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Mill cylinder head/seat work without pilot

General engine tech -- Drag Racing to Circle Track

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tt911er
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Re: Mill cylinder head/seat work without pilot

Post by tt911er » Mon Dec 30, 2019 7:08 am

Hello all,

Firstly I'm pleased all the replies and comments and hopefully more of them coming.
If the idea cannot stand the criticism then it's not good enough or reasonable. Simple as that.

1. challenge is to get the guide straight up with x/y in place.
- if that is not possible to learn to do in a reasonable time by sweep dialing the guide hole then it will be very time consuming specially on a multi valve heads and makes no sense. If the guide hole is not round enough then that need to be fixed first with or without pilot I believe. If the needed guide work can be done on a same machine the position is there.

If the positioning can be done in a reasonable time then the idea was rely on the spindle mass and accuracy without any other movable parts.
Does this give the hoped results with quality vs. time. I don't know. That is the reason why I like to hear the comments.

Like I mentioned earlier I probably ending up using pilots and ball head but just wanted this forum to roast this idea.

And if we could leave the head fixture out of this. It has to be solid.

Happy New Year!

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Re: Mill cylinder head/seat work without pilot

Post by ptuomov » Mon Dec 30, 2019 7:35 am

So where can I get my 4-valve heads cut to specific valve depth with a cnc that can index to an existing valve guide without a pilot? I’m in New England.

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Re: Mill cylinder head/seat work without pilot

Post by HDBD » Mon Dec 30, 2019 11:23 am

tt911er wrote:
Mon Dec 30, 2019 7:08 am
Hello all,

Firstly I'm pleased all the replies and comments and hopefully more of them coming.
If the idea cannot stand the criticism then it's not good enough or reasonable. Simple as that.

1. challenge is to get the guide straight up with x/y in place.
- if that is not possible to learn to do in a reasonable time by sweep dialing the guide hole then it will be very time consuming specially on a multi valve heads and makes no sense. If the guide hole is not round enough then that need to be fixed first with or without pilot I believe. If the needed guide work can be done on a same machine the position is there.

If the positioning can be done in a reasonable time then the idea was rely on the spindle mass and accuracy without any other movable parts.
Does this give the hoped results with quality vs. time. I don't know. That is the reason why I like to hear the comments.

Like I mentioned earlier I probably ending up using pilots and ball head but just wanted this forum to roast this idea.

And if we could leave the head fixture out of this. It has to be solid.

Happy New Year!
OK I get what you are saying but why are you trying to do this and what is wrong with the ball head tooling? If you use carbide pilots and get everything centered and level to the spindle (not the ground) the seats will be fine. I cut seats like this for many years using a Haimer Centro to center up the guide axis and a level I made myself. The pilot in the guide is what I measured not the guide hole, much easier. Contrary to belief the tapered pilots, from Rottler, are accurate and have the proper taper to do a good job. Only reason I bought the Serdi was speed. And it is a huge time saver, and stress relief. Dialing in each seat is a pain.

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Re: Mill cylinder head/seat work without pilot

Post by tt911er » Mon Dec 30, 2019 12:55 pm

First of all there is nothing wrong with pilots and ball head.
I have used (old) Mira and consider to upgrade my tooling. Just like also to hear more comments if someone works without pilots. Why and what issues they have faced before make the decision about the set up.

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Re: Mill cylinder head/seat work without pilot

Post by Greenlight » Mon Dec 30, 2019 1:25 pm

While I appreciate machining valve seats as accurately as possible, if you consider that the valve temperatures and seat temperature are in the 600F to 1500F range, and with spring loads in the 90 lb. to 800 lb. range, it would seem that the thermal distortions are way beyond the need to have seats machined so accurately. It would seem that the spring loads would "pull" the very hot valves squarely against the seat.

