[JEC3039]

Looking for a machining source to D-dish a set of flat-top L2262F forged pistons.

I thought this would be an easy task but after visiting several local machine shops in the metro Detroit area plus calling Reichert Engines up in Owosso (MI) (they used to do it but no longer) as well as visiting Lingenfelter's engine shop in Wixom (MI), I'm finding no one wants to mess with the setup.

Hoping this forum can point me to a shop somewhere that has the experience and is still willing to do the work.

Thanks.

[ID67goat]

Probably easier to order new pistons with the dish you want and sell these ones.

[dataway]

When I did mine on a BP I made a fixture to hold the pistons, had previously calculated the necessary dimensions of the cut, operated the wheels by hand and watched the DRO.

A "Machine Shop" as opposed to an "Engine Machine Shop" might be what you need. Engine machine shops are usually pretty busy and have all their stuff setup to do typical engine work. A regular machine/fabrication shop is used to doing jobs that require all kinds of setups. However you would probably have to do the math yourself, make sure crown depth was suitable and offer a general pattern of the shape and location of the dish.

I used the same pistons as you and just machined off a 7cc symmetrical section of the bar between the valve reliefs which leaves plenty of squish area left over. These were for use with #16 heads with 72cc chambers.

[steve25]

What heads are you running and what size over Bore if any?

[Formulajones]

Likely hard to find an engine shop that will do something like that without having control over the entire build these days.

[mgarblik]

I see those pistons are $416.99 + shipping on the Summit site. A shop using a manual vertical mill and a piston vise would have 2.5- 3 hours time in cutting a D shaped dish in 8 pistons. So $250-300 to cut the pistons in that shape. With $700-750 invested in a 45 year old piston design your almost into custom, lightweight modern ring pack high quality piston territory. I would investigate that possibility as an option. If someone has a CNC program to cut those pistons that could reduce the cost substantially. A simple round dish would also be less expensive. A piston vise and a fly cutter would take half as much time. Good luck with the project.

[rwfisher]

Are these New or Used pistons?? If used, are the pins pressed in?? If they are used and the pins have to be pressed out you run the risk of distortion / cracks depending on the skills of the shop. When your done you have an expensive set of used pistons... If the ones you have are new, sell them and you have money to put towards a set of dished pistons from a longer list of manufacturers. When I asked the same question a few years ago of Butler engineering the offered to do them but laid it out to me in this same fashion. I bought new ICON forged with the 14cc D dish instead.

[dataway]

As a person who used the exact same pistons, and machined the dish, and used press in pins ..... I agree with the people above. If you have the option, use a different piston with the dish already machined, with floating pins, whatever offset you want for deck height etc. etc.

I used those pistons because it's what I used 40 years ago and I bought them before I consulted this forum. Machine shop warped one of them pressing the pin in ... then I had to try to find a single .040 piston ... not easy. The pressed in pins can make life more difficult on assembly and checking clearances.

If I had it to do all over again I would not have used them. That said, engine went together and runs nice.

[Old Man Taylor]

I had the piston manufacturer do mine.

[JEC3039]

This forum is amazing. Full disclosure on my part up-front would have been helpful, so here goes:

- building two 389 engines side by side.
- both will have 093 heads and both will be 4.120 bore dia (steve25 asked this).
- first one is a 389 of special value to me and will get DSS pistons with custom D-dish and custom compression height (cost is not an issue).
- second one is a throw-together 389 where I was going to re-use the TRW pistons mentioned in my initial post.
- these pistons are from a low mileage previous build and are otherwise in good shape, but yes they are very old and yes probably saw some distortion when pressed out of the rods.

Had I been able to find a shop to D-dish the used pistons for engine #2 for a couple hundred bucks, I was simply going to be thrifty with that build. As most have suggested here, probably not a good idea.

Thanks.

[Scarebird]

I always wondered why not do this with a router? Make a plywood "D" guide pattern screwed to a wood clamp - use a bit with rounded edges.

[dataway]

I guess the odds of those pistons being fine after being pressed on originally, then pressed off, then pressed on another set of rods .. would be iffy. I'm sure it's been done, but probably not a recommended practice

Like they say, you can pay now, or pay later

[Cliff R]

If they were pressed off the rods most likely you will not be able to re-use them.

At this point you'd be better off to just purchase a set of stock cast replacement pistons with the 8 valve reliefs in them. If it's a "throw together" build they would be fine, and lower the compression for you at the same time........Cliff

[steve25]

There are things you could do like getting the Pistons cut for pin locks,but the cost makes it cheaper in the long run to get new Pistons especially since you have not it seems checked out if the ring grooves have ware.

Any compression ring to groove clearance in terms of a street motor greater then .004" and you would be building a compression leaking oil burning , poor performing nightmare!

Piston wise, or custom pistions wise here's what I find you need.

Bore 4.120"
Cylinder cid= 49.99
With the use of a common Fel pro head gasket, a deck clearance of .045", the 70 CC of your heads and a added 1.5 CCs of top ring land volume you will have a compression ratio of 9.63 with a flat top piston, so a tad too high I would say!

A added 4 CCs of valve notch volume would get you into a nice 9.2 to 9.4 compression range.

[AC445]

I have read for years how terrible pressed pins are. I agree, in principle ,floating pins have merit in race type engines. In the 70's we used a lot of Arias pistons that supplied "buttons" to retain the pins. It seems it would be simple to fabricate "buttons" to retain and float pins in the old TRW & SpeedPro type pistons. What do others think?

[Jay S]

I can not see it worth the time to create a pin button on a old set of pistons. We worked on an engine last year and had to order 1 new piston only to find FM changed the pin width on a replacement piston, making the replace piston 30 grams lighter. I consider creating a button, modifying the other 7 pins, possibly even cutting a new groove for the retainers. None of it was feasible, 8 new pistons made more sense.

I have d shaped dishes and concentric dished engines. In theory the D shape makes sense. On engines that are pushing compression we have had better results with concentric dishes. I don’t know why. It seems like pump gas contest type engine it is not unusual to see a concentric dish either, and most often that is with closed chamber heads. Kind of goes against the D shape theories.

On some occasions the concentric dish may even hold some advantages over the D shape. Whether this is one of those occasions it is a little hard to say. I would chuck the pistons up in our lathe and do do the basic concentric dish if it were my project. Last year I had one engine I cut a concentric dish into a flat top. Another I created a step head design. With my meager skills on a lathe I am sure a veteran machinist could do that stuff easily.

I am just mentioning the concentric dish as an option in case you know of someone with a lathe.

Once you figure out how to hold the piston firmly and get it square, the machining goes pretty fast. Find someone with a lathe in their garage and you could probably get a dish cut into a piston pretty reasonably.

[mgarblik]

Aluminum piston pin buttons are actually a complicated little part, at least the ones I have used. The ones we have used for decades have a radius on the OD so they match the piston skirt. They also have a shelf machined in them to support the oil ring rails and expander. They don't look like much but would be time consuming to make without a cnc lathe. You would need 16 pieces.

[dataway]

Yes they can be complicated little pieces.

Here are some buttons Arias sent me with some custom pistons I had made ... yes they have a notch for the ring land.

Not to worry, my next design used a thinner ring set that negated the need for the notch .. but the pin hole was VERY close to the oil ring

Spun these to about 11,000 rpm no problem. Course the stroke was about 1.5"