Atkinson frustrations

[bluejets]

Is this the single cylinder engine i.e. not the opposing piston type?

I built one of these years ago and it works fine.
Mate of mine knocked up some castings for the barrel, head, uprights and conrod, the rest is machined.
Very touchy on the fuel needle so once set I leave it be.

Also plug can get fowled up easily so I up-ed the voltage on the coil to 12v and works fine now.

Fuel is just unleaded petrol with around 5% oil. Have tried methanol as well with castor, seems much the same.

This next bit is a mystery to me....perhaps the inlet could be a poppet valve but the Exhaust????

Due to the design of the intake and exhaust valves there is a very short part of the stroke between exhaust and intake. Both valves are atmospheric operated, that is no mechanical opening, only exhaust pressure and intake vacuum opens the valve

There should be a video of my engine on youtube somewhere, see if I can find it and put in a link.

 

[Ramoye]

Is this the single cylinder engine i.e. not the opposing piston type?

I built one of these years ago and it works fine.
Mate of mine knocked up some castings for the barrel, head, uprights and conrod, the rest is machined.
Very touchy on the fuel needle so once set I leave it be.

Also plug can get fowled up easily so I up-ed the voltage on the coil to 12v and works fine now.

Fuel is just unleaded petrol with around 5% oil. Have tried methanol as well with castor, seems much the same.

This next bit is a mystery to me....perhaps the inlet could be a poppet valve but the Exhaust????



There should be a video of my engine on youtube somewhere, see if I can find it and put in a link.

 

[Ramoye]

This is the engine with opposing pistons in one cylinder. It has been a challenge to get it to run! I have tried everything I can think of. Decided to make a new cylinder from stock 1.125 inch I.D. No boring and brazing, which I hope will make a better cylinder. Will need to make new pistons, piston rods, and rings.

 

[Ramoye]

Gordon,
My piston rings could be suspect, but they do seal well in certain locations of the cylinder when applying pressure. I can wiggle the flywheel and hear them seat.
Had a good day today, for the most part. With the cylinder raised 1/16 of an inch (used a 9/32 drill bit as a height spacer from the base plate to the bottom of the cylinder attach plate (2x3 inch plate), changing to 1 7/16 links on both sides, and advancing the spark, I am getting consistent and strong pops (best run-in to date). Still not enough to run on its own, but getting close. Had an issue with the set screw coming loose (the threads in the aluminum oscillating arm wore out) on the right oscillating arm to piston rod, allowing the pin to come out and contact the cylinder. No damage though (got lucky). I fixed it by drilling a 1/16 hole through the piston rod ear and pin, then using safety wire to secure it (worked well and I don't ever have to worry about that pin coming out again). Will come up with something more professional looking once I get the engine running.
Tomorrow, I plan on raising the cylinder some more to reduce the piston rod angle (hopefully it will help with piston ring sealing, and gain more power). I will need to slot my cylinder mounting holes some more to accomplish this. I will raise it to the point where the two pistons just about touch using the two 1 7/16 links. Reducing the piston rod angle is really helping.
I have used the same connecting piston rods throughout the project, but used various lengths of link arms to adjust the port clearances, as well as moving the cylinder around. For the rings, I built a fixture to put the rings in and placed them in my foundry for heat treating (heated fixture and rings to barely red hot, then allowed them to air cool). I did a final machining (after heat treating) of the rings using a fixture similar to the one in the book. My rings are made from cast iron. My rings have about 1 to 2 thousandths side wall clearance in the piston groove. I may be too deep on the groove depth (about 0.012" in addition to the ring thickness). I hand filed the gap to just barely go into the cylinder when compressed. The first set of rings I made was a learning curve. The second set of rings I made was used initially, but I felt the gap was too much, so I made a third set I am currently using. The piston rings should be tight enough to seal with hand starting. I have tried varying the electric motor speed to see if it helped anything with the running of the engine, but did not seem to make any difference. Ray

Gordon, I raised the cylinder today from 9/32 to 11/32 from the bottom of the cylinder mounting plate to the base. Ran worse. Dropped to 5/16 and saw some improvement, but not as good as 9/32. I have decided to pull the plug on this cylinder, piston, ring combo. Got my cylinder material in yesterday, so will start on a new cylinder and pistons. Should be able to buy 1.125 rings at a reasonable cost. For my current cylinder I.D. (1.167), I could not find rings so had to make some rings for myself. Having any success on your engine? Ray

