well, my sister did not end up getting her car,ruby after all.which is fine with me because I will have a chance to make the engine run as best it can.I am checking the valve clearances.
I am confused with 2 exhaust valves with only .006 for clearance.Far from the .012-.014 that they should be.I have not checked all valves clearances yet. Please help me understand how this very small clearance can happen. There are 200,000 miles on the odometer. No wonder the engine is not running right. Any info will help me on where I should order shims. Mark
Generally, clearances tend to decrease with mileage, not increase, although there are factors weighing in both directions. Wear/recession of the valve seats is, I believe, the factor most often cited for clearance tightening up. Shims are available from several sources; I will leave it to others to tell you the which vendor is best. Be sure to determine all sizes needed; often a rejected one at one location can serve as the new one at anotherâbe sure to flip them over when reusing. IMHO.
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Wear on the valve seats makes the clearances tighten up. Wear on the tappets makes them open up. Sometimes an automaker gets really lucky and these tend to cancel one another, and it looks like the clearances never need adjusting. But then something happens like they take the lead out of gasoline which changes the valve seat wear rate so the clearances start changing again.
Whatever, itâd be a good idea to put those clearances back in spec.
The bottom line is wear.
now if there are only two valves with that much wear. I would be concerned. but I lean to be somewhat of a dooms day kinda guy. I know that about my self.
Anyway. where the wear is? good question.
- could be valve seats, (very possible)
- could be a burned valve (definite maybe)
- could be tops of the valves, (not likely - unless the shim took a walk and the engine has had the piss revâd out of it)
- could be the valve shim took a bit of a walk (not likely - unless the engine has had the piss revâd out of it)
- could be the tappets are dished (likely). New oil doesnât have the zinc in it like the old days. the zinc works or did, as bit of a cushion for parts that impacted one another intentionally that is.
Whatâs the compression look like? especially on the cylinders with the minimal valve clearance?
thank you for your reply that helps me. Can these .006 exhaust valve clearances be the problem why the engine doesnt run /idle smooth like it should? also I found the camshafts are not exactly aligned perfectly. I bought an alignment plate tool in the past, when I got the notches of both cams as close as I could to be right. Mark
This is the XJ list so my answer must be I donât know. On the V12 the answer would be an emphatic yes. The V12 cams, at least the later ones on the EFI engines, have what are called âquieting rampsâ on the cam profiles. If you closed up the clearances that much, the result would be these valves opening too early and closing too late, and by a surprising amount â many degrees. Idle would suck. Roger Bywater once recommended that we set the clearances a little on the wide side, especially on the exhaust valves, to get a smoother idle and a measurable increase in low-end torque.
But, like I said, I dunno if the engine weâre talking about here is in the same predicament.
Whatever, I would certainly be curious to know why just those couple are that far out. Usually, all the clearances tend to move together â unless something goes awry. Or somebody made an error in measuring them. That is another thing about those quieting ramps: You canât just be a little off the lobe when you measure the clearance, youâve gotta be all the way around on the back side to be sure.
Short version Yes.
best case the valve isnât opening enough to evacuate all of the exhaust gasses out of the cylinder. Those cylinders arenât leaving the same amount of volume for the incoming air/fuel mixture. meaning these cylinders arenât providing the same amount of energy as the other cylinders.
Worst case, dropped valve seat, or burned valve.
Best place to start
pull all the plugs (mark the plug wires so you know what goes where later), open the MAS flap all the way, and do a basic compression test (leak down test later). the numbers should ring at about 145psi.(Federal Cars Euro models Idk) This number can vary about 10% straight across or between the cylinders) which is pretty much normal. Oh by the way⊠How many miles? whatâs the oil pressure like at an idle and at about 1500 revs? does it vary much?
Short version - Yes.
Detailed version
The adjustment plates should be dead nuts on - for both cams. unlike hand grenades and horse shoes (the game) close doesnât count.
What does this mean?
- The cam chain has stretched - which is pretty common as an engine gets older
- cam chain gears are worn - pretty common if oil changes arenât a high priority.
- The cam chain tensioner guides are worn - pretty common wear item. especially if adding / changing oil is an after thought.
visual inspection - Poke it with a stick.
