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Engine basics => Engine set up tips => Topic started by: Terry Caron on June 11, 2015, 07:20:47 PM
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Hi all -
I'm bench running a recently acquired Forster .35, OS 6/A3 plug, 10-5 APC prop.
Using the same fuel I use in my other iron/steelies (Morgan Omega 15% + methanol + castor remix to 8.5/26) it has a crackling sound in the exhaust and a distinct misfire.
The Forster has noticeably higher compression than the other engines so I mixed up some 13.5/26, thinking it maybe needs more nitro, but it has the same miss/crackle.
Then I mixed some 0 nitro/25 castor and the miss went away but it still crackles.
My concern is that I think I've read that a crackling sound indicates pre-ignition.
I'll also note that it seems to run noticeably hotter than my others (while mostly running in 4-stroke) and turns <11K with all my mixes, a full 2.5K less than the rpm noted in the review posted on SceptreFlight, tho' nitro content wasn't stated in that article.
Thoughts?
Thanks.
Terry
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I have one of the older 29 rear intake ignition Forsters, and it likes to run in a wet 2 stroke on a 10-6 prop. I have run it on glow but it never had that crackling sound you speak of. I would try adding another head gasket, and maybe going to a colder plug like a Fox standard non idlebar and see what that does for you. I would also stick with the 0 nitro fuel until you find what works. As I remember that guys that flew these back in the day all ran them in a wet 2 stroke because they did not work well in a 2-4 break.
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Hi Jim -
I've read of it's preference for a wet-2, and it doesn't have the 4-2 break rpm spread of my other .35s when I rotate it 90 deg.
With the 8.5N mix, I tried a colder (unknown brand) plug and on starting, same needle setting, it dropped from ~8.9K on the OS to below 8K, then lost another 400ish rpm w/o the igniter.
So I had to lean it considerably to get a wet 2 (9.2K-ish) and it would barely make 10K full lean.
I admit the plug may be too cold but truth to tell, it ran so punily I didn't bother to notice whether it missed or crackled.
I've considered an extra gasket, but they're a groove-fitted composition type (NOS has no doubt turned to unobtanium these days) so prone to damage upon head removal.
I have a "possibly-parts" engine on the way which I'll try to get apart w/o destroying the gasket; if that's successful, I'll be more confident about taking this one apart.
FWIW, the review article noted 9:1 C.R.
Terry
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Hi Terry:
I think that you have been misled by a very optimistic engine report. The H.P. and rpm figures in that report seem too high for a 1956 engine of that type! What you are getting, seems more plausible.
In my experience, the higher c.r. engines would run well on no nitro. If one wanted to run more nitro, one would reduce the c.r. In Old Country, I ran no nitro for years and had no problems. If this engine runs well on no nitro, so be it! I have had engines that seemed to crackle on the ground but sounded great when in he air.
The crackle that you hear may just be the normal sound of the that engine when it is running. I have had old engines that sounded much differently than the more modern engines. Don't sweat the sound!
Yesterday, I was having a problem with one of my favourite engines and it turned out to be the NVA! For some reason, fuel would not pass through the nva despite the holes in the nva being unobstructed! A new nva cured the problem. ????????????????? What the problem was wil remain a mystery! Lol
I would enjoy the engine for what it is and if it liked no nitro fuel, then that is what it would get. It is less expensive also! Does it start easily? If so, it is a keeper!
Good luck my friend,
Frank
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I agree Frank, the report seems optimistic for a .35 with a 10-5 prop.
However, though he doesn't say so, Martin does lead one to believe he's reporting his own test results.
I've done more tests with fuel mixes down to 20% oil and less oil seems to result in smoother running.
I tried FAI 80/20 (straight castor) and 14.5/65.5/20 (Omega 15% + castor) and both run smoother than higher oil content mixes.
As might be expected, the 14.5/20 runs noticeably cooler; oddly, it still won't turn 11K; MOF, very little more than the 80/20.
Not mentioned in my original post, with 26-28% oil the engine at times has a rather memorable kickback, which goes away with 20% oil.
I'm beginning to think that the extra oil is raising compression even higher, but seems that would result in higher rpm capability, particularly with the added nitro.
And I don't know what to make of this:
On a whim, an MAS 9-5 wood on 14.5/20 maxed at 12.2K, while FAI maxed at 12.4K!
I'm not sure if 20% would provide sufficent protection over time (Forster recommended 25%) though I think Enya recommended 20% in his older iron/steel engines.
Performance is certainly sufficient for usual .35-size airframes, I was just expecting a good bit more.
Terry
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Rex Abbott ran a Forster .35 for awhile, but I think he got over it. In an "International Stunt Winner", if I remember correctly. It seemed pretty fussy to me. I'd suggest contacting him, and also would suggest that the 10-5 APC is a lot of prop for it. Going to a cooler glowplug would also seem like a good idea, if you're actually getting pre-ignition. Less prop load would not make it heat up as much, so that should also help. Nitro does produce heat, but is actually pretty difficult to light afire...I don't think nitro or compression ratio is the problem. Plus, a lot of older engines are known to have a pretty nasty "bark", but I don't know if there's a theory about why. ??? Steve
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Thanks for your comments Steve.
