I’m attempting to correct th gaps on my valves ('77 4.2) Spec calls for .0012 -.0014, I had .0004. The engine had been running fine until it began “tapping” at #3 &4 intake valves.
After getting everything lined up I pulled cams lifted each bucket, and measured the shims. From there I determined the correct new shim, and replaced. After everything was back together and the chain tensioned, I rotated the engine and remeasured each gap.
EVERY STINKING ONE WAS LESS!!!
Now, it seems to me, that if I have a gap of say .008, and a shim of .925, going down to .920 would give me a correct gap.
Yeah, no. So, have I missed something here?
Oh, and just to add to my fun; as I’m rechecking my previous shim selections, I realize the steel(?) liner at #4 intake appears to have been shaped (roughly), as if someone took a Dremel around the inner lip.
I have pics, but not seeing how to add.
Anyway, there are NO metal shards in the valve spring area, so I’m thinking (hoping?) this isn’t a problem.
No, you haven’t missed anything, depends on where you measured the old shim , they normally depress a little where they contact the valve stem, all my tappet liners are chamfered, your spec means you have a series two 4.2 motor, clearances don’t cause tapping, loose tappets do though, make sure your rough edged liner isn’t contacting the cam, these things need strapping down you know…
Well I didn’t before, and do now!
Funny, there are two straps on the exhaust side.
Any way, contacted Welsh, and have a set coming for the intake side.
Guy I talked to said this is a real popular item these days on the 4.2s.
The likelihood of the them coming loose on the exhaust side was/is high compared to the intake so many people added the stake down kit to the exhaust side of the head only. Now, it’s becoming more common for people to stake down both the exhaust and intake sides. The kits are cheap compared to the cost of the damage they can prevent.
$35 for a kit? My god! the Humanity!
Gawd!! I’m ready to bang my head on something hard.
Yeah, I know - this sounds like a whine …
I’ve now changed shims three times on the intake side, twice on exhaust, and I’ve gained a grand total of .001 to .002 in gap.
Just as an example: #3 intake; I’ve gone from the original .870 to .850, and now .840. I’ve gone from a gap of .008 to a gap of ,010
Spec says .012 -.014
I’ve already been buying the thinnest shims Welch lists.
So I’m down to just two questions:
Am I missing something?
Can this engine survive being up to .040 out of spec?
I have had to resort to trimming the valve stems down with a valve grinder that I was lucky enough to be able to borrow.
I ended up dry fitting the valves to the head with no shim and no springs, making sure the valve was fully seated, I then measured the clearance with the cam in place. Deduct the clearance you want from the measurement, that should give you a close starting point.
Mitch,
I’m either very confused or you are. There’s no such thing as an 0.840 shim or anything like it. The shims are nominally 0.100 thick, with common sizes from 0.085 to 0.115. If you mean you went from a 0.087 shim to a 0.085 shim you are only going to open the gap by 0.002 (2 thousanths). If it’s me that’s confused then please ignore my comments, but it looks like you’ve just got your decimal point in the wrong place…
-David
I would not run it with such tight clearances…gaps seem to close up even more as wear occurs. And to be clear, the shims are .087", .085", .084"…or…87 thou etc.
I told you this is driving me crazy; Shim sizes were .087, etc, not .87.
I guess what I was trying to say is that by the math, if I have a gap of say, .008, with a shim of .087 and I go down in size by .005, I should now have a proper gap (.013). Instead I’m getting little or no difference. So I’ve gone down another .005. Nada, zip, no difference.
I must be doing something wrong, but can’t figure it.
Gaps are checked with feeler gauges, with the bearing caps tightened but not torqued.
I guess I go back to square one, and re-figure everything. Meanwhile - Merry Christmas eveyone!
You are sure the shims do stand proud of the spring retainers, correct? Don’t know why you wouldn’t torque the cam caps though.
Mitch,
In this example did you try a 0.082 shim? Your early quote says:…
When you correct the .870 to .087 etc, what you report is pretty much what you’d expect. That is, you reduces the shim size by 2 thou (and then by an addition thou), and your gap increase by 2 thou. Seems correct to me (within the measuring tolerance of 1 thou).
-David
New shims are sitting exactly where the old ones sat.
The only reason I hadn’t torqued was because I wanted to ensure proper gaps first.
Just double checked Welsh and XKs, neither lists below .085. I found a .084 among the shims I have, but nothing smaller.
85 thou is the smallest standard size. You don’t want to go much thinner than that, but going down to 80 is probably fine. When I needed one or two in this range Dick Maury at Coventry West was able to supply me with what I needed. As for not torquing the cams down while checking your shims, I don’t think you will get consistent results unless you do.
-David
Make sure some rebuilder didn’t grind down the valve stems instead of changing shims. If they grind too much it will never touch the shim. Without replacing the valve the only option is to grind the periphery of the shim so it fits down into to follower. Been there done that!
Thanks all.
Plenty to think on.
Trying something here.
I put together an Excel spreadsheet years ago to facilitate tappet shimming. XLS files can’t be uploaded to J-L so I’ve renamed it as a .pdf file. You will need to download it and rename the file extension to .xls before it will work.
File format is Excel 97-03 but should also work in later versions.
The spreadsheet is not advanced. Input fields have to be cleared manually (TAB-delete), though it wouldn’t take much to unprotect the sheet (no password required) and record a macro if you’re so inclined. - be sure to protect the sheet after. It will not recognise an erroneous entry so you need to be careful to plug in the numbers as measured.
XK tappet shim calculator.pdf (28.5 KB)
IIRC, a baseline measurement, from the valve stem to the base circle of the lobe is 0.320” ( it’s been a loooong time, but I think that’s correct.
I would set those distances after the seats wete fitted, on a stem grinder, using a weak spring in place of the real ones, cams bolted in.
Mitch,
Are you sure that the tool that you are measuring the valve shims with
is reliable and accurate? I had a similar issue about 15 years ago with an
XK engine valve adjustment where I couldn’t get all the valves to
specification despite swapping out shims many times. There was a variably
to my readings that just didn’t make sense. It turned out that my new
digital caliper was not reading accurately and reliably. Once I started
using my father’s old school analog dial caliper all the variability went
away and I was able to adjust the valves clearances to spec. Since then I
have always used my father’s analog caliper for things that matter,
especially something as important as engine valve clearance adjustments.
Something else that I learned over the years is to look closely at the shim
for any depression or dimple caused by contact with the end of the valve
and if there is a dimple put that side facing up towards the tappet. The
shims take a pounding and the dimples can affect the valve lash measurement
if they are deep enough and if the shim is installed with the dimple facing
the end of the valve.
I have successfully adjusted Jaguar engine valve clearances many times. The
most recent time was on the 5.3L V12 in my wife’s 1990 XJ-S convertible
where there are 24 valves to worry about, and not just 12.
Good luck.
Paul