<VV> Lifter question
Mon, 30 Aug 2004 09:52:30 EDT
Please see my comments below.
In a message dated 8/29/04 7:38:55 PM US Mountain Standard Time,
> Original symptons...reason for the teardown...pulls strong to 3k, but no
> power after, in any gear.
Well, did you do any diagnosis before tearing down the engine? That problem
should have been chased down so you know the cause first.
> Should I be able to push in a lifter plunger with my hand, whether it be a
> SBC, or Corvair specific?
Lifters have an internal piston the slides up and down within the body. If
the lifter is filled with oil, the piston will not easily move down into the
body. But if it is only partially filled with oil, then the piston will collapse
easily. Your lifters may not be filled with oil. Use a trigger-type oil can
and fill the lifter with oil from the side hole. Then the piston should not move
down. If it does the lifter may be bad.
> Cam is definitely not off a tooth - I can see the 0 on the cam gear, thru
> the crank bolt hole.
It's possible that the gear on the crank slipped. Check that the #1 & #2
pistons are exactly at TDC when the timing marks are opposite each other.
> I just did everything but crack the case on my Corsa 140. (it's amazing how
> many pieces will fit in that small, confined area.) The cam, measuring with
> a dial indicator at the lifter, is doing close to what the specs say, for a
> used ISKY 280, not an Otto 30, around .270-.275 for most of the lobes on the
> passenger side.
OK, if you have an Isky 280 cam, then the lift should be 0.440 inches at the
valves and about 0.280 inches at the lobes.
> Who wants to explain how all this works? You've got a lifter, that has a
> spring in it, that as it's pushed by the cam, the spring compresses, pushing
> oil up thru the push rod, to the rocker. So, you're not supposed to get as
> much lift at the rocker as the cam is capable, w/o solid lifters. But how
> much is too much?
See my above description. Your description is not correct. Oil to the pushrod
(and rocker box) is metered by a flapper valve, not the spring, etc.
> With the rockers still installed, before the heads cam off, I was barely
> getting .175 on several of the exhaust. The instakes seemed okay, but only
> around .260. I did notice, that as I put pressure on the lifter, I could
> see them bleed down, rather quickly, on the dial.
Well, first, to make these measurements with the valve springs installed, you
MUST use a fully pumped up lifter or better yet, a solid lifter. You do not
want the lifter collapsing when you are trying to make these measurements.
Here is what to do now with the heads off. Repeat your lobe lift
measurements (on all lobes). You can use a fully pumped up lifter (see above for
instructions to pump up) and a dial mike. Just look for max lift which MUST be about
.280 inches and MUST ALL be within .005 in. of each other.
> Are my valves not opening enough due to the lifters? The valve spring is
> obviously a lot stronger than the lifter spring, and it seems it SHOULD be.
> When the lifter bottoms out, then, and only then, does the valve move.
Probably the problem
> How do I test what's happening, short of throwing money at it, and just
> buying new, Corvair specific lifters? I don't mind doing that, as long as I
> *KNOW* that is the issue.
> Forget the lifters as a problem for now. Make those lobe measurements first.
Then pump up each lifter as instructed and see if any collapse by manually
pushing on the pushrod seat. If any do, replace those ones. Most of all this is
covered in my book, THE CLASSIC CORVAIR, if you have a copy.
Keep up posted on your measurements and progress.