mi16 timing belt
MTAYLOR.US.ORACLE.COM (MTAYLOR@us.oracle.com)
29 Apr 97 19:06:55 -0700
Hello all,
the Mi16's going to have at least 2 pair of bent valves upon l;osing the
timing belt. As all like valves for each cylinder open and close together
(pairs of intake/exhaust valves) you get a pair bent for each one that is
open. The engine will make at least 10 revs open shutdown, so much force is
moving when the engine loses its belt. When the pistons slam a pair of valves,
that tends to kill most of the momentum. The engine won't make much more than
two revs due to hitting the valves. To remove the cams, you must remove the
distributor base, and all pulleys that are attached to the cams will be either
coming off with the cams or being removed separately. You must pull the head
cover ( also known to us as the valve cover) and then remove the 24 or so
bolts for the cam bearings, there are 5 cam bearing sets that cross both cams.
Each end bearing is actually the end of the head, making up the top half of
the oil seal landings. The crank will have to be set to the pin locking
position, which is a hole in the main pully on the crankshaft indexed at 12:00
relative to the engine's position. This places the crank such that all
cylinders are at middle of their strokes. It would then be safe to rotate any
camshafts. There is no spot on either cam that has no valves open. The pistons
come up to around 3 mm short of the top of the cylinder deck at top dead
center. There are reliefs in the top of each piston for each pair of valves,
allowing clearance for the outside face of each valve into the piston. If you
were to see a piston, it would have two pair of half moons relieved near the
edges where the valves sweep. The valves are almost flush with the lower bound
of the head's deck, while closed. If a valve is even partially opened when a
piston drives upward, there would be approximately 10-15 mm of common area
that would result in a crushed valve set. From all I have heard of this
phenomenon, the valves bend and their guides are also susceptible to
non-linear movement.
Let's face it; the valve train is damaged, and the head needs to be pulled.
The $300 to remove the head is not unreasonable. The labor to remove the head
is certainly in the 4-6 hour ballpark, unless you are not being orderly in the
removal process. If they are talking of a $1000 total head rebuild and
re-timing, you are being fairly treated there as well, as the quote I received
was $2000 for such a catastrophie. I was told during my tear-down that the
valve guide work is very tough to get right (as told by Arlo at the Imported
Car garage in Burlington, VT, an Mi16 fanatic and owner of the business) and
that he sends out his work to a machinist in Connecticut, as Arlo puts it,
"the only one that can do it right". That guide work alone is a $600 job.
As far as the cost of a complete engine rebuild and clutch replacement, I just
completed mine at around $1300 complete, doing all of my own work. In that
regard, $1000 is kind of steep to get the head repaired, but it is worth it to
have such a fine automobile to drive.
The head will definitely have to be reomved, so please just let them do it and
see where you can go from there. You may be able to get your hands on a good
used head, although the $400 figure was quite astoundingly fair of Mr.
Cullemore to sell back to the dealer. You may find yourself paying much more
than that if you are to find one.
As for belt life expectancy, it all depends on how the maintenance is. You
must watch the belt's life progress, and maintain the correct tension
throughout its life. If the installer gives too much slack when new, it will
be a relatively short run before retensioning is necessary. I found mine to be
noisy a few months back, and to my astoundment, it was constantly slapping off
the front side of the timing cover below the intake cam pinion. It gets some
harmonics at different RPMs which look even more violent for the belt.
Good luck Sandy.
Mike Taylor