jimmyjames213

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I'm lookin at building my own glow engine I have someone that can machine it for me I'm just wondering what materials I should use for the piston/liner I was hoping to keep it ringless (for reasons I won't explain) but I cont chrome it so what are my options? I'm guessing aluminum for the piston and either steel,brass or nickel for the liner, what would be my best option (if non of those what else could I use)
If ringless won't work w/ the given materials would a steel liner, aluminum piston w/ a ring be fine?

Motorboy

I am model engine builder,.. if you are using non ringed engine, select cast iron for piston and high tensile steel for sleeve. And the ringed engine, use same material as old piston from car engine. Melt the old piston and remove slag from melted material before pouring in a steel tube. Now you has a aluminium bar as piston material. And the sleeve are still made of high tensile steel and piston ring made of cast iron.

The important note!
The sleeve must be tapered to keep compression when the engine are cold if you are using non ringed piston.

How to check the fit are correct:
1. Dry sleeve and piston, the piston are tight in sleeve.
2. Oiled sleeve and piston, the piston are moving easy in the sleeve.
3. Check the piston are tight a little before TDC in the sleeve.

The Aluminium piston must be tapered calculated by expansion of aluminium when the working temperature are known (250-300 degree celsius in top of piston, 150-200 in wrist pin zone, 100-150 in end of piston skirt after my knowledge when i experienced the piston ran and locked in the sleeve without the piston was tapered when the engine was in working temperature).

The ring gap are between 0.001 mm and 0.02 mm depend on boring diameter and range of heat due expansion of ring by heat.

Never polish the sleeve as a mirror both in non ringed and ringed engine, it is to improve lubricating of the piston. It must be crossed lapped surface. The sleeve wall has a lot of hill and valleys to keep oil at place.

Both sleeve, piston and piston ring are lapped (aluminium piston are not lapped since it is not piston as a sealing materiale as a lapped piston will do it).

The piston/sleeve materal who i selected for my engines are best to run with castor oil 20-25% for non ringed engine and 18-20% for ringed engine.

Read this what i did: http://www.rcuniverse.com/forum/m_4929500/tm.htm

Visit the homepage: http://www.modelenginenews.org/

Edit: Wrote about oil..

TFF

I would build a ringed engine and use a ring from another design, so you dont have to make the ring( or have Bowman make them), but the machining of the piston and sleeve should be easer without the taper. Aluminum piston and a steel sleeve iron ring. Model Engine News is the place to learn; I read i at least once a month.

Kweasel

My Feedback: (29)

Look at a K&B 61, they solved the problems of using common industrial materials. Basically non hardened cranks require pressed on bearings and a hard crank pin. Bar stock pistons require more clearance and bronze bushings for the wrist pin just like the rod.

Sport_Pilot

I would go with a ringed engine. Get with Frank Bowman, he may be able to find a ring you need, and the proper dimensions for the ring groove, then buy the ring from him. Now you just have the sleeve and piston to worry about. To build a good cast iron piston you have to use a fine grain cast iron and it would be way heavy if you cannot machine it to very thin walls and crown. IMO it would be very difficult to machine.

blw

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That is an excellent link.

Motorboy

How do make own piston ring:

The ring formula: Bore/30 or Bore/25= ring tickness, Ring tickness = ring height, Tickness x 4 = ring gap

1. Turn to tupe are 0.1-0.15 mm bigger than bore.
2. lap the tupe to the tupe fit very very light press fit in bore. (Break-in the engine will make pistonring fit to bore and keep tight.)
3. Part off the rings where the thickness are a bit bigger than ring groove.
4. Grind the rings to fit the groove with plain fine hone stone + oil. Do not grind in one way or rotate, grind as in "8". The ring must rotate free in groove without play.
5. Break off the ring and add the spacer between ring gap who are measured ring thickness x 4 = ring gap.
6. Hold the ring between the two disc who are bigger than ring and thicker than 6 mm with bolt and nut in mid of disc.
7. Heat up the disc with ring inside to 500-600 degree celsius.
8. Let it cool down and dismandle disc and ring gap spacer, now you has a ring who are bigger than bore and can mount in bore. The ring will be elastic.
9. Adjust the ring gap with needle file.
10. The ring are ready to use. Mount piston ring careful in ring groove. The ring are brittle.

Ring can be made of cam shaft or brake disc, both are made of cast iron. Cast iron are not hard to machine compared to machine steel, cast iron are brittle than steel, but works very well as bearing against steel, less expansion when the engine are in working temperature.


