Replacing Valve Guides

[Parzival]

The machine shop that I took my heads to, called and told me that my valve guides are worn and need to be replaced. I've not seen much talk about people replacing the valve guides during their head gasket procedures. Is it common to have to replace these when have the heads rebuilt? I've heard that it is not.

[David T]

It would be unusual to have to replace them. If they are loose most shops have a process where they knurl the inside to make a tighter fit on the valve stem without having to replace the guide.

[Ron]

Short answer is yes.
It depends on mileage and maintenance (oil changes etc). Valve guides (and rings) will wear quickly if the oil is contaminated with fuel, coolant, etc. or subjected to excessive heat. If you don't know the engines full history, you have to trust the shop or have them show you the play.

FWIW, I've noticed you have done a nice job on everything I've seen so far -- If they offer to knurl them, I'd just have them replaced. Knurling leaves you with less than half of the wear surface of a new one.

[Parzival]

I told them to go ahead with it. I was just worried why they would be worn. The engine only has 27K on it. I guess not know the full history of the engine I'm at their mercy, They never offered me knurling as an option, Just Replacement.

As far as doing a good job goes, thanks for the kind words. I'm trying very hard to do everything the very best I can.

[David T]

You have to be able to trust the shop as to what they recommend. Before I send parts out I measure the parts myself and discuss the job with the shop before any work gets done. Knurling is commonly accepted as "Good Practice" but replacement is always better if practical. On some engines the valve guides are not easily replaceable. Should not have to replace valve guides on a motor with 27K on it unless it was not well taken care of. Now you have to check the bearings and rings.

[Parzival]

You have to be able to trust the shop as to what they recommend. Before I send parts out I measure the parts myself and discuss the job with the shop before any work gets done. Knurling is commonly accepted as "Good Practice" but replacement is always better if practical. On some engines the valve guides are not easily replaceable. Should not have to replace valve guides on a motor with 27K on it unless it was not well taken care of. Now you have to check the bearings and rings.

Well, compression test gave me 170 at every cylinder. everything inside the crank case looks like new. I don't know what to say, at this point they are replacing them. I don't know if it got over heated at some point and it caused them to become worn. I'm pulling the liners and pistons out, I guess I'll see how the bearings look, altho I suspect they're fine.
How can I make doubly sure that when I put this back toghether that it wont happen again? Make sure oil is getting through the passages to all the parts. The time to make sure is now, while its apart, not later.

[Bitsyncmaster]

Knurling the valve guides was considered better because it would hold oil longer. It was done with a threading tool that just pressed the metal higher in areas and then the reamer just pressed the metal back to size. So no metal is really removed. The guides were mostly soft bronze but a lot of GM engines used no guides so knurling was the only option.

[Parzival]

Knurling the valve guides was considered better because it would hold oil longer. It was done with a threading tool that just pressed the metal higher in areas and then the reamer just pressed the metal back to size. So no metal is really removed. The guides were mostly soft bronze but a lot of GM engines used no guides so knurling was the only option.

Yeah, I see the trade off there, the down side with knurling is you have less material to wear, but more oil. Interesting compromise. I told the shop to do what they wanted to do, so my decision is kind of made at this point. My concern is finding any root causes I can fix before putting the heads back on. After all the expense thus far I must make sure it's right. Doing all this to still have a problem is unacceptable.
If anyone here has any input on things to double/triple check please do me a solid and take the time to fill me in. I have my timing cover and oil pan off so now is the time!

[Ron]

Knurling the valve guides was considered better because it would hold oil longer.$.02

I agree that better lubrication is a pro for knurling, but overall it is not a better option because they will not last anywhere near as long as a new set (or bronze inserts, which is even better if OEM are cast iron...).

======

All you can do is put it together clean and change the oil/filter religiously.

[Parzival]

$.02

I agree that better lubrication is a pro for knurling, but overall it is not a better option because they will not last anywhere near as long as a new set (or bronze inserts, which is even better if OEM are cast...).

======

All you can do is put it together clean and change the oil/filter religiously.

Do you think I should remove and inspect the oil pump?
and is there a way to inspect the oil passages?

[David T]

The key to long engine life is use the best oil you can and change it regularly along with the filter. Some engines are prone to wear in the valve guides, some engines are OK with some wear. Typically wear in the valve guides is due to not enough oil but if you get too much oil it gets past the seals and you burn it so like most things in life it is a trade-off. Not knowing how bad it is there is no way to say what to do. As always the best thing is to refer to the engine manual specs to see what the wear limits are. The PRV is not known to have a problem in this area usually so if you have excessive wear in the valve guides, it is probably due to how it was taken care of (or not). If lack of oil was a problem the camshafts would have gotten torn up, the valve guides are lubricated from the splash from the cams.

[Parzival]

The key to long engine life is use the best oil you can and change it regularly along with the filter. Some engines are prone to wear in the valve guides, some engines are OK with some wear. Typically wear in the valve guides is due to not enough oil but if you get too much oil it gets past the seals and you burn it so like most things in life it is a trade-off. Not knowing how bad it is there is no way to say what to do. As always the best thing is to refer to the engine manual specs to see what the wear limits are. The PRV is not known to have a problem in this area usually so if you have excessive wear in the valve guides, it is probably due to how it was taken care of (or not). If lack of oil was a problem the camshafts would have gotten torn up, the valve guides are lubricated from the splash from the cams.

