timing will also jump
around. I put in a new one when I rebuilt my motor as insurance.
The bearings in your dizzy can be worn out, and can allow the
cam that activates the points to jump around. This is a common source of
spark scatter, and should be checked before you tear into the motor.
With the engine stopped, pop the dizzy cover and pull off the rotor. Try
to wiggle the shaft back and forth. If the shaft can be wiggled, it is
too lose and you should have your dizzy rebuilt.
The drive gear for the dizzy can be work or damaged as well, and
cause similar symptoms. If the Dizzy is OK, check the drive gear (access
it by removing the dizzy and use a magnet to fish it out of the block).
To have some slop in the crank to rotor rotation is normal, as
there will be some slack in the cam chain, drive gear, etc. The question
is whether 10 degrees is excessive. While it may seem like a lot, I
can't get past the fact that the timing is jumping around at idle. This
seems like more than a loose chain, perhaps other listers can correct me
on this point. My sense of it is that a loose chain is not like to cause
scatter at idle. I had some slop in mine after my rebuild, but I did not
see any scatter, so I know that at least some slop does not matter for
the spark timing. I can't say if I have more or less than 10 degrees,
though. Never measured it.
I would check this stuff in the following order:
1. Dizzy shaft bearings
2. Dizzy drive gear
3. Cam chain tensioner and cam retainer.
Most common cause seems to be worn dizzy bearings....
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of Dave Murray
Sent: September 06, 2006 3:09 PM
To: 6pack@autox.team.net
Subject: Timing chain tensioner
Listers,
I have ~10 degrees of rotation of the crank before the rotor begins to
move,
clearly excessive, especially on a freshly rebuilt motor with new timing
gears, chain, tensioner, etc. The car runs strongly but tends to surge
at
idle and when cruising easily explained by the 10 or so degrees of
timing
change visible at idle using a timing light.
Two questions:
1) Is it possible the tensioner was not installed when the engine
was
reassembled? I was out of town when the engine was reassembled and have
only the word of the gentleman who does not wish to pull the engine
apart.
2) Is there an adjustable tensioner or uprated tensioner available
for
the TR6 assuming the tensioner is installed correctly?
Dave
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