Valve Guide Removal - 911 2.4
 

Techies,

I have recieved two opinions on how to remove valve guides from a 911 head from two different experienced machinists whom I am evaluating for redoing my heads.

One says the valve guides can be driven out after the head is properly heated.

The other says the guides must be machined out.

There is an obvious cost difference & yes it matters. Both could be correct. Does anyone have first hand knowledge if heating them properly is adequate for removal? How hot? Is there a published procedure?

Searched forums, no luck.

Thanks,

Bill

When I consulted a local machinist about doing heads, his price for labor alone was about what having the whole thing done (new guides, springs checked, spring height set, etc) by Atlantic Enterprises. If you don't need new valves it under $400 with 2 day turnaround. All AE does are heads.
-Chris

Don't know about right or wrong - but here's what worked for me. Heated the heads with a propane torch, got them pretty hot, probably well over 150 degrees. Sprayed the guide down with WD 40. One guy (me) held the heads steady while my machinist friend drove out the guide with an air driver and a special steel shaft that is the same OD as the guide. Need to use caution not to flare the end of the guide so that it no longer fits through the hole. It took some serious work, but all twelve guides eventually came out OK with no damage to the surrounding aluminum. Good luck.

flaring out the guide is the main issue. it will score or crack the guide bore if it flares/expands as you drive it out.

to keep from doing that, the guide is bored 2/3 way thru with a special stepped drill bit, available thru Baum Tools. the leading end of the bit is 9mm, and centers the bit in the guide so the drill can't go off-center into the aluminum head. this effectively collapses the guide so it's easy to drive out. no head heating needed. i use a air hammer and a bit i made that fits the drilled guide nicely, but a large hammer and a good fitting punch/drift will work in a pinch.

a word of caution!!, replacement guides usually have a raised collar/ring that butts up to the head on installation so the guide sits at the correct height. YOU DO NOT WANT TO RUN THIS COLLAR THRU THE GUIDE BORE! the safest way to avoid this is to do the drilling from the valve head side of the guide, and run it out the spring side. this also puts less stress on the end of the guide bore in the valve pocket, so there's less chance of cracking it.

use a micrometer on the old guide and be sure the new guide is the same diameter. spray the guide bore and guide with WD40 or equivilent, and again i use an air hammer and 9mm guide driver to run them in. no heat. (it's a personal thing, use heat if you feel like it). i put a thick washer on the guide driver to assure a flat surface contacts the guide on installation, to prevent distorting the top of the guide where the seal attaches. then it's reamed or honed to be sure the ID is straight and has proper guide to valve clearance. the seats are then machined. you can't replace the guides without recutting the seats.

John, how do YOU do your valve seats?

And what do you drill the guides with after they are installed?

i'm an old school stone user. the new machines cut all 3 angles at the same time.
9mm expandable pilot, 45° stone, grind until it cleans in the area you are going to use. 30° stone above the top edge of the 45, until it narrows the seat enough from the top, so that the outer edge of the valve face just overlaps (just a C hair) the top edge of the 45. narrow the 45 from the bottom with a 60° stone (if you don't have a hand cutter) until the seat is the same width all around, approx 1 to 1.5mm, exhaust slightly wider than intake, for better heat transfer. i prefer a hand cutter with a single blade for the bottom cut. it's easier to trim just where you want to, rather than let the stone take off metal where IT wants. stones tend to follow the hole. most of the time you have one side of the seat a lot narrower than the opposite side, before doing the bottom cut, and can't afford loosing any seat area on the narrow side.
that's simplified, on a good day. various problems can pop up to make the job more difficult.

Thanks for all the advice guys. It looks like there is no magic required here so I am going to give my local guy who has been doing engine work for 30 years at the local NAPA store the job. He even has a Serdi head machine. His labor price: $5 per guide.

Bill