With the cam covers off (duh), using a screw driver, on the outside edge of the cam chain. The farther down away from the cam gear you can reach is the best. There should be very little to no back and forth movement. The procedure is like checking to see if the chain is tight enough on your bicycle. While youâre looking down the hole where the chain disappears into the blackness of the engine. you should be able to see the top of the upper cam chain tensioner guide. Look for grooves from the chain. small grooves are pretty common on older engines, deep grooves not so much and would indicate a guide change. Also the guide should be black (plastic bonded to metal looking) and NOT all shiny metal. Shiny would indicate the guide material has worn away and the chain is running against the metal backing. Youâd here this when the engine is running It would sound like a sewing machine. This isnât that common and should be addressed sooner rather than later
Good news, cam chain adjustment is an easy fix and can be done in an afternoon - scraping the gasket surfaces takes most time. Out of all of the XJ manuals. the Series 1 illustrates the procedure the best. though, now that I think about it all three event the Series III manual does a pretty good job. If you donât have these manuals, PM and I will email the pages out of one of mine. I would also suggest picking one up. OTPubs.com (Not my favorite people - as Iâm quite sure Iâm not theirs either). have a great XJ manual. XKS.com has the same thing. I think SNGBarratt.com also has it. out of the 3 SNG would be my first choice. OTPubs is good as long as you donât need their tech support. which sucks⊠and this is a topic that I wonât go into here.
Itâs late here, and Iâm getting a bit tired. PM me if you want any more information about cam timing. Iâve purchased a no runner that had a loose cam chain with 1/4 of slack on the intake cam side. It would idle great. accelerate great until I came to a stop - usually too far to push it home. Then it would stop. wouldnât start. Then out of the blue it would fire up and run great. then the circle continues.
fixed the cam chain - fires up first click every time. and runs better than the 85 XJ with half the miles. Yea me!
Hope this isnât too much information. the bottom line is youâll have to get to the bottom of why the cams are off.
Cheers!
Mark
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Yes, Mark - but the main danger is that the valves do not close completely with engine hot. This would lead to blowby and the valves/seats may burn. So the valves should definitely be adjusted for that reason alone - and a compression test is strongly advised, on both accountsâŠ
Frank
xj6 85 Sov Europe (UK/NZ)
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i bought a micrometer to find the thicknesses of 5 exhaust valve shims. i get different readings from different areas of the shims, naturally from wear over along a time.please give me advice on the proper way to end up with an accurate reading of these shims,so I can order the correct thicknesses. And where to purchase at a reasonable price.What I have seen so far online seem to me to be high. I do appreciate all the help you all have given me for so long. Mark
If you get different thickness readings on different places on a shim, Mark; there is no way to be sure - itâs in trial and error territoryâŠ
Sort of take the average of the readings - and hope that the 0,012 - 0,014 leeway covers the difference - or order enough different shims to cover eventualities. Since the shims are out, I assume you noted down the actual valve clearances and placing for each shim - the shims you have may fit in a different position?
It is not uncommon after carefully selecting and fitting new shims; the clearances do not fit the computation, or is within specs - and a repeat is called for. The reasons, apart from messed up measuring or computations; selecting wrong options in averaging measurements - the averages not really being the âoperatingâ thickness. And trusting the thickness markings instead of actually measuring them.
Frank
xj 85 Sov Europe (UK/NZ)
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Mark,
for what itâs worth: due to exactly this reason it is recommended in these woods to either buy the entire set of shims or turn to a pro who has sufficient shims of all kinds available.
Trial and error, as Frank describes, on the basis of on online order and delivery following days after is even more tedious than if the necessary shims are on the bench and all it takes is a feeler guage, a pencil and a sheet of paper to calculate âŠ
All that being said: these shims canât be made of titanium. Even precision making + processing doesnât justify the prices indicated by our usual suspects. Shouldnât there be generic shims of adequate quality around, maybe for machine industry? Has anyone around found a good source?
Good luck
Jochen
75 XJ6L 4.2 auto (UK spec)
Seems my sisters car is bound to fight me all the way! The 5 exhaust side shims I have calculated to need fall between the measurements of : from 2.594 to 2.524. Any shim offered I have seen, dont come close to these measurements. Am I in left field or what?
Help, Mark
scratch my message frank please.I have blundered again ,Looking at the micrometer,I now see that I have been taking measurements in thousandths of an inch, instead of mm.
Back to the drawing board, Mark
Boy am I eating humble pie!
Mark
Now I believe I was measuring right in the beginning,oh brother!!
This car is going to get me yet!!! Mark
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It would need an awful amount of pie to cover my errors through the years, MarkâŠ
The important thing is to detect and rectifying errors - so stop eatingâŠ
Frank
xj6 85 Sov Europe (UK/NZ)
well, in the end, If I would have read the instructions that came with the micrometer,I would have been better off. The button on this battery powered digital micrometer has to be press in for at least 5 seconds to bring the display mode to thousandths of an inch.
After all that, I now see .100 to .102 back to what may very well be normal. So I will deduct what is correct for the five out of six exhaust valve area clearances needed from what I have found. Then order .I see these shims from the edge view, have half shiny,like stainless/or chrome.Then regular steel color ,the other half. Where does anyone suggest that I order safely from please Thankfully, Mark
I have the idea that this 4.2l engine is an interference type. Where if I were to install the camshaft back in the engine, then turn the camshaft to check clearances , the exhaust valves would be damaged ,which I will not do. Is this right? Mark
Without connecting the chain spocket to the camshaft, Mark