Basic 2 stroke engine help

[isaiah lowe]

Looking to make a 3 cyl 2 stroke scaled down snowmobile engine design with a few questions!

- bearings? Will it get enough lubrication with a sleeve Or shall I try find a needle bearing small enough?

- new to machining just bought a small mill and metal lathe I have been on here for quite some time in interest and am just getting started up now! can someone point me in the direction of some basic machining skills that would help me for making an engine

-spark plugs !
Can I make my own spark plugs from a turned down bolt would love to know what people have used for insulators that will withstand pressure and heat

- crankshaft seals
What do you use

 

[lohring]

What scale are you interested in? I have a lot of experience with 23 to 36 cc single cylinder engines. For an idea of what we've done see this article. These engines run tuned pipes and the 36 cc engine was dynoed at almost 12 hp with our modifications. In this size range there are a lot of stock parts to make your engine building easier. Look at this twin cylinder engine for an idea of what a 23 to 30 cc cylinder can make. The parts can be found at Dave's Discount Motors. I would be glad to make suggestions. A triple using these parts would only need a crankcase and crankshaft build. Both stock and aftermarket ignitions could be used with adapters. Below is the crankshaft center section from a twin. A triple would need two center sections. The crankshaft would need a jig to press the parts together. I've built these things for a twin.

A much smaller engine could also be built. Below is a twin with 3.5 cc cylinders. It has a drum valve induction system and glow ignition. Again, using stock piston and cylinder liners with matching cylinder heads will make the build much easier. Then there are the various Cox engine builds. This is a thread on some of the possibilities.

Lohring Miller

 

[isaiah lowe]

What scale are you interested in? I have a lot of experience with 23 to 36 cc single cylinder engines. For an idea of what we've done see this article. These engines run tuned pipes and the 36 cc engine was dynoed at almost 12 hp with our modifications. In this size range there are a lot of stock parts to make your engine building easier. Look at this twin cylinder engine for an idea of what a 23 to 30 cc cylinder can make. The parts can be found at Dave's Discount Motors. I would be glad to make suggestions. A triple using these parts would only need a crankcase and crankshaft build. Both stock and aftermarket ignitions could be used with adapters. Below is the crankshaft center section from a twin. A triple would need two center sections. The crankshaft would need a jig to press the parts together. I've built these things for a twin.

A much smaller engine could also be built. Below is a twin with 3.5 cc cylinders. It has a drum valve induction system and glow ignition. Again, using stock piston and cylinder liners with matching cylinder heads will make the build much easier. Then there are the various Cox engine builds. This is a thread on some of the possibilities.

Lohring Miller

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Wow cheers dude wasn’t expecting a reply like this that helps a lot!!!

 

[kf2qd]

Have you built a single cylinder 2 stroke? For a 3 cyl, you will be building 3 single cylinder units on a common crakshaft, each section must be sealed from the others and have its own induction port.

 

[Cogsy]

Spark plugs are relatively easy to make. I use Corian as insulator material (acrylic kitchen counter top off cuts) and sewing needles as electrodes. No need to use a bolt as a starting point, you can make them from round bar. I make mine with an M6x1 thread.

 

[isaiah lowe]

Thank you!

 

[isaiah lowe]

where can i find a needle bearings like the one above in the two cylinder that splits into 2 as id like to make the crank one piece

 

[lohring]

Wow cheers dude wasn’t expecting a reply like this that helps a lot!!!

Have you built a single cylinder 2 stroke? For a 3 cyl, you will be building 3 single cylinder units on a common crakshaft, each section must be sealed from the others and have its own induction port.

My twin uses a single crank pin and is an alternate firing opposed twin with a balance shaft. Below is the picture with the seal ring in place.

Lohring Miller

 

[isaiah lowe]

My twin uses a single crank pin and is an alternate firing opposed twin with a balance shaft. Below is the picture with the seal ring in place.

Lohring Miller
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Okay I may make a 2 cylinder seems heck of a lot easier but I’m curious why it needs to be sealed if both cylinders fire at same time on your model ? Also will the ring have a bit of bypass for oil so it’s not metal to metal on the crankcase

 

[lohring]

They are horizontally opposed and fire alternately. There would be no change in crankcase volume as the crankshaft rotated.

