I made up a head without fins , is this OK or would I get more power with some tall fins maybe on the next one

It depends on the engine. The smaller engines tend to benefit from more heat being kept in to aid in combustion whereas the larger engines need some cooling fins to help take some of the heat away so there isn't too much heat being kept in the engine.
I would suggest just trying it and see what happens.
If the engine starts to detonate a lot after it warms up, and you wind up having to back off the compression a lot,  then you probably need more cooling fins.

... or much less ignition improver.

That is a good point loctite401.

Basically you want to keep some heat in, but not too much heat of course.<br type="_moz"/>

i would say if you had less fins you need to use less ether than if you had all the fins.by the way what engine is it.

Cat, I bought this head from Mr. Davis for the exact reason that it had no fins. It was an unrun proto-type so I bought it as I would any other. I run the exact same Davis ABC mix fuel as all others others with no issues. I enjoy being asked about it though. This head by AJCoholic on my Fitzpatrick .61 is a clone of the glow head and has virtually no fins either.

Here is my OS 40 LA with a DDD head on it too. Not a lot of fins on it, if any.



now my Fox .15 and Fox .45 DDD heads have a few fins on them though.

Earl, I like the new annular fin style, I have one on my Webra .50, oh yeah, on my LA .65 also.

Idoubt that any amount of head fins would give you 'more' power as not as much heat is lost through radiation as one would think (Ray might know better but Iseem to recall its only about 20% of all heat generated by a model IC engine is lost through its fins and you are mentioning those on the head only) and the rest via the exhaust and heat soakage elsewhere. But I see that you are angling at the possibility of overheating here.

Overheating is situational, is the engine cowled, are there any amount of fins elsewhere on the engine, what is its untended use (marine engines get by spendidly with no fins at all), and what type of head did you make? A conventional lapped contra piston or an 'O' ring insert type? And out of what material, I believe that aluminium conducts heat far faster than does cast iron.

So there are many variables outside of simply having fins or not.

Ihave two A J Coholic heads on MVVS converted diesels, one with fins and one without and both seem to run just dandy and I consider tall finning like that found on hotter glow engines to be a concession to aesthetics on a diesel more than anything else - fins give definition to the shape of the engine and add 'speed lines' or the impression of motion in that direction.

Many, many tradition old school diesels simply have a screw on jacket with a solid head disk and only fins cut against the liners side and when you consider that the contra piston only has contact to the outside world through its peripheral edges onto the side of the liner then having fins well above that may not help much at all.

Do you have a pic of what the head looks like mate?

Davis did the right thing by dumping the fins on the head, if he thought they were needed they would still be there, it gives the engines a nice clean look, I guess it was just well cosmetic tradititon (fins) about as useful as tail fins on a 1950 Cadillac martin

Martin,
Do the new Davis heads still have the locking device of an angled grub screw (its hard to tell from the pics) or some other method of ensuring that the comp screw doesn't back out?

Thanks.

I would say yes on Earls head in his pix I see a hole at 2-0 clock by the compression screw ,Martin

notice he has the davis logo on the side head turned 90 degrees that puts the grub at the rear as usual on the davis heads

dup in error

Will try to get a picture,,,,,,, it took more than 1/2 an hour to load last time ., its an OS15
I am trying to make up a multi jet carb like a Cox type but it didnt work out , thanks for answering the fin question , apparently they are not imperative on Diesels looks like , I guess to all the carbon in the motor stops the heat getting out too , mine gets carboned up fast with 25% Castrol M

That is a pretty small engine so it should work just fine.

RF, here you go.

Thanks for that Dave, the new position of the locking screw looks to me a lot simpler to machine but may be in accessable if the cowl sat flush to the engine's head.

But I really like the look of the new DDD heads, they seem distinctly 'diesel' to me!

Davis heads rarely if ever need re-adjusting once set up and the tension screw even less often but the head could be mounted with the tension screw facing forward. You would never need to turn it while running.

G'day

On the subject of "finless heads", I had several Super Tigre G2015 diesels in the 1970s similar to the one below. They had no fins on their heads and ran really well and never got hot when used normally. I still have one which I made from junk parts and used to use in 2.5cc rat race. It still runs well.

If you look at the photo you can see that there were originally more cooling fins on the earlier versions. The 1960 version had all the fins, but by 1965 one had been filled in and by 1970 another had been filled also. Possibly the earlier versions used to over cool and removing the number of fins improved performance. They were very powerful engines for their time. By the 1970s when I was using them, they had been relegated to "second tier" racing events like Goodyear and the serious FAI team racers were using modified Super Tigre G15 glow motors converted to diesel and other specialist motors like those made by Paul Bugl.

I also had a Super Tigre G15 RVD (rear valve diesel). It was intended for FAI team race and was very similar to the G20 but it was outclassed by the more specialised motors. And, they were famous for breaking the crank pin off the crank shaft. Mine did too. It was very common.

Mike from Oz