ADA: Ask Doc Anything!

[DocsMachine]

Is it possible to freak bore a PMI trracer barrel? Not sure there is enough meat on it... if not, any other option?

-I seem to recall, no, but it's been a while and can't recall exactly why. The two usual culprits are the breech hood or barrel thread being too shallow, and in the case of a Trracer, that snp-ring groove for the pump stop might have been an issue. I'd check, but I don't have a Trracer on hand.

The other option I tend to recommend for various markers that need a 7/8" OD barrel to clear the pump (SL-68, Sterling, etc.) is find one of the new smaller-bore Phantom barrels, and have it rethreaded to fit.

Doc.

[Alexndl]

Is it possible to freak bore a PMI trracer barrel?

Not sure there is enough meat on it...

if not, any other option?

[DocsMachine]

What platform that car was built on?

-It's basically just a rebodied '77 Chevy Blazer. 4-bolt 350, Turbo 350 trans, NP203, 14-bolt with a Detroit in back, and a D44 up front. It's loud and rattly, but I also put 16,000 miles on it.

And, if I ever have the time, money and workspace (triple-HA!) I have a 2014 GMC 2500 frame I'd love to mod and roll under it. 6.0L LS, 6L80E, NP208 I think, and the modern 11.5" rear. IFS, EFI, ABS, shift-by-wire, remote start, overdrive....!

All I need is the time, money and space to do it.

Doc.

[Edit- that pic is the original layout, that still had the 6-lug 44 in front and the 12-bolt in the rear- with it's broken Gov-Lok. I swapped engines and axles a few years later.)

[DocsMachine]

Doc, Can you send me back the 2 solenoids I shipped you? I have a guy here local that can machine the housings for me.

-Er, I already bought and cut the material, and spent quite a bit of time doing up some proper drawings.

And considering I invented it, and producing and selling products like this are literally what keeps my lights on and the cat fed, I'd appreciate the opportunity to complete the job.

Doc.

[Indeed]

Doc,

Can you send me back the 2 solenoids I shipped you? I have a guy here local that can machine the housings for me.

Thanks

[Alexndl]

What platform that car was built on?

[DocsMachine]

Porting a two-stroke does two things: First, in the conventional sense, it smooths and opens the passages to improve airflow into and out of the cylinder. The easier the flow, the faster and more completely the chamber can fill, and thus make more power.

This is simply done with small grinders to smooth and shape the inner passages. There's arguments on both sides about how smooth the walls should be, but generally speaking, you want some amount of roughness to help keep the fuel in suspension in the air. Too smooth and the fuel can fall out of suspension and "puddle" on the inner walls.

Second, porting can change the "timing", or how soon and how long the intake and exhaust ports open. In a two-stroke, if the intake port opens too soon, you lose energy from an incomplete power stroke. If it opens too late, you reduce the time the fresh charge has to fully fill the combustion chamber.

Exhaust timing is just as important- in a two-stroke, the bulbous exhaust pipe helps the exhaust pulse expand, and as it does so, it creates, for a few milliseconds, a slight vacuum, a lowered pressure area behind it. That helps draw the next fuel-air charge into the cylinder.

AND... the shape of the pipe as it contracts back down at the end, causes a sort of reverse pressure pulse, which is "timed" to arrive back at the exhaust port right when the cylinder is "full". That helps keep the air/fuel charge, or most if it, anyway, from escaping out the exhaust pipe.

This sort of thing can be changed by the same grinding techniques- but as grinding can only remove metal, you can only have the ports open earlier, close later, and stay open longer.

To actually move the "timing"- that is have the ports open later, close earlier or stay open a shorter time, you have to re-sleeve the cylinder, or in some cases get in there and weld the ports, and then re-sleeve or re-line the cylinder.

The only real drawback to all this, is that generally speaking, you won't add much HP, what you do is change the powerband- that is, where the peak HP happens. For something like a motocross bike, you need mid-high RPM power. For a weedwhacker, you need basically nothing but max RPM HP. For an off-road or dual-purpose bike, you want midrange or even low-end HP. Boosting midrange usually steals HP from the high end and vice-versa.

However, most 2-strokes, at least those in bikes, quads and jet skis, have a "power valve"- a sliding gate in the exhaust port that alters the timing by sliding up or down. That widens the powerband over a straight two-stroke.

Some engines will even have an intake valve of some kind- Skidoo used to have (or may still, I haven't kept up) a rotary valve. Basically just a shutter wheel, that gave more control over the intake charge than just reed valves.(Kind of a one-way flap valve used in a typical 2-stroke.) Combined with a good variable exhaust valve, that typically gave a usefully wide powerband- most often useful on snowmachines, that needed both low-end grunt for starting out, and high-RPM HP to keep on top of the powder.

That's a very short and highly summarized description- this is the kind of thing that can and has filled entire textbooks. I used to know a lot more of the minutiae back when I had a small fleet of bikes and quads...





But I'm pretty rusty on a lot of it these days. I'd sure like to have my old 250R back- that sucker kicked ass.

