[bluechevelless]

Few months ago I had problems with my heads on a new engine build. The guides were shot. I took them to the machine shop and paid a ton of money to have them fixed. Well I had a bad knock on the motor that magicly went away a couple days ago. While investigating I found that one cylinder only had 70psi of cylinder pressure. So the motor came out thinking that I had blown a ring land or something. Got it apart and the top of 2 of the pistons are beat to complete hell but the cylinders look great. I notced the valve seats had shiney marks around them so I pulled the valves and the guides are shot. I can wiggle the valve about a 1/4" inch. One of the guides had the bottom part of it broken off and thats what beat the hell out of the pistons, and the suspected knock. The valve seat on the cylinder that had low pressure was worn out and not sealing anymore because of te guide.

I dont know what to do. should I go fight the machine shop? I have around 1000miles on this motor and only 12 quarter miles passes. My short block seems fine but I think im gonna have to replace the pistons that got beat up. What would cause the guides to wear out so bad?

 

[VORTECPRO]

Few months ago I had problems with my heads on a new engine build. The guides were shot. I took them to the machine shop and paid a ton of money to have them fixed. Well I had a bad knock on the motor that magicly went away a couple days ago. While investigating I found that one cylinder only had 70psi of cylinder pressure. So the motor came out thinking that I had blown a ring land or something. Got it apart and the top of 2 of the pistons are beat to complete hell but the cylinders look great. I notced the valve seats had shiney marks around them so I pulled the valves and the guides are shot. I can wiggle the valve about a 1/4" inch. One of the guides had the bottom part of it broken off and thats what beat the hell out of the pistons, and the suspected knock. The valve seat on the cylinder that had low pressure was worn out and not sealing anymore because of te guide.

I dont know what to do. should I go fight the machine shop? I have around 1000miles on this motor and only 12 quarter miles passes. My short block seems fine but I think im gonna have to replace the pistons that got beat up. What would cause the guides to wear out so bad?

The guides and the valve job were not done correctly.

 

[blue66]

The guides and the valve job were not done correctly.

X2........even poor rocker arm geometry I don't think could cause your troubles that quick. But after getting things fixed I would definitely go over your rocker arm geometry very carefully. You surely shouldn't be going through guides like that.
Have you checked your piston to valve clearance carefully?
And if the guide is coming out of the head, there were some installation issues.

 

[bluechevelless]

Thats what Im guess at. All my troubles have been on the same head. I have not checked rocker geometry but I will for sure. The springs are very tight in the head so they will not move but the retainers are not real tight on the spring. I asked about that when the heads were getting worked on previously, the machinist said that it will be fine.
Another problem is that its a well known machinist that is a good family friend.

 

[steelcomp]

Weak springs can wreak havoc on valve seats and guides. Check your spring pressures while you're at it.

 

[bluechevelless]

all springs were checked and set up according to the cam specs by the machine shop. The solid roller spring pressure was too high for my valve spring remover and installer. So that would be another one on the machine shop...

 

[steelcomp]

all springs were checked and set up according to the cam specs by the machine shop. The solid roller spring pressure was too high for my valve spring remover and installer. So that would be another one on the machine shop...

So how did they "re-do" the guides? Are they cast iron? Bronze? K-Liners?
Do the actually hone to size and check with a bore gauge, or just ream and go? Do you know what clearances they used? Did they re-do the valve job after the guide work?
When you get this stuff back, how do you KNOW it's done right?
Maybe you need a new machine shop.
I'm just sayin...

 

[ChevelleRob]

Any pics ? What kind of head ?

 

[BillK]

Danny,
What type of engine and heads ? Big Block ? Small Block ? Pictures would be nice too. For a guide to wear out that fast something seriously has to be wrong with geometry or the way the valve job was done. If the valve seat is not machined peerfectly concentric to the guide, it will make the valve move to one side every time it opens and closes. That will wear out a guide real quick. I dont think the material of the guides is really as important as a lot of people make it out to be. In the past I have put cast iron guides in full roller drag engines and they have lasted several seasons with no issues. The finish, sizing of the guide and the valve job are the important part.

You also mentioned that the spring was tight in the head ? Without having it in front of me its hard to guess, but the spring should have a little room to move. Usually as the valve opens the spring gets a little bigger diameter and could be binding ?

One other thing to keep in mind ..... if the affected valves are exhausts, and the heads do not have hard seats in them, you may have a problem with the valves receeding into the head material. It can happen very quickly, especially if you have a fuel or other issue that is causing those particular cylinders to run very hot in the combustion chamber. Any chance it was numbers 5 & 7 ? the plug wires could be crossfiring and causing combustion issues. Vacuum leak ? Etc.

I would not be too hard on the machine shop right off the bat. Ask them to look at the head and see what they think ? It could very well have been something they did wrong, but give them a chance to look at it under good terms first.

