How do I make a flat bottom pocket for valve relief?

atomarc · Oct 20, 2014

I have 8 pistons that need two pockets each on top. These are 1.700 diameter X .065 deep pockets for valve relief and their location has been found using a transfer punch through the valve guides. The pockets are parallel with the top of the piston.

I have no CNC capability. I have a piston fixtured on a 4 jaw on the lathe and was thinking about using this method...figure it would take about 49 years to finish. I have a boring and facing head for the Bridgeport but again, it seems like it would take forever.

Is there an easier method? Can I make a pocket boring tool that will cut a flat bottom pocket and not chatter and scream.

Stuart

67Cuda · Oct 20, 2014

Since you're using punch marks to locate. Set it up on a rotary table and use a keyway cutter. You can walk the cutter down a few thou at a time for a flat bottom.

Just a thought.

Tom

bjorn toulouse · Oct 20, 2014

I had a couple of tools made from old valves for doing just this job. Don't remember what happened to them, though.

There were 4 pieces (more like slivers) of HSS soldered to the face of each valve, and a collar with a set screw on the stem to control depth.
The cutters were in a chunk of cylinder head. You did one cylinder, unbolted and moved to the next, etc.
Took about an hour to do a small block Ford or Chevy.

Rex

mnl · Oct 21, 2014

Volstro head for your Bridgeport. They can be had for not much money these days.

eTekTool · Oct 21, 2014

bjorn toulouse said:
I had a couple of tools made from old valves for doing just this job. Don't remember what happened to them, though.

There were 4 pieces (more like slivers) of HSS soldered to the face of each valve, and a collar with a set screw on the stem to control depth.
The cutters were in a chunk of cylinder head. You did one cylinder, unbolted and moved to the next, etc.
Took about an hour to do a small block Ford or Chevy.

Rex

That is how my father did their VW race engines. I have also seen somewhere someone used PSA abrasive disc on the end of a valve.

ernieflash · Oct 21, 2014

silver solder a piece of HSS to a old valve grind a cutting edge on it go to town been doing it like that for years just saying same as bjorn-toulouse said .Easy

CWB · Oct 21, 2014

JME designing and beating on them, but if its not a gallery cooled piston you really should measure the thickness before even considering cutting them. Many modern stock pistons are already near/at minimal thickness already, in my case youd be cutting my minimum by about 1/3rd. Aftermarket and/or old production pistons OTOH tend to be heavy, clunky turds by comparison, so youre probably safe in that case. Cracked pistons really suck in either case.

Personally I use the rotab and an end mill, occasionally a boring head and ground form tool.

Bill D · Oct 21, 2014

you will want to put a good a radius on the edges to allow better airflow. What are the odds these pockets will fill with carbon and either cause interference at extreme rpm or at least pinging?
Bill D.

michiganbuck · Oct 21, 2014

Bridgeport or even boxed in on a drill press in a 4x4s and C clamp fixture might be better than the 4jaw lathe trick.
The tool bit hand ground to half form notched and brazed or silver soldered to a post shank as mentioned, even notched in and held with a couple set screws better than the lathe. *A piece of an old cut-off (parting tool) would be the berries(good).

Cast iron or aluminum pistons? doesn't matter that much just a little different top rake... or not.

atomarc · Oct 21, 2014

Thanks for all the ideas. A few things I didn't mention are that these pistons out of a Ford powerstroke diesel engine and they have a big swirl (?) hole in the center. I think this will allow me a 'starting point' for a boring tool setup in the lathe so I'm going to try that first.

Stuart

moonlight machine · Oct 21, 2014

I do them in the Bridgeport with a fly cutter. Do you know the location for sure?, I always time the cams and assemble the valve train with light springs. Then with a degree wheel on the crankshaft and a dial indicator on the valve I turn the crank and check the v-p clearance every 3* or so. then mark the center of the valve with a transfer punch through the valve guide at the crank angle that gives the least v-p clearance. then when you are all done and are sure you have it put a bit of modeling clay on the piston and turn the crank and let the valve crush the clay to prove you have enough clearance.

moonlight machine · Oct 21, 2014

michiganbuck said:
Bridgeport or even boxed in on a drill press in a 4x4s and C clamp fixture might be better than the 4jaw lathe trick.
The tool bit hand ground to half form notched and brazed or silver soldered to a post shank as mentioned, even notched in and held with a couple set screws better than the lathe. *A piece of an old cut-off (parting tool) would be the berries(good).