How to make own lapped piston/sleeve:

Lets take a look at a typical lapping job - that of producing a fine finished bore and piston for an IC engine. In fact, piston and bore are both lapped in separate operations (NOT both together). All of these operations will be carried out in the lathe (and I need hardly mention the importance of keeping lapping compounds off the machine, particularly the chuck and slideways). For the bore an expanding lap is ideal, and this should be some 3-4 times the total length of the bore. The first grade of abrasive would be mixed with light machine oil (10W or lighter) and liberally coated on the inside of the workpiece. Similarly, the slurry would be added to the outside (and inside assuming it is of the ventilated type) of the lap. The lathe would be started at about 300rpm (for a nominal 1" bore) and the lap passed rapidly through the bore, keeping it moving back and forth without it coming out the bore. How to hold the lap? well, perhaps the best way is with a 'floating' tailstock holder, and failing this holding with the hand is a method as good as any. Be careful when holding the lap by hand as it's possible it may jam, hold it lightly and expect the unexpected. Remember also that unless the lap is maintained dead parallel with the bore (an almost impossible task) it will tend to bell-mouth the bore a little - hence the reason for making the work a little longer than finished size and trimming to length later. When the inside of the bore has achieved an all-over grey appearance, with the fine scratches appearing even and criss-crossing both ways, and with no evidence of any deeper scratches (as might be left by the reamer) it's time to move onto the next finer grade. The work will have to be removed from the chuck to clean it properly, and this should be done with clean paraffin oil followed by hot soapy water. The same procedure applies to the lap and all traces of the abrasive must be removed. The process continues until you reach the 'flour' grade of abrasive by which time the finish on the workpiece should be very fine indeed. A final polished finish, should this be deemed necessary, can be achieved using metal polish (diluted Autosol, or some liquid chrome cleaner). The lap should be a separate 'finishing' lap so there is no chance of contamination with the coarser grades of abrasive which might be embedded in the main lap. The piston is treated in a similar way except of course the lap is female. Work will continue with the coarse abrasive until (using the un-trimmed bore as a gauge) the piston will not *quite* enter the bore. At this stage finer grade abrasives are used and work continues until the piston will just enter the bore tightly. At this stage, it is usual to finish mating the two parts by using metal polish and briefly using the piston to lap the bore directly. Great care needs be taken but this method ensures that the fit is good for the entire length of the bore.


It is not strictly necessary to harden the crankshaft, use high tensile steel. The bearing can be aluminium , bronze, cast iron (in model diesel engine only) or ball bearing (need special tools to make precision and true between ball bearings).

jimmyjames213

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thanks for all the info, any more tips would help out a lot. asumb i know nothing and start from scratch if you want.

TFF

I like to look at what I can make out of what. Look at bolts like stainless; turned down to make valves. Car axel into a crankshaft. Like in Motorboy's thread, he melted down car pistons and cast into usable material. They are very high quality metals that when bought used can be had for pennies which is good when trying to figure things out. I collected about 10 titanium bolts from work over the years just waiting to be turned into something instead of going in the trash.

Aussie Maddog

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What about buying the piston/ring and making the sleeve. Pistons are relatively inexpensive and come with the piston pin and retainers ready for your rod.
For a novice, this maybe the way to go and you would have a better chance of a reliable running engine.
Make your own pistons later with the experience you have gained.

jimmyjames213

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ok so i bought a supertigre .51 to get measurements and see if i can make something similer. what am i going to screw up when i build my own engine? i know thats a big question but what is most likely to fail, im guessing the tolerance of the piston/ring/sleeve. what im asking is should i buy more rings? i would like to try and make my own piston thats can use the gs-51 rings more for the fun of it than anything.

my main concern is tolerance issues, im designing this engine on a CAD program then getting it cnc cut (well most of it) how much spaceing should all the parts have? such as rod on crank, rod on piston pin, ring to sleeve, ball bearings to crank case/ crank shaft(how hard would it be to steal the bearings from the gs-51 and use them? do ball bearings make it that much more complicated?)

i dont know much about metal expansion and whatnot so any advice on that would be very helpful
thanks

Motorboy

After all part are made in CNC, the parts need grinding/lapping to remove tool marks and the tolerance are not allways exact as original size of product made by factory. All fit and tolerances in engine are trimmed and adjusted by honing/lapping or reamer (not piston/sleeve) when you are making own model engine. The necessary to make fixed measure tool to measure the size of bore in crankcase before ball bearing are mounted with a right size of tolerance when you are using boring tool in the hole inside the crankcase. The other proplem are the ready make piston ring will not have right ring gap if the sleeve are home made due difficulties with tolerance.. The best solvent are to make the sleeve and lapped, then make the ring who are adapted for this sleeve and the ring gap are trimmed to right size.

The tolerance in hole in the con rod in two stroke engine are not critical, the clearance will be zero since there are allways force by compression and combustion at piston to keep the con rod pressed togheter with wristpin and crank pin in whole time. The crank shaft and main bearing has a running fit at 0.01-0.03 mm (my own experience).

Expansion not problem in the engine except the aluminium piston must be tapered in ringed engine to prevent locking the piston in sleeve by heat or the sleeve must be tapered in the ringless engine to keep compression when the engine are cold. The sleeve must have a light press fit in the crankcase cause the aluminium will expand more than steel due heat transfer will be bad if the sleeve was loose fit in the crankcase.