gerryndennis

It might have been Delryn you were thinking of. Whipper Snipper cord sounds like the easy answer though, good idea Firey, I'm filing that one away for later use.

Dave H

1QwkSport2.5r

Yeah, that's it!! I'll edit my post about that. I'd hate to look like a dumbass on an Internet forum..

gerryndennis

Me either, I better go and change 'Nylon' in my post cos that was wrong.

Can't have anonymous people on the web that I don't know, and who don't know me, thinking I'm wrong about stuff.

1QwkSport2.5r

Looking like a dumbass comes naturally to me.. . I was labeled by a poor fellow in California loosely quoted as "lacking all technical prowess" and I'm an engine destroyer.. Wait until my next Frankenstein machine runs again. This little .40 engine suffered broken wristpin clips 4 times. Three times in the original piston/liner and once with a brand new one. The old piston wasn't scored that bad, but the old liner is. New piston is scored pretty bad, but the new liner is not. So I put the "good enough" parts together and will make a running engine from it and put a diesel head on it (incidentally for a K&B .40).. I'll have to loosen it up on glow fuel and then run it on diesel. The iron/steel P/L fit is pretty snug.

It may survive, and it may not. We will find out together... I used a pair of hardened steel C-clips to retain the wristpin this time. That should hold together well, but the Rod/crankpin may be another story.

1QwkSport2.5r

My next conversion experiment will but on a Fox .40 compact case engine that has suffered several wristpin retainer failures between two Piston/Liner sets. I put the best piston and liner together of the two sets to get a reasonable fit. The one scratch in the piston goes from the top of the piston down most of the skirt. Compression isn't that great. This engine still ran after the last failure, but I didn't expect it to be all that reliable. It actually runs pretty good considering the circumstances. I ran it on glow to see how healthy it is, so I tried a few props and this is what I ended up with:
APC 9x6 at 14,400rpm peak
APC 10x6 at 12,300rpm and 12,500 rpm (used a SuperTigre plug for most tests, the second figure is using a Fox idle bar gold post plug)
MAS 11x6 at 11,400rpm but ran hot and sagged. Backed off 700-1,000rpm rich and it was happier.
MAS 11x7 at 10,300rpm. Ran hot and sagged. Backed off fairly rich and it was fine.

It it would hand start within 5-6 flicks from cold and 2-4 flicks warm on all prop except the 11x7. I had to use the starter on it briefly to fire it off. The throttle transition was pretty good actually, so it should run O.K. On diesel.

Best stable idle was 2,200-2,500rpm depending on prop. Fuel is 7% nitro 20% castor, high compression Fox head, liner shimmed .010" higher. The liner is shimmed up and the diesel head are shimmed too. The head would hit the piston without any shims. To get enough head spacing, I shimmed the liner .010" and the head .020". Not the practical approach, maybe not proper, but it's just an experiment. The glow head was not shimmed for testing. So I'll find out if the crankpin and/or Rod will hold up to diesel abuse or not. The engine doesn't seem to want to die yet.

1QwkSport2.5r

For comparison, the old Fox .40 with twin ball races I recently gave away turned a 10x5 APC at 12,800 with the high compression head button and 5/20 fuel. So I think this one despite the scored piston isn't down on that much power. Diesel on!

Hobbsy

My Feedback: (102)

Tim, you should see the piston in my SuperTigre 4500, It looks like someone used it for a road grader. Bob Davis suggested I use jewelers file and clean it up and see what I got. It had eaten both it's circlips, the top of the piston has acne real bad and there are grooves in the skirts. A Bowman ring and some delicate filing made it hold compression like an abc engine. This is the 3000 with a Bowman ring.

1QwkSport2.5r

I remember you talking about that awhile back. I wish the .40 had come ringed - then a new ring would make it like new. Not such is the case here unfortunately. The one is good old mehanite.

1QwkSport2.5r

Tried to run the little .40 on diesel tonight. Couldn't get a single puff, burp, fart, or otherwise from it. Given the compression loss last the piston though the scratch down the side of the piston, I think I'm gonna decrease the head spacing .005-.010" and see if that makes a difference. I doubt it will; I couldn't get a burp from having the compression screw buried. I hand flipped it for 15 minutes and resorted to the electric fist (finger) and still nothing. I'll try it again tomorrow with some shims removed and see what happens.

1QwkSport2.5r

I was able to get the cobbled together basketcase Fox .40 compact engine to run off a prime today. I lowered the liner .010" to its factory location but kept .020" worth of shims under the head. Remember this head isn't for this engine, it dips into the cylinder .202" and the piston is about .185" from the top of the liner. To get the right head spacing, I split the difference and shimmed the liner .010" and head .020". By doing this I figured I'd have adequate head spacing (and raising the timing a bit) to get it to run or at least burp or whatever. The only way it would start is with the comp screw all the way in. With the screw all the way in, the contra is not flush with the squish band - it's still recessed .001-.002" or so. Thinking I should find a longer screw or put a thin washer between the screw and the contra..

More to come...

1QwkSport2.5r

I was finally successful in running my beat up basketcase Fox .40 compact case engine on diesel today. It was a brief run. Seen here: http://youtu.be/i6AvBZ-BcOw

I need a little more travel of the contra piston so it will go flush with the squish band. Currently it's recessed .001-.002" or so with the compression screw buried. The head clearance is very tight likely because of the scratched piston not building compression very well. This may get better with time as the piston gets varnished up. I'll find a longer screw and try it again. It still won't die!!

Hobbsy

My Feedback: (102)

Tim, something that was mentioned the other day was the tension screw, check and see if there isn't a Heli coil in the Davis head, many have them. The tension screw pushes on the heli coil.

1QwkSport2.5r

The Fox .50 head doesn't have anything in front of the tension screw - I backed the screw out completely and only had a threaded hole.

