Resurfacing Aluminum Cylinder Heads on a Bport Mill? 50Ra surface?

dalmatiangirl61 · Nov 23, 2021

A friend works on Subaru cars, Subaru only. Her bread and butter is cylinder head jobs, she tries to keep rebuilt heads on the shelf ready to go, but the good rebuild shop has a 2 month lead time, and they are banging her for $350 a set. She tried another shop recently but whatever machine they are using cannot cut a smooth enough surface and they leak with a basic pressure test after installation. The gasket manufacturer is telling her the surface finish needs to be 50Ra or better.

She would like to start rebuilding the heads herself, so the question is can a 50Ra surface be achieved on a Bridgeport style mill? Heads are 10" long x 8" wide, so I don't think table rocking would be an issue.

EmGo · Nov 23, 2021

dalmatiangirl61 said:
...can a 50Ra surface be achieved on a Bridgeport style mill?

Don't know about a Bridgeport but a Gorton would have no problem

dalmatiangirl61 · Nov 23, 2021

EmanuelGoldstein said:
Don't know about a Bridgeport but a Gorton would have no problem

Yeah, well she can't have it

. I know I can make a nice pretty surface, but never owned a profilometer to test how good it was, forgive me lord, I have sinned

. I get to do the shopping for her, just want to make sure it is achievable before I spend her money. The heads are so small you could surface them in a lathe, fixturing them to the faceplate would probably be a pia though.

Turbowerks · Nov 23, 2021

If the spindle is tight, use a pcd insert flycutter. Jamison equipment sells them for a bridgport if you want to buy it or making one isn’t a big deal finish will look like a mirror if you want

When I find it I don’t need it
When I need it I can’t find it!

Milland · Nov 23, 2021

Unless you can find a nearly-new machine that's not been beat on, I'd worry that a BP will rock unacceptably, even over just 15" or so. Remember, you have to add the diameter of the flycutter or whatever she'll be surfacing the head with to the travel distance, and the table support is so short that it doesn't take much wear to give significant height changes.

Maybe look for a used bed mill? Not nearly as common, but probably a better choice for head surfacing. Like this, except manual (unless there's serious money to throw around): TRAK Toolroom Bed Mills featuring the ProtoTRAK RMX CNC

Just be sure to lock the Y axis before use.

EmGo · Nov 23, 2021

dalmatiangirl61 said:
never owned a profilometer to test how good it was, forgive me lord, I have sinned.

It's not as good but there are electrochemically etched sample plates for various surface finishes that give you a pretty good idea. Supposedly your teeth are more accurate than your fingernails (if the part is small enough, might be embarrassing to get caught nibbling on a Buick bumper

)

implmex · Nov 23, 2021

Hi dalmatiangirl61:
I've never done Subaru heads but I've done Mazda heads and I did them on my surface grinder.
I had a 10" x 20" Kent grinder and it did a perfect job...flatter than flat, and way better than 50 microinch.

I found it easier to do on the grinder...easier to fixture and easier to control the DOC and the flatness within close limits.
I slathered the head with Relton A-9 aluminum cutting fluid before each pass and ran a 46J standard aluminum oxide wheel.
Came out perfect and didn't take very long at all...maybe 15 minutes per head? (it's a LONG time ago).

So if your friend is considering tooling up for this, she might want to consider a grinder instead of a mill.
Only problem is, grinders are not very versatile in a normal shop, whereas a Bridgeport can be used for a gazillion things.

Cheers

Marcus
Implant Mechanix • Design & Innovation > HOME
Vancouver Wire EDM -- Wire EDM Machining

dalmatiangirl61 · Nov 23, 2021

I pulled up the link below, I'm going to assume now she meant .50Ra , she said the heads that leaked had the roughness of vinyl LP's.
Surface Finish - Destiny Tool

Ken hosford · Nov 23, 2021

the answer in my book is get a lapping plate much bigger than head and lap it flat This is the best way to take least possible of heads you need to block out plate to get even wear A cutter that does not cover hole head will likely leave lines were the 2 or more paths cross A lapping plate will not Use kerosene or gasoline with oil with the lapping compound

kustomizer · Nov 23, 2021

I think there is a head surfacing machine in a cheap or free pile just over the mountain from you in San Andreas CA, gunsmith there got a good deal on a shop with one and took it home, I don't think he has any use for it. It kinda looks like a tiny bridgemill with a giant shellmill in it

triumph406 · Nov 23, 2021

If it's 8" wide that means you need min 8.25" diameter (or more) flycutter. and if the heads 10" long then your going to be traversing 18.5" in X, so unless it's a brandnew BP it's going to rock. And then there's the issue of tramming the head perfectly so the flycutter doesn't create a dished surface.

