Generation IV Internal Engine - valve spring height micrometer?

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05-23-2012, 06:29 PM
Can anybody tell me a vendor and a part number for a valve spring height micrometer that will work with PRC dual valve springs for LS heads? I ordered a Comp Cams 4929, that is definately a no go!!! Thanks for any help that you can provide!


05-23-2012, 09:24 PM
Is the retainer too big to fit the ID of the Comp Mic?

05-24-2012, 02:04 AM
Yeah, you got it. Just a very small bit to large to sit down into the mic. The retainer rests right on the beveled edge on the top where it goes from the very top flat surface that you should use and the inner step. I have 2 options if I want to try and use the 4929 mic with these retainers. Option 1 is to make an insert on the lathe that will sit down in on the step in the mic like vettenut did or option 2 is to chuck up the top half of the mic up and open it up a little bit so the retainer will sit down in on the step and make sure and take that distance into account when measuring my installed height.

I saw the mic that Comp makes for the beehive springs but the hole in the top surface looks to small for the retainer to sit flat on. I'm leaning towards option 2 as this would take the least amount of time to do. Hate having to do this to a new tool but if it has to be done then it has to be done lol. Any other thoughts or suggestions?


05-24-2012, 08:35 AM
Seems most all of the std height mics out there are similar in dimensions other than the beehive where the retainer sits

05-24-2012, 12:22 PM
I'm pretty sure the reatainer is supposed to sit on top. Check it against a caliper.

05-24-2012, 01:18 PM
Can you snap a photo of how it's sitting and how you think it's supposed to sit?

05-24-2012, 04:17 PM
KCS, you are correct, it is suppose to sit on the very top edge of the retainer. I talked with the guys at Texas Speed, pretty helpful I might add. As far as they know and I haven't been able to find one either, nobody makes a valve spring height mic for the LS family of engines.

I was searching and reading through some post about this and saw a solution that Vettenut did. He machined a peice to fit down into the cup ontop of the mic. This allowed his retainers to sit properly. Here is a link to that shows a very similar height mic. The very top flat surface is where the retainer should sit. My retainers sit right where the rounded or beveled edge is were it transitions down into the first step in the mic.

I will take a pic and try and post it up. Texas Speed also suggested slightly offsetting the mic a tad in order for the retainer to sit on the very top edge correctly. Since it is not under any pressure per say this should work just fine to get my measurements. I'm probably being WAY to anal about this but what can I say, I'm a nerd that loves the little details lol!!! Guess I could have put the link huh lol! Here it is

05-24-2012, 09:12 PM
Actually I have seen beehive specific height mics out there. Not sure where though, some catalog somewhere...

05-24-2012, 10:37 PM
Mell00, you are correct. I think Comp Cams actually makes 2 different kinds and Proform also makes one as well. One is regular height and the other is a really short one. They are very specific about them being used on beehive springs also. The hole in the top of the mic will only allow them to be used with the beehive retainers.

I think what Texas Speed was referring to was that nobody really makes one specific for the LS engines that run duals. I am purely assuming that is what they meant though.

In all though I shouldn't have a problem using the one I have. At first it seemed like a big no go but taking second look and letting the mind come up with a few ideas I shouldn't have a problem getting the Comp 4929 to work just fine. Guess the main question I was wondering is if there was a company that does make one specifically for our LS engines running dual springs.

Good thing there is plenty of room on the PRC heads for this particular mic. I don't know if there would be enough room on my stock 0821 casting for the body of the mic to sit on the spring seat and still clear the head material.

Thanks for the replies and input folks. Once I get the springs installed I will try and get some time to put up my how to or how I did it thread for others to reference to when needed. Have a great evening!


05-25-2012, 06:25 AM
Have you looked at this one, by Proform?

05-25-2012, 09:15 AM
I just used a Crane Cams height mic on a stock LS1 head yesterday with a dual spring retainer. I dind't have any issues that were obvious. I guess though now that I think about it you can't use a std mic with the stock seal. I use the good PC seals so i didn't think anything of it.

05-27-2012, 12:51 AM
Have you looked at this one, by Proform?

That is the mic I used tonight with the PRC .650 dual spring retainers on LY6/L92 heads. The step down diameter is very close to the retainer diameter - I measured the OD of the retainer to be a mere 1/16 larger than the ID of the top step on the mic. It felt like it self centered a bit, which tells me it is slightly falling into the top of the mic. So I tried measuring both on center and with the mic offset to one side. Here is what I got for one valve:

Centered with the retainer: 1.8025in

Offset to one side: 1.7975

That's about 0.005in difference in measurement on the same valve, so it would appear the edge break chamfers (retainer OD and mic ID) are riding on eachother. I think the offset measurement may be a better estimate, but they are still pretty close.

At what point do you need to start thinking about shimming?

05-27-2012, 07:19 PM
LS1MCSS, yes I did look at the very mic by Proform. They guy at Summit said they are essentially the same mic just different package. Take that for what it is though lol.

Bandit, Thank you for posting the pics and discription!!!! That is exactly what I was running into. I did the same things you did, what I noticed when offsetting the mic though is that it had a tendency to slant the retainer which could lead to false readings. I did the same thing though and did it both ways and found about the same variance as you did.