Davis diesel head improvement

Don't forget plumbing shop O-rings, as the standard rings last much longer than the original McCoy soft rubber rings. I've been using them in my McCoy .049 diesels for years. Mine use the size 10 rings which are an easy stretch over the McCoy contra pistons, but snap right into the groove, seal very well, and last a long time.

I bought my first McCoy .049 diesel in 1953, and I don't remember seeing O-rings used on any US diesel engines before then. The rings used were soft white rubber and shredded in just a few runs, so the head and contra piston had to be removed regularly to flush out the mush. I called McCoy to order more rings, but they insisted they would send me some just for the asking. The bag they sent lasted far longer than the engine was in my possession.

Bought several McCoy .049 diesels in later years, and haven't worn out any plumbing rings yet.

One precaution I would recommend for any diesel engine, is using care when installing the contra and new ring, so the ring is not damaged during installation.

Bill

okey i got my hardend shaft today
and i ran a engine on a 120ml tank
took over 40 min to drain it
it ran great
and it starts great

i have to change one or 2 things on the drawing and then i am calling it finished

I dont like the latest version of the head
I have been running it for a while now
but there are things I want to improve
wider oring groove
and the concave inside does make the engine run better
so back to the drawing board

Any updates on this project?

atesus wrote:Any updates on this project?

due to personal problems most of my projects were put on hold
I hope I will be able to start some back up (again)

I hope you resolve your problems quickly and get back to your projects.

I am reading this thread with interest and noted the references to a brass disk instead of teflon for the Davis set up. How are you cutting the disk? It would seem some level of precision is needed to achieve a proper seal. I am totally new to the diesel scene and nobody around me is into it so all advice is appreciated.

I use pop cans myself
and a good paper punch works great

I use this set:

https://www.amazon.com/gp/product/B0002T87E0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

I used it for 049 and 020 engines. There's an exact size for one of them, the other one needs a bit of sanding, not sure now which one is which though.

Aluminum cans also work fine, though shorter lived.

In any event, I suggest to consider diesel conversion heads from Mecoa which are O-ring based. I had much better luck with them.

--Atesus

https://www.amazon.com/EK-Tools-Circle-Punch-0-50-Inch/dp/B0090JVDNA/ref=sr_1_5?crid=2N8D271TCYCWN&keywords=paper+punch+0.5&qid=1669929286&sprefix=paper+punch+0.5%2Caps%2C244&sr=8-5

something like this is what I use XD

Thanks for the ideas all. I have quality vintage punch set (Enco I think). I was unsure that the edge might deform enough to cause problems. I suppose that with enough torque, the head will squash it back into shape. Thinking out loud. I will look into the o-ring type heads available on aftermarket but since I have the Davis heads in hand, I wanted to give it a try.

Oldenginerod wrote:As far as I know, most European diesels never ran an o-ring to seal the contra-piston. The piston was just a very tight machine-fit.  It looks like the o-ring is an American idea, as I've only seen them in OK Cub diesels and the RJL conversion heads.  Certainly of the dozen diesels I have, none use an o-ring.  Australian, British, Russian, Chinese, Indian.  All have a machined-fit contra-piston.  The only real disadvantage is that it's common for the contra-piston to stick, particularly if someone unwittingly screws the comp screw down too far onto part of the bore which has carbon build-up. It can be very hard to budge a stuck contra and many diesels have been damaged by the owners trying.  Generally, the first time the engine fires it will shoot the conta back against the comp screw.

Actually the 1957 Frog 80 Mk1 used an o-ring sealed contra....probably inspired by the McCoy 049 and 09 diesels-or the small OK diesel Cubs.....it (the O-ring comtra) was not well received by UK and Commonwealth users, though there was nothing wrong with the engine overall- and the Mk2 version of 1961 reverted to the traditional lapped contra....and so things remained until Bob Davis hove into public view around 1979....

ChrisM