I have personally on many occasions had drag race engines with "bent" exhaust valves (caused by the valves hitting the pistons on a run) run exactly the same ET as before the valves were bent. A leak down test would show 40%, 50%, 60%, …… leakage, all going by the exhaust valves. I have also seen the same engine "repair itself" when just a couple of runs later the exhaust valve seated again. I assume the high temperature on the valve head accompanied by the high spring loads pounded the bent valve back into shape.

Source:
https://www.researchgate.net/publicatio ... ine_valves
"Average temperatures for operation of the valves are between 300-400°C for intake valves and 500-900 °C for exhaust valves, as shown in figure 2. Also from mechanical point of view, the valves are strongly solicited because the operation at very high speeds, which can reach values of 600 m/s."
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Re: Mill cylinder head/seat work without pilot

Post by HDBD » Mon Dec 30, 2019 7:35 pm

In 5 axis cnc machinery I prefer Hermle. But this is not in the reach of a shop looking to use a knee mill to cut seats

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Re: Mill cylinder head/seat work without pilot

Post by peejay » Mon Dec 30, 2019 9:28 pm

Greenlight wrote:
Mon Dec 30, 2019 1:25 pm
While I appreciate machining valve seats as accurately as possible, if you consider that the valve temperatures and seat temperature are in the 600F to 1500F range, and with spring loads in the 90 lb. to 800 lb. range, it would seem that the thermal distortions are way beyond the need to have seats machined so accurately. It would seem that the spring loads would "pull" the very hot valves squarely against the seat.

I have personally on many occasions had drag race engines with "bent" exhaust valves (caused by the valves hitting the pistons on a run) run exactly the same ET as before the valves were bent. A leak down test would show 40%, 50%, 60%, …… leakage, all going by the exhaust valves. I have also seen the same engine "repair itself" when just a couple of runs later the exhaust valve seated again. I assume the high temperature on the valve head accompanied by the high spring loads pounded the bent valve back into shape.

Source:
https://www.researchgate.net/publicatio ... ine_valves
"Average temperatures for operation of the valves are between 300-400°C for intake valves and 500-900 °C for exhaust valves, as shown in figure 2. Also from mechanical point of view, the valves are strongly solicited because the operation at very high speeds, which can reach values of 600 m/s."
Meanwhile, I have heard from people who build high power (200+hp per cylinder) Subarus that they cut the seats with the heads heated and torqued to a kind of inverse torque plate, because things move around so much on them that valves that seal cold will leak when everything is hot.

Mind you, Subaru themselves call for an additional 90 degrees of torque angle on the center two head bolts. I don't quite understand what is so noodly about them relative to any other aluminum 4v head, but clearly something is going on.

I have experienced bent valves sealing just fine too. The big issue with that is you are expecting the valve to flex the stem at every closing event, which will lead to two piece valves sooner or later. And two piece valves beget pistons you can remove through the oil pan drain plug, and see-through cylinder walls. My favorite example of this entailed picking mostly-intact piston rings off of the lower control arm...

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Re: Mill cylinder head/seat work without pilot

Post by PRH » Tue Dec 31, 2019 12:51 pm

I have refreshed the seats on a number of Subaru heads.

The heads off turbo motors always have several exhaust seats that are very wide on one side....... and very narrow on the other.
In other words...... poor seat/guide alignment as from the factory....... at least in running conditions.
The intake seats are usually much better in that regard.
Somewhat handy with a die grinder.

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Re: Mill cylinder head/seat work without pilot

Post by SchmidtMotorWorks » Tue Dec 31, 2019 1:26 pm

HDBD wrote:
Mon Dec 30, 2019 7:35 pm
In 5 axis cnc machinery I prefer Hermle. But this is not in the reach of a shop looking to use a knee mill to cut seats
Found this excellent video tour of Hermle.

Especially interesting is the apprenticeship program 15:45

http://www.schmidtmotorworks.com Prototypes, Tooling, Molds.

