MUKAK

why would this matter?

LFZ

LOL....ok.

Tech

I beg you.. please use punctuation.. or even press <enter> after each sentence. I'm interested in what you have to say but I have to re-read portions of your post just to surmise what you're trying to convey.

outhouse

That is wrong.


AHP PM guides are harder then bronze or stock PM.


Not all PM guides are made equally.

Unreal

And not all stock PM guides wear out. It isn't a guide material issue.

C5 Hardtop

This was the findings of the GM Regional Engineer that looked at my blown motor (an '08) about 4 years ago. However, they said it was the machining process at fault with the heads I had, not a design defect. I posted those findings here back then and the information was validated here through a member that had connections.

How to pick up a set of heads and verify if they are machined right is the million dollar question.

RamAir972003

Sorry phone texting ill type better just for u brother. I drive it 30 miles about oil never went above 200 temps....

RamAir972003

I understand that but has anyone driven the car enough to actually validate that just because ah says this I understand they are good company but I don't know what type pm guide Dallas Performance used back then...hope you understand....

Tech

Just fyi.. you can press <space> <space> on most phones and it'll insert a period.

Michael_D

What's the lift on that cam Angelo? Did Darin check seat run out when he looked the heads over for you?

RamAir972003

Have you checked and tested this, so whats the issue then I'm curious then what causes the wear then.

RamAir972003

Oh Michael call me asap pleas 972-824-0793.....

RamAir972003

Oh Michael call me asap pleas 972-824-0793.....I did a gt20 cam on a 112lsa .....sorry everyone in typing from a phone not at home so bare with me please I know everyone has questions....

Unreal

There are people with 60k+ miles, and guides check in fine. It is rare, but does happen. If they are machined and installed correctly the material can last just fine. Problem is GM supplier can't seem to install/machine guides properly so the vast majority have guide issues. Almost every factory car uses the same style PM guide, so if it was a material issue, it would effect all LS7s, and tons of other cars too that use the same material.

Michael_D

Sorry bud. Back to back meetings. I'm cheating right now....and fixin to get caught...


Make sure you re-read the thread I created a couple years ago about what causes guides to wear. I don't think very many paid much attention to it.... It's factual though, with no BS opinions.


https://www.corvetteforum.com/forums...uide-wear.html

RamAir972003

Ok guys Darin is going to measure will get back to everyone will make video....

outhouse

From what I can tell it is a combination of issues.


Stock PM guides are softer then the rest, combined with an aggressive stock valve train.


Sort of a hair under engineered and it does seem to effect more cars then not.


And safe to say since many were poor quality control and released from the factory out of spec guides compounded this issue.



My opinion is with the aggressive stock valve train, the guides should have been a hair harder, and or valve train geometry/rockers to reduce side loading.

MTPZ06

What lobes does it use?

Too many I don't knows to surmise what the issue is here...for all we know, those heads could have been untouched OE's other than swapping out the exhaust valves for solid stainless.

Angelo, you have the gt-20 cam in your car now? You made mention of a different cam...which one?

I'm sure Darrin is more than capable of rebuilding the heads the right way...i.e. known materials (CHE guides or AHP's PM guides, etc.; lighter exhaust valves - Ti, stock, or f2042p; check for proper runout, concentricity, etc.). You really can fix this...but it has to be done the right way from the start.

RamAir972003

Yes we specked cam for this set up ....softer lobes. Per Darin Morgan these heads were checked the reason we left pm guides in back then there were no good valve guides bronze so factory was good plus he galled them a little so oil will lubricate them...he told me to post results when he is thru going over them and having actual measurements.

I know I have been on here trying to help people but we can't speculate what causes the issue the heads are being checked right now so I will post everything so we can have for the record.

Geometry will be measured also which I don't think its that ...rocker arms swipe pattern looked good no misalighnment....I will keep everyone informed most important thing is i caught it in time....as far as lobes i don't know what 21century uses its not a big cam at all look up specs.. True it can be fixed and will be fixed but I'm like u I want to see results from other people having bronze or pm guides that measured in spec....i understand I went 23k in these and I'm lucky....i guess but any help I will appreciate everyones input.....

grcor

PM and bronze valve guides have been used in many engines with great success, so why are there guide wear issues in the LS7? We know from the work that Hib Halverson has done that new OEM heads are not machined correctly. But now we are seeing the issue on some of the reworked heads from reputable vendors who have correctly machined the heads. So is there something unique about the LS7 or the Z06 that is causing this problem?

The 2006 – 2010 Z06s use a large air/oil cooler mounted in front of the radiator. This method of oil cooling works well at the track, but in normal street driving it keeps the oil too cold. On a 50 to 60 degree day, it is common to see oil temperatures in the 120 to 140 range (DIC). The DIC is reading oil temperature from the bottom of the external reservoir, from the reservoir oil first travels to the oil pump, then thru to the oil filter then thru to the oil cooler before it enters the engine. So the temperature of the oil entering the engine is even colder than what the DIC says. Then starting in 2011 Chevrolet changed the Z06 to a coolant/oil cooler assembly that had been used on the ZR1 since 2009 to cool/warm engine oil. Why?

AHP PM guides have oil retention spirals/groves cut into them to aid valve guide oiling. Darin Morgan thinks that you need to use an oil with “the necessary balance of Zinc, phosphorus and other anti wear additives” to reduce guide wear. UPDATE: Look at Post #46 below, in the last paragraph Darin Morgan talks about removing the spring on valve stem seal to increase the amount oil getting valve guide. In addition he also uses a razor to put slice on the exhaust valve seals so the guide gets even more oil. You don't have to do this on other street engines to make the valve guides last, so why is it necessary on the LS7/Z06?

I believe the LS7 valve guide wear issue stems from engine oil that is too cold (thick) to allow a sufficient amount of oil to get past the valve stem seal for proper lubrication. We really need the oil up in the 180 to 240 degree range. Keep in mind, most of us use our cars only once a week for a short trip, not as daily drivers where the engine is running for long periods of time. This is why I removed my air/oil cooler and converted to a DeWiits EOC radiator for my 2008 Z06.

Some other contributing factors to valve guide wear are high lift cams with OEM rocker arms, and the stem finish on TI intake valves. AHP sends the Ti valves back to Del West to have the stems polished. GM made the stem finish requirement more stringent on the C7 Z-6’s LT4 Ti intake valve then on the C6 LS7 Ti intake valve.