 

[Gordon]

Still no luck. I thought that I had found the problem. There was air leaking around the spark plug boss. I smeared JB Weld on the joint to see if that fixed the problem. It fixed the leak but still would not run. It would fire occasionally but would not run. My bore is 1.128 and I made the rings and pistons accordingly. I do not understand why the rings seem to have a descent seal when I put air in the cylinder but they do not seem to generate pressure when it is rotated. I am making new linkage arms at 1 1/2 C/C which raises the whole assembly. Not sure about your theory of angular pressure on the piston. A lot of engines have a rather steep angle on piston to connecting rod. If I raise it much more I am going to have further problems with the top of the intake valve stem hitting the oscillating arm. I already have whittled out a big chunk of the arm.

I have turned over the engine about 3 hours on the latest set of rings and the rings are not polished all the way around the circumference. The latest rings have about .0015 side clearance and about .002 gap. Any self respecting engine should be showing some cooperation with those characteristics.

I have run into two problems with the design which I find strange because so many others have made this engine and no one else has remarked about it. The hole where the pivot pin goes through the oscillating arm is not really clearly specified. It is not at the center of the radius and I think that I guessed wrong. Also as stated above the intake valve stem interferes with the oscillating arm.

Gordon

 

[Ramoye]

Still no luck. I thought that I had found the problem. There was air leaking around the spark plug boss. I smeared JB Weld on the joint to see if that fixed the problem. It fixed the leak but still would not run. It would fire occasionally but would not run. My bore is 1.128 and I made the rings and pistons accordingly. I do not understand why the rings seem to have a descent seal when I put air in the cylinder but they do not seem to generate pressure when it is rotated. I am making new linkage arms at 1 1/2 C/C which raises the whole assembly. Not sure about your theory of angular pressure on the piston. A lot of engines have a rather steep angle on piston to connecting rod. If I raise it much more I am going to have further problems with the top of the intake valve stem hitting the oscillating arm. I already have whittled out a big chunk of the arm.

I have turned over the engine about 3 hours on the latest set of rings and the rings are not polished all the way around the circumference. The latest rings have about .0015 side clearance and about .002 gap. Any self respecting engine should be showing some cooperation with those characteristics.

I have run into two problems with the design which I find strange because so many others have made this engine and no one else has remarked about it. The hole where the pivot pin goes through the oscillating arm is not really clearly specified. It is not at the center of the radius and I think that I guessed wrong. Also as stated above the intake valve stem interferes with the oscillating arm.

Gordon

Gordon,
Seems like your bore and ring fit is spot on. I had to grind my oscillating arm as well to get the intake valve stem to fit, as well as chamfer the piston rod edges to clear the cylinder. I thought my piston rod angle theory might be correct after I raised the cylinder to 9/32 and it was running better, but raising it more made it worse, so maybe my theory is not correct. I still have leakage past the piston rings at the far ends of the cylinder (could just be the cylinder is a bit banana shaped from brazing heat warpage). My rings are shiney all the way around, but there is a small area (1/4 inch) on the circumference where it is shiney across part of the width (rings could be a tad out of round). I bet I have put close to 200 hours on this engine in trying to get it to run.

I know what you mean about the oscillating arm/piston rod pivot hole. The drawing was not clear. I noticed the pivot bar hole location in the frame assembly (for the oscillating arms) was triple dimensioned, leaving me guessing on which dimension to use (note: I have cast the front and back panel twice now).

On your engine, have you tried squirting some heavy oil in the carb. to see if the rings seat better? To keep my engine firing I have to occasionally squirt some oil in the carb. (downside is a fouled plug, requiring frequent cleaning). With my cylinder/pistons/rings combo I cannot get it to produce enough power to run on its own, but it does fire with the electric motor (I think the increased speed of the electric motor overcomes the ring leakage enough for it to fire). The weird thing is that occasionally the engine will fire loudly (like a gun going off).