CalG · Nov 23, 2021

Modern head gaskets do not want a smooth surface. They want a surface that is "just right" for the sealing materials and technology applicable.

We may note that 50Ra is very coarse indeed. and that is my experience. Lapping, as we may think of it, is strictly OUT unless you are running the work over Black Beauty blasting slag.

I'm sure a BP could do the job. Motorized table feed for controlled rate. Better might be a Blanchard.

ETA

Consider, It will be the TRAILING cut that produces the surface finish when using a fly cutter or face mill.

dalmatiangirl61 · Nov 23, 2021

kustomizer said:
I think there is a head surfacing machine in a cheap or free pile just over the mountain from you in San Andreas CA, gunsmith there got a good deal on a shop with one and took it home, I don't think he has any use for it. It kinda looks like a tiny bridgemill with a giant shellmill in it

Do you have a link or contact info? Friend is in Texas, maybe I could get her to haul a load of stuff out here for me in exchange for a surfacer

10 fingers · Nov 23, 2021

In northern New England, Subaru may be the most popular brand. Head gasket failure on older models such as the 2.5 was near 100% by 120K miles. On one of my cars was able to lap the head flat using a granite plate with sheets of 230 grit lapping film. Several years later was running trouble free. Objective being, aluminum heads move a lot between -20 deg and 210 deg. Critical the head gasket tolerate creep. Being flat within .0005 and a fine surface finish best accommodates that that. Following the gasket manufacturer's guidelines is a great starting point.
How To Clean a Cylinder Head Mating Surface | Fel-Pro Gaskets

dalmatiangirl61 · Nov 23, 2021

CalG said:
Modern head gaskets do not want a smooth surface. They want a surface that is "just right" for the sealing materials and technology applicable.

We may note that 50Ra is very coarse indeed. and that is my experience. Lapping, as we may think of it, is strictly OUT unless you are running the work over Black Beauty blasting slag.

I'm sure a BP could do the job. Motorized table feed for controlled rate. Better might be a Blanchard.

ETA

Consider, It will be the TRAILING cut that produces the surface finish when using a fly cutter or face mill.

I'm thinking she meant .50Ra, waiting for her to confirm.

Edit: I'm confused, the Destiny link in post 10 says 50Ra is "rough cast", yet the Felpro link in post 17 says to finish aluminum heads to 50-60Ra??????????

Edit again: OK, I see there are 2 Ra scales on the Destiny chart, Ra um and Ra micro inch, I'll have to learn the difference.

CalG · Nov 23, 2021

dalmatiangirl61 said:
I'm thinking she meant .50Ra, waiting for her to confirm.

It will depend on the gasket technology. Check it out. "creep" is the killer these days.

kustomizer · Nov 23, 2021

dalmatiangirl61 said:
Do you have a link or contact info? Friend is in Texas, maybe I could get her to haul a load of stuff out here for me in exchange for a surfacer

I just called him, he sold it not long ago, he still has a belt sander type and a surface grinder, both big enough for this job I would imagine but the other would have been perfect. Sorry

slowmotion · Nov 23, 2021

50Ra is the correct figure but my dedicated head surfacer cuts a 12Ra on aluminum. IMO 50 Ra is way too rough for mls, even though the manufacturers use that number. I sold the last 10" CBN/PCD milling head with R8 shank that my buddy built and sold (now retired). He built head fixtures for vertical mills that come with the milling head and sold a bunch of them so using a vert mill is definitely do-able, especially a short little Suby (I've cut a million of them).

CarbideBob · Nov 23, 2021

triumph406 said:
If it's 8" wide that means you need min 8.25" diameter (or more) flycutter. and if the heads 10" long then your going to be traversing 18.5" in X, so unless it's a brandnew BP it's going to rock. And then there's the issue of tramming the head perfectly so the flycutter doesn't create a dished surface.

I would think 8.25 would be a tad undersized.
Given that you want only one side to cut that adds a lot to table travel.
Any cross cut or hatch is usually bad here so a very tiny tilt is used.
In production the often rule is if the ass end of the cutter touches or leaves a mark the tools need need to be changed out.
Yes this means a dish. Which is why on a 8 inch surface one wants a 14 to 20 inch cutter body.
There is not only a dish but a dive/raise as one goes goes across full load and then the lighter Z load as you cross the big holes.

B1 SCOTT · Nov 23, 2021

Pinnacle Fly Cutter - YouTube Pinnacle fly cutters seem to be popular for Bridgeport style head surfacing.

Resurfacing Aluminum Cylinder Heads on a Bport Mill? 50Ra surface?

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