Manganese Bronze Valve Guides: Are there any benefits?

[dr.occa]

A quick discussion I had with a long time C4AG member:

y does everyone want to change guides?

The 4AGE is one of the easiest engines on valve guides I've seen. I've had to replace 3 guides in total with all the 4AG heads I've worked.


So, please enlighten me... why change your guides if there is no need???????????????

Most likely for worn guides. With valves expanding as they heat and the factory (cast iron?) guides seeing side load, over time (20+ years) there's a good chance of clearance changes in the guides. Manganese Bronze has a tensile strength of ~65K lbs psi. Another benefit other more experienced engine builders have mentioned to me is to reduce galling and wear due to the material's natural anti-seizing and wear qualities. Bronze is also purported to have good heat dissipating attributes and can last 2 to 5 times longer than cast Iron. I'm not a metallurgist and my knowledge in the field is quite limited. I do my best to get my information from trust worthy sources.

I know the exhaust valves are more susceptible to more obvious out of tolerance clearance changes due to the fact that they deal with more heat than the intake side so even just changing the exhaust valve guides has its benefits.

[mooreofit]

insurance. you really want to replace a 6,000 dollar motor for a 1 dollar piece of bronze. thats 20 years old mind you.

[dr.occa]

Looking at the several 4AG heads I have the factory guides look to already be of a bronze type material. I myself haven't really had issues with the 4AG valve guides but for maybe a few on a head. And that head I already knew had a checkered past. Dan (aka oldeskewltoy) does have a point to a certain extent: "if it ain't broke, don't fix it".

[Sam-Q]

insurance. you really want to replace a 6,000 dollar motor for a 1 dollar piece of bronze. thats 20 years old mind you.

or how about if you change it it's one more thing that might not go right due to substandard parts, poor install, etc... All of our engines have bucket and shim valvetrains, this means that there is no sideloading of the valve guide and hence next to no wear. Add to this some very light sping loading and there is only a small indirect pressure on the guide. This is unlike the backwards pushrod engines where the rocker arm indirectly pushes against the valve and they wear more on one side and they have very heavy springs to push their bulky valvetrain back into place.

I do see your point and if someone is spending 6000 a motor you would hope it would just be one more thing they check and make an educated choice based on that.

[mooreofit]

im saying that at 20 +years of use there will be wear to the bronze guide minimal it may be but there will be some sort of patterning on the guide then you replace your valves with some oversized ones and they start to wear in on their own pattern and walla you have excessive valve guide clearance.thats why parts should go back exactly where they came from. im just saying they are so cheap to have the machine shop replace them while its there. however if i had a mill i could see your point.

[Sam-Q]

if you replacing the valves it's a very point you make, well said

[mooreofit]

thank you sir.