Tomorrow I will start on a new cylinder. I plan on making this one air cooled with fins. First, I need to spend some time tuning up my milling machine (cheap mini-mill which I do not care for much, but it gets me by). Ray

 

[mic]

hi
i made this engine a few years ago and had the same problems, finally worked out that the bore length was to long for the hone length. which made the bore not dead true and bypass of the rings, decided to find longer hones and gave up as cost to high for commercial, its sitting under the bench waiting
mic

 

[Ramoye]

hi
i made this engine a few years ago and had the same problems, finally worked out that the bore length was to long for the hone length. which made the bore not dead true and bypass of the rings, decided to find longer hones and gave up as cost to high for commercial, its sitting under the bench waiting
mic

I am starting to make a new cylinder with 1.125 I.D. DOM steel. I should not have to bore it, but just hone it. No brazing, fully machined (making it air-cooled with fins). On the cylinder I have been using, it warped on me during brazing (about .070 banana shaped). I pressed a slug through it while heating and was able to straighten it to .010 banana shaped. It was then bored, which came out to an I.D. of 1.167 (some clean-up from the slug being pressed through). I have wondered if maybe the boring bar tried to follow the banana shaped hole somewhat. Took measurements of the cylinder and measured no more than .002 over the 1.167 at any one spot the total length (before honing). I have also wondered if the hone stayed on the ends longer than the middle as it went back and forth. It was a fine stone brake cylinder hone you buy at the auto parts store. I am measuring a slightly bigger I.D. on the ends than the middle (after honing). Thanks for responding. Ray

 

[Gordon]

I have actually lapped the cylinder and I can not find any spots where the bore varies. I do not have any way to accurately check if the bore is parallel throughout the length. I actually used a piece of copper tube about a foot long and chucked it in the lathe. I then added lapping compound the that and ran it through the bore so I am pretty sure that the bore is a consistent diameter and straight. I do not have the precision equipment to check everything. I am using a snap gauge to check the bore but the readings are coming out consistent. It would seem like the bore would have to be quite a bit out of parallel to affect the compression as long as the bore was consistent diameter.

I am beginning to think that I am getting air leakage around where the various mounting bosses are brazed to the main cylinder tube. Yesterday I discovered that I had an air leak around the spark plug boss which was actually coming out around the cooling tube which indicated that I may actually be leaking into the cooling tube. I am thinking that the solution may be to make the whole cylinder assembly out of a solid piece of square stock so that no welding or brazing is required. I thought that by doing a rough bore about .010 under size , brazing, bore to about .001 under size, hone and then final lap would solve the fit problem. By doing a final bore to size after the brazing should solve any size or parallel problem.

I am going have one more try at making new linkage today. If that does not work the next step is to make one piece cylinder with integral mounting boss for intake, exhaust and spark plug.

Gordon

 

[mic]

we have the same problems, using a brake hone was the cause of my problems. the hone is to short for length of bore.if you used lapping compound on a long tube after using the brake hone it would take a fair bit of time to get all the bore dead true again, try using coarse then changing down to fine. use liquid soapy water around rear of pistons when try compression if bubbling, its rings or not true, rings will quickly get better if not its out of true.
mic

 

[Ramoye]

I have actually lapped the cylinder and I can not find any spots where the bore varies. I do not have any way to accurately check if the bore is parallel throughout the length. I actually used a piece of copper tube about a foot long and chucked it in the lathe. I then added lapping compound the that and ran it through the bore so I am pretty sure that the bore is a consistent diameter and straight. I do not have the precision equipment to check everything. I am using a snap gauge to check the bore but the readings are coming out consistent. It would seem like the bore would have to be quite a bit out of parallel to affect the compression as long as the bore was consistent diameter.

I am beginning to think that I am getting air leakage around where the various mounting bosses are brazed to the main cylinder tube. Yesterday I discovered that I had an air leak around the spark plug boss which was actually coming out around the cooling tube which indicated that I may actually be leaking into the cooling tube. I am thinking that the solution may be to make the whole cylinder assembly out of a solid piece of square stock so that no welding or brazing is required. I thought that by doing a rough bore about .010 under size , brazing, bore to about .001 under size, hone and then final lap would solve the fit problem. By doing a final bore to size after the brazing should solve any size or parallel problem.

I am going have one more try at making new linkage today. If that does not work the next step is to make one piece cylinder with integral mounting boss for intake, exhaust and spark plug.

