Davis Diesel 1/2A Parts

Ken Cook wrote:           Matt, I've been interested in a .020 diesel head if available. Please let us know. I would really like to know as to the whereabouts of the Jet-X Powermax units Bob had.

Hi Ken, there are definitely some 020 diesel parts. Looks like there are two different head types that were used over the years so I have to make sure all the parts are there to complete a head, but will set one aside for you.

Not sure on the JetX items, but will check.

Marleysky, I could always add a copy to the Instruction Sheets list on the forum.

About a dozen years ago, I bought out all the Cox parts and the shop junk box of a dying LHS. There was a DDD headed Pee Wee with a broken crank.
I called Davis for more info and fuel and mentioned the Pee Wee .020.
He strongly advised using his product an a Pee Wee and very strongly said never use a Davis head on a Tee Dee .020 !!!
I guess that's why he stopped production of .020 size DDD parts.
FWIW Steve...

Thanks to Rene, the Davis Diesel conversion manual is now available: https://www.coxengineforum.com/h24-instruction-sheets#related_docs

66 Malibu wrote:
He strongly advised using his product an a Pee Wee and very strongly said never use a Davis head on a Tee Dee .020 !!!

Yes, and that is because his heads are faulty.  

The counter piston is to thick and the compression ratio cannot be reduced enough. On top of that, the Teflon gasket doesn't seal well and there will always be small leaks there. So when turning the engine over one will not realise that the compression ratio is too high (even with the screw fully backed out) and if you manage to get a pop from the engine anyway, something will break...

The fix is to put the counter piston in a lathe and to remove about 0.1-0.2mm from its height. Next step is to throw those silly teflon gaskets away and use a sheet of brass instead (lasts longer than aluminium ones). With that you now have a head that seals well and the compression ratio can be adjusted low enough. With a good diesel fuel you only need a compression ratio that is slightly higher than on a glow engine, nothing more.

Here is an example of how the PeeWee runs with these simple mods, it spins a 6x3 prop at around 10krpm:

Surfer_kris wrote:

66 Malibu wrote:
He strongly advised using his product an a Pee Wee and very strongly said never use a Davis head on a Tee Dee .020 !!!

Yes, and that is because his heads are faulty.  

The counter piston is to thick and the compression ratio cannot be reduced enough. On top of that, the Teflon gasket doesn't seal well and there will always be small leaks there. So when turning the engine over one will not realise that the compression ratio is too high (even with the screw fully backed out) and if you manage to get a pop from the engine anyway, something will break...

The fix is to put the counter piston in a lathe and to remove about 0.1-0.2mm from its height. Next step is to throw those silly teflon gaskets away and use a sheet of brass instead (lasts longer than aluminium ones). With that you now have a head that seals well and the compression ratio can be adjusted low enough. With a good diesel fuel you only need a compression ratio that is slightly higher than on a glow engine, nothing more.

Here is an example of how the PeeWee runs with these simple mods, it spins a 6x3 prop at around 10krpm:

Agreed and I am going to run new tests under both brass and copper.