Just my opinion,

 

[VORTECPRO]

Thats what Im guess at. All my troubles have been on the same head. I have not checked rocker geometry but I will for sure. The springs are very tight in the head so they will not move but the retainers are not real tight on the spring. I asked about that when the heads were getting worked on previously, the machinist said that it will be fine.
Another problem is that its a well known machinist that is a good family friend.

First the valve guide HAS to be round and strait and be clearenced correct to the valve stem with the proper finish, this is done by honing the guide srait and round to the right size and finish. Second, the valve seat has to be concentric to the valve guide with the proper contact patch so heat can be transfered away from the valve, when this is done right seat recesion is not a problem. Third, the valve must be ground correct with very little run out. This being said the problem finding a shop that can do this correct will be a challenge to find, you will have to go to the best shop your town has to offer.

 

[bluechevelless]

no pics right now

The heads are casting 840 Rectangle ports for 427
The valves are stock size 1.72 2.19 Stainless one piece under cut valves
The cylinders affected are 2 and 4, 4 being the one with the broken guide. Both were intake valves and were good on the last motor. I had about 5000 miles on them before I took them to get worked one because of an exhaust valve guide that was cracked and worn on the same head. These were on a 9 second motor before I got them that ran every weekend.

 

[sleeper]

From reading I believe you have a solid roller cam. You mentioned the spring pressure was too high for you to disassemble. How high was the spring pressure?

How much lift on the cam? How much rocker ratio? What is the cam intensity? What kind of valve seals?

I have had the best luck with a high quality (severe duty) valve from Manley, Ferrea, or REV with a quality chromed stem. If the valve does not have a quality chrome stem I have problems with guides and roller cams with high pressure. I define high pressure as anything above 250 on the seat and 600 open, especially for street driving.

I always put a quality bronze guide for a roller cam. The higher the quality the better. Guides are like everything else, some cheaper, some higher. Most of the time the higher priced guides are a better alloy. I have not had good luck with cast guides, solid roller springs, and valve seals. If the valves seals are left off or leak a little the cast iron might live, if sealed up good I cannot get cast to last any period of time.

Before we condemn the shop we need to know the stress the guides were under. There are some things that are not going to last, especially on the street. It is easy to say the shop did it wrong but everyone in the automotive repair business have had failures doing everything right. Sometimes the combination is better suited to 1/4 mile at a time instead of thousands of street miles.

 

[bluechevelless]

heres the cam

http://www.compcams.com/Cam_Specs/CamDetails.aspx?csid=498&sb=2

Im unsure of the springs, they were installed by the machine shop. I cannot remember the specs, I will have to find were I wrote it down.

 

[sleeper]

That cam should be fine for street use. If it is on a -8 core (cast) the spring pressure will not be excessive.

I would look elsewhere for the cause of the guide failure, it is not the cam.

 

[bluechevelless]

Yea I was just stating that I cannot take the springs off because of the pressure and my flimsy crappy remover.

 

[bluechevelless]

The machine shop is trying to say that my rocker geometry was wrong and I had valve float. Thats bullcrap. I know I dont have valve float and my rocker geometry was fine. I even looked at the tops of the valves before i took the heads to them that the scuff marks were right in the middle of the valve stem.
He said that pretty much ALL the valve guides were loose while some were just shot. Im not too happy.

 

[BillK]

Danny,
Something just does not add up here. Either there is something strange going on in the heads, or something is not being done properly in the machining/assembly. You said that the bottom of one of the guides was broken ? That leads me to believe that they are cast iron guides ? If so, did they install a complete thick replacement guide, or just a 1/2" diameter cast iron "sleeve" ? When I do big block heads I always replace the entire guide. A lot of shops dont like doing this because of concentricity problems with the oem guides, but I really have not had problems with it. The only time I use the 1/2" guides is with bronze guides.

Either way, something else has to be going on for the bottom of the guide to break. Valve too tight in guide ? Seat concentricity waaaay off ? Valve hitting piston, even slightly ?

Although it may cause some hard feelings, I think at this point you might want to get a second opinion on the thing from another machine shop. You might want to have someone look at the entire engine, you might be missing something else that is causing the problem ? You did say that you had the broken guide problem before you took the heads to this machine shop the first time ?

Just curious, what rocker arms are you using ?

 

[machine shop tom]

What kind of valve seals are you running and are you running any kind of restricton to the lifters or rockers?

tom

 

[bluechevelless]

No restrictors. I have a High Volume pump, solid rollers and no valve stem seals.

I think they are the hardened cast iron guides.

My rockers are the black anodized 1.7s, I think they are Trick Flows.

 

[bluechevelless]

got the heads back, the machine shop covered the labor, but I paid $200 for parts. 4 new valves and all new guides.
Got them on and changed all the rocker arm studs and guide plates off an engine that I know didnt have any valve train issues, the new guide plates held the push rods a little tighter so they arent moving around as much. I then proceeded to check the geometry. they all hit pretty much perfectly in the center of the valve stems.
Anything else I should check?
I also had him install new valve stem seals.
He checked all my springs and said that they were 180lbs seat pressure, He jumped the seat pressure up some with some shims also.