Gordon

Gordon,
I had a cracked braze joint around the intake boss, I put J.B Weld around it, but it could still have a leak. Also, there seems to be a leak path on the bottom of the boss to the screw holes. Could be leaking around the valve body mount screw holes. I have decided to make a cylinder from one piece of metal. Bought a five inch long 1.375 OD 1.125 ID DOM steel tube. I plan on cutting flats (slots) in it for the valve assemblies to mount, tapping for the spark plug boss, and machining cooling fins. I will mount the cylinder by machining 1/2 inch flats (slots) on top and bottom of the cylinder and bolting 1/2 square bars to it (top and bottom). I will then weld the other end of the 1/2 square bars to a 2x3 (1/4 inch thick) flat plate that will be bolted to the front panel. I agree Gordon, brazing is not the way to go with this, too many chances for leakage via cracks and warpage. If cooling fins are not enough, can always connect a small DC electric motor to the battery to blow air over it (might have to make a cooling shroud out of sheet metal. We will get there eventually! Thanks Gordon. Ray

 

[Gordon]

Mic: I used a brake hone just to remove tool marks. Just for a short period of time. Then I lapped. A piece of copper tube just fit in the bore so I used lapping compound until the whole length of the bore turned freely and was polished the entire length.

Ray: I just ordered a piece of square cast iron to remake the cylinder. That will eliminate the air leakage around the various bosses which I feel is probably where I am loosing compression. There are other plans by Brooks Pendergrast which use that setup. I am quite sure that my cylinder bore is adequate and is straight. Are you sure that you have enough material on the tube to mill flats to mount the intake, exhaust and spark plug without encroaching on the bore especially at the mounting screws?

It is interesting how little the cylinder assembly moves to completely change the piston position at exhaust, intake and firing ports. About 1/32 seems to completely change the relationship.

Gordon

 

[Ramoye]

Mic: I used a brake hone just to remove tool marks. Just for a short period of time. Then I lapped. A piece of copper tube just fit in the bore so I used lapping compound until the whole length of the bore turned freely and was polished the entire length.

Ray: I just ordered a piece of square cast iron to remake the cylinder. That will eliminate the air leakage around the various bosses which I feel is probably where I am loosing compression. There are other plans by Brooks Pendergrast which use that setup. I am quite sure that my cylinder bore is adequate and is straight. Are you sure that you have enough material on the tube to mill flats to mount the intake, exhaust and spark plug without encroaching on the bore especially at the mounting screws?

It is interesting how little the cylinder assembly moves to completely change the piston position at exhaust, intake and firing ports. About 1/32 seems to completely change the relationship.

Gordon

Gordon,
I like how you lapped the cylinder with lapping compound and copper tubing. I think I will try that versus the brake hone with my new cylinder. My I.D. on the stock DOM material is measuring 1.118. I hope to lap an additional 0.003 to .oo4 off on the radius to give me a final I.D. of 1.125. I noticed in the book a design for a lapping tool. Does the copper tube work just as well? How long would it take to lap three to four thousandths off the radius?

Started machining my new cylinder today. My wall thickness is 0.375 inches. This allowed me enough material to cut a slot for the valve bodies. Gives me 0.231 thickness left to tap 6-32 (bottom tap) before encroaching the cylinder bore. Being steel, should give me enough threads to mount the valve body (I hope). I cut a 1/2 inch wide slot to attach a 1/2 square bar. I will weld the other end of the square bar to the 2x3 inch mounting plate. There will be a square bar on top and bottom of cylinder for mounting.

For the spark plug boss, I will machine male threads on the outside of the boss, female threads for the cylinder, then screw the boss into the cylinder. I will coat the threads with J.B. weld before screwing into the cylinder. Inside of the boss will be tapped for the 10mm spark plug.

Thanks Gordon. Ray

 

[Gordon]

Ray:
If you have 3/8 wall thickness then it probably will be OK. You said previously that you had tube which was 1 1/8 ID x 1 3/8 OD which would only give you 1/8" wall thickness.

If you are going to take .003 to .004 by lapping I would estimate that you would have 1 to 2 hours but I am not sure. It would depend on how coarse the compound would be. Some folks seem to use diamond compound which cuts much faster. Others advise against diamond compound because diamonds are forever and would get embedded in the cylinder wall.

Gordon

 

[Ramoye]

Ray:
If you have 3/8 wall thickness then it probably will be OK. You said previously that you had tube which was 1 1/8 ID x 1 3/8 OD which would only give you 1/8" wall thickness.

