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Valve shims on V12

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CJD

CJD

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I am working on a '95 XJS. It flunked emissions testing (of course), so, among other fixes, I would like to set the valve lash and cam timing. This will be my first experience with the Jag lashes. I am having a problem finding shims for the valve lash. Most sites do not list the thinknesses at all, and the ones that do start at .085" and go up.

For a .016" clearance, I expected the thinnest shims to be thinner than .085". Like closer to .001". That means the closest I can set the clearances is +-.0425", which is farther off than I am used to dealing with.

So am I missing a trick or something?

Thanks,

John
 
Well, just talked to one of the parts shops. I expected the shims to be a stack of various thinknesses that add up to the desired thickness. Just learned each valve uses a single shim...OMG! Could Jag have possibly come up with a more difficult set-up?

So, this knowledge brings up the next question...if the valve has recessed so that .085" is still too thick to get the correct lash, does that mean time for a new valve and seat insert? Is grinding the stem still a no-no, like on other cars?

Thanks again,

John
 
You could "tip" (grind) the stems slightly but not a good idea. Grinding the shims would be your best "quick fix" but they need to be lapped with a magnetic chuck so there's no deviation in thickness. If you DO decide to R&R the heads (mucho $$ and time!), set the valve lash on the bench. Much easier than after they're back on the block. And why V-12's are so costly to own if you don't wrench on 'em yourself... How'd you end up agreeing to do this, John? It can be a real "can-O-worms". Keep the "buckets" in original order, too.

Shims are in the early Jags, too... and Alfas, Lotus, VW. At least the Germans made it so's the shims can be swapped without removing the bump-sticks. Not so with the others.
 
I am guessing this is a 4.0 Fairly unusual to have a seat problem with them. The thing is, on the 6 cylinders, the head bolts also hold down the cams, and there was a set of special tools to bolt back down so you didn't unseal the head gasket.... Unless something is really wrong, the stock shims usually do just fine. The tip of the valve stem and the keepers are recessed in the spring retainer so the correct shims work. Probably mose stable at high RPMs... Measure the clearance, remove the cam, and pull up the buckets w/ a magnet. Measure the shim, and record. You may be able to switch some of them so that you don't need to purchase all of them. British Parts International used to have a reasonably priced shim kit available.

If a V12, then the job MIGHT be easier. There is a special tool to "set" the cam chain tensioner to the locked position. Very hard to do without it. The chain tensioners are plastic and can break. The front cover can be removed with the heads in place... just be careful.If you EVER have to remove V12 heads, BUY the head pulling tool. Not cheap, but way better than spending days fighting the heads off.

Hope this helps a little.
 
Thanks Doc, Jesse,

Hmmm...shave the shims instead of the valve stems. I think that would be very doable.

The only reason I am planning this is because it failed emissions with high HC and CO last week. Last year it did the same, but I managed to tune the heck out of the ignition to get a pass...barely. It has an occasional stumble at idle, so I assume that after 80k the timing chain must have stretched and delayed the cam timing. That could account for the stumble and high emissions.

Since the valve covers will be off and there are 80k miles on the engine, setting valve clearance just seems like the thing to do. I may be wrong, but I picture that maybe a couple of exhausts are probably zero lashed by now and may burn if not opened up...or I may just be reading into it.

Thanks again for the tips!

John
 
In street trim, the 12's are well under-stressed, I'd be surprised to find seats so badly hammered they go to zero lash at 80K miles. Much more likely you have a chain/tensioner issue, IMO.

By all means, check the valve clearances but the high HC/CO, IMHO, would be more likely the result of something going 'sideways' in the fuel management system. <span style="font-style: italic">A shop manual</span> and some time going thru that may yield an answer. Throttle position switch/sensor, fuel rail pressure regulator, leaking injector(s), clogged O2 sensor... Add up a bit of "slop tolerance" in any two of those and things can be out of whack. It may also be a good idea to beg/borrow/steal an A/F ratio measuring device to give you good data as you go (maybe "steal" isn't such a good piece of advice. :wink: ).

And if it comes to pulling the heads, take Jesse's tool recommendation to heart. We've both done more of these engines than most folks even <span style="font-style: italic">see</span> in a lifetime. The things are mechanically fairly straightforward if you've spent a lifetime with 'em. I've kept shim sets for Lotus and Alfa but not too many Jag shims. That box got sold. The good news is: a Jag shim is a Jag shim for all the "modern" engines. Jesse's hint about shim "juggling" is spot-on, too. I use a Sharpie marker to write clearance on the head "lip" for the cam cover then when measuring the shim for each, write that number on there too. Makes the job a bit less confusing... and hospital O.R. protocol is a good idea. Clean/wipe everything as you go.
It ~is~ surgery. :wink:
 
Last year I also put in new injectors. After recently changing both fuel pumps (for what turned out to be an intermittent connector...ouch!), I know that the fuel reg is also working. The Throttle switch and O2 ARE unknowns. I'll definitely put those on the to-do list.

I'm glad to hear the valve seats are so durable. After hearing from you guys, it sounds like it's a job best put off till more serious work is needed.

After reading Kirby's Book, I am a bit scared of the chain tensioner. It sounbs like a little "snap" here can add several days and $500 to a cam timing job...

John
 
John said:
I'm glad to hear the valve seats are so durable. After hearing from you guys, it sounds like it's a job best put off till more serious work is needed.
Click to expand...