Doc.

[un2xs]

Explain in layman's terms what it means to port a two stroke. Why is it done. How is it done? I normally see it mentioned in regard to chainsaw engines.

[DocsMachine]

Doc,
Have you been able to make any progress on the led solenoid housing?

-Not yet. That's one of about five big 'to do' things on the workbench right now, but my current problem (at least with that particular project) is that I can't find my boxful of LED bodies. I know I have at least two, if not three, plus a fair fistful of parts. Thing is, I haven't needed that box since my TekAngel build...



And I think that was back in '15.

The box is around here somewhere, I just have to find it.

Doc.

[Indeed]

Doc,
Have you been able to make any progress on the led solenoid housing?

Thanks

[Brew]

-Sorry, Brew, I don't have a sister, and even if I did, she probably wouldn't like that kind of thing, anyway.



Doc.

🤣 Thank you Doc and have a Merry Christmas! 🎄☃️

Sent from my SM-G950U using Tapatalk

[Midnite-Penguin]

-No. Been there, done that, didn't even get a T-shirt.

On something like a 007, polishing can help- usually just consistency, but it helps. That's because the factory 007 hammer is unplated and relatively soft steel on unplated and relatively soft steel. That combo can wind up with a surprising amount of friction, though even that is minimized with a drop or two of oil.

In the Phantom, it's a hard nickel-plated hammer in an anodized tube- anodizing is thin, but it's surprisingly hard. Add a drop of oil here and you're looking at about the lowest coefficient of friction you can get, beyond some exotic materials or coatings.

And speaking of exotic coating, I've tried several of those, too- among others, I had a LAPCO hammer coated with a bake-on molybdenum disulfide dry-lubricant coating, and I had a Phantom hammer plated in titanium nitride. (The gold coating you see on drill bits and endmills.) Near as I could tell, they made no difference whatsoever. (The Tinitride hammer, by the way, all told cost me over $100, not counting shipping.)

The thing is, the hammer in a Nelson system is simply not stressed or cycled to the point where any kind of marginal gain by a special coating or polishing is going to gain you anything. It's like putting the wing from a drag racer on your Radio Flyer wagon- you're just never going to get enough airflow over it to do anything.

No, a far better use of your time would be to experiment with a spring kit, maybe different barrel bores (or inserts) and velocities. (One trick- if you're shooting 12-gram pump, consider how and where you play. If most of your shots are sneaky-backdoor close, think about dropping your velocity to 250-260 rather than 280-290. That can be worth another ball or two per cartridge.)

Doc.

Excellent information , I appreciate it. I like to play up close and personal, i feel like its the only way to be worth your weight while playing speedball with a stock-class marker, so I’ll experiment with lower velocity. Though i felt like 280 was a sweet spot compromise already.

To be honest unless I get shot off the break or get through less than a tube of paint im generally swapping in a fresh co2 regardless. Its hard enough playing SC vs semis without having your open shot at someones exposed back drop 20 feet short to save a buck 😂

I just like the idea of a finely tuned machine. Maybe ill pick up a spring kit.

thanks again.

[DocsMachine]

Do you think its "worth it" to try to polish the internals on a CCI Phantom?

-No. Been there, done that, didn't even get a T-shirt.

On something like a 007, polishing can help- usually just consistency, but it helps. That's because the factory 007 hammer is unplated and relatively soft steel on unplated and relatively soft steel. That combo can wind up with a surprising amount of friction, though even that is minimized with a drop or two of oil.

In the Phantom, it's a hard nickel-plated hammer in an anodized tube- anodizing is thin, but it's surprisingly hard. Add a drop of oil here and you're looking at about the lowest coefficient of friction you can get, beyond some exotic materials or coatings.

And speaking of exotic coating, I've tried several of those, too- among others, I had a LAPCO hammer coated with a bake-on molybdenum disulfide dry-lubricant coating, and I had a Phantom hammer plated in titanium nitride. (The gold coating you see on drill bits and endmills.) Near as I could tell, they made no difference whatsoever. (The Tinitride hammer, by the way, all told cost me over $100, not counting shipping.)

The thing is, the hammer in a Nelson system is simply not stressed or cycled to the point where any kind of marginal gain by a special coating or polishing is going to gain you anything. It's like putting the wing from a drag racer on your Radio Flyer wagon- you're just never going to get enough airflow over it to do anything.

No, a far better use of your time would be to experiment with a spring kit, maybe different barrel bores (or inserts) and velocities. (One trick- if you're shooting 12-gram pump, consider how and where you play. If most of your shots are sneaky-backdoor close, think about dropping your velocity to 250-260 rather than 280-290. That can be worth another ball or two per cartridge.)

Doc.

[Carp]

Sure....but, only if you use the tears from an Agglet as a rubbing compound, that and Leland 12 grams. 😋

[Midnite-Penguin]

Do you think its "worth it" to try to polish the internals on a CCI Phantom? I run back-bottle stock class and I'm looking to increase shots per 12gram.