Cast iron or aluminum pistons? doesn't matter that much just a little different top rake... or not.

Cast Iron pistons??????

michiganbuck · Oct 21, 2014

moonlight machine said:
Cast Iron pistons??????

Way old...That is part of the reason for such long strokes in some older engines to 1957 GMC Diesel.

Western Auto was selling cast iron rings even in the 60S (POS) but some thought why have a hard ring when the cylinder was cast.

http://www.vapinc.com/pistonsandrelated/castiron.html

CI rings http://www.grovercorp.com/materials/cast-iron.html

Summit racing rings http://www.summitracing.com/parts/slp-e-251k30/overview/

atomarc · Oct 21, 2014

Aluminum pistons. All of the location info and pocket depth has been done by the customer...the engine shop. I just don't want to screw up a set .010 over pistons experimenting on the best setup. This has go me thinking about a small CNC mill, even a benchtop retro job. It would be a way to ease into a subject that is daunting to me. For now it's turning handles.

Stuart

moonlight machine · Oct 21, 2014

What is the big deal? I have been milling pistons for valve clearance since the 70's, every one on a B P.

Metalcutter · Oct 21, 2014

Use a half round drill through a Jig. On the drill: You have a cutting edge along the radius perpendicular to the drill axis. Then grind the relief on the cutting edge. Grind away everything else for chip evacuation.

You need to have the piston tied down, and a ridged mounting for the drill. Just run it slow 100rpm to start, and easy taking a chip. If all works well, tease it for a bit more feed to make sure it's cutting ok.
This is not like a regular drill. It will look like 1.700 steel bar with a described here cutting edge and turned down on the other end for mounting. Get a GOOD grip on the piston and drill.
Should be a piece of cake. Practice on some aluminum until you realize what you are doing.

Regards,

Stan-

CWB · Oct 21, 2014

moonlight machine said:
Cast Iron pistons??????

Maybe he meant forged steel?

Realistically machining is the easy part of doing these, its the fixturing and setup that can be a PITA when you have to make per-print, ie. locating features on a part that has varying degrees of ovality and taper and on which everything is located off the vertical centerline and the wrist pin. Luckily for the OP it sounds like he's dealing with a hot-rodder, not a picky engineer.

atomarc · Oct 21, 2014

CWB said:
Luckily for the OP it sounds like he's dealing with a hot-rodder, not a picky engineer.

A picky engine shop! These guys work in tenth's all day long and if it's not right the result is engine seizure or engine scatter. I'm puckered when I do this shit. And you're quite correct, the fixturing is the key and the time consuming item.

Stuart

moonlight machine · Oct 21, 2014

CWB said:
Maybe he meant forged steel?

Realistically machining is the easy part of doing these, its the fixturing and setup that can be a PITA when you have to make per-print, ie. locating features on a part that has varying degrees of ovality and taper and on which everything is located off the vertical centerline and the wrist pin. Luckily for the OP it sounds like he's dealing with a hot-rodder, not a picky engineer.

Fixturing is dead easy....Google "piston vice" lots of ways to do it. I have a vice like the "power house" one shown, made by another mfr. though...Me. I have used the type that uses a 3 jaw lathe chuck and grips in the oil ring groove.

shamanj · Oct 21, 2014

Piston to the top of its stroke and braze on some cutters to an old valve + 1. Valve guides are good and I've seen people do it with a power drill. Set it so the chuck becomes your stop.
Also... no sharp edges when done, file down, then sand (with a dremel) all sharp edges! Even if you have an old valve and cut it right you can score the surface, then take the piston out and mill from there on a rotary table as you should have a decent circle scored on the surface.

How do I make a flat bottom pocket for valve relief?

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