Lohring Miller

 

[Cogsy]

where can i find a needle bearings like the one above in the two cylinder that splits into 2 as id like to make the crank one piece

Bearing supply places like SKF, etc. will be able to get them for you, but they're not going to be cheap. Also, the shaft and housing will need to be hardened (and ground ideally). If either of them is left soft, the bearing will destroy the housing, the shaft and itself in very short time.

 

[nel2lar]

Lohring
Is it very hard to synchronize the carbs on the little wonder? Beautiful engine.
Nelson

 

[isaiah lowe]

Bearing supply places like SKF, etc. will be able to get them for you, but they're not going to be cheap. Also, the shaft and housing will need to be hardened (and ground ideally). If either of them is left soft, the bearing will destroy the housing, the shaft and itself in very short time.

I have bought some one piece needle bearings because they were cheap hoping I may be able to get away with splitting into 2 pieces with a dremel I’m looking into doing a small scale about the size of a model airplane engine so not sure if they would have split ones that size ?

 

[nel2lar]

Isaiah
It is an idea but it will never work. The size of the bearing and the cage are made to be a unit. You cut on it you will more than likely ruin the bearing.
Nelson

 

[lohring]

Bearings and other partsfor the pictured twin are available at these links.
https://www.gizmomotors.com/index.p...-engines-and-parts/twin-needle-bearing-detail
https://www.gizmomotors.com/index.p...roller-bearing-kt-17-23-11-half-pair-1-detail
https://www.gizmomotors.com/index.php/online-store/gzr-rcmk-inline-engines-and-parts

Lohring Miller

 

[isaiah lowe]

Bearings and other partsfor the pictured twin are available at these links.
https://www.gizmomotors.com/index.p...-engines-and-parts/twin-needle-bearing-detail
https://www.gizmomotors.com/index.p...roller-bearing-kt-17-23-11-half-pair-1-detail
https://www.gizmomotors.com/index.php/online-store/gzr-rcmk-inline-engines-and-parts

Lohring Miller

Thanks been searching everywhere

 

[isaiah lowe]

Seals for end of crankcase any recommendations what to use?

 

[lohring]

The standard end seals for these engines are available here. I'm not sure what the center section seals are but they look like o-rings. The small diameter one goes on the flywheel end. All assume that the shaft diameter is 12 mm. I have no experience with the pictured twin so I don't know what its crankshaft diameters are.

If you are serious about this size engine (23 to 30 cc per cylinder), I would put together a twin from existing components first. People have had issues with the stock twins center sections having too little clearance. Gizmotors sells crankcases with this problem fixed. Otherwise I would encourage you to build a Cox based triple (easiest) or a fully custom built 3.5 cc per cylinder engine that uses as many standard parts as possible. The high precision parts are the piston, liner, and crankshaft. The multi cylinder Cox engines and the pictured engine gets around the center bearing issue with a multiple piece crankshaft and plane bearings. Below are 2 exploded pictures of the hex 4. A triple could be similar with different valve timing and crank pin locations.

Lohring Miller

 

[lohring]

The standard end seals for these engines are available here. I'm not sure what the center section seals are but they look like o-rings. The small diameter one goes on the flywheel end. All assume that the shaft diameter is 12 mm. I have no experience with the pictured twin so I don't know what its crankshaft diameters are.

If you are serious about this size engine (23 to 30 cc per cylinder), I would put together a twin from existing components first. People have had issues with the stock twins center sections having too little clearance. Gizmotors sells crankcases with this problem fixed. Otherwise I would encourage you to build a Cox based triple (easiest) or a fully custom built engine that uses as many standard parts as possible. Cox parts are available here while a little larger engine is available here. You need a cylinder tap if you build custom Cox engines. Buying complete engines can be less expensive than buying parts. The high precision parts are the piston, liner, and crankshaft. The multi cylinder Cox engines and the pictured engine gets around the center bearing issue with a multiple piece crankshaft and plane bearings. Below are 2 exploded pictures of the hex 4. A triple could be similar with different valve timing and crank pin locations.

Lohring Miller

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