Is a micrometer always required for valve adjustment? Are installed shim sizes reliable?

Hi XJ folks,

Question: is a micrometer required for valve adjustment?

It seems that a micrometer is not mentioned in the valve adjustment write-ups I have seen, but it seems that it should be required.

Here is my reasoning:

1) Suppose I find that a valve clearance is out of spec. I pop out the installed shim and note the size, and grab the Yamaha shim chart. I look up the out of spec measurement, the installed shim size, and the chart tells me what the new shim size should be.

2) However, it seems that people say that old shims are worn, and their indicated markings are not reliable (a 280 shim isn't actually a 280 shim after some time).

3) Therefore, if the old shim sizing can't be trusted, then the new shim size is also off.

4) The only way to reliable know new shim sizes, therefore, is to MEASURE (and not read) the old shim size.

5) You need a micrometer.

However, no one talks about micrometers.

What am I missing here?

Finally, I have been a lurker here for two years. Many thanks for the incredible contributions. The information is so valuable restoring an old XJ750 barn find.

 

A micrometer is not required unless the marking on the shim has worn off.

The shims are precision made parts, and will not wear under normal use. There is some variation in thickness due to manufacturing processes, but not enough to cause a shim to be so thin as to put the calculated adjustment out of the specified range.

Feel free to meaaure every shim if you wish, but in practice it just isn't necessary.

 

Are the shims case hardened like the camshaft lobes?

 

After I insert the new shim, I turn the engine over a few times manually, and recheck clearances with a feeler guage just to verify everything in spec.

 

Yes

 

Thank you, everyone. Really appreciate the quick replies. Looks like the consensus is that installed shim markings are considered reliable. I'll be sure to re-check all of the clearances (and then double check) when the job is done, before starting her up again.

 

I thought that hence the reason they don't really wear. The clearances get smaller with the interaction of the valves and their seats due to mileage. .

 

Besides, even if the current shim is "worn", if it the clearance is out of spec, it's out of spec putting the correct number will put it back in spec some where in the spec range. You don't need to worry about specific measurement, you want to be in the range.

Close only counts with horseshoes, handgrenades, and being in the acceptable clearance range.

 

They are through hardened, like the camshaft is. Case haredening isn't used much in large-scale production anymore.

Though some of the older shims may have been case hardened (and there is some evidence of that).

 

I set mine at the maximum as far as I could Hogfiddles so I should not have to change them for a while although I will check them at the service. My brother had a Ford car k-moe at least thirty years ago and the valves and camshaft were making a horrendous noise so we took the cam cover off. Metal filings everywhere. Don't know how it didn't seize. There was an over camshaft pipe that sprayed oil onto the cams but it had got blocked. After that he adhered to the oil change schedule.

 

I'm not understanding what you're saying there......you simply make sure that the clearance is in spec. If it's not, you look at the chart and put the correct shim in-----it doesn't matter if it's just in. In spec is in spec. If it's just BARELY in spec, it's IN SPEC and you don't have to do anything til the next check. It may be just barely in next time, too, it may stay just barely in forever. It may be out the next time, in which case you put it back in spec

 

I believe what you’re saying is the interval is the interval. Trying to get shims in the higher end of the clearance won’t change that, you still gotta pull the cover and check them when it’s time regardless. The real time saver is writing down what’s in there now so next time you do the clearances you don’t need to pull them to see what’s in there.

 

what if?
the range is 15-20, three valves measure 20, one is 16. so do i stop here or change the 16 to 21?
now is the time for micrometers if you have a few shims to choose from. i'd go for the thinnest 21 i could get.
now if it were 3@19 and a 16, i'm done

 

But the range is .16-.20mm
.16 is still in spec

 

Slightly loose is better than slightly tight (for valves anyway).

 

here's how i think of it, 21 makes all the cylinders closer to the same than 16 does. then use the mic's to get the tightest 21 you can.
i wouldn't take 22 but i think a 21 comming in is better than a 16 going out.
in a perfect world all the valves should be the same and 21 is samer than 16 if all the others are 20
your right though in is in and out is out

 

I could not get a 0.16mm feeler gauge in between the cam base and the shim on two of the exhaust valves when I got the bike, PO said they had been done so he was either dishonest of did not know what he was doing. When I fitted the correct size shims the clearance was nearer to 0.20mm. As the valve clearances decrease over time if the clearance is 0.16mm it will go out of spec as it is near the minimum required clearance than if it was 0.19mm for example that is what I meant. But I agree if it is within 0.16mm to 0.20mm the clearance is in spec.

 

Yes my bike would not run properly as the clearances were too tight.

 

It's possible he might have done the valves, but:

1. Did the enough miles ago that they're out of spec

2. Didn't know what he was doing

3. Had a shop do them-- which is sometimes a dangerous thing.... some shops changectome to get as close zero clearances as possible so that "valves are nice a quiet again", or any number of other issues that have arisen when shops do them incorrectly

4. actually didn't

When valve clearances are too tight, the valves open too soon, stay open too long, and close too late.

 

. I assume compression would be lost to some extent if they close too late.

Yes Hogfiddles I agree with your comments but they they were too tight but the bike is running really well now. I don't like valve clearances too tight as I have heard the exhaust gasses can damage the valve seats and it is more difficult to disperse heat from the valves to the seat. I was used to the screw and locknut type valve adjustment on my old Honda CB 750 K2. This is the first time I have adjusted the clearances on my XJ 900f and it is easy because I have got the tool which bolts to the cylinder head. Most important thing is to keep the cam clear of the tool as you know to prevent damage to the cylinder head. I will be checking them regularly.