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FROG 2.49BB

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Old 11-11-2011, 05:30 AM
  #1  
gcb
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Default FROG 2.49BB

How many have flown these old relics? Although I have not (yet) experienced it, I understand that they split their crankcases easily.

Lets hear your war stories about this engine.

My only experience is to fly it sport in a Jr. Flite Streak many years ago.

George
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Old 11-11-2011, 09:40 AM
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Default RE: FROG 2.49BB

I've been using various examples of the FROG249 BB for almost 50 years now, with complete satisfaction. I have never experienced a problem with the cases splitting, nor have I previously heard that this was an endemic issue with them, as it was (for example) with the AMCO 3.5 BB models. A lot of reputations of this nature get started because someone has a problem with one example, immediately concludes that it must be endemic and spreads the word. This may be such a case. I recall several engines which acquired undeserved reputations for weak wrist pins, for instance, simply because a few owners over-compressed them or put them into a hydraulic lock.

I've always found the FROG249 BB to be a well-made and well-mannered engine with a more than acceptable performance by the standards of its day. In fact, at the time of its initial release in late 1955 it ws the most powerful mass-production 2.5cc diesel on the British market. The earlier ones (up to 1962) were made by International Model Aircraft, while the later ones were made by Davies-Charlton Ltd. In my experience, the IMAexamples are the superior products, although the D-C ones are generally quite acceptable. You can tell the difference by the serial number - the ones made by D-C have a "T" prefix. What are the serial numbers on your examples?

There are two versions of the 249 BB. The "standard" ones with plain cooling jackets have Oliver-syyle porting with the transfer ports drilled upwards at an angle through the pillars between the exhaust ports. The "modified"versions have red-anodized heads and feature horizontally-sawn transfer ports below the exhaust openings, along the lines of the A-M diesels and many others. The "modified" engine was supposedly more powerful, although the difference in my experience is not that great. But more to the point, the "standard" version is far more amenable to careful tuning by someone who knows what they're doing. My own tuned example is installed in a "Chaos" vintage diesel combat model and hauls that large airframe around at a rate of knots! It's very little down on a standard Mk. III Oliver for performance in my direct experience.

I wouldn't have any reservations about using these engines. I've doneso for years, with no problems whatsoever.

Good luck!!
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Old 11-11-2011, 11:17 AM
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Default RE: FROG 2.49BB

i have to agree on the comments on the Frog 2.49. I had 2 of the standards and ran them for years with no complaints. They were truly satisfying to own and i hope that whoever stole them from me got some enjoyment from them.
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Old 11-11-2011, 09:31 PM
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Default RE: FROG 2.49BB

Ditto-I think there may have been a bit of confusion somewhere along the line between the Frog 249 and the Amco 3.5BB (or PB for that matter)-the Amcos did get a justifiable reputation for breaking crankcases and shafts respectively. But the Frog never had a reputation for breaking in my and my modelling circle's experience......it DID have a reputation for being thirsty-and needing a lot of nitrate in the fuel, but not for being a fragile engine. In some circles it was considered the poor man's Oliver!

ChrisM
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Old 11-14-2011, 12:04 PM
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Default RE: FROG 2.49BB

My Frog 2.49BB is a finger biter, especially when compared to my A-M 2.5, which is very docile in comparison. I've not flown the Frog; however, the A-M turned a lot of circles towing a Jr. Flite Streak in the day - that day being some 50 years ago now that I look back upon it. That said, I started both engines about three years ago when I got a PAW 1.5 R/C to try in an Electroflite Fokker VII. Worked the PAW to hard and I think it;s got a broke rod..tho I can't get the backplate loose to check.

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Old 11-14-2011, 01:24 PM
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Default RE: FROG 2.49BB

Heat the engine case up with a heat gun and the back plate will/should come off. With easy access to parts these engines are meant to run...
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Old 11-14-2011, 01:47 PM
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Default RE: FROG 2.49BB

Thanks, I'll give it a try when I get home next month; otherwise I'll send it back to Erik for repair.

