I’m helping a friend with a headless Witte model. Has way too much compression and I’m looking to get the dimensions or a snippet of the drawing of the piston to see how to modify it to reduce the CR. Apparently pistons/kits for this were sold by DeBolt but I don’t see it on his current web site?? He lives several hours from me and this is sort of a surprise for him. He also told me that the kit was offered with pistons for two compression ratios...I’ve seen the two engines with the high and low CRs and both are too high for my liking. Don’t want to violate any copyright concerns so please pm me the portion of the piston from the drawing set. Plan is to make it out of aluminum. Any help appreciated.
Witte headless model, 2” bore, piston dimensions needed
- Thread starter myrickman
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Contact Paul directly by phone or email. He's a stand up guy and if it is one of his kits, he will get you what you need.
DEBOLT MACHINE, INC.
4208 West Pike
Zanesville, OH 43701
Phone: 740-454-8082 e-mail: [email protected]
DEBOLT MACHINE, INC.
4208 West Pike
Zanesville, OH 43701
Phone: 740-454-8082 e-mail: [email protected]
The only thing you can do is cut something out of somewhere.
You can increase the combustion chamber size but in a model that is assembled and ready to run that may not be an option.
You cam re-machine the top of the piston but ring grooves being where they are that may not be an option
You can make a new piston with the wrist pin higher on the piston. That will move the top of the piston down in the bore.
You can make a shorter connecting rod. That will also move the piston down in the bore.
You can re-time the cam so the exhaust valve closes later. That will delay the intake of fuel so there will be less to compress.
Shorter rod may be the best option. You can make big changes and usually a connecting rod is easy to make if it's not too fancy.
You can increase the combustion chamber size but in a model that is assembled and ready to run that may not be an option.
You cam re-machine the top of the piston but ring grooves being where they are that may not be an option
You can make a new piston with the wrist pin higher on the piston. That will move the top of the piston down in the bore.
You can make a shorter connecting rod. That will also move the piston down in the bore.
You can re-time the cam so the exhaust valve closes later. That will delay the intake of fuel so there will be less to compress.
Shorter rod may be the best option. You can make big changes and usually a connecting rod is easy to make if it's not too fancy.
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Don't forget that the piston is exposed at BDC so any changes you make, other than skimming the top, will move the skirt further out of the bore. You may be able to reduce the piston skirt length to compensate. It might be a good idea to lay it out in cad with the various options before removing any metal.
So my friend dropped off the Witte model and I was able to get some measurements. Originally the head space was a tad over 1/2” and the stock piston was about 2.8” long. So according to my calcs, the CR was near 5:1 ! I was able to make a 2” long piston and cut down to two rings. The head space was now nearly 0.9” and new CR at about 3:1. Instead of the skirt sticking out about 0.7”, it now sticks out 0.35”. What a difference in running. Easy to start and can be slowed down much more. The new piston is about half the weight of the iron one.
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That's a much better piston design and material choice.
Nice work.
Chuck
Nice work.
Chuck
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