1QwkSport2.5r

I got a longer screw for the diesel head which worked perfect on the compact .40 Fox. Needed another 3/16 turn to hit the sweet spot. For a beat up engine, it did okay I think. It ran smooth on top, but only showed about 7,500rpm on a 12x6 MAS K-series prop. Still trying to get a sub-3,000rpm idle but I doubt it'll happen. It'll idle and throttle up pretty good from about 3,100rpm.

Hobbsy

My Feedback: (102)

That was passed on to me as being for a K&B .40, does it fit the bore snugly? Thanks

1QwkSport2.5r

Yes, the K&B and Fox .40s both have a .840" bore. The only differences are the head spacing and the screw orientation. The head is slightly askew, but it works. The piston has a bad scratch in it so it isn't sealing super well. For this reason I suspect it won't hand start on diesel. For a .25 sized .40, 7,500rpm ain't bad. I might get 8k out of it with a little more tweaking.

1QwkSport2.5r

Well, I think I have seen what a beat up Fox .40 compact case engine can do on diesel. I ran three different props and though the numbers aren't stunning, it didn't run hot and sag on the big props like it did on glow. It's down on power compared to glow, but when I consider it ran consistent, it can't be too bad. Not as good as a big case .40, but then again it might run better with a better piston seal.

12x6 MAS 7,600rpm http://youtu.be/2GX8Dl2vkqg
11x7 MAS 9,500rpm http://youtu.be/NvqJdzuadYk
11x6 MAS 10,700rpm http://youtu.be/9U8u0Sl1vJ8

1QwkSport2.5r

I recently received a gift in the mail from a friend. I have a SuperTigre GS45 ABC with a Davis Diesel head. It didn't sit on the shelf 24hrs before I had to go run it. Runs great, starts awesome. Using my homebrew fuel mix and an APC 12x7 prop, I got a solid 1,830rpm idle and 9,900rpm top end. I felt more comfortable running it a little richer and compression set just tight of burping. It throttled pretty well too, though it seemed undercompressed in the midrange. I'm still learning the adjustments so I may be interpreting what I heard wrong. Either way, it's a fantastic engine that I'll enjoy having it.

Short video of this engine idling: http://youtu.be/NTaPA3t___0

Hobbsy

My Feedback: (102)

Sounds good Tim, I started this thread in May of 2007, it has lasted quite a while.

1QwkSport2.5r

Yes it certainly has. I think it was only about 4 pages before I started my little escapade in diesel. I'm having a lot of fun and learning a lot. I might try my G51 on diesel too. That was more or less a gifted engine as well. It has a Bowman ring in it. The G51 on 5% glow fuel went 10,800 on a 13x4W APC, I wonder how it would do with a 13x5 or 13x6 as a diesel? My G51 has a narrow spraybar though. It originally had a round spraybar that I shaved down. It ran a lot better that way on glow fuel.

Hobbsy

My Feedback: (102)

My .51 will turn a 12x6 three blade at 10,400, yours should do better with a better ring. I should have anew ring for my .51 Monday.

1QwkSport2.5r

I don't have any 3-blade props, so I'll try a few of my big 2-blade sticks and see what happens. I went ring crazy and had gotten two rings for the .51 - one to install and one for a spare. I replaced the bearings and piston ring not log after I got it. Before bearings and new ring it went 10k flat on the 13x4W the previous owner tested it with.

Hobbsy

My Feedback: (102)

I have a lock on the last G-51 ring Frank Bowman has in stock, I'll use it instead of the Tower ring that's coming Monday. This engine, (Dieselized of course) powered a USAircore Knighthawk in the early 90's and has many many hours on it. If it's the correct picture

1QwkSport2.5r

So what's the trick to getting a good transition after a period of idling - say 8-10 seconds? I can get a peak setting on top and I can get a good idle speed, but after several seconds idling and going WOT (actually 80% throttle) it burps like its undercompressed/retarded and doesn't recover. If I advance the compression, it cleans up but sounds a bit rattly. Retarding the compression gets rid of the top end rattle but makes it burp going back to full throttle. If you run idle to WOT back and forth, it throttles nice and smooth. I've noticed this on both the Fox .50 and the ST G51 and GS45. In this video, the engine reacts to going WOT from 80% throttle opening the same as it does going from a 5-8 second idle to WOT/80% throttle. It doesn't beat back up and smooth out without adding compression. http://youtu.be/HehWrvPxQvU

Put the beat up Italian G51 with Bowman ring on the stand with the Davis head from the .45 and Davis Soundmaster muffler and ran it up. 12x7 APC gave a good idle of 2,100rpm and a peak top end of 10,100rpm. This engine has a narrowed spraybar. It was hard to get started initially, but restarted good after it had run some. It's been in the drawer for a year or so. This one has about a gallon of glow fuel through it after I replaced the bearings and piston ring.

The tach reading in the pic of the 10k figure flickered as the shutter snapped, but I did see a solid 10,100 figure for a short bit.

Jennifer Curtis

Running a little rich may help the acceleration
after idling. It effectively increases the compression
because there is more fuel and oil (which are not
compressible) in the mix. Running a little rich
also keeps the high speed slightly cooler, so there
the compression doesn't increase itself as much
due to heat buildup.

Even running a little rich there is still a limit on
how much idling you can do and still expect
smooth acceleration. You just have to know
it and plan your maneuvers accordingly.
For example don't wait till the last second
before you abort your landing, and hit the
throttle before the end of your dive when
doing square loops or Cuban eights.

When you decide to idle, you might also
bump the throttle up one or two clicks
rather than keeping it at rock bottom idle.
Most maneuvers except landing aren't
adversely affected by a slightly high idle.

Jenny