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Re: Mill cylinder head/seat work without pilot

Post by BILL-C » Tue Dec 31, 2019 5:40 pm

Does anyone know how seats are machined on brand new heads?Are Seats made on lathe will all the angles, frozen, and dropped in place, or installed raw and machined in place?
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Re: Mill cylinder head/seat work without pilot

Post by strokersix » Tue Dec 31, 2019 8:07 pm

If you rework the guide and seat in the same setup you might have a chance of success with ordinary toolroom equipment.

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Re: Mill cylinder head/seat work without pilot

Post by mt-engines » Tue Dec 31, 2019 9:03 pm

SchmidtMotorWorks wrote:
Sun Dec 29, 2019 12:49 pm
You can produce more accurate seats on a machine without pilots.
The clearances and taper involved in pilots are multiples of the accuracy of a good machine even if it is interpolating.

The main advantage of CNC milling seats is that you can have designs where the non-sealing faces have shapes or angles that change around the the perimeter of the seat. The best shapes in the center of the cylinder are different than the best shapes along the chamber walls.

I was doing this at Honda in the 90's with new CNC machines for that era, it wasn't fast but the work produced was excellent.
With modern CNC equipment the same work could be done in seconds to tolerances and finishes vastly superior to what a single edge cutter could do.
Try doing it on a head that has 100,000 mikes and get back to me.. Unless you are doing the guides then seats to make sure it's parallel, it's not going to happen..

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Re: Mill cylinder head/seat work without pilot

Post by HDBD » Tue Dec 31, 2019 10:34 pm

It is my understanding on new parts the most common method to machine the seats is in a combined operation of both boring / ream the guide hole and form the seat. A tool very similar to what is used to machine hydraulic ports.
https://www.mapal.com/fileadmin/00_PDF- ... 05_eng.pdf

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Re: Mill cylinder head/seat work without pilot

Post by SchmidtMotorWorks » Wed Jan 01, 2020 12:40 am

mt-engines wrote:
Tue Dec 31, 2019 9:03 pm
SchmidtMotorWorks wrote:
Sun Dec 29, 2019 12:49 pm
You can produce more accurate seats on a machine without pilots.
The clearances and taper involved in pilots are multiples of the accuracy of a good machine even if it is interpolating.

The main advantage of CNC milling seats is that you can have designs where the non-sealing faces have shapes or angles that change around the the perimeter of the seat. The best shapes in the center of the cylinder are different than the best shapes along the chamber walls.

I was doing this at Honda in the 90's with new CNC machines for that era, it wasn't fast but the work produced was excellent.
With modern CNC equipment the same work could be done in seconds to tolerances and finishes vastly superior to what a single edge cutter could do.
Try doing it on a head that has 100,000 mikes and get back to me.. Unless you are doing the guides then seats to make sure it's parallel, it's not going to happen..
I have already done it back in 1994, today it would be much easier.
Making a routine to probe the guides and save the locations and angles is easily done, it is just a matter of choice.

Most newer FANUC and Siemens 5 axis controls and some other 5-axis machines have a G-code that can make it easy; G68.2

It is commonly used to finish parts that return from heat treat with some distortion. Rather than re-justify the contact points on the part or shim it up, you just set-up a compound angled work-plane in the control. If you make a routine to do it, it takes only seconds.
http://www.schmidtmotorworks.com Prototypes, Tooling, Molds.

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Re: Mill cylinder head/seat work without pilot

Post by SchmidtMotorWorks » Wed Jan 01, 2020 12:49 am

HDBD wrote:
Tue Dec 31, 2019 10:34 pm
It is my understanding on new parts the most common method to machine the seats is in a combined operation of both boring / ream the guide hole and form the seat. A tool very similar to what is used to machine hydraulic ports.
https://www.mapal.com/fileadmin/00_PDF- ... 05_eng.pdf
That is what they did at Daimler when I was working there, all holes at once.
Roughly 1 minute (or less), head to head.
http://www.schmidtmotorworks.com Prototypes, Tooling, Molds.

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