Don Terrill’s Speed-Talk

Hello,
I have a question about a set of GM LS heads (2008 L92 / 6.2 truck motor) on the valve stem to guide clearance. The guides are magnetic...not sure if they are powdered metal or not. The valves are new.

I measured the ID of the guides with a snap gauge. Then I rechecked the measurements by setting the snap gauge just a touch above the measured ID and tried to insert the snap gauge. This verified the measurements. I measured some of the valve stems with a micrometer. All those measured were very close to 0.3130".

The tightest valve stem to guide clearance is 0.0020".
The loosest valve stem to guide clearance is 0.0035".
The average valve stem to guide clearance is 0.0026".
There is one guide that is a good bit looser than all the rest (that's the 0.0035" one).

The factory service manual says clearances for both intake and exhaust are:
Production: 0.0010" to 0.0026"
Service: 0.0037"

Clearances look to be on the loose side to me. Would you bother with replacing and resizing these guides?

I could not find replacement powdered metal guides for these heads. Sealed Power has a VG-1434 valve guide for these heads but the material is not specified. According to the ID of this replacement guide, clearance would be at 0.0024", which isn't all that great.

Sealed Power VG-1434:
https://fme-cat.com/overlays/part-detai ... 01500&vin=

Thank you for any help,
Paul Lohr

Jmo replace the loose guide then use the the heads as they are.
Rember when u replace the guide it may tighten up after installation and need to be resized.
John

Ferrera also lists a couple of different guides, none being the one you listed. I suspect these are manganese bronze.

VG1066 for intake guide
VG1067 for exhaust

.501" ID & 2.000 length. Uses valve guide seal VS1021

midnightbluS10, thank you. I will check into the Ferrea valve guides in terms of how durable they are compared to powdered metal.

John, thank you. Replacing the guide that is loosest might be the most reasonable idea. Good point about the new guide tightening after installation. I wonder how much a powdered metal guide's ID would tighten in an aluminum head?

If anyone knows where I can find powdered metal guides, or has other ideas, please feel free to share.

I know Texas Speed and Performance has PM guides as an option for guys running stock type rockers on their heads, you may try to buy one from them, i think PM guides also run a slightly tighter clearance iirc?

Just to ask since this post came up. Guides wear like an hour glass, more at the ends than in the middle. Instead of using a snap gauge, I hold the valves off the seat approx.,lift of cam,I use a piece off vacuum hoseto hold them up, and then rock them with a dial indicator and divide the movement by 2 to obtain the guide clearance. I think several manufactures used to promote this method. Using a snap gauge you have to take multiple measurements and average the results. Does anybody use this method, or am I all wet?

Honestly, have someone with a sunnen p series valve guide measuring gauge double check before you spend money on the guides

Aren't those clearances sort of large for a "modern" engine? What is the seat run out?

I measured the ID of the guides with a snap gauge. Then I rechecked the measurements by setting the snap gauge just a touch above the measured ID and tried to insert the snap gauge. This verified the measurements. I measured some of the valve stems with a micrometer. All those measured were very close to 0.3130".

The tightest valve stem to guide clearance is 0.0020".
The loosest valve stem to guide clearance is 0.0035".
The average valve stem to guide clearance is 0.0026".
There is one guide that is a good bit looser than all the rest (that's the 0.0035" one).

The factory service manual says clearances for both intake and exhaust are:
Production: 0.0010" to 0.0026"
Service: 0.0037"

Remember the guide clearance increases as the engine temp increases.
And as for clearance.0012" on the intake and .0015" on the exhaust. You can go .001" on the intakes as they run cool with the airflow over the valve stem but the exh. needs a bit more.

All those heads use an interference style valve job using 2 different angles between the valve and valve seat. If you look close at the seats you will see seats worn wider on 1 side or the other making the guide replacement mandatory if you want to do a good job on the heads.

You can get stepped bronze press in guides to repair the issue from several suppliers and in manganese or phosphor bronze materials. But a tighter guide clearance will make the guides last twice as long as loose fit guides and also the extra clearance will cause leaky valve to valve seats reducing HP potential greatly as well as drink more oil when the seals wear out faster on a loose guide

Guys, thank you so much for your help with this.

Truckedup, I don't have the tool for measuring seat run out.

ProPower, so you're talking about removing the old powdered metal guides and replacing them? Just so I'm understanding, you're saying that the bronze-based guides that you mentioned will last as well or better than factory powdered metal guides, given the clearances are proper? I have no idea if this is true, but talk on one one of the LS forums has been that roller rockers should be used with most of the bronze guides. Again, I don't know if this is true.

houser45, there is a decent shop nearby that might be able to double check my measurements. That's a good idea.