If you are going to take .003 to .004 by lapping I would estimate that you would have 1 to 2 hours but I am not sure. It would depend on how coarse the compound would be. Some folks seem to use diamond compound which cuts much faster. Others advise against diamond compound because diamonds are forever and would get embedded in the cylinder wall.

Gordon

Gordon,
My mistake, the O.D. of my tube is 1.875 (0.375 wall thickness). I drilled a mounting hole for the intake valve body this morning, 0.170 deep (still have 0.051 before encroaching on the cylinder bore. Waiting on a 6-32 bottoming tap I ordered. The valve body fits nicely in the 1.0 inch wide slot. Dimensionally, the valve bodies should fit the new tube at the same position as when it was mounted on the brazed boss of the old cylinder. Only difference is that the valve bodies are mounted in a recess vs. on top of a boss that was brazed to the top of the cylinder.

I assume your cooper tube was not expandable for lapping? If not, did you have problems first turning the tube with the lapping compound on it? I have both a course and fine lapping compound.

Ray

 

[Gordon]

Ray:
I had two pieces of copper tube. The standard thin wall copper was a couple of thousands undersize and the heavier wall was right on 1.125 so I started with the thin wall tube and then went to the thicker wall piece. I guess go visit a plumbing supply with your micrometer. I got the thin stuff from Lowes and the heavier stuff from a plumber friend who had it in his scrap pile. I started with the bore about .001 to .002 oversize and lapped it to about .003 oversize. I started by trying to make the lap as shown in the book and found that the thin wall stuff was not working well so I went to my friend and got a heavier piece and discovered that I could just insert the whole 12" length in the cylinder.

Gordon

 

[Ramoye]

Ray:
I had two pieces of copper tube. The standard thin wall copper was a couple of thousands undersize and the heavier wall was right on 1.125 so I started with the thin wall tube and then went to the thicker wall piece. I guess go visit a plumbing supply with your micrometer. I got the thin stuff from Lowes and the heavier stuff from a plumber friend who had it in his scrap pile. I started with the bore about .001 to .002 oversize and lapped it to about .003 oversize. I started by trying to make the lap as shown in the book and found that the thin wall stuff was not working well so I went to my friend and got a heavier piece and discovered that I could just insert the whole 12" length in the cylinder.

Gordon

Thanks Gordon. Talking about copper wall thickness from Lowes, I had to replace a valve in my house and bought a copper coupling to solder the pipes together, but the Lowes coupling would not fit my thicker older copper house plumbing. I had to sand and sand the I.D. to get it to fit. What should of been a minute job turned out to be 30 or 40 minutes because of that coupling. Ray

 

[Gordon]

The different thickness of tube is supposed to be in the ID. The OD is supposed to be the same. Needless to say commercial copper tube is not precision stuff. You may have to measure them to get the right size to fit your bore. Your bore is quite a bit under size so you may have to split a piece to get down to your initial diameter then change to a stock piece. I just purchased an Acro lap from KBC for $22 so you cannot do a lot of playing around with the home brew stuff.
Gordon

 

[Ramoye]

The different thickness of tube is supposed to be in the ID. The OD is supposed to be the same. Needless to say commercial copper tube is not precision stuff. You may have to measure them to get the right size to fit your bore. Your bore is quite a bit under size so you may have to split a piece to get down to your initial diameter then change to a stock piece. I just purchased an Acro lap from KBC for $22 so you cannot do a lot of playing around with the home brew stuff.
Gordon

Not sure what the deal was with the Lowes coupling, but I had to do a lot of hand work to make it fit. Maybe my housing tubing was out of round where I cut it. Soldered up nicely without any leaks though. That was a couple of years ago.

Sounds like $22 well spent. I will check it out.

Thanks Gordon.

Ray

 

[Ramoye]

The different thickness of tube is supposed to be in the ID. The OD is supposed to be the same. Needless to say commercial copper tube is not precision stuff. You may have to measure them to get the right size to fit your bore. Your bore is quite a bit under size so you may have to split a piece to get down to your initial diameter then change to a stock piece. I just purchased an Acro lap from KBC for $22 so you cannot do a lot of playing around with the home brew stuff.
Gordon

Gordon,
I looked up the Acro lap on the KBC site. It states the lap will expand 15%. When they say a barrel lap is a 1 1/8, does that mean it expands from 1 1/8, or do they mean max expansion is 1 1/8? Not sure if I need a 1 1/16 or 1 1/8?