Oshin11

I'll give you a teaser, it has to do with ERROR BARS and the fact that you are using two feeler guages that have difference distances from the nominal .002857" spec. People need to understand this, more later today.

MDL

I would like to hear what Pete Z has to say about this method...

Oshin11

Ok so I just got to LA so I have some time to explain this. I will try to explain how I WOULD do the backside method.

1. Try to engage the .003 shim/gauge through the backside between the cam lobe and the rocker arm. If it goes through, you need to make an adjustment to lower the clearance between the lobe and rocker arm. If it gets stuck and cannot pass through, good, move to step two.

2. Try to engage the .0025 shim/gauge through the backside just as in step 1. It should go in pretty damn easily without any fuss or playing with it. If it goes through very easily, you are PROBABLY pretty close to spec size of .002857 (.004 at elephant foot). If the shim does not go through between the lobe and rocker arm you need to make an adjustment. Make your adjustment accordingly with the screw and go back to step one.

NOTE: All measurements done in inches.

CAVEAT: I suggest doing the .003 shim first, that is because the .0025 shim measurement is MUCH more important. The .003 shim should only be there as a "yes .003 doesn't go in" test. HOWEVER the .0025 shim has a much bigger margin of error. By the I mean that the .003 shim only deviates from spec by about 5% whereas the .0025 shim deviates 12.5%. If you do the check in my method, and the .0025 shim just barely fits and it takes a lot of fidgeting to get in there, you are probably just a tad off spec (either too tight or loose I won't specify because it is merely convention to call it tight or loose). If the .0025 shim goes in easily, you are more likely closer to spec. Remember .002857 is nominal so .003 is closer to specifications than .0025. The .0025 should be used to guide you because it is supposed to be able to go in so you can feel the amount of resistance between the lobe and rocker arm. On the other hand the .003 is NOT supposed to go in so you can't really judge how far off you are from spec by something that DOESN'T go into the cavity. I hope this HELPS people understand and doesn't just confuse you more. PM me if you need a phone call to clear things up since there are a few people that are currently doing this project.

old man neri

Why I tried to mention earlier is the spec is 0.004 +/-0.002. That's 50% either way.

Now, how accurate do you think your shims are?

What if you do the test when the ambient is +30C outside, what if you do it when it is +5C outside.

Does the viscosity of the oil have any impact? Will it great a different film thickness?

These are all minute changes. I personally think you might be going a little too overboard with your precision. Of course, that's just my feelings on the subject.

psychoideas

That's a big + 1 old man

Oshin11

1. Viscosity of Oil--I think this would have a minimal impact. maybe +/-2-3%
2. Shim Thickness--I think these are pretty dead on, micrometer shows +/-4%
3. Ambient Temp-- I think 60 degrees faranheit will have no effects, its probably same as nominal.
4. Did you just say .004 +/- .002??? I don't think so. That means the error bar can be +/- 50 percent? No way, that means valves would never really get noisy, I doubt between inspections that they move +/- 50%. Are you really sure? I think its .004 +/- .0002.

I think being careful like I said makes a big difference.

old man neri

That's what's on the sticker says on my engine lid. I don't have my bently with me either. It's all in the car and it's hellish outside right now :P

Oshin11

Bentley doesn't give margins of error. Where on the decklid does it say +/-.002? That seems ridiculous.

old man neri

This is from memory. There is a sticker on the inside of the rear decklid, it's at the top right when it is open, it's gold colour, at the very bottom of the sticker towards the left it should be written there. There is a lot of other information on that sticker, I think it has mostly to due with emissions. Again, this is purely from memory. Currently it is just above freezing outside, it's dark, it's raining soon to turn to freezing rain/snow, and the winds are 55kph gusting 70kph. I am in no mood to try to take a picture for you. I will try tomorrow if you don't find it on your car.

Mine is a 3.2L if that makes a difference.

You have to think that although 0.002 is a lot in relative terms (50%) in absolute terms it's very very little. I wonder what the manufacturing tolerances and capabilities of machining were like in the 80s. Really, this is getting to the point of the thickness of a human hair if not less. The other method involves feel, how accurate do you think that is?

My friend, just drive your car and enjoy it.

Amber Gramps

Ya I've never done this job, never been an engineer, and the last car I ajusted valves on was a '67 hemi dart in about 1985. But, I am surrounded by very high end Porsche race shops that think nothing of noisey valves. When they start up a race motor it is loose and loud. It's not the cold temp that they tune to, it's the hot temp. I'm sure once our engines are hot, the gap is no longer .004 but much less. I think what is most important is that they are all the same. not too loose when cold, and not too tight when hot. Trying to figure out oil viscosity, ambiant temp, and the like, is all trumped by all the different types of metal used in the drive train that all have different expantion characteristics. We could even get into cam chains, degrees of lift, lobe shape, octane, altitude, spark, and a 1,000 other things that effect how well a car is tuned. lets just stick to .004 across the board, or better yet getting all 12 valves the same. fine tooning beond that should be left to the individual's butt dyno. You do have a butt dyno?

old man neri

I do have a butt dyno, however I find it hard to calibrate it due to the different thicknesses of my trousers.



Honestly Oshin, just drive your car and enjoy it.

Amber Gramps

when you look at a cam lobe in relation to the rotation of the motor you have 720 degrees of rotation with half usable by the intake and the other half usable by the exhaust. let's say we have 270 degrees of lift and a lift hight of 1/2 inch. If the gap of the rocker is too loose you can reduce the 270 and the amount of lift to be zero if you really had it loose. you could also have it too tight and not close the valve long enouph or not get it closed at all. Ideally you want intake and exhaust valves open as much as possible as long as possible to flow air/fuel, but not soo long that you have an overlap or have no compression stroke or power stroke. I'm sure 100's of different profiles have been tried with differnt degrees and heights of lift. Our street cars probebly have a very mild cam compared to what we could have. Now to figure out how many .0001 at the rocker equal how many degrees of usable open valve time at the cylinder. Anyone?

old man neri

Ya the issue is more that you want to ensure they always close fully. If not you will burn a valve.

And my guess is that you want to them too lose cause they might suffer a bit impact force if you can picture it.

Again, I adjusted my valves this method. I am not going to loose sleep over it. Just like I am not going to lose sleep over the fact that might oil is 0,01% too low in zinc....etc

Amber Gramps

let's not go there

old man neri

Ya, you're right. I am just trying to jest a little, have some fun, while trying to reach a peaceful informed consensus. Isn't that that this forum is all about?

Anyhoo, the beers is working it's way to me and I am exhausted from work. I might have to crash soon.