Quick Valve Guide Check: Question

[skinny z]

What's your method for quickly determining if a guide is worn or not?
I've generally gone with the setup pictured below.
Anything beyond about 15 thou is beyond the service limit.

Guides.jpg

Dial is set to measure parallel to the rocker arm. Valve about an inch off the seat.
Pushing back and forth I'm getting close to a tenth.

Before I'm critiqued too heavily, this is all preliminary. No cleaning or pre prep. Much of this build will depend on whether these heads need another valve job. I'm hooking up with my new machine shop on the weekend with the crank that's needs inspecting. (GM 1182 forging that's been detailed but is getting up there in mileage).

From this quick measurement , I'm going to say I'm good to go.

FTR, these heads are less than 8000 street miles old. They got new valves and guides when worked over last time. Nice valve job. Decently pocket ported too.
Pics to follow.

[Nut124]

You are measuring close to a tenth? Do you mean 0.010". A tenth would be no good at all.

[skinny z]

That's kind of funny actually as I come across this before.
I work in a machine manufacturing facility. A tenth to us is ten thou or .010". Not 1/10th of an inch or .100".
But I appreciate the comment. My engineering racing buddy gets caught by that when I'm rambling on about measuring something.

But to the point, at less than .010" deflection, maybe .008"-.009", both directions combined, I'm thinking these heads are still good to go.
At least I hope so.

[modok]

Valve "rock" tends to be 3-4x actual clearance.
So that is ok but I think it is faster/better to use go/no go gauges,
but any tool.... if you aren't going to use it at least once a year then you can live without it.

[skinny z]

Fortunately, working where I do, although not in the capacity of a machinist, is that I've got access to every conceivable measuring tool imaginable. At least so far as measuring machined components is concerned.
But with this benchtop method (at home I might add), with a simple dial, I've understood that .015" is at the limit. Measuring less than that, I'm thinking it's full speed ahead with these heads and all that follows.

As a follow up I should probably mike the stems and gauge the guides.

[rebelrouser]

Rasing the valve off the seat the amount of cam lift and measuring the movement, and dividing in half, is an old Chrysler shop manual technique, I taught it to my students for 26 years, as well as other methods. Not as accurate as a ball gauge and a micrometer, but it is quick and tells me if I have an issue to deal with. Being an old flat rate mechanic, I learned to answer two questions customers always asked, as quickly as possible, " How much and How long?"

[hoodeng]

Pin gauges will give you the clearance in a parallel guide [new finished] they will not tell you how much wear is at the ends [hour glassing] an internal bore gauge will tell you variance from a given size, out of round and taper. A worn guide is one that measures out of spec in any dimension.

A tenth to me has always been one ten thousandth of an inch .0001".

[skinny z]

Rasing the valve off the seat the amount of cam lift and measuring the movement, and dividing in half, is an old Chrysler shop manual technique, I taught it to my students for 26 years, as well as other methods. Not as accurate as a ball gauge and a micrometer, but it is quick and tells me if I have an issue to deal with. Being an old flat rate mechanic, I learned to answer two questions customers always asked, as quickly as possible, " How much and How long?"

Semantics aside, based on that experience, what would be your go/no go value?
I've relied on .015" total (for and aft combined) as the threshold for serviceability. That would be for your typical bronze guided 11/32" stem SBC.
At under .010", I feel there's room to install the heads without the need for another valve job.
A little clean up in the combustion chamber, get another cc value and bolt them on.

[arlancam509]

That's kind of funny actually as I come across this before.
I work in a machine manufacturing facility. A tenth to us is ten thou or .010". Not 1/10th of an inch or .100".
But I appreciate the comment. My engineering racing buddy gets caught by that when I'm rambling on about measuring something.

I have worked in manufacturing facilities all of my life and they all called .0001, a tenth. .010 would be ten-thousandths. I suppose it is just like soda pop here is coke there.

[skinny z]

I have worked in manufacturing facilities all of my life and they all called .0001, a tenth. .010 would be ten-thousandths. I suppose it is just like soda pop here is coke there.

It might also be an electrician trying to talk like a machinist.
And I may have moved a decimal point one way or the other in my description!
And to think I'm well schooled in math (true story).

[hoodeng]

This reminds me of an anecdotal conversation between two butchers, one says, 'this meat is five days old, do you think it's nearing its use by date?' the other says,' what are you doing with it? buying it or selling it?"

Service wear limits are typically guidelines set by a manufacturer for parts that they know will give acceptable service in the dimensions observed. So if the part had a new fit of .0015" clearance, they know they can get away with acceptable service if that clearance went up to say .0035". this does not mean you have a range at repair of .002" and still fall into what the manufacturer wants. But when at .0035" will still give acceptable service life going forward.

If servicing new parts you would aim for new part tolerances if that is going to service your requirements [after market parts will use their own tolerances] so if the situation asks for .0015" i would give myself a tolerance of + and - .0002" this is easily achieved with recognized machining processes/practices in the automotive industry.

I have seen guys chase down to the near perfect clearance specified even when that clearance is only used because it avoids extreme running issues. Most things can be run in the minus range of clearance without running on the plus side and give no trouble at all.

Pin gauges can be easily turned up, get within a couple of thousandths and linish to size if your machines won't hold the dimension you require.

Cheers.

[rebelrouser]

Rasing the valve off the seat the amount of cam lift and measuring the movement, and dividing in half, is an old Chrysler shop manual technique, I taught it to my students for 26 years, as well as other methods. Not as accurate as a ball gauge and a micrometer, but it is quick and tells me if I have an issue to deal with. Being an old flat rate mechanic, I learned to answer two questions customers always asked, as quickly as possible, " How much and How long?"

Semantics aside, based on that experience, what would be your go/no go value?
I've relied on .015" total (for and aft combined) as the threshold for serviceability. That would be for your typical bronze guided 11/32" stem SBC.
At under .010", I feel there's room to install the heads without the need for another valve job.
A little clean up in the combustion chamber, get another cc value and bolt them on.

depends on the clearance recommended for the guide, I always used .010 for most cast iron heads, that would be .005 wear, and I believe most manufacturers called for .003 wear limit in general. Like I said if it has as you say .015 rock that would be .0075 wear, that wou8ld flunk all the guides I know of off the top of my head. Bronze guides from my experience run a little tighter than cast iron guides for a clearance spec.

[skinny z]

Well, like the title of the thread says: Quick Valve Guide Check.

I'd say from the replies that there really isn't such a thing.
While I'm confident that the guides aren't worn as I have build notes from when they were toast, they shouldn't be considering the mileage (around 8K) and the amount of effort I put into the geometry.
I'll have to break out the tools and have a thorough look.
I have to get back to the shop who did the work and see where there target was for a clearance spec.

Thanks.

[Charliesauto]

Sunnen P-310

[skinny z]

That's pretty slick.
Working in this shop we're a licensee to maybe two dozen or more patented machining processes. We have some pretty intense gauges for our QA. They're not unlike that guide tool.
Remember though this is being built in the spare room in my house. It qualifies for some snap gauges and a micrometer but probably not a Sunnen P-310.