Valve Clearance Issue

I checked the valve clearance and found five out of spec. I ordered everything I needed from Chacal last Sunday and received it Friday. This morning I swapped out shims and 4 valves came into spec as they should. Number 4 on the exhaust has me baffled. The original measurement was .11mm with a 265 shim. Replaced it with a 260 shim and it measures .1mm. Is it possible there was something on the valve seat that wouldn't allow the valve to close completely therefor giving me a false measurement? I cleaned where the shim sets 3 times to make sure that wasn't it. I measured the shims to make sure they were the proper size (which they were). Thanks.

 

The valve could very well have been stuck open slightly when you got your first measurement; especially if it was actually dead-tight (but stuck slightly open.)

Be sure all the plugs are out and roll the motor over three or four revolutions, then re-measure. Either the new shim didn't sit down in the bucket correctly or as above, you had a false initial reading.

If it keeps coming up tight, throw a 255 or 250 in and re-check; you may end up needing a 245.

 

run the bike and measure it warm. Perhaps assembly lube between the shim and bucket lifter is shortening the clearance. Also think about how the valve will expand when its hot. It will get longer but it will also expand wider, which with a tapered valve seat means it will sit farther into the cylinder.

Anyways, try turning the starter motor over for a minute and see if that effects the clearance, if not try running it till hot and then recheck.

Also anytime you replace cams, lifters, valves or shims you want to run the engine at 2000-2500 rpm for 20 minutes to properly seat them.

 

Valve clearances are ALWAYS measured STONE cold, the specs are designed to take into account thermal expansion etc & setting them hot will result in mahoosive clearances & (potentially) the danger of being able to "spit" a shim :?

I understand you're saying to just MEASURE it warm, but the reading will be a meaningless one with no data to refer to.

I guess it's also possible somebody thinned down the 265 shim instead of buying a thinner one, perhaps it's worth making sure it really is a 265 still?

 

Agreed. This needs to be done with the engine cold; DO NOT run the motor until this is sorted. If it's an improperly seated shim, it could quickly become a spit shim if you fire the mill up.

 

And a spit shim means this...

http://xjbikes.com/Forums/viewtopic/t=3 ... +head.html

Not pretty :cry:

What does the Fitz reckon on possibility of a thinned-down 265? possible?

 

You wouldnt crack the head just because the clearance is too small, you would probably round off the camshaft(wear the lobe right off) or the valve would burn/valve seat would degrade rapidly. Most likely would take hundreds or thousands of miles.

But yes as fitz said if the shim is wedged in funny you could have some issues

Oh and the shims are hardened steel. You can try to sand them thinner but it will take hours of sanding to remove even a few thousandths of an inch. Use a perfectly flat surface like glass to sand with. Lay the sandpaper on the glass and run the shim over it in figure-8 patterns, rotate the shim and sandpaper often. Start with 80-220 grit wet/dry sand paper for material removal, constanlty measure with your digital caliper until you reach the desired thickness(also make sure one side isnt thinner or thicker because of sloppy sanding technique). Next you need to sand with 200, then 400, 600, 800, 1000, 1500, 2000, and finally 2500 grit sandpaper to reestablish a mirror finish.
Its much easier to just buy a new shim

 

Nobody was implying that you could crack the head because of a tight clearance.

My point was that you DO NOT try to troubleshoot or correct an issue of this sort by running the motor; very bad things could happen.

Obviously, something goofy is going on. I would suspect a hung valve that caused an inaccurate initial reading before I'd consider an "altered" shim.

Although anything is possible. Regardless; it needs to get sorted before running the motor at all. I wouldn't even spin it with the starter.

Altering shims is likewise a bad idea; they're NOT hardened all the way through. Shave off too much and you get into the soft part; and again, bad things could happen.

 

After turning the motor over numerous times (which takes awhile with a wrench) number 4 exhaust came into spec. Turned it over a bunch more and it's still right there. Rechecked all the valves and all is right with the world.
Big Fritz, I hate to admit this but this is the first I've checked the valves in six years. I just didn't know. My bad.
Next up, complete re-do of the front brakes. Stainless Steel, here we come!

 

The shim just wasn't seated. They're a tight fit and sometimes you have to "squish" them into place to force the oil out from under them.

The main thing is, you DID check them, and it sounds like you caught it in time. The next time you check, 5K miles from now; you'll probably only need to adjust one or two, if that.

Good job. And brakes are fun! :wink:

 

Didn't suggest you would, I said (and it's evidenced in the link I posted) that if you had either way big clearance or badly seated shim then the shim can "spit" off the top of the bucket, jam between cam lobe and head, et voila *crack*

I also realise it'd take ages & damage the case hardening of the shim to do that, but these are old bikes that have been through many less caring hands before us all & was just throwing out there another *possible* reason why a 250 shim would tighten up a clearance compared to a shim believed to be 265.

As it happens it seems the O/P has sorted it now & looks like it was just badly seated. Good thing you didn't try to fire her up bmarzka, and you're a very naughty boy leaving your poor valves so long lol joking

 

It will be awhile before I fire the old boy up ( it's not a "her"). It has the original brake hoses (another thing I didn't know about), so I'm going with SS brake lines and re-building the master cylinder and calipers. I had the front seat redone 2 years ago and now I'm having the back seat and sissy pad done. When the weather gets so I can get it outside (it's in the basement) I want to synch and colortune. Thanks to this forum I was able clean and redo carbs last winter. I'm thinking that the "Good Reverand" will be looking pretty sharp this summer.

 

All old bikes are referred to as "her" or "she." If they were male they wouldn't require so much maintenance :lol:

 

Sorry bmarzka's bike, didn't mean the gender faux-pas :lol: Don't normally name my bikes but the XJ's turned out to be a bit special so I think I'll call her Ella (dunno why but when I look at the model E-II (29R) it puts me in mind of that name!)

Agreed, I've said it before that this forum is literally a life-saver when it comes to tyre date code and brake issues warnings & less literally with the tech threads on carbs and the like. Don't know where half the XJ's on the planet would be without this resource (probably in china being made into cheap refrigerators or coke cans by now :cry: )

Only trouble with a bike having such an active, knowledgeable & helpful community as this is that they quickly become addictive (I'm currently half-looking for another less rare & less tidy XJ that I can use without worrying about dirt/original finish/cagers)!

Best of luck getting him all done in time for the nice weather 8)

 

Over the years I've a couple of vehicles with personality. The rest were just modes of transportation. My XJ has personality and I nicknamed him "The Reverand Mr. Black". Anyone who knows old-time country music knows where that came from. The reason for the name was because we had a chance to meet God one morning. Or maybe it was Satan. Thankfully we both survived.

 

Love Johnny Cash so much

Just went to youtube & put him singing this song on now was the first version that came up...