wvarn1957

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Since I had surgery in late March, I haven't been able to persue many of my normal activities. However, in searching for something to keep me busy I got this wild idea of trying to convert a "weedy" 2 stroke engine to diesel. I have a number of these engines I have converted for RC use ranging from 21cc to an 85cc chain saw engine. However, being basically very conservative, I didn't want to "sacrifice" one of my potentially good conversion engines. I had a well used 22cc MacCulloch engine from an edger which seemed to be a good candidate to be a "proof of concept" engine. I wouldn't have used it for a RC gasoline conversion anyway because of the relatively low power capability of these engines. What I wanted to see was if it was possible, mechanically, to convert one of these type of engines to diesel. There was a fair amount of machining involved, but the actual conversion of the cylinder/head/contra-piston was very easy. I haven't tried to run it yet, but probably will get it mounted and try this weekend.
If anyone has some suggestions on a fuel mix for an engine with needle bearings on the con rod I would appreaciate it.

If this works OK I will convert the 21cc Kioritz in the last picture. It is a much stronger engine.

AMB

Let us know how it goes with ball and needle bearings I would think
davis ABC fuel a good start,and all that ignition junk gone, will keep
the signals clean to the reciever look Ma no RF shielding needed
looks awsome should have a lot of punch martin

Hobbsy

My Feedback: (102)

WW, I pose this question on occasion, so far with no luck, I've been looking for years for a Maloney 125 conversion head, if you ever stumble across one please let me know, Thanks.

wvarn1957

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Hobbsy,

I saw a Maloney at a swap meet a coule of years ago, but it didn't have a diesel head. It seems that about the only diesels I see around this area are the small ones. Not many people run diesels, only one " old timer" like me in the Club. Two other clubs in the area have no one with a diesel. That said, If I ever run across a diesel head for a Maloney I'll let you know.

air mail rcu

wvarn1957, I very interested in the concept. Please let us know how everything works out

Where was the most mechining involved? I have a small lathe can all the work be done on that?

Oh by the way great job.[8D]

wvarn1957

My Feedback: (3)

Air Mail,

All the work was done on a Harbor Freight mini lathe and a drill press. If you are interested I'll e-mail you a detailed discription of what I did. Not that the way I did it is the only way, but it worked for me.

minipower

wwvarn1957, I too am very interested in what you have done. I've got the tools (lathe & mill) and an engine. Any details you can provide would be greatly appreciated.

Tom @ Buzzard Bluff

Add me to the list of those interested in the results of your experiment. How did it work? Is it a success in the eyes of the builder? Will you do another? Please give us all a report on your project good OR bad.
And add me to the list of those possessing the tools for the conversion who may be interested in the project depending on your progress report. TIA, Tom

wvarn1957

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Well, I wouldn’t consider the conversion to be a rousing success, but it did run. The choice of basically a worn out engine was, the primary reason that it didn’t run very well. The piston/cylinder clearance and a worn ring just would not seal well enough to raise the compression properly. I could only get enough seal for it to fire by running almost 40% castor oil and giving it a shot of pure castor before trying to start it. It was also had quite a bit of mechanical noise as the crank passed TDC. Again that was probably due to the worn condition of the engine. I am going to try it again, but with an engine that is in good shape.

I think the best chances for success are with an engine that has a two ring piston and is in good condition and runs strong on gas. The Walbro carb seems to work fine on diesel mix. I have an Echo 21cc that has new rings and seems to be a good candidate. The other choice is a 23cc Shindawa.

The first thing that I did was to turn a length of aluminum to the cylinder ID with about 2 thou clearance. I did this so I could chuck the rod tightly and put the cylinder over it. I didn’t want to chance trying to chuck the cylinder directly because it would not have been very secure. Since the Mac has a vertical spark plug, I used a boring bar and bored out the top of the cylinder until it was about 50 thou smaller than the regular cylinder bore. I didn’t want to take a chance on flaking or peeling the NiSil liner. Using a small diamond bit in a dremel I tapered the edge so that it would be smooth and wouldn’t catch on the contra piston. I then turned off the top fin and finished the outside of the cylinder wall.
I made the cylinder head from a piece of 2” round 6061 aluminum. I bored out the piece to the cylinder wall OD with 2 thou clearance. The depth was slightly (1/16”) less than the distance from the first fin to the top of the cylinder wall to allow clearance between the head and fin. I then bored the head an additional 1/8” to the same diameter as the top of the cylinder. Grooves were cut to make outside fins with a 3/64” parting blade.

The contra piston was turned from a piece of 1 ½” dia 6061 aluminum to a dia 2 thou less than the top of the cylinder. The height was 5/8” and two 1/8 inch grooves were cut for the viton “O” rings. The rings were 1” ID and 1/8” thick. The depth of the grooves was carefully cut so that with the O rings installed, the contra piston (well lubricated) would fit tightly in the upper cylinder bore.

The head was drilled for 8 6-32 allen head bolts and used as a guide to drill and tap the cylinder. If you have any additional questions, e-mail them to me and I’ll try to answer.

AMB

If it wil fit run a brake hone thru the cylinder and put in a new ring worth a try?? martin

Motorboy

Do not hone liner, it is thinn layer of NiSil at aluminiumliner, risk to peeling of NiSil from liner. Replace pistonring only. When running-in, pistonring will fit and make more tight.

Jens Eirik

capin

My Feedback: (11)

Here's my homelight 25 cc conversion that is getting ready to be completed now it run's . Hard to pull and no flywheel effect make it a bear but, it work's. Doubled the string so that mean's a bigger prop right!!!!!!! Sound's like my os 160 but muffeled better. Brian