Philip Duclos Fire Eater

[CFLBob]

I don't envision this as a build thread, because I have so little to contribute, but I could use some help with questions as I muddle through my build of this engine, from "The Shop Wisdom of Philip Duclos".

I'm going by the book, and now making the second part, which is the cylinder. After cutting to finished size, cutting the fins, turning the shoulders, and drilling the bore up to the biggest drill bit I own (1/2"), the next operation is to bore it to size. The plans say to bore it to 1.00 - which is funny because that's only two decimal places. The piston's drawing says to turn it to 0.9980 to 0.9985. Four decimal places.

The piston isn't ready to fit to the cylinder because the order of the build (in Duclos' book) has me build the cylinder and set it aside. The piston is a few parts in the future.

I bought a CRS steel bar for the piston (the drawing says "bronze, cast iron, or CRS"), 1" diameter, which is really a bit undersized at 0.9990 to 0.9984. I figure when I put that in my lathe to do the turning, I'll lose more than .001 just turning it in the lathe. I don't know what my 3-jaw chuck's runout is, but .001 is way too good for a 3-jaw.

What I'm thinking is to bore the cylinder to something smaller than 1.000, then turn the piston to size. Say I bore it to .990 or .980. I shouldn't have to go as far as .980, but just to make sure I can turn the piston to the right fit. The only problem I see is that I bore the cylinder without knowing what size I can make the piston.

Does that seem like the right approach?


CFL Bob

 

[Cogsy]

It's always easiest to size a piston to a bore size rather than the other way round. At least that's what I find. As it can be very difficult to measure a bore to a high level of accuracy (precision is easy, accuracy is much harder) you cut your bore then when you get close to size as you're turning the piston, you can test fit it to the bore while it's still mounted in the lathe. And I don't see 0.020" making much power difference to the engine so the slightly smaller bore should be perfectly fine.

 

[CFLBob]

It's always easiest to size a piston to a bore size rather than the other way round. At least that's what I find. As it can be very difficult to measure a bore to a high level of accuracy (precision is easy, accuracy is much harder) you cut your bore then when you get close to size as you're turning the piston, you can test fit it to the bore while it's still mounted in the lathe. And I don't see 0.020" making much power difference to the engine so the slightly smaller bore should be perfectly fine.

Thanks. I was thinking that was the right way to go.

I have experience with one engine, a wobbler, and with that one, I cut the piston (12L14) and hand fit the cylinder onto the piston, like you say.

 

[jchevy]

When I built this engine I found the best material for the piston was graphite.

 

[el gringo]

When I built this engine I found the best material for the piston was graphite.

I have built three engines of this type and graphite pistons give excellent results. Self lubing also.
Ray M

 

[CFLBob]

When I built this engine I found the best material for the piston was graphite.

The piston has a hole in the middle of the top. It looks like it's threaded for the wrist pin but I don't see where he calls out the thread, just that it's a #29 drill. I think that's 8-32? Can you tap graphite?

 

[CFLBob]

I have built three engines of this type and graphite pistons give excellent results. Self lubing also.
Ray M

Three? I'd love to see some pictures of them.

 

[jchevy]

The piston is drilled and countersunk for a flat head screw , the screw attaches to another part inside the piston which the wrist pin attaches to . I hope this makes sense .

 

[CFLBob]

It makes sense, I just don't see it in the book. It looks like the pin is threaded and either screws into the piston or that nut on the side?

 

[el gringo]

Three? I'd love to see some pictures of them.

[ame]https://www.youtube.com/watch?v=FhfXnPnCidM[/ame]

[ame]https://www.youtube.com/watch?v=dd-Ytq-OJ5k[/ame]

[ame]https://www.youtube.com/watch?v=GMqkD0Bua28[/ame]

[ame]https://www.youtube.com/watch?v=MIxq9sohs9c[/ame]

 

[Brian Rupnow]

I have the same book and the same article. The threaded portion of the "wrist pin yoke" goes right thru a hole in the piston and gets a #6-32 nut on the far side of the piston. The nut is setting there in the picture you posted, and there is one #6-32 nut called up in the bill of materials. A #29 drilled hole is 0.136" diameter. A #6-32 thread is 0.136" diameter. It'll go thru if you hold your breath.---Brian

 

[jchevy]

I guess I tapped the part that holds the wrist pin and used a screw to hold the piston on for what ever reason , both ways should work .

 

[CFLBob]

https://www.youtube.com/watch?v=FhfXnPnCidM

https://www.youtube.com/watch?v=dd-Ytq-OJ5k

https://www.youtube.com/watch?v=GMqkD0Bua28

https://www.youtube.com/watch?v=MIxq9sohs9c

Very cool. I like your modification to the support pedestal on the Duclos engine. Mine seems like it should press on, although I haven't tried to press it on in case I can't get it back off. That's tomorrow or the day after. I might need to do this.

I've had troubles boring the cylinder that deep. It's like my 8-12x20 lathe isn't rigid enough and something keeps moving. The tailstock has slid and the QCTP has rotated around its mount on the cross slide.

 

[Cogsy]

Can you tap graphite?

I have a tapped graphite piston in my Ridders internal valve flamelicker and it holds just fine, but it's a fairly slow revving engine and I don't know if it would at high RPM like I've seen some Duclos engines run.

 

[el gringo]

"I've had troubles boring the cylinder that deep. It's like my 8-12x20 lathe isn't rigid enough and something keeps moving. The tailstock has slid and the QCTP has rotated around its mount on the cross slide."

what are you using for a boring bar?

 

[CFLBob]

"I've had troubles boring the cylinder that deep. It's like my 8-12x20 lathe isn't rigid enough and something keeps moving. The tailstock has slid and the QCTP has rotated around its mount on the cross slide."

what are you using for a boring bar?

Nothing special. Something like this Little Machine Shop set.

It has made me want to get something more like a larger diameter bar with a replaceable carbide insert. The small shaft to the end with the brazed carbide head on what I have seems more likely to allow flex.

 

[el gringo]

I would use the larger 5/8 shank....works for me.
A little nose radius on that type helps also.

 

[CFLBob]

Agreed. This is the first time I've bored something this size, it's both larger diameter and deeper than anything I've done before. I'm using the tools on hand rather than buy new ones, and I got the boring bars back when I got the lathe from Little Machine Shop. The biggest QCTP holder I have is for a 1/2" boring bar.

I don't really know how to measure to see if it's tapered with anything I have on hand, other than to try to turn a cylinder of a close diameter and see if it wants to get stuck. Seems risky.

 

[el gringo]

When I built this engine I found the best material for the piston was graphite.

I don't really know how to measure to see if it's tapered with anything I have on hand, other than to try to turn a cylinder of a close diameter and see if it wants to get stuck. Seems risky.[/QUOTE]

Inside calipers?

 

[CFLBob]

Inside calipers?

Don't have any with 2.5in inside jaws. A search for calipers with long jaws only showed long outside jaws.