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Old 11-14-2011, 06:57 PM
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Default RE: FROG 2.49BB


ORIGINAL: John C

Thanks, I'll give it a try when I get home next month; otherwise I'll send it back to Erik for repair.

John C
Of all the traditional diesels, PAW's must be the most difficult there is to unscrew the backplate. It's designed to be removed with the aid of a UK 10P coin IIRC.

This almost never works for me.

Heating the rear of the engine is most difficult 'cause if you heat the crankcase the backplate will also expand.

One foolproof technique I found is to carefully grasp the backplate rim in a 3-jaw chuck of a lathe and place a towel over the engine.

Twist the chuck and engine in appropriate opposite directions, gently tightening the chuck till it just grips.

So far it's worked every time.

Ray
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Old 11-14-2011, 07:07 PM
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Default RE: FROG 2.49BB

I had one in the late 1970's with the red head.  I could never get it running.  It was my fault.  I was a kid,  stuck to glow after that.  Someone got it running for me and it went great. Pulled the c/l combat around pretty good. I thought it was pretty heavy but went ok.  I couldn't get it going after that day and sold it. 
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Old 11-15-2011, 04:13 AM
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Default RE: FROG 2.49BB

But first one has to have a lathe . Actually, I may have a 10p coin around the house to try too. The coin in a vice and turning the engine may work. This engine has no scars from attempted disassembly and I'd like to keep it that way

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Old 11-15-2011, 05:12 AM
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Default RE: FROG 2.49BB

Well I think this is the failure that you are talking about. From my understanding, this was in fact a fairly common failure with the early Frog 2.49 BB engines. These were the non anodised engines with the Oliver style ports.

I have 2 of the early engines in this condition. One I broke myself in a Vintage A racer that I built in the early 90's, the other in one I bought sight unseen to hopefully acquire a decent crankcase It had all the fractures neatly covered in Devcon or JB Weld !

I had a shaft fail in my engine. I made a new shaft and the power was back up and then the case failed.

The later red anodised engines with the DC style porting were supposedly much stronger and not so prone to this problem. I have one of these too but I have to make a new piston and contra piston as it's well down on compression. These red anodised engines were also known as the modified version.
I always thought that the DC porting with the wide transfer slotted ports directly under the exhaust port to be actually a detuning of the engine rather than a power increasing move.
I'm sure if there were any performance benefit to be had, Mr J Oliver would have also used it ? anyway that's another subject.
Here's a picture of my dead 2.49 BB crankcase []
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Old 11-15-2011, 09:03 AM
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Default RE: FROG 2.49BB

Interesting! As stated earlier, I've been using these engines for almost half a century, as have a number of my mates. Between us, we have yet to encounter this issue. Sounds as if the experience of ChrisM (ffkiwi) is similar. Clearly it can happen, but I still don't believe that this is an endemic issue - if it was, more of us would be experiencing it!

I have also yet to encounter a shaft breakage with one of these units, either with my own engine or anyone else's. I think that Raglafart was a bit unlucky there - I'm satisfied in my own mind that this too is not an endemic flaw. That said, any model diesel can break a shaft - all it takes is a manufacturing flaw in the component or some heavy-handed treatment in service.

I had a look, and I can't readily see any design differences between the red -head and plain-head cases. Perhaps they switched to a stronger casting alloy??

I agree with Raglafart that the switch to sawn ports from drilled ports with the so-called "modified" engie was a step backwards in design terns. My own tuning efforts have clearly showed that the original Oliver-ported version had far more potential. They should have stuck with that and developed it further. A well-tuned one of these can give a Mk. IIIOliver a good run!

Finally, the "finger-biter" issue noted by John C is not unfounded - in fact, it's a common issue with ball-race diesels, in particular those with short strokes. Short stroke engines tend to snap over faster than long-stroke ones in any case, andthe addition of ball-races simply exacerbates this problem by reducing the snap-over resistance! This is why Olivers are so user-friendly - that slightly longer stroke.