Good to know, Dana AKA DMC-81 was nice enough to go buy the shop that has my heads today (its nice to have friends) since its near his home, and about an hour from me. It seems that the shop is on the more thorough side. They are also replacing the freeze plugs, and repairing 2 of the stud holes that were drilled out. (they will be returned to the correct size)
He also reported that the cams and journals are in good shape, so oil delivery is not likely an issue. (I will still be inspecting everything I can possibly get to)

[Ron]

Do you think I should remove and inspect the oil pump?
and is there a way to inspect the oil passages?Hehe...I'm prone to replace oil pumps when I one. Seriously tho:
Did it have good oil pressure?
Was the valve train quiet?
Ask the builder if anything looked oil starved. (If so, I would at the very least check it for scars etc since metal has to go through the pump once before it is filtered out...)

If not removing the pump/chains, I guess you could pressure one passage up and see how the others flow with a little rigging.

Peace of mind trumps for me.

[Parzival]

Hehe...I'm prone to replace oil pumps when I one. Seriously tho:
Did it have good oil pressure?
Was the valve train quiet?
Ask the builder if anything looked oil starved. (If so, I would at the very least check it for scars etc since metal has to go through the pump once before it is filtered out...)

If not removing the pump/chains, I guess you could pressure one passage up and see how the others flow with a little rigging.

Peace of mind trumps for me.

According to the machine shop the cams and journals look good, so I guess oil is getting to where it's supposed too. The only oil related thing I can mention, is if I cam to stop real quick the oil like would rarely flash on for like a fourth of a second, but I think it was my RPMs dropping real low, my oil pressure was always really high when driving. I remember thinking it was too high when I first got the car.

[David T]

According to the machine shop the cams and journals look good, so I guess oil is getting to where it's supposed too. The only oil related thing I can mention, is if I cam to stop real quick the oil like would rarely flash on for like a fourth of a second, but I think it was my RPMs dropping real low, my oil pressure was always really high when driving. I remember thinking it was too high when I first got the car.

If you mean you were watching the oil pressure gauge and it was always "pegged" high, the OEM sender was never calibrated properly to the gauge. It was either all the way down when the motor was not running or all the way up when it was. You can replace the sender (the one by the oil filter) with a more compatible sender that will more accurately indicate oil pressure. With low oil pressure you will lose the bearings way before you lose valve guides. Bearings must have a lot of oil and that takes pressure to build and maintain the film of oil that keeps the journals from rubbing directly on the bearings. Other areas of sliding contact like cams, rings, and valve guides rely on the lubricity of the oil and it's ability to cling to the parts. That doesn't last forever and as the oil ages it loses these properties. One of the main reasons the oil has to be changed, to replace the additive package that gives the oil these properties. Now, if you saw the oil pressure light come on, THAT'S when you KNOW you don't have oil pressure! That or the wire going to the sender got cooked.

[Parzival]

If you mean you were watching the oil pressure gauge and it was always "pegged" high, the OEM sender was never calibrated properly to the gauge. It was either all the way down when the motor was not running or all the way up when it was. You can replace the sender (the one by the oil filter) with a more compatible sender that will more accurately indicate oil pressure. With low oil pressure you will lose the bearings way before you lose valve guides. Bearings must have a lot of oil and that takes pressure to build and maintain the film of oil that keeps the journals from rubbing directly on the bearings. Other areas of sliding contact like cams, rings, and valve guides rely on the lubricity of the oil and it's ability to cling to the parts. That doesn't last forever and as the oil ages it loses these properties. One of the main reasons the oil has to be changed, to replace the additive package that gives the oil these properties. Now, if you saw the oil pressure light come on, THAT'S when you KNOW you don't have oil pressure! That or the wire going to the sender got cooked.

Well, My oil pressure gage moves from like the middle of the gage at idle, to up near the top when driving. The light has flashed for like a spit second when stopped, but again, I think it was the RPMs dropping to low, the light comes on I guess at 5PSI not zero. The sender unit for the light was also leaking, so it may have read a reduced pressure due to that. Its been fixed, not sure if I saw the light come on after that or not, but even when it did it would shoot right back up as soon I gave it any gas at all. I'll pull the pump, and inspect it to be sure.
Oh and there is still that broken o ring I found in the oil pick up, that could have been a factor too?

[DMC-81]

Good to know, Dana AKA DMC-81 was nice enough to go buy the shop that has my heads today (its nice to have friends) since its near his home, and about an hour from me. It seems that the shop is on the more thorough side. They are also replacing the freeze plugs, and repairing 2 of the stud holes that were drilled out. (they will be returned to the correct size)
He also reported that the cams and journals are in good shape, so oil delivery is not likely an issue. (I will still be inspecting everything I can possibly get to)

Anytime Austin. Yes, in addition to what Austin listed, the machine shop tech reported that all valves were measured (mic’d) to spec, meaning they were not worn. The shop manager felt that there is no specific reason / problem in the bottom end other than normal wear for the valve guides. They are apparently cast bronze.

Here are some pictures of the heads (torn down but not cleaned, or worked on).

Cam journals:
61536

Cams and valve train:
61537

The tech demonstrating the play in the guides to me:
61538

Incidentally, the shop is one of the highly recommended businesses in the area. They resurfaced my DeLorean flywheel, and took over the shop that rebuilt my Magnum heads. I toured their working area, and it looked like a clean room. Today, the manager showed me the CNC machine which they just used to precisely port a legendary Toyota 2JZ (inline 6) head of Supra fame. There probably isn’t knurling in that job.
61539

61540
I thought that was pretty cool.