911 Valve Seat Grinding

[AV8TOR]

First let it be said that I am a neophyte head re-builder. My work to date includes
removing and installing valve guides, reaming valve guides, grinding valves, NOT
grinding seats. I am not able to be an understudy to one of the great Porsche 911head re-builders, so I turn to you fellow Pelicanites, for a web based discussion.

Several years ago I purchased a B&D valve grinding machine, seat grinder, and reaming kit. Recently I purchased 30, 45, and 75 degree valve seat grinding stones from Goodson.
I am rebuilding a '69 2.0L "T" motor for my 914-6 restoration.
So........
I lightly oiled the stones, and slightly lifting the seat grinder, tried to grind squeezing the grinder trigger for just a few seconds with each stone.
I am not getting satisfactory results by my estimation. You can see in the first picture the seat does not have the nice sharp edges at the 3 angles.
Perhaps my first mistake was using a good head.

What should I be doing differently?? Are the Porsche seats too soft for the ruby stones? Should I use more oil? Should I do the grinding by hand??
HELP!

[AV8TOR]

Advice???

[shbop]

I've always used "Neway" cutters. While I don't have any experience with the stones; do you have a tool that dresses the outside of the stone prior to use? It would seem that the stone might need to be re-dressed before each use. Just a thought.

Neway Manufacturing Inc.

[hcoles]

my shop uses a machine, looks like a boring tool of some sort, that takes a special cutting tool and cuts all the proper angles/etc. I forget the name.

[tocobill]

Originally Posted by shbop

I've always used "Neway" cutters. While I don't have any experience with the stones; do you have a tool that dresses the outside of the stone prior to use? It would seem that the stone might need to be re-dressed before each use. Just a thought.

Neway Manufacturing Inc.

Ballpark cost on the neway set up? The website wasnt very informative. thanks

[hcoles]

Originally Posted by hcoles

my shop uses a machine, looks like a boring tool of some sort, that takes a special cutting tool and cuts all the proper angles/etc. I forget the name.

I remember now, he uses a SERDI machine.

[AlfonsoR]

I don't think you should be using stones to cut the seats. You should be using carbide or machine tool steel at a minimum.

Google "valve seat cutting tool". Maybe watching this will help..... Quick valve job with 3 angle form carbide blades..wmv - YouTube

[shbop]

I just spoke to a friend that has used the stone cutters. While he builds Honda motors, not Porsche, he said it's imperative to dress the stone prior to use. Repetitive use cutting seats changes the outside shape of the stone. He said that if you got a complete set, you shold have the correct tools for dressing the stones. This may be why you're not getting a sharp, clear radius. just another 2 cents

[AV8TOR]

Reading the Neway Seat cutter ad on the web page says it all about using stone to grind the seats........grinding with a stone "relies heavily on the finesse of the operator".........

[john walker's workshop]

i use stones exclusively. i don't ever use oil on them. it takes some time to get good at it. they need to be dressed all the time. exhaust seats are hard and clean up easily. intake seats are soft and clog the stone with metal smears after only a couple of short buzzes. i don't use a 75 degree stone for the bottom cut to narrow the seat and get it even all around. they tend to follow the hole and take off metal where you don't want to lose any. i use a bousfield engineering single blade hand cutter for that. 45 first, narrow the top with a 25 or 30 until the valve overlaps the 45 just a bit, then hand cut the bottom where needed to both narrow and even out the seat width. that's with a best case scenario. sometimes the 45 is so beat up that they don't clean for a while and the width gets pretty wide in the process, so you need to use the 25 or 30 and narrow from the top and then go back to the 45. carrera heads are like that on the exhaust seats.

not big on neway cutters. they tend to leave chatter marks when used by hand. difficult to cut the seat evenly as you bear down and turn the T handle, then release and bear down again multiple times. they should be used with a power feed.

[lindy 911]

Who's going to chime in about radiused seats with no angles; the hottest new thing.

[HawgRyder]

I have heard about radiused deats...but my first question would be...how do you set the contact patch with the valve head?
With a radius type seat being a curve...the contact area could be just a mm wide.
That would not be enough to seal and transfer heat to the head from the valve head.
Just my $.02
Bob

[lindy 911]

Actually, the entire area of the valve head ends up being the contact patch with much greater contact area, better heat transfer and better seal not to mention the flow improvements without the edges of a typical three or five angle grind.

[HawgRyder]

OK...I am now informed...thank you.
So...the curve of the seat area is duplicated on the seating area of the valve head?
Neat idea.
Bob

[lindy 911]

Yes, that's how it works. I've been told 15% flow increases over angle cuts and better heat transfer. It seems this is a pretty well kept technique and requires some very expensive tooling ($20K). Imagine a E stock SC with 15% better flow because of a valve grind.

[AlfonsoR]

Originally Posted by lindy 911

Yes, that's how it works. I've been told 15% flow increases over angle cuts and better heat transfer. It seems this is a pretty well kept technique and requires some very expensive tooling ($20K). Imagine a E stock SC with 15% better flow because of a valve grind.

Who does this type of valve job? Xtreme?

[Two Rivers]

You will need to get all the oil out of the stones. They are used dry. There is also a spring with bearing that goes over the pilot to hold the stone off the seat and with light pressure lets the stone contact the seat.

Dressing the stone is important.
It takes awhile to get the hang of it but light pressure holding the power tool helps.
Also you need to make a V block to hold the heads so the valve guides and stone are 90 deg. to the work surface.

[afterburn 549]

I have tried various cutters in the past.......Blade type might be OK for fast work...I have never liked them. They leave chatter marks.
Stones require a lot of finesse.But provide a very smooth done surface.....
Side point with stones there is NO limit on angles....I lost count on my own heads...The big deal is a straight and true pilot tool the correct and matching angle to the valve ( In the Ole days we would cut the seat 1deg off from the Valve seat)..
So......Get your seat width correct and located, then angle away....I doubt there is much difference between a 3 angle cut and a 100 as far a Real Hp.........But have at it.

[larrym]

get one of these

.

.

[afterburn 549]

JC Whitney ^ LOL