gerryndennis

Hi everyone,

I've always been interested in model Diesel engines, but I haven't had much experience with them.

I have an Indian Mills in a Smeed Courtesan that is a lot of fun, and am currently building a Super Scorpion for an ED Racer. I don't want to use the Racer for day to day flying so plan on using an OS 20 FP instead. In keeping with the vintage theme and because I like Diesel I thought I would try a Davis Diesel head on it.

The FP runs so well, with great transition and easy starting that I am now considering converting another engine for normal sport flying.

The candidate engines I have are; OS 40 FSR, OS 46 SF, and an OS 61 SF.

Unfortunately Bob Davis says he doesn't have heads for any of these engines, but does have a head for the OS 40 FP. The FP and FSR use the same part number glow head so I am surprised he says the FP head isn't suitable for the FSR, perhaps the engine isn't strong enough for Diesel conversion.

Mecoa sells the RJL head for the 40 FP which also fits the 40 FSR, but I understand they are a bit slow to deliver at the moment.

Davis sells a head for both the OS 46 FX and AX. My SF has exactly the same bore as these engines and I suspect the 6 bolt head of the FX would fit but I'm not sure how far the FX head protrudes into the cylinder. It might be the same as the SF? The AX has a four bolt head.

I have read that someone by the name of A COHOLIC makes heads for engines. I don't know if he does this commercially or not, but don't have his contact details either.

Bob Davis sells entire OS 46 AX and Super Tigre 46's with Diesel heads which would be ideal but I would rather modify one of my existing engines than buy another one.

My preference would be to modify one of my SF 46's, and there's probably a good chance that the Davis FX head would do the job.

Another option would be to buy either the RJL or Davis 40 FP head for my 40 FSR.

Or buy an entire engine from Bob.

Is there another option?

I am interested to hear the opinions of all the Diesel experts here, and would like to thank you in advance for your help.

Dave H

brokenenglish

Hi, I've owned several hundred diesels for decades and I use real old diesels a lot (mostly English, French, American and Italian).
I've never felt the need for a conversion head so I shouldn't knock something I've never tried, but I can't imagine that they would better the (perfect) performance that I'm getting from my PAWs.
In your situation and if you need to fly with a throttle, my only option would be to buy the appropriate PAW.

Recycled Flyer

'ajcoholic' is a member of this site so why not PM him?

He does make wonderful diesel heads where 'angels fear to tread.'

Good luck.

gerryndennis

Thanks Brokenenglish,

I've only heard good things about PAW as well, but hadn't really considered them for a modern sports/aerobatic type model. No reason why they wouldn't work fine though I suppose.


I was hoping to save a bit of money by converting one of the engines I already have, but I can see myself buying one for the Super Scorpion after reading how WarrenB's model goes on a PAW 35. I'll try the OS 20/Racer first though.


It seems to me that nearly all of the currently available Diesels are either vintage style or vintage replica, or are very specialised competition types.


Thanks for your reply,


Dave H

gerryndennis

Thanks Recycled,

I thought he was a member at the Canadian site but didn't realise he was here as well.

I would feel a little awkward sending him a "Hey I hear you make Diesel heads, can you make me one" PM. He could be very busy. Maybe he's happy to do it though so I'll try contacting him.

Thanks for the suggestion.

Dave H.

Lou Crane

To the original post:

Most glow fuel-resistant dopes or paints are nicely resistant to raw or exhaust-residual diesel fuel. Light butyrate colors may take on a yellow stain; plan accordingly. Some enamels are kerosene, or mineral spirits (turpentine?) 'dissolved.' These do not resist diesel raw or exhaust liquids! I recall launching a friend's small RC model painted with enamel. There was more paint on my hand, than on the model when it landed. Laquers seem more resistant, but not totally.

I'd match the model's color to the expected 'stain.' Personal experience...

Lou Crane

As to diesel conversion heads -

Bob Davis has excellent conversions for everything, in my opinion, except the Cox 1/2A heads. That is due to the fragility of the highest production reed valve Cox engines. His teflon(c) discs fail before the shaft does, by design. For other engines and sizes, his heads are outstanding! The engines are designed to withstand such loads, while the ancient high volume produced Cox units were not.

The RJL conversions do not fit as many engines as Bob D can, but they work well, too, for .049-.061 and OS .40 clone engines.

In my personal experience...

gerryndennis

Thanks Lou,

I have a couple of test frames covered and painted with my normal system. I was going to do the raw fuel test and the hold it in the exhaust test but hadn't considered a stain test. I'll make up a frame with lighter colour and see how it goes.

I did have to play around with the head shims and the compression screw length on my 20 Davis head, but now it's working very well and I am very happy with it.