Cheers!
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Old 11-15-2011, 01:03 PM
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Default RE: FROG 2.49BB

I wasn't old enough to be a user of these engines when they first came out so my experiences are only from the last 15 - 20 years since my return to c/l and dabbling with vintage A team race models.
My Frog was used in the first vintage A racer I build back in the early 90's. It was a Footprint and I still have it. When I built it I even included the angled forward kinks in the u/c wire but later removed them to simplify the landing gear. It even had the ridgey didge flat bottom "Clark Y" section !
Anyway I digress.
I think it's only when you push the Frogs really hard that this case weakness becomes a problem.
According to Ivor F, he related a tale of one of the importers of the time having a load of returned engines in a drawer all with the same problem.............broken cases and in many examples the case was in 2 parts, all breaking around the rear bearing housing area.
Now I know I was giving my engine a hard time. It was in a racing model. I do believe however that there is some substance to this type of failure with the earlier models.
I would advise conservative settings to avoid heart break, you don't see too many brand new Frog 2.49 BB crankcases floating around looking for new homes

I don't think there is adequate meat around the front bearing.
To this end I have bought new bearings of smaller OD and was going to make a one piece sleeve of steel to tie effectively beef up this area and tie the front of the case to the rear of the case.
Easier to draw than to explain. It's pretty low on the list of to dos out in the workshop, but I have the R110 bearings and will get around to it at some time.
Stan Pilgrim, a very well known and highly respected Australian engine tuner with a long list of success's was of the opinion that the earlier version Frog 2.49 could be made to go very quickly if one wanted to. I think he may even used one in the earlier years of vintage A.
There is no doubt though the Oliver is a far superior and much more robust design much better suited to the rigors of racing.

Here's a pic of the Footprint with the Frog 2.49 BB.
All the wing damage was done when loaned to a friend
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Old 11-15-2011, 01:24 PM
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Default RE: FROG 2.49BB


ORIGINAL: locktite401

Of all the traditional diesels, PAW's must be the most difficult there is to unscrew the backplate. It's designed to be removed with the aid of a UK 10P coin IIRC.

This almost never works for me.

Heating the rear of the engine is most difficult 'cause if you heat the crankcase the backplate will also expand.

One foolproof technique I found is to carefully grasp the backplate rim in a 3-jaw chuck of a lathe and place a towel over the engine.

Twist the chuck and engine in appropriate opposite directions, gently tightening the chuck till it just grips.

So far it's worked every time.

Ray
Hi Ray,
what has worked for me with my PAW 19 and 15 in regards to the screw in backplate is heat around the back on the case (but try and avoid the back plate obviously) and then place the upwards facing engine's back plate onto an ice cube.

Then of course the old mud guard washer gripped in a vice is used as a key, but must admit that even then it involves some muscle!

You are lucky having a lathe mate.

Cheers.

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Old 11-15-2011, 02:05 PM
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Default RE: FROG 2.49BB

I guess I've been lucky - I've always run my Frog 249 BB's really hard, mostly in combat models, with no trouble.  Now you've got me worried after all this time!!  I suppose I'll just keep on using the things and enjoying them while they last! 

One thing that may have helped my tuned engines to survive is the fact that part of the tuning process involves lightening the piston by a considerable amount.  As a result, vibration levels are really low - always good both for performance and reliability.  However, the periodic contacts with terra firma remain just as hard!

Another factor that might affect things is the tightness with which the bearings are fitted in the case.  Some of them in my experience are pretty tight. If the outer races are fitted too tightly they will set up considerable internal stresses in the case material which could combine with operational stresses to exceed fatigue limits. While the engines are apart for tuning, I've always extracted the bearings and checked that they weren't in any tighter than necessary.  A push fit with the case at around 40 degrees Celcius seems to be about right. I've had no trouble with skidding races.

