want to adjust valves…found quite a few would require new pads to bring them into proper tolerance.
decided, as advised, to check Cam Bearings…and sure enough, the front ones showed wear (as expected)…so I ordered a new set from XKs Unlimited (now Moss Motors)and replaced all cam bearings and lubed them up.
installed existing Tappets and the original Pads back in their original positions…and installed the Camshafts…only one in at a time…to see what readings I would get on the valve clearances ( really expected no significant differences, if at all ). Well, Surprise !!!
PROBLEM: really different readings:
Cylinder 6: Exhaust was .oo7 and is now < .oo2 ( ??? ) Intake was .oo4 and now is .oo5
Cylinder 5: Exhaust was .oo8 and is now > .o12 ( ??? ) Intake was .oo8 and is now < .oo2 (???)
Cylinder 4: Exhaust was .oo8 and is now .oo5 ( ??? ) Intake was .oo7 and is now . oo6
Cylinder 3: Exhaust was .oo8 and is now .oo9 Intake was .oo6 and is now < .oo2 ( ??? )
Cylinder 2: Exhaust was .oo8 and is still the same. Intake was .oo7 and is now .008
Cylinder 1: Exhaust was .oo9 and is still the same. Intake was .oo6 and is now .oo7
What could cause major differences in cylinders 6, 5, 4, 3 ??? ( With 5 being the worst…with both Exhaust and Intake way out of wack ? )
My experience with valve clearance measurement is that the results are hard to replicate - i.e. what seems to be a simple math exercise to adjust the clearance does not always work out that way.
With the change of bearings the random number generator has an additional variable to work with.
Sometimes all you can do is accept your latest readings and proceed from there.
How do the cam to bearing clearances look? My guess is they were pretty loose before.
That would explain the tighter readings. Would be worth seeing if it’s riding right near cyl 5 on the exhaust side, and there’s nothing hiding behind the bearing shell or a burr or something. Though I would expect it to effect the neighboring one more too.
Thanks…and understand. That’s why I initially took two readings with before I pulled the Camshafts out and put new bearings in. The readings were very similar then. With the new bearings, a few are WAAaaaaay out ! Seems just too bizarre…
I see most are now smaller. There are 4 things I can think of
Did you put oil on the shim or inside the bucket? A thin film of oil will cause it to not be in full contact with the shim until it’s gone through a few cycles. I always leave mine fully dry while measuring, and add a drop when it’s going back together.
You may have mixed up the shims, hopefully not the buckets as that would be bad. It’s important to have good methodology and sorting. The patented Jerry Mouton method was an egg carton (labelled)
You changed the bearings and that alone will affect valve lash because the cam is riding in a different place.
By far the most likely thing is that you simply flipped the shim over. A used shim will have a dimple from being pounded by the valve stem. If you flip it, then the dimple will now be in contact with the bucket seat which is quite a bit larger than the valve stem. Often when clearances have closed up too much, we flip shims to regain clearance. Yours may have been flipped once. If you flipped back, instant gap closure.
I did not clean the shims or the interior of the bucket. They all had a thin film of oil on them when I took them off… which tended to hold the shim in place when I put the tappet back in.
I did not flip the shims. Same side to valve stem as before.
I meticulously noted what went were ( laid out and marked on cardboard, including the D washers, split washers and nuts) camshafts, bearings, tappets, shims and hardware).
I did wipe clean clean the seats where the bearings are set.
I did put pre-lube on both shells of each cam bearing (inside only) after I installed the new shells.
I did torque the second camshaft down to 15 ft. lbs, to see if that would help. It didn’t.
However…WHEN I FIRST STARTED BREAKING DOWN THE CAMS, I DID ROTATE ONE OF THE CAMSHAFTS ABOUT A QURTER TURN FROM TDC WHEN I WAS TRYING TO GET AT THE OTHER CAMSHAFT SPROCKET BOLTS. THE OTHER CAMSHAFT BOLTS HAD ALREADY COME OUT … AND I THOUGHT IT WAS DISCONNECTED FROM THE SPROCKET. MAYBE IT WASN’T AND I BENT A VALVE OR TWO ?? DIDN’T FEEL IT THOUGH. PLEASE SAY NO !
Hrm can’t say for sure, 90 degrees is rather a lot. If a valve bent though that would increase clearance, likely dramatically as it would prevent full closure.
As a rule, not a general rule but a golden rule, never rotate any of the 3 rotating shafts unless the other two are known to be out of the way.
Even if one cam is fully disconnected, don’t rotate the other one unless the pistons are 15-20 degrees BTDC because with two pistons at the top, the valves could collide with them if you rotate a cam.
Sorry HJK you don’t want to hear this but…it’s amazingly easy to bend valves. I’ve done it, simply trying to bolt down the bearing caps and having the cam snap off the bucket it was trying to push down. I’d suggest you take the cams off and do a leak down test - you can get a tester from Harbour Freight if you don’t have one or can’t borrow it. At a minimum put some WD40 into the port on the suspect valves and see if it leaks away.
I’ve certainly flipped shims once, but once flipped you can’t really flip them back. They’re too hard to predictably measure with dimples on both sides.
Never seen it to be an issue: the wear spot is somewhat slope-sided, and its centralized position on the valve stem is constrained by the spring retainer.
Not sure if it’s common practice on the XK, but I’ve heard of folks pulling a cap with the cams still coupled to the timing chain and clamping a piece of paper between the bearing and the cam to lock that side from turning. Of course you absolutely need to remember to take it out before trying to turn it intentionally, so write a reminder on the part that sticks out if necessary!
Thanks to all for your info / insight. Once I did the leak-down test, found 4 of 6 cylinders had valve leaks; most not much, but one was very bad. So, into the machine shop for tests, cleaning, inspection of the valves and head. Lucky to have a great shop nearby in Jacksonville, FL. Result: valves and related all good…just needed cleaning and machining / valves lapped. Head straight & true, no cracks. Only $214 to get the machine work and cleaning all done. Now to adjust the valves ( properly, this time ) and reattach the head. Block studs all good and threads cleaned ! Will be fitting a new Payen head gasket.
Speaking of small lash (not really related to our engines, but… a lash issue) -
Watching “Engine Masters” and they put solid roller lifters on a hydraulic grind cam. Push rod Chevy motor, but Aluminum. Set the manual lash at 0 !! They said they sometimes they set them at 0.002 or 0.001, but it was easier to hold “0”. As soon as she warms up they open up just fine!
I know if I opened the 0.020" Isky in our Corvette to 0.030, like the Duntov 30/30 cams, you’d pick up vacuum.
