Pocketting Pistons

[Willie.]

Not referring to visiting Burton and stealing engine components, rather the process of machining valve cutouts in pistons.

 

I'm just wondering how people go about machining pockets for the valves. Butcher a valve to become a cutter and use an old head as a jig? Put plasticine/engineers blue on the piston and press valve in? How do you physically mark and machine the pistons?

 

Calculation/measuring wise, do you do it at TDC and as deep as max valve lift with no gasket, and this should be enough to cover you regardless of cam timing?

 

Any advice/tips/suggestions greatly appreciated. I may be having to do this shortly.

 

Willie

 

 

[Dickie Normuss]

I would suggest that pocketing pistons is not a DIY job

 

 

 

VX HPC - Loud and proud here

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[Jason Plato]

what engine and what cams ?

 

here is my Duratec R .... C7 TOP

Taffia joint AO with Al

 

[I.Mupferit]

I would suggest you drop a blatmail to Dave Andrews (Oilyhands) who will, I am sure, be happy to provide the answer.

 

 

[Willie.]

My theory is every job started by someone doing it themselves...so I should try everything 😬

 

I have access to a milling machine (My own isn't wired currently), but I'm just wondering how others have gone about it. Do you mark the piston, then remove and machine (at the valve guide angle) by eye, or whats the best way?

 

Havent got the cams yet, but wanting to go as mad as I can get away with. If pocketing pistons is going to be a major headache, I mightn't go as wild with the cams.

 

Willie

[Bricol]

Depends on what you want to do.

 

For a crossflow a number of years ago, I simply clamped the pistion down, and ran straight in from the side to the centre, enlarging the existing slight pocket to the required clearance. Tickled the sharp edges off and shoved them in. Not pretty, but worked well for 6yrs.

 

Bri

[Roger King]

Are you trying to deepen the pockets or increase the dia?

 

If you have access to a mill, you'll need to work out a way of holding the pistons - this can often be done by clamping onto two old gudgeon pins, one protruding from each side of the piston, although this is only really of use for one-offs. If you're doing lots, it's much better to make a jig.

 

It's easy enough to pick the centre of the pocket up from the o/d if your pockets are vertical. It's a little more tricky if the pockets are inclined. An easy (sort of bodge) way to pick up the centres on angled pockets, or even pistons that have no pockets to begin with, is to do a dummy build with all piston rings fitted, drop the cylinder head on and then lightly centre punch the crown down the valve guide using an old valve ground to a point.

[Jason Plato]

as him says above

 

you can run a fairly wild cam in a K with std pistons without pockets, the duratec can also run 210 spec cams with no pockets - as in the R400.

 

 

 

here is my Duratec R .... C7 TOP

Taffia joint AO with Al

 

[Willie.]

Thanks for the replies gents, appreciate the help.

 

Not wanting to give too much away, but its not a Duratec I4 or K Series. Its just a wee project that I'm working on. Haven't actually pulled the head off yet, but I'm pretty certain the pistons aren't pocketed. I'm hoping to get at the engine shortly.

 

I was wondering about holding the pistons, as I was for grabbing them with the 4-jaw, putting a bar through gudgeon pin and clocking along it. Maybe making a jig of some sort would save time in the long run.

 

I suppose I can make a centre mark as Roger has suggested, then slide a bar down valve guide (With head off) and measure the angle off the head to get the angle to tilt the milling head at. I could also use the valve/centre dab in the mill to pick up the centres and record on digital readout.

 

Willie

 

 

[k80rum]

You really are getting your hands dirty Willie! Best of luck with it..

 

Darren E

 

K80 RUM Website and Emerald maps library

 

Home of the long-term, supercharged Duratec project

[Roger King]

Bear in mind that if you do use the centre punch down the guide method, there is a certain amount of piston rock in the bore, so you need to allow a bit of extra clearance on the o/d of the pockets to allow for any inaccuracy from this.

[Geoff Wilcx]

Done it before.

 

The major challenge was the jig to securely hold the piston. My solution started from a square block of aluminium into which I machined a pocket / hole to a few thou' larger in diameter to the piston and about 10mm more shallow than the height of the piston. You're looking for a nice slipping fit.

 

Then measured the location that the gudgeon pin would be in when the piston was installed and bored a hole through the jig.

 

Then at 90 to this bore I cut a slit through the side of the jig (top to bottom and all the way through the base.

 

Lastly turned a soft aluminium bar that would slip through jig hole and the piston pin holes.

 

To use - pop piston in jig - locate by inserting pin and clamp in vice of mill. The cut slit allows for the jig to firmly pinch the piston to prevent it chattering.

 

If you work it through and cut flats for mounting in vice then each piston will always be presented at the same position to the cutter.

 

The only reason I did it was because I had FOC access to all the materials and machines and of course fancied a challenge.

 

If you tot up the cost of materials and time for making the jig and then the time of cutting each pocket then you are most likely better of in paying some-one to do if for you.

 

My Winter '08 Upgrade was to a screaming DVA K05.

 

www.geoffwilcoxphotography.co.uk

[Willie.]

I enjoy a challenge (And saving money). And I just prefer to be able to say "I did that" as much as possible.

 

Totally understand your method Geoff, makes sense . Sounds like a good way of getting a really solid grip of the piston. I'm dying to get a move on with the project and get into the engine.

 

Most of my thoughts so far have been by putting something through the pin bore and clamping it down via it. I suppose you wouldn't get too much chatter from an alloy piston, although it is a fairly big diameter cut. Had been thinking about a "gudgeon pin" with a good flange at each end to locate in vice, and have it drilled and tapped so I can screw into it to pull the pin/piston assembly down into the vice. As Geoff has mentioned though, I mightn't get a sturdy enough grip this way.

 

I had also wondered about machining a bit of bar a nice fit in the valve guide, grinding a bit of tool steel and fitting to the end, then fitting a stop to the spindle and machining the piston in place. Totally heath-robinson...but I'm paranoid about putting the pockets in the wrong place.

 

Thinking about it, and hearing the suggestions makes me think that its not going to be the end of the world if I have to do it, so I'm happy enough to go with the wild cams and if I need pockets I can do it (To be honest, I'll be a bit dissappointed if I don't).

 

Willie