On the matter of potential, I can endorse Ray Pilgrim's comments completely - in my own direct experience, a well set-up tuned Frog 249 of the original type is a real goer!
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Old 11-17-2011, 11:44 AM
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Default RE: FROG 2.49BB


ORIGINAL: Diesel Die-hard

I can endorse Stan Pilgrim's comments completely - in my own direct experience, a well set-up tuned Frog 249 of the original type is a real goer!
So was mine.................................. until it broke []

I can't believe you've never had a case break flying combat !
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Old 11-17-2011, 12:10 PM
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Default RE: FROG 2.49BB

Fly over soft ground........and fly to avoid mid-airs. You don't win as many matches that way, but the equipment stays alive a lot longer!
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Old 04-22-2016, 04:08 PM
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Looks like a long time since a new post to this forum so hopefully I will get a reply.
I just acquired a FROG 2.49 redhead "modified" in almost new condition and I am
wondering if this engine will pull a full size Flitestreak on a 8x6 prop on 60 ft lines.
Would it be better suited for the smaller Jr Flitestreak on 45 ft lines?
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Old 04-22-2016, 04:26 PM
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Originally Posted by Speedy-Gonzales View Post
Looks like a long time since a new post to this forum so hopefully I will get a reply.
I just acquired a FROG 2.49 redhead "modified" in almost new condition and I am wondering if this engine will pull a full size Flitestreak on a 8x6 prop on 60 ft lines.
Would it be better suited for the smaller Jr Flitestreak on 45 ft lines?
You might be more satisfied with a profile "Peacemaker". It also was designed by George Aldrich but is sized between the full-size and the Jr. and was designed for a .15 (2.5) diesel. The original was powered by an OT diesel.
You could run it on a full-size Flite Streak but you would probably want to use 52'x.012 lines. IMO it is too heavy and powerful for a FS Jr.

Good luck with your FROG.

George
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Old 04-22-2016, 05:08 PM
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OOPS! double post

Last edited by Speedy-Gonzales; 04-22-2016 at 05:11 PM.
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Old 04-22-2016, 05:09 PM
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I see Stuka Stunt has plans for the "Peacemaker" for $10 plus shipping. I might just take my Flitestreak plans and have them resized to 38" wingspan.
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Old 04-23-2016, 12:13 PM
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Originally Posted by Speedy-Gonzales View Post
I see Stuka Stunt has plans for the "Peacemaker" for $10 plus shipping. I might just take my Flitestreak plans and have them resized to 38" wingspan.
That is the one. It has a shorter aspect ratio than the original Flite Streak and is/was a top selling plan from Aeromodeler magazine. Don't confuse that one with the full-blown stunt plane George Aldrich designed for a .15 diesel and is also named "Peacemaker".
You can resize the FS plan but wouldn't it cost about the same? I would recommend the Peacemaker. Your choice.

George
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Old 04-23-2016, 03:46 PM
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I flew a Jr. Flite Streak with an AM .15 for several years many years ago. I don't think the Frog would be adequate for a full size Flite Streak on 60' lines. I flew with 52' IIRC.

My 2 cents! YMMV!!!

John C
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Old 04-24-2016, 09:41 AM
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Originally Posted by Speedy-Gonzales View Post
Looks like a long time since a new post to this forum so hopefully I will get a reply.
I just acquired a FROG 2.49 redhead "modified" in almost new condition and I am
wondering if this engine will pull a full size Flitestreak on a 8x6 prop on 60 ft lines.
Would it be better suited for the smaller Jr Flitestreak on 45 ft lines?
Hi Speedy, Go For It! My friend Barry Baxter has flown several FliteStreaks using various 2.49cc diesel engines.

I have a FliteStreak that fly's with a Russian Meteor 2.49cc diesel engine. I use .015" X 55' lines.

We had a friend, Dennis Lien(Passed on); that used to fly a FliteStreak using an MVVS 2.0cc(.12cu")

plain bearing engine on .015" X 60' lines with no problems. One of my old time stunt models is

a CLC Super Clown(365sq"s) that I fly on 55' X .015" lines using a Marz 2.49cc bb diesel, swinging

a Taipan 8 X 6 prop. I do advise that you try to keep the weight down. My friend and family control line trainer

is a Veco Tomahawk that has seen four different diesel engines in the nose, the last engine powering the

model was a Yin Yan plain bearing Chinese 1950's design; flown on .015" X 60' lines. I tried various props,

a 9 X 4 and an 8 X 6. the Tomahawk was tight on the lines during overhead manuvers.

I'm sure your Frog 2.49BB has a lot more power than that Yin Yan 2.49cc engine.

Best of Luck;

Tony
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