If I was sure that his 46 FX head wood fit my SF then that would be the obvious choice. I know his 40 head will fit my FSR even if he thinks it doesn't, but it's good to know that the RJL head works well too.

thanks for your reply,

Dave H

ddd

Hi Lou,

Please remember that we have been making heavy duty crankshafts for Cox reed valve engines for as many years as the conversions., as for failure of the diesel disc this is by design as a safety when their is overheating which can easaly occur when running on a bench.rather then in flight.

ddd

We don't make many heads where the engine is out of production for 20 or more years, as for one head fiting another engine the only ones that do are the 40 FSR and the 40 FP.

gerryndennis

Thanks for clearing that up Bob, I will place an order for the 40 head through your web site in the next week or so.

I completely understand that you can't make heads for out of production models, pity the 46 FX head won't fit my SF though.

I am really enjoying running my 20 with your head on it. A great product.

Dave H

Hobbsy

My Feedback: (102)

Dave H. I'm another Dave H., I could heartily recommend an OS LA .46 conversion, its a strong conversion, very smooth running and carburets cleanly.

ddd

Just to clarify, we no longer make the OS 40 heads, I was just mentioning that the 40 FSR and 40 FP's were interchangeable. Our newly updated website has our current production items. Thanks, Bob

gerryndennis

Thanks Hobbsy (Dave),

I was hoping to use one of my existing engines if possible, mainly because of the grief I get on the home front if I buy 'yet another engine, you haven't got models for all the ones you have already'. But I may end up having to go down the route of buying an engine to suit what Bob Davis is currently selling.

I've enjoyed your posts and YouTube videos (I think they were yours) of operating diesels, very enjoyable.

Dave H

gerryndennis

Thanks, I see that your web site has changed in the last few days.

I should have purchased the 40 head back when I bought the 20 head, except that back then you said it wouldn't fit.

Do you have an old stock OS 40 FP head left over by any chance?

Dave H

Recycled Flyer

But that was exactly what I did though.

He is a very nice chap who wants to see more diesels in the air.

Hobbsy

My Feedback: (102)

Here is an example of his work, this head is on a Fitzpatrick Brothers .61. AJ is also a contributor to RCCanada magazine testing many engines for them.

raglafart

My Feedback: (10)

I've done several diesel conversion heads based on the Nelson design that have worked very well.
My Dieselised Taipan Gold Head was going particularly well until the crankshaft let go (not an uncommon occurrence even as a glow!)
The Rossi is a MK 3 and I copied the external features of a Stock MK 2 Diesel head. Again, it works very well.

gerryndennis

Hi Recycled and Hobbsy,

I was wondering where people got their AJC heads from, sounds like you just have to ask him. Which is what I've now done. I'm hoping for a reply to my PM soon.

Dave H

gerryndennis

Raglafart,

Nice work on those heads. I do have a friend with a lath, but I'm not sure if we would have he skill or time between us, to make our own head. It's an option though. I would have to research the design and fitting of contra pistons etc.

Or were you offering to make me a head?

Dave H

gerryndennis

Well Andrew Coholic didn't reply straight away to my PM so I had a look around the net and found his email address in another thread. While I was looking around I discovered that he is a very talented and busy man, and also very generous with his time. There are threads on the Canadian web site mentioning how generous and well regarded he is, he is a renowned guitar builder and woodworker as well as his engine work and magazine articles. I found myself wondering how he found the time to help out other modellers.

Which is why it was completely understandable when he said that due to family demands on his time he was unable to make me a head.

I did find an article that he had written on how to make Diesel heads so I am very tempted to have a go at a head for my OS 46.

I have also ordered an RJL head for my 40 so hopefully I will be able to do a bit of sport Diesel flying in the future.

Thanks to everyone who has contributed to this thread.

Dave H

Prohack01

Hi Gerry,
Please post how you like the conv. I just picked up an RJL to try on the Thunder tiger gp 40, figured for the price it was a great way to try diesel, and really looking forward to it, just need time to finish my kit and mix some fuel...

karolh

I the early 60's when diesel engines were popular here I bought a British 2.5cc ED Redhead racer which was quite a potent little C/L Team Race engine though not in the class of the Oliver Tigre.

gerryndennis

Hi Karolh,

I quite like my Racer, but I haven't quite worked out how to start it without getting my finger whacked yet.

Dave H

gerryndennis

G'day Prohack,

I really like the RJL head. They shipped it the same day I placed the order and it arrived here in NZ about a week later. Shipping was a bit of a killer, about half the price of the head again, but that's still cheaper than the alternative. It seems to be pretty standard for anything I've bought from the States though, the box was big enough to fit 24 heads (I checked). Maybe United States air is really valuable because that's what the box was mainly filled with.

I initially thought the head was slightly too big to fit in the OS' bore but it did slip in fine in the end. I used a wooden skewer to line up the ports before I nipped up the head screws.

MECOA recommends 1/3,1/3,1/3 olde English mix, but I used 20% oil, 30% ether, and 50% kerosene with an additional 1% ignition improver. Starting was easy once I got the compression settings and priming sorted out (the last three starts I did were one flick). I was getting right on 12000 rpm with an APC 10X6 but I,m not sure I was fully lean and maybe slightly under compressed (the engine does 12500 on glow leaned right out).

So I'm very happy, I'm still very tempted to try making my own head for my 46.

Good luck with your head,

Dave H