Again, I've been approaching everything here as though Martin's review was accurate/applicable.
Posts on SSW lean toward a 9-6 prop, 'though one poster liked an 11-4.
It has occurred to me that my thinking this to have been a used engine (therefore broken in) when I got it may not be the case.
Mods to the exhaust stack led me to that idea, but I also noticed no marks on the lugs.
It may be that the recent cooler running is due to wear-in and more running is the proper approach, but with the 9-6 for the lighter load and 25% oil to be safe.
Terry
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You might want to check with MECOA as they have built quite a few of those and do have parts. I have purchased a timer and intake venture from them. I also make gaskets for most of my old engines either from aluminum sheet or Testors gasket material from Tower.
Most of the older engines had reasonable timing and compression ratios, but my Orwick 64 has 10 to 1. I added another gasket to tame it down and it did help. It still has plenty of power and runs smoother for control line. I think Henry Orwick did lower the compression on his later engines for that reason.
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Hi Jim -
Fiddling with old engines, I've made a few gaskets before using card and gasket material, but with quite mixed success.
Neither an X-acto nor my cheapie circle cutter (not to mention my skill) do a very good job.
Would you be willing to give us a seminar on technique and tools?
Terry
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Well Terry, my way is not perfect and sometimes I have to cut 2 or 3 to get one I really like but here goes. For cutting them out of aluminum I mark the inside hole and use a large paper punch to go around just inside the mark to make the hole. I then take my Dremel with a sanding drum and finish it out. You will have to take a knife and clean up the edges of the hole. If it is a narrow gasket that fits inside of a groove in the head, I use scissors to cut around the outside to fit.
If it is fiber gasket material, I use an Exacto #11 blade and cut it out. The only fiber that will work for head gaskets is the Perfect gasket material from Tower. I said Testors above but it is the Perfect brand. Sometimes you can get black asbestos rubberized gasket from the auto parts stores, but it is hard to find in the right thickness. Card stock works well for back plate gaskets and such but will blow out and leak very quickly in head gaskets. On thin back plate gaskets I some times use brown butcher paper or grocery sacks. After marking the inside hole in paper or fiber gaskets, I cut with that Exacto knife very carefull going only slightly into the material on the first pass. I find that if I keep turning the material to where I am always pulling with the knife I can usually get it cut without slipping and cutting where I don' want to. On backplates you can cut the inner hole and bolt up the back plate, and then cut around the outside with the knife.
As someone once said you just cut away everthing that is not a gasket.
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Thanks Jim - I just finished adopting some of your techniques. ;D
A couple follow-ups:
What method do you use to lay out holes - measurements, some sort of pattern transfer from the parts or..?
I usually punch through boltholes with a scribe; sometimes they tear out, at best tattered material makes it hard to start the bolts - do you have a better way?
Terry
P.S. -
Checked and MECOA does list gasket sets for it! :D
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I use a small paper punch for the bolt holes after marking them. It works on aluminum and fiber really well. The secret is getting them punched in the right place after marking them. Once the center hole is done you can slide the gasket onto the back plate or what ever and mark the holes. Then remove the gasket and punch them out. If you really want an exotic tool you can buy a leather punch but paper punches have worked just fine for me.
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I guess a paper punch is on my shoppping list. :)
I'm happy to report that, after more running, the engine is getting better.
Still has black residue in the exhaust but the miss has gone away and, on 75/25 fuel, it peaks the 9-6 APC at 12.2K, 10-5 APC at 11.4K.
While a few owners report good 4-2 performance from theirs, this one picks up only about 500 rpm in 4-2; anyhoo, a wet-2 run is ok with me.
But who knows, after more running it may become one of the rare 4-2'ers. ;)
Terry
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I spoke with Rex today at the contest. He said a 9-6 was about it for the Forster .35. Also said it wouldn't be a good choice for a Smoothie or something of that size. Does RSM make a 9-6? If so, get one to try! H^^ Steve
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Thanks, I very much appreciate your interest Steve H^^, and yes, Eric lists a 9-6.
I noticed fuel leaks on the head when running it today, and when the head bolts wouldn't tighten, I decided I'd take a chance.
Pulling the head, the gasket, stuck inside the groove, came off the cylinder w/o damage and I found what appeared to be carbon build-up on the piston and cylinder gasket seating ring.
A careful examination of the mounting lugs also revealed thread marks in the holes, though nothing shows on the lug surfaces, so it certainly has a past.
I cleaned everything, discovered that a spare McCoy .35 RH gasket was a near-perfect fit over the Forster gasket and reassembled it.
No more crackle, no more leaks.
I don't know how it'd perform in the air, but with the 9-6 on the 4-2 edge at ~9900 rpm, it breaks to ~11.1K in 2-stroke mode.
And Rats! Smoothie is top of my all-time favorites.
Terry
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A Veco Warrior would be pretty sweet choice! The one that looks like a small Chief...good flyer if kept light. H^^ Steve
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Well, I do have about 4 dozen all-time favorites. ;D
Terry