Valve Guide Installation Input Needed

FL911 · 02-26-2009, 07:01 PM

There may be a post on this and if so please let me know.
My question is ...... my machinist is finally working on my heads of off my 81 911SC and the new valve quides that I ordered I believe where the first oversize guides that were offered.
Anyway...my machinist says the guides are way too tight to press into the heads so he is going to have to do some machinist engineering to get them to fit.

My questions are ...
1. Did I purchase the wrong quides which are the first oversize? Is there other guides sizes other than the first and second oversize such as OEM size?

2. If the guides I bought are the correct ones, what is the process for installing them? It does not seem normal to me for a machinist to have to modify the guides in order to install them.......or I may be in left field?

Any information regarding this process or my mistake by getting the wrong guides?

I just want some input to "speed things up" at the machine shop so I can drive the car!!!!!!!!!!

Thanks,
Frank

4sd911 · 02-26-2009, 09:13 PM

Factory valve guides are one size, over size, the are intended to be machined down to fit the hole. You measure the hole in the head and turn the guide down on a lathe, I think about .003 larger than the hole (there should be instructions in the manual). Other types of guides sold are by the size. You need to first remove the old guide then measure the hole in the head then you can determine which size you need. A guide to big can crack the head at the guide hole, to small and it will come loose under use.

T77911S · 02-27-2009, 03:06 AM

if he really siad "i have to do some machinist engineering " that would scare me unless he is kidding. has he done porsche heads before?

FL911 · 02-27-2009, 04:34 AM

That is what I thought about the "sizing" of the guides! I was originally thinking that I may have bought the wrong size, but it sounds like a routine process to fit the new guides.

And no, he did not say that I phrased that myself! He is an extremely meticulous and crafty machinist, I would say the best in the St. Louis area.

I simply wanted your input regarding the size because I do not want to pay him big money to have to lathe the guides if it was not necessary thats all.

Thanks to you both for the input.

coxy · coxy's Garage

Not a hard job, one of these "Adjustable Hand Reamer" can get the job done

cgarr · cgarr's Garage

The first oversize or know as first replacement should be around .515 which should be real close if this is the first rebuild on the heads. Otherwise measure the head and make the guides .0015 to .0025 larger than the head on a mandrel. Oh BTW, machining the guides to fit should be part of the head rebuilding costs too, not extra.

afterburn 549 · 02-27-2009, 12:56 PM

You are scaring me
A valve job is a valve job...sort of.
A 911 eng is much more critical the most anything your machine guy has ever done...not that he cant....Just will he learn and charge you for it ..? (and get it right )
To get the contact puuurfect takes a bit of...patients
to get the spring HT correct
to get the stem to guide correct...
Not a slam dunk like lots of heads

ChrisBennet · ChrisBennet's Garage

The process goes something like this:

Heat heads
Remove guides
Measure holes (once heads are cooled)
Machine guides to correct press fit
Heat heads
Install guides.

-Chris

afterburn 549 · 02-27-2009, 02:09 PM

I heated mine twice after the guides were in just to make sure there was not going to be any more shuffling around B4 the seats were done ( I am paranoid)

T77911S · 03-02-2009, 10:26 AM

craig
are special machines needed to do porsche guides vs other engines.

cgarr · cgarr's Garage

Quote:

Originally Posted by T77911S

craig
are special machines needed to do porsche guides vs other engines.

Just a good accurate lathe: You can drive them in as purchased if the interference is correct but I have not found many with usable concentricity.

afterburn 549 · 03-02-2009, 10:42 AM

The tighter the better (to a PT ) as the heat transfer works much better the tighter the fit.
Dry ice helps alot Listen to the funny song when you toss the guides on the dry ice

spjuvern · 03-04-2009, 01:01 AM

Quote:

Originally Posted by ChrisBennet

The process goes something like this:

Heat heads
Remove guides
Measure holes (once heads are cooled)
Machine guides to correct press fit
Heat heads
Install guides.

-Chris

how much heat to the heads before remove the guides?
and what kind of tool to remove them the best way?

i have heard of some drill them thiner before taking them out to minimizing problems

afterburn 549 · 03-04-2009, 09:28 AM

The tool is a jig thing so you can safely run a drill dwn through the guide , remove most of the material and then it taps right out.
Going back in you want a bunch a heat for a hour or so .
.( I would have to look up the temp gain ..maybe 400 deg? )
like I sad I reheated mine after installation too.......just in case any thing wanted to move after the 1 st heat cycle

spjuvern · 03-05-2009, 01:03 AM

is there maybe i thread on the forum with pictures that i have not found?
of the tools and the way to do this good

i don't want to end up cracking my heads

afterburn 549 · 03-05-2009, 09:05 PM

You can drill the guides out with no special tools if inteligence is used....in so doing you loose less aluminum for the next round........

spjuvern · 03-11-2009, 01:49 AM

Quote:

Originally Posted by afterburn 549

The tool is a jig thing so you can safely run a drill dwn through the guide , remove most of the material and then it taps right out.
Going back in you want a bunch a heat for a hour or so .
.( I would have to look up the temp gain ..maybe 400 deg? )
like I sad I reheated mine after installation too.......just in case any thing wanted to move after the 1 st heat cycle

400 deg Fahrenheit, Celsius not i guess

i have heard about 120 deg Celsius i good

was it no hard at all to remove them when you have heated them?

did you use a mandrel (don't know if it is the right word) and a hammer to get them out when heated? did you not drill anything out of yours?

john walker's workshop · 03-11-2009, 07:31 AM

geeze, just get some stock, normal sized guides and install them in the stock, normal bores. i do it all the time and there is no fitting issue. always important to use a micrometer and compare the old and new size so you don't split the guide bore. new ones tend to be a couple of hundredths of a mm oversize anyway, which is a good thing. 1st over is way too big.

afterburn 549 · 03-11-2009, 08:35 AM

Yes, all that JW said...somewhere along the line someone said to use a dash of talcum powder to ease the drive home (guides )
Once my heads were heated and the guides ffrozen ..they hammered in. Seemed about the right effort to other heads I have done

vreference · 03-12-2009, 01:09 PM

I'm in the Saint Louis area as well and used a local Machine Shop that I've been doing sporadic business with for over a decade. They build a lot of domestic race engines but weren't phased by the air-cooled parts. I even received a box with every part that came out of my heads and I was extremely pleased to find them all meticulously numbered. If something changes PM me for the name.