Machining the valve guides.... not what your thinking

[narf]

I have a 2 g head with about XXXX worth of port and valve work alone. everything is freshly machined and ready to go together right now. the head was sandblasted and cleaned with glass media before any machine work was done. after cleaning and machining we found media between the valve guide and the cast of the aluminum heads itself( we were busy cleaning oil ports and overlooked it). there has been 2 weeks in attempting taking the media out 1 by 1. it's so tight in you cant even get a tool in the gap to pick the media out. I'm sure with my luck it will fall out while the engines running, no doubt. Rather than risking damage to the deck, and the facts new guides would require a new cut and lap because of concentric run out, we had the idea to machine the guide ends (that are inside of the runners) flush with the aluminum surface... milling the media as well. Any downside I'm not thinking of? The guides length is all that's changing, I've also upgraded to a stainless valve. On the plus side its removing a good amount of material that the air dose not have to bend around in the runner

 

[bryanwheat]

So you are saying that that there is material between the guide and inner bore? That is almost impossibly because the guide would push it out when you are installing it. They are an interference fit, so they are actually a tad bigger than the bore. Also i wouldn't machine the guide that short. It's length will keep the valve more stable and less likely to bind in the guide, and it also transfers heat from the valve, so less area can lead to less cooling of the valve. Also one other thing to consider, if you remove the guides than you will have to re-cut the seats as you already mentioned. If you already cut them once after a guide install than the seats might be a little to thin to safely re cut them.

 

[narf]

The guides were never removed, otherwise you are correct.. the media would have just fallen out. the seats will have 3 cuts on them that I know of if I take the guides out now, 2 if we just machine the guide shorter. I agree on the whole shortening and heat displacement.... but the length inside the head is more ridged than the overhang. Were only talking .250-.350 of material here

 

[JacksonAuto]

It's not advisable. The job of the guide is to support the valve. By shortening the guide, the valve is unsupported.

 

[TexasTurbo]

I've seen people do this on race motors to increase the airflow past the guide areas that stick out into the port.

Has anyone ever seen a cut valve guide like this cause an issue? That's where I'd start is with people that have done it before and can tell you the results. Of course removing the material will weaken the guide, but does it weaken enough to cause an issue, and if it does, has anyone seen this happen or proved it? In theory it will be weak and "not work" properly, but in reality is a different story.

 

[JacksonAuto]

You'd be surprised at how much it doesn't help the airflow.

We've had heads at the shop that experienced premature guide wear and when we tore them down found that the guides had been ground out. Installed new guides, did a valve job and magically the problem went away. It's not a myth.