wjnjr

The subject car is an '09 with approx. 17,000 mi, stock, no track, Mobil 1 every 3k mi.

The wiggle test was done on the car in the usual manner using the familiar dial indicator on a gooseneck set up from Harbor Freight. Only the exhaust valves were checked as it was expected that they would show the worst wear. The test results showed excessive valve stem to guide clearance and the heads were removed.

After the heads were removed and cleaned up, the valves and valve guides were measured using a Mitutoyo digital mic on the valve stems and a bore gauge with a digital indicator on the guides.





Resolution of each tool is 0.00005, measurements were rounded to 0.000x.





The worst guide was #6 exhaust





Here's what we've been looking for, the results of the wiggle test done with the heads on the car compared with the measurements taken in the shop. Actual clearance = guide diameter - stem diameter.

Uncle Meat

So are we saying that the wiggle test is not a good indicator of actual valve stem/guide clearance? Reason I ask is the warranty on my '09 expires in about a month and I am planning on taking it in to the local dealership to have them check it out or possibly performing the wiggle test myself. I have a little over 30K on the car so I figured I better get it checked.

U.M.

Undy

Was the math done with the wiggle test ( test/2-0.005") or is this just actual measurement? If the math wasn't done it's actually pretty close in most measurements.

It appears here and other reported measurements that the wiggle test repeatedly (with a very few exceptions) shows more wear than the actual heads off measurements show. Maybe we need to redo the wiggle test math.

In spite of the inaccuracies the wiggle test is the only guide wear barometer we have to decide whether to pull the heads or not.

Good job OP!!!

FWIW, It's a damn shame that some of our board vendors didn't step up to the plate on this and do the same, especially when they're making big $$$ off our miss-fortune. SHAME ON THEM!!

ClarksZ06

Looks to me that the wiggle test was extremely accurate if u take the wiggle measurement and divide by 2. The actual measurements are just about exactly half of the wiggle measurements at the bottom of the guide.

Excellent comparison terrible results though.

Thanks for sharing

ctsv510

Nice job, I'd say the results were quite accurate. Much better than mine!

'06 Quicksilver Z06

Yeah, these look to be very close to the actual measurements.

Mark2009

Major drool over that digital bore gauge

Assuming the wiggle number is the raw measurement (not yet divided by 2) then it looks pretty good except for #6 (something must have happened there... but I suppose 7 out of 8 ain't bad).

Undy

Yep, that would be enough evidence indicating that the heads need to be pulled.

I'm still a firm believer that the level of the wiggle test accuracy lies in the skill of the person accomplishing it and the tools utilized. I don't think the test itself is flawed.

double06

Depending on some cases where you measure from is the what you get from the wiggle test is to be divided by 2. Looks like on many of them if you did that you would be spot on. I would agree with the guy above the wiggle test is just a gauge on weather to go forward or not. Also the wiggle works if the taper is in a certain way. You could have the bottom way off and the middle and top top tight and you would not know as the other two measurements help hold it from wiggling. However, on these it appears once the bottom goes the other two measurements follow. I think so many of these have been off/defective by now that it should be just chnaged as a precaution because it may pass the test at 15k miles but may not at 30K miles so just get it fixed now. Not what you want to here but the number are adding up.

vertC6

Yeah but how can you trust a guy who drinking Coors Light

Great job!

Vette @ 71

Kudos to the OP for establishing the "wiggle " as a legitimate screen/first order approximation for guide wear.

wjnjr

OK, let me go back over the procedure in case it wasn't really clear:


The wiggle test numbers were read off the dial indicator in the usual way.





The individual guides were measured in three places with the bore gauge.




Next, the individual valve stems were measured in three places with the mic.




In each case the recorded numbers are comparison measurements vs a std. valve stem diameter of 0.3135, rather than absolute measurements of the guide or stem. This produces a valve guide oversize measurement and a valve stem undersize measurement

Then, the 'actual clearances' were calculated by adding guide oversize to the stem undersize.

Mathematically it's the same as subtracting the measured valve stem diameters from the measured valve guide diameters but in practice it's much easier, quicker, and more accurate, as the machinists in the crowd will attest.

At any rate it did take a little while to do all those measurements

But hopefully these numbers added to other data from worn out or failed LS7 heads can help us figure out what causes this problem and how to fix it once and for all

Disclaimer:

I've made no attempt to come up with an equation to make the wiggle test = shop measurements to the fourth decimal place.

It will take a lot more data from a lot more tests to attempt do that, and at best any relationship can only be approximate, maybe + or - 0.001, or 0.002?, due to the vastly different accuracy and repeatability of the two tests.


Here's the raw measurements from the valve guides:




And the raw numbers from the valve stems:





And finally, the total clearance between stem and guide:

wjnjr

Busted!

sublime1996525

Thanks for taking the time to do that

Michael_D

Were the bore measurement points max bore after rotating the tool 360 deg? Did you find the bore to be oblong, for to aft or right to left?

Blackonblacksls

I recently had a set of heads checked out and after 100k miles in a stock motor all the guides except 1 were in spec.

I have another set that were low mile take offs. But another 20k or so cammed with dual springs.
This set had several intakes and exhuast way over recommended clearance.

Both used stock valves, both measured at my local machine shop.

So I don't believe it's guide material or valve type. Or it would me more consistent.

Maybe machining issue? Maybe a valve job to insure concentricity could be all it takes to make these heads a little more reliable?

wjnjr

Good question.

I set the bore gauge up to measure the guide diameters in the intake port to exhaust port direction, across the head rather than lengthwise, or athwartships rather than fore and aft if you will. Hope that makes sense.

I did not check the guides for out of round. That would be interesting to know, I might go back and check a couple of the worst ones. Wouldn't be surprised if they are.

Undy

So, all in all, it would appear that this wiggle test proved fairly accurate in comparison to the actual valve guide bore measurement, using my previously mentioned wiggle/2-0.0005".

'06 Quicksilver Z06

Good to see this comparison in light of the prior one.

propain

A very thorough job, nice work.

Looks like the wiggle test is back in the fight. That's good news. In light of this it seems like its possible the previous test might have been the technician not the technique.