Just heard back from the machine shop and although they are not finished I thought it was interesting that they said the intake valve guides looked fine but a lot of the exhaust valves were terrible. I'm just curious as to why the exhaust valves would be so much worse? Bad luck? Previous owner habits? Truck has had a Banks sidewinder for about 120k before I bought it. Would running the engine hard and hot without proper cool-down period cause deposits to form on the exhaust guides and then lead to excessive wear?
Worn exhaust guides--intakes look good. Why?
- Thread starter DirtyWood
- Start date
Heat vs cooler intake charge
Someone just did 1/2 of the job
Different manufacturers and materials
Just my .02
Someone just did 1/2 of the job
Different manufacturers and materials
Just my .02
IDIBRONCO
IDIBRONCO
7.3 exhaust valve guides always wear out quicker than the intakes. It doesn't seem to happen to 6.9 heads. Why is up to debate. The symptom while the engine is running is called chuffing. That happens when the guide is worn badly enough that the valve doesn't seal completely. The solution is to install bronze liners in the exhaust valve guides.
scsmith42
Registered User
Former automotive machine shop owner here.
Exhaust guides typically wear out more quickly than intake guides. Intake valves tend to be cooled by the incoming air/fuel mixture, versus exhaust valves are heated by the hot exhaust gasses. This causes 1 - greater expansion of the valve stem, 2 - greater loss of lubrication on the valve.
The greater the clearance between the valve stem and the valve guide, the more wear can occur due to the rocker arm action putting a side load against the valve stem.
Additional factors are that intake ports are typically under vacuum, which causes some oil to be pulled down from the top of the heads around the intake valves - helping to lubricate them. Versus exhaust ports which are not under vacuum so oil replenishment in the guide is more difficult.
Back before unleaded fuel was mandated, the lead in the fuel typically served as a lubricant on the exhaust valve seats. When they started running unleaded fuel through older engines w/o hardened valve seats, we would see excessive wear on the exhaust valve faces and seats.
I saw this extensively back in the 1970's and 80's when unleaded fuel first became common.
Exhaust guides typically wear out more quickly than intake guides. Intake valves tend to be cooled by the incoming air/fuel mixture, versus exhaust valves are heated by the hot exhaust gasses. This causes 1 - greater expansion of the valve stem, 2 - greater loss of lubrication on the valve.
The greater the clearance between the valve stem and the valve guide, the more wear can occur due to the rocker arm action putting a side load against the valve stem.
Additional factors are that intake ports are typically under vacuum, which causes some oil to be pulled down from the top of the heads around the intake valves - helping to lubricate them. Versus exhaust ports which are not under vacuum so oil replenishment in the guide is more difficult.
Back before unleaded fuel was mandated, the lead in the fuel typically served as a lubricant on the exhaust valve seats. When they started running unleaded fuel through older engines w/o hardened valve seats, we would see excessive wear on the exhaust valve faces and seats.
I saw this extensively back in the 1970's and 80's when unleaded fuel first became common.
Indadesert
Registered User
The right solution is to drill them out and install new factory steel ones. Bronze would never hold up to the head.
Indadesert
Registered User
Exhaust guides wear more on exhaust valves on ever engine ever made. They are hotter. Aaand have more pressure behind them.
Don't quote me, but I don't believe the valve guides are serviceable, so you can drill em' out and press whatever you want in.
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