Stirlingengineforum.com

I just snagged one of these cheap: http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... K:MEWAX:IT

And yes, I've read everything I could find about using a v-twin compressor pump as a starting point for an Alpha-type engine, and know it takes quite a few mods (but looks like it's all pretty basic stuff). Let's see if I can get one working.

Dave

Thanks Ian. From watching the Greenpower video's on this, I'm thinking it *might* seal well enough to just take the piston rings off and try that, we'll see. I'm not sure what materials this one is made from...it's black, so I'm hoping cast iron...the aluminum ones are usually silver, but I'll see when it gets here.

Btw, I remember seeing a post from you regarding friction coefficients of different materials...going to try to find that again and copy it as a new post...that one is worth having easy to find as a reference.

Cheers,
Dave

The Teflon plumber's tape is a good idea...thoughts on how to get it to stick in the piston groove?

Cheers,
Dave

OK, this compressor pump just came and I see what you guys mean. The flywheel is a stiff turn...wow! First I'll try removing the piston rings and see how much friction that alleviates.

I've heard it mentioned that the bearings need to be replaced with something lower friction...where are the bearings in question? I don't have time to fool with it right now, but just want to get a mental image of where I'm heading.

Dave

OK, got the cylinder heads off, cylinders off, rings removed...that helped, but still quite a bit of friction. Will try the teflon tape tommorrow. The piston arms seem to be pretty low friction, so I'll assume the bearings for the crankshaft are the next area to look. Any thoughts on what type of bearings and where to get them?

I'm assuming what I've got is essentially the twin cylinder compressor pump sold by Harbor Freight (although I snagged this off Ebay for much cheaper), so here's the manual for HF's compressor pump:

http://manuals.harborfreight.com/manual ... 698%20.pdf

The exploded view and parts list is what I was primarily looking for...presumably, bearings #43 and #51 are the ones I probably need to replace.

Cheers,
Dave

Try removing the seals off the bearings. This can have a big impact on some bearings, especially rubber sealed ones.

(no use for long term use though!)

Ian S C wrote:...Take the shields out of the inside side of the main ball bearing races and clean out the grease, lub with light oil. Ian S C

Do you mean try this with the existing bearings?

I've seen you suggest needle roller bearings before...is there some particular reason? Do they just tend to be lower-friction bearings?

Btw, the model I have is rated for 2hp input, but it appears to be pretty much the same as the 5hp model shown in the manual.

Cheers,
Dave

Not sure I know what "shielded bearings" are. What's in there for the crankshaft are bearings with balls inside of a small open frame, the frames touch each other but prevent the balls from touching each other (if that makes sense). It's open on the side I can see, so I can try cleaning the heavy oil out of it. It looks most like the first picture shown here for "ball bearing": http://www.ahrinternational.com/introdu ... arings.htm

Ian, I assume you are suggesting to replace both bearings with the type shown in the 2nd picture labeled "roller bearing".

I connected a high-torque drill to the flywheel bolt and it can spin the pump without too much difficulty...but friction still stops it quickly after I take the drill off.

There are no bearings on the connecting rod/crankshaft connection. There doesn't seem to be much friction there though (based on just moving the connecting rod with my hand while the cylinder is off). The connecting rods appear to be cast iron or cast steel, and the crankshaft appears to be cast iron or cast steel, with the section for the connecting rods machined to a smooth surface.

The pistons are indeed aluminum, it *looks* like the cylinders are cast iron/cast steel (it's hard to tell, they aren't that heavy though so possibly cast aluminum...I can check it with a magnet, just haven't done that yet). Btw, I tried putting teflon tape into one of the piston ring grooves, but that seemed to create more friction rather than lessening it. Regardless, I ran out of teflon tape, so I may try it again.

I'm going to look at Home Depot/Lowes/etc. for some 2" diameter pipe over lunch today and some longer cylinder head bolts (part# 4 in the exploded diagram in the manual linked above). The cylinders (part# 22) are 2" bore, so I'm thinking I can create the necessary airspace for the hot cylinder by cutting a section of 2" ID pipe and holding it in place between the cylinder and the cylinder head using 4 longer cylinder head bolts (looks like this should work nicely and it's pretty simple). Not sure how long to make this piece of pipe though, so I suppose I need to figure out how to do the calculations, eh?

I don't have a sufficient heat source for something this large that I can think of (again, need to find and do some calcs to see how much heat I actually need), so I'll see if I can pick up a propane torch or something along with the pipe over lunch today. I forgot to bring a cylinder head bolt with me, so I'll have to guess on the size and thread pitch (I'm thinking 3/8" and fine thread...unfortunately, it doesn't say in the exploded diagram)...I'll prob just grab some threaded rod and bolts, and cut it to whatever size I end up needing.

