Mike,
Below you mention that several push rods appear to have been making
contact with the cylinder head. Does it look like they made contact as a
result of being bent, or do they look well scuffed at mid point like they
may have been rubbing on the cylinder head for a number of miles, and then
subsequently failing.
I just recently purchased my 74. About 15 years ago I had a small resto
shop where I owned, repaired, and basically, "lived and breathed", British
cars. If I remember correctly there should be plenty of clearance between
the push rods and the cylinder head in the stock configuration. Later this
afternoon I may pull the valve cover off of mine and have a look.
The 1.7:1 ratio rockers that I made years ago for the 6 engine not only
represented a geometric difference, but also a difference in force upon the
camshaft and pushrods. The stock rocker arms are at a ratio of 1.445:1.
Increasing the ratio to 1.7:1 meant that the adjuster stud with ball had to
be moved in, (closer to the rocker shaft). With this; the push rods were
nearly touching the head, but not close enough to cause any problems.
Finally, the added ratio has the effect of increasing the force upon the
push rods, the cam to lifter contact area, and the cam bearings. In 50K
miles I never had a problem. I realize that this doesn't really have
anything to do with diagnosing your problem, but it does go to show that
even with a modification the push rods do not make contact with the head.
Possible reasons for bent push rods:
1. Tappits hanging up in up position
2. Rocker hanging up in closed position. (Not likely.)
3. Friday 13 again!
4. Your best diagnostic hypotheses gratefully accepted.
1) If the Tappet were to hang in it's bore in the "up" position, then
the
push rod could be bent by only one action. The piston slamming the
valve!
2) I think it would take a total lack of oil to cause a rocker to seize
to
the shaft. Other components of the engine would fail long before this
could happen, unless of course the rocker shaft assembly was somehow
improperly installed, causing a blockage of the passages that carry oil
through the shaft. I don't remember if this is even possible.
3) This begins to gain credibility when you have skinned knuckles, dirt
in
your eye, no more beer, and just basically mad at the world.
4) Are you making this repair yourself, or is it in a shop?
-----Original Message-----
Great answers, everyone! Of course, just like Dick says, it's great fun when
you're not staring at the broken toy.
Sorry, Dick! Jim wins the prize this time. #5 push rod sheared at mid
point.
(4 others showed signs of contact with cylinder head, also at mid point.)
So,
#3 cylinder exhaust valve failed shut.
Suck; squeeze; bang; whoops! Nowhere for exhaust gas to go until adjacent
intake valve starts to open, just before TDC. Out goes the exhaust product,
right through the front carb.
Possible reasons for bent push rods:
1. Tappits hanging up in up position
2. Rocker hanging up in closed position. (Not likely.)
3. Friday 13 again!
4. Your best diagnostic hypotheses gratefully accepted.
Thanks again, team. You are the best.
Mike N.
CC75088L MoneypiTR
|