That'd be my conclusion. Check lash anyway. Better sure than hoping. :wink:

John said:
After reading Kirby's Book, I am a bit scared of the chain tensioner. It sounbs like a little "snap" here can add several days and $500 to a cam timing job...
Click to expand...

If you're a "detail oriented" type, no hammers, etc. you'll be fine. Take your time and don't force anything.

:thumbsup:
 
Good luck.

And remember: We like feedback, too. :wink:
 
Like Doc says, with 80K on it, it is not likely to be anything big. The "Boook" has scared plenty of folks. While it is true that these things happen, it is not as likely as it might seem. My 89S has 155K on it, and the only reason the cam covers were EVER off was to replace leaking gaskets and D plugs. Have you looked at the cap and rotor? Look real hard and find GENUINE MARELLI parts. Last time I looked "FasterJags" still had them. Pricy to be sure, but the real cap must weigh twice what the replacements do. Use the correct factory specified spark plugs (only!!), gapped correctly. Do the engine set up exactly. .002 feeler gauge on both throttle plates, then set the throttle pot as close to the lowest end of the voltage spec as possible. Then adjust the rods so that it all moves in unison. There is a timing switch on the pedastal. Make sure it is adjusted, and that it works. I can't remember if it is true on the 6.0s, but on the 5.3s there is a connector in the trunk near the ecu, that has a "plug" with a loop of wire connected to it. If it does, remove it for the test The cars used to go into open loop when in park or neutral, and removing the connector bypasses this "feature" These cars normally run fairly clean, so just putting it all to exact spec should cheer it up.
 
Well, dove into the project. It turns out the valve clearances were all within .001" of where they should be. I was surprised to say the least. Also, I expected the chains to have retarded the cam timing...but they were both right on also.

That's the good news...the bad is I cannot blame the emissions failure on the valve train!

On to the cooling system next.

Oh, by the way, got the tune up stuff from FasterJags. The cap is not Marelli, but it does say made in Italy. Not really sure what it is...

John
 
Be certain the distributor advance mechanism is working. About every V-12 I've ever seen had the dizzy advance either frozen completely or bound up enough to be a problem. Physically inspect it for proper operation. :wink:
 
Thanks Doc. This is a Marelli, so the advance is all electronic. In fact, I don't even have timing marks on this car!!

I am a little concerned, once again because of "the book", about the possibility of the crank balancer having turned on it's hub. I tried to measure TDC through the 1A plug hole, but the piston never rises high enough to get a dial indicator on it. I had to base all cam references to the position of the electronic pickup.

Is there a trick to finding TDC without removing the heads?

John
 
If the crank balancer turns, it does not affect the timing. The "fingers" that the sensor reads are on the solidly mounted center. If the balancer was loose however, the key can shear, and then there are timing issues. Unbolt the AC compressor, and move it to one side (don't disconnect the hoses), and you can use a long thin screwdriver for an approximate TDC locator. Wrap it with tape for an easy visual reference There should be a 1A mark on the balancer, and some sort of timing mark on the bottom of the cover. Read "the book" and then take several grains of salt. It is a compilation of worst case scenarios, and fixes in search of a problem. I have had my 89 since new, 155,000 miles, and other than the valve covers leaking with the original paper gaskets, the engine has never been touched. (In spite of being garage kept most of its life, it has rusted though..... ) These cars are tough as nails as long as you don't let them run hot.
 
Thanks Jesse. I'll quit worrying about the balancer. I have to say that so far I am very impressed at how well this engine has held it's tolerances for 16 years. I think I was just spooked after reading "ThE BoOk!!

John
 
:lol:

I should have reread the entire thread. Marelli, not Joe L & Sons. My bad.

And again, the 12's are really under-stressed in street trim.
 
Well, finished up. A few lessons for future viewers. The Fasterjag distributor cap is actually the same one sold by Standard. It's made in Italy, but definitely not a Marelli, although it's advertised as such. Best I can tell, if you are not paying over $280 in 2011 dollars, you're not getting a Marelli.

Two ports were wet on disassembly and those plugs noticeably more fouled. I switched the location of those injectors to the side that does not get "sniffed". In the emissions test. Later I'll pull the plugs and see if the fouling moved with the injectors. The injectors are new, but the cheapest I could find...so may leak.

This "tune up" included:

Valve clearance check
New cap
New rotor
New plugs
New plug wires
New thermostats
Recored radiator

If this doesn't do it, then the PO must have shelled the catalytic converters. Don't plan to change those. After spending what I have, Texas allows a "low mleage" emissions waiver. THAT will be my next step!

Next week we'll find out if the cat will pass...

Thanks again for all the tips!

John
 
Well, 2 weeks work and a grand, and she failed with exactly the same numbers as before I did anything. That means it's either the injectors/ O2 sensors/ or cats. But, that will have to wait till next year to troubleshoot. She runs great, and I have spent much more than enough to get a waiver on the smog tag.

So, to be continued next year!

By the way, got a chance this weekend to take her on a road trip from Dallas to Houston and back. Forgot what fun these Jags are on the open road! On the way back it covered 200 miles in a hair over 2 hours. Finally got pulled over...of course...but the Trooper was just laughing when he got to the window. Said he was glad I stopped, as it would've taken him 2 counties to catch up. We talked about the car for some time and he let me off with just a warning...a warning! Well, back to the lumbering real world. But it was fun for a couple hours...

John
 
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