Just curious: Is there any such thing at Teflon spray lube that sticks to the surface and stays there?

Cheers,
Dave

davesisk wrote: Just curious: Is there any such thing at Teflon spray lube that sticks to the surface and stays there?

I'll answer my own question...yes, looks like Teflon spray is indeed available. Here's a link: http://www.sealfast.com/d_teflon_spray.html

Ahh...looks like something similar is available at Lowes...which one, the dry or the wet?

Dry (wax): http://www.lowes.com/pd_213197-39963-D0 ... t%3Dteflon

Wet (silicone): http://www.lowes.com/ProductDisplay?par ... &cId=PDIO1

Cheers,
Dave

The current flywheel is fairly heavy (cast iron/steel), but I think I can probably add some weight to it. Any guesses on how much weight?

I grabbed some dry graphite lubricant spray, and I've coated the aluminum pistons and walls of the cast iron/steel cylinders with that. I've also sprayed some degreaser on the crankshaft bearings and attempted to coat the crankshaft section where the connecting rods sit with the graphite dry lube (I think I'll have to disassemble more of it to do that probably though). It is now spinning with less friction, but methinks I've still got a ways to go on this.

The largest pipe I found was 2" OD rather than 2" ID, so my best bet is prob to just buy a piece of the right diameter tubing to attach between the hot cylinder and cylinder head. Which would be the best choice for that...aluminum, stainless steel, or mild steel? All are available. This is where the heat will be applied.

Davesisk, apparently in the UK the cans that 'Tango' soft drink comes in are made of stainless steel, James G. Rizzo collects them on visits from Malta. Ian S C

Ian S C wrote:Davesisk, apparently in the UK the cans that 'Tango' soft drink comes in are made of stainless steel, James G. Rizzo collects them on visits from Malta. Ian S C

Going to the store in a bit, I'll get some Tango to see :D

Hey Junkie, how did you get on at the store, do they have Tango, and what difference is there in the can, just querious, I ain't coming over to get one, its too far to walk. Ian S C

Ah....someone with a parallel project that mirrors my own.
I too am using the same 5hp compressor. My method is going to be is to de-stroke the crankshaft to a 30mm stroke instead of the stock 60mm. With the pistons falling short by 30mm, they will be capped with a 30mm graphite top with a teflon seal. The top piston ring on the stock piston will be nitrile rubber. (still sourcing the right size ring) The graphite should provide a certain degree of insulation and oil isolation as well as lubrication. As we all know, hot air + crankcase oil = boom. I intend to use helium, but will probably be stuck with nitrogen. I intend to run about 100 psi of pressure or more. I will use the normal crankcase piston displacement to pressurize the system as needed. I have no intention of defeating the splash-oiling system. The piston rings need oil in order to polish the cylinder during break-in and until I run full graphite pistons, it shall stay that way during my feasibility study on this design.
The biggest headache will be turning out a new crankshaft with my mini-lathe, but if I make it in pieces and weld it at work, it should be fine for the 1hp goal I am aiming at.
My research indicates that a 30mm stroke is the same as many automotive research stirling engines, and I am working within their research. Too bad I can't run at 2300 psi, but I am not equipped to produce castings and such. The guy on youtube really had no idea what he was doing when he tried using this compressor. Too lazy to do the research, I guess.
I am using the NASA MOD II stirling engine research paper to guide me.
The plumbing for this engine will be external to reduce thermal short-circuits and loss.
The big front bearing is a NBK 6307 (35mm I.D. x 80mm O.D. x 21mm wide)
The small rear bearing is a NBK 6304 (20mm I.D. x 52mm O.D. x 15mm wide)
The front oil seal dimensions are 35mm I.D x 55mm O.D. x 10mm wide
The front shaft is 35mm, and the tail end journal is 20mm
The connecting rod journal is 31.8mm diam. x 46.5mm long.
The front snout of the crankshaft tapers from 32mm to 35mm. (have the taper angle wrote down somewhere)
Piston compression height is 31.6mm. (center of piston pin to top of crown)
Connecting rods are 136.9mm center to center length.

Oh, just joined up recently, thanks to our fearless leader.
I work as a certified master mechanic for about 20yrs, and might be able to help things along.

vile fly, hi, sounds interesting, a bit worried about using piston rings, have you weakened them a bit, you only need the lightest pressure on the cylinder, maybe make rings out of teflon.
What sort of hot end are you going to use, and are you staying with air cooling. Ian S C