installing oversize valve and relocating the valve guide

[ampor]

What do machinists do when they install a larger valve and move it over a bit? This is in an 2 valve alloy head with an installed guide and seat.

When a larger valve is desired and it needs to move due to interference with the exhaust valve, what is typically done to relocate the valve guide?

Is the guide driven out and the hole welded up (along with the seat register), then machined for a new guide and seat?

Or is a larger valve guide "blank" installed and then offset drilled to accommodate the relocated valve?

Just curious about how this is done.....

Thanks

[stevieturbo]

People use various methods. As to which is best is debatable I'm sure.

I had one company do this for me years ago on a turbo mini head, and they made a complete and utter F... up of it. Mostly down to not leaving enough guide clearance. Valves seized in the guide inserts ripping them out of the head, then when they drilled and grub screwed them in, the actual guides got ripped from the head.

I went to another head shop after that.

Options.

Blank valve guide with an offset hole drilled. I actually think this is the best as long as sufficient guide material is retained.

Drill the head larger, install a plug/sleeve to fill the hole, then offset drill this and insert a full guide as normal.

Drill hole for a larger OD guide and again offset drill this as required.

I guess welding may be possible on some heads, it will depend on design, depth of hole, waterways etc.

[ampor]

Thanks for the reply, that's pretty much what I suspected.

For an oversized guide, what grade of iron is desirable? I'd rather use iron than bronze for intake guide material.

[stevieturbo]

ampor said:

Thanks for the reply, that's pretty much what I suspected.

For an oversized guide, what grade of iron is desirable? I'd rather use iron than bronze for intake guide material.

Puma would be better placed to advise there. I wouldnt have a notion !

[Pumaracing]

In an aluminium head you want to offset you'd normally just make an offset guide which would allow about 0.5mm to 0.75mm of offset in most engines before the guide gets too thin on one side. This can be done on a lathe with a 4 jaw chuck to hold the guide blank offset by the target amount but it isn't simple. Trying to drill a 7mm or 8mm hole a couple of inches long without wandering miles off centre ain't easy. I've made dozens of my own normal concentric bronze guides and I always drill and ream the hole first and then finish turn the o/d concentric to the hole because the hole will always wander like crazy unless you have a really rigid and accurate setup with special drill bits. So trying to make an offset guide which is accurate and with the hole parallel to the o/d isn't something I'd entertain on my own equipment and I'd suggest most people who think they could do it having never tried before would come unstuck.

Trying to machine the existing guide bore in the head oversize and offset is also not easy and means not only doing that but also making custom oversize guides. Offset hole machining has to be done by boring or milling because a drill bit will just try and follow the hole that is already there.

The only truly easy offsettable heads are cast iron ones where the stock valve runs direct in the head in say an 8mm hole like the Ford Pinto or Crossflow for which replacement o/s guides are readily available. Then it's a piece of piss to run a 12mm milling cutter through the head offset by the target amount, finish drill and ream that to 1/2" and fit a concentric guide in the new position.

However I'd seriously suggest just making the exhaust valve a bit smaller which is a heck of a lot less work and unlikely to make a scrap of difference to power output.

By the time you've made the guide bore offset, remachined the valve spring seats, fitted new seat inserts concentric to the new guide position, ported the valve throats and ports and solved any cam and valve lifter issues which the new valve centres cause you'll wish you'd never started.

Cast iron guide material from the major manufactures will usually be custom alloys of primarily grey cast iron with perlitic structure and sometimes enhanced with chromium, phosphorus and other elements. I wouldn't even bother trying to find suitable material in bar form from general metal stockholders when bronze in various suitable grades is so easily sourced.

[ampor]

Thanks for the reply and insightful information. I hadn't thought of making an offset guide on the lathe and then installing it; getting it indexed correctly would have to be done very accurately I suppose. I appreciate your advice on drilling long, deep, and straight holes.

Puma said: "By the time you've made the guide bore offset, remachined the valve spring seats, fitted new seat inserts concentric to the new guide position, ported the valve throats and ports and solved any cam and valve lifter issues which the new valve centres cause you'll wish you'd never started."

Yes, it is a lot of work, but since I've retired I've always wanted to try and do this. I have access to a lathe and mill, and have lots of free time. I'll give it a try and report back in the future.

Again, thanks for the advice.

[Pumaracing]

If you do decide to go ahead I can advise on machining methods and fitment tolerances, best methods of fitting guides and seat inserts etc.