Valve Clearances - '82 XJ750J

Just got done checking intake & exhaust clearances....

My readings suggest that my clearances are tighting ....not widening.....I would except that they should be widening so that one replaces with a higher shim number.......

Would is happening internally in the engine to suggest the tightening of valve clearances...which means I have to go down in size for the shim number

Can anyone sheds some light on this question.....

Thanks in advance....

 

i thought the same thing, but what is going on is that every time the valve closes - it pounds it's way deeper into the head and that shortens the clearance

 

But if you look at the replacement charts, it leads you to be that the clearances should be widening.......hence you would buy a thicker shim....

The charts only have a few clearances going the other way...hence suggesting to buy a thinner shim.....

So did you have to buy thinner shims then when your clearances were tigtening up ???

Thanks skeeter....

 

Not sure how you reached that conclusion.

Skeeter is correct, the valves wear into the head making them stand up a little higher and reducing the clearance. There is very little wear at the cam end of the valve because all that stuff rides on an oil film.

 

yes - thinner shims when clearance tightening up. if you think about it - to increase the clearance you have to remove material from somewhere - hence, the thinner shim.

micarl - i'm guessing that the clearances on the chart increase from left to right, so one would assume the natural progression is from left to right and, therefore, the clearances increase.

 

Absolutely makes sense that your valve clearances get tighter as the valve pounds into the head over time......I understand that now......so makes sense that your measured clearances get tighter....

I just dont understand the intake & exhaust replacement shim charts then

'82 XJ750J

Example:

Ideal measured clearance for intake valves should be .11 - .15 mm
Ideal measured clearance for exhaust valves should be .16 - .20 mm

However when you look at the chart:

they give you 2 or 3 rows of choices where your measured clearances are under & about 20 to 25 rows of choices were your measured clearances are over the ideal clearances

Seems to me that your measured clearances would always be under from the ideal clearances since your valves would always be tigteneing up.....not widening

So why so many rows of choices above measured clearances....

What am I missing here.????

My thinnest blade on my feeler gauge is .152 mm......Where do I get a feeler gauge that can measure down to .01mm so that I can get an accurate reading on my measured clearances....since I cant get a reading now because I cant get a blade underneath them now

Any suggestions

Thanks in advance



5ofakind

 

Any thoughts by anyone ????

 

my gauge was in inches, i believe. if memory serves, i had .005, .006, .007, .008, and .009 gauges. i just used that to get as close to right as i could. there were metric equivalents stamped on it - but my hayne's manual gave clearance values in both units, so i went with what i had.

it would be nice to have a set in .01mm increments, but i don't think they exist . . .

i'm gonna go out on a limb and guess that you might be reading the chart incorrectly - i can't see why there would be so many rows for different measured clearances. (no offense intended)

if you post your measured clearance, shim value and whether it's an intake or exhaust. i'd be happy to double check what your replacement should be. (i'm sure some other folks here will confirm).

 

I just picked up a 26 blade set at Advance Auto that starts at .003".
My bent set starts at .005" You really just need a go/no go and .001 is tight enough of a tolerance.

I was 19,000mi.+/- since the last check and my tightest clearance was .oo4".

 

Sorry to beat a dead horse here but I have attached a pic of shim replacement chart for '82 XJ750J....

Ideal measured clearance for intake valves should be .11 - .15 mm
Ideal measured clearance for exhaust valves should be .16 - .20 mm

However when you look at the chart:

they give you 2 or 3 rows of choices where your measured clearances are under & about 20 to 25 rows of choices were your measured clearances are over the ideal clearances

Seems to me that your measured clearances would always be under from the ideal clearances since your valves would always be tigteneing up.....not widening

So why so many rows of choices above measured clearances....

What is happening in the engine that your measured clearances would be the ideal clearances.......the chart shows about 20 to 25 rows above the ideal clearances....

I guess I am just looking for a satisfactory answer to all the rows in the chart above the ideal measured clearances ( the rows that are below the blank line in the chart )

Again, sorry for beating a dead horse.......

5ofakind

 

Because you can take your Cams and send them out to a Specialist Firm who will Grind the Lobes of the Cams to provide you with more performance.

The Cam Lobe is reshaped to add more Lift and Duration.

 

fiveofakind, the chart gives you only one choice, in the left collumn is the what you have read with the feeler gauges, look along horizontally until you come to the size of shim that was fitted (top line ) where the two intersect is the shim you need, if your reading is borderline, use the next shim smaller.

 

Wizard,

I do understand how to use the chart....

Thank you....the question was about all the rows underneath the default or ideal clearance....

Thanks & will drop this issue......

Thanks to all that answered.....

5ofakind