doxilia

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Alright,

after a few honey do's today I'm back home and luckily a post man was in training so his trainer decided to stop by my place and drop off my Tower order containing an OS 905 (Code #71905200) aluminum radial mount. First of all, this mount accomodates the following OS engines: 60FP, 65LA, 61-91FX, 65AX, 75AX, 75AX-BE and the 95AX - that's quite a range of engines using the same identical mount pattern. The first thing I did was to take out my NR Speed/13 and see if it fit as we supposed and it is indeed a perfect mount pattern - this confirms that a similar repertoire of NR engines would most likely fit on this same mount as the Speed/13 does. Being a RE engine, there are some issues with the clearance of the header (as often happens with radial mounts and RE engines) but Dremeling out about half the depth of the mount in a semi-circular pattern centered on the top rear will allow NR headers to pass and mount on to the engine. I have yet to pull out an OS 61VF and a 61RF to check the exhaust status but otherwise I'm certain these will be also be a perfect mount pattern as well as the above listed engines.

I also checked a YS 60FR and the engine also mounts perfectly, side-to-side, on either pair of the mounting holes: front or rear. This confirms the 52 mm center-to-center mounting width between mounting bolts. However, as already mentioned, there is the 20 mm vs 25 mm lug width difference between bolts. As to the thrust washer offset between the NR Speed/13 and the YS 60FR IF the YS is mounted using the position of the rear bolts, the difference in location of the thrust washer (spinner backplate) is exactly 1mm. This is due to the rear bolt center to thrust washer distance differing by 1 mm between the S13 (77 mm) and the FR (78 mm). In other words, if one were to re-use the rear mounting bolts used for a S13 and switch to a YS FR, AR or Classic, the YS engines would end up with a 1 mm larger gap between the nose ring and the spinner backplate. Not great but 1 mm is a little over 1/32" so I believe that might be generally acceptable for a quick swap from NR to YS. If the opposite were done (YS to NR), one might end up a little tight on clearance between nose ring and spinner unless one left 3/32" spacing between the two when mounting the YS initially. Once swapped, the NR would be just shy of 1/16" so snug but workable.

Another way of looking at this current manufacture engine option and replacement if using a radial mount (and using the exact same location for the rear mount bolts) would be to mount the NR using a 1/32" ply spacer between the FW and the mount. Then, if one were to replace the NR for a YS, one would simply remove the spacer and the thurst washer would be in the correct place to within 0.2 mm - perfect!

Next will be to check the thrust washer of the OS engines and compare to both the YS and the NR. Last would be a comparison to vintage engines such as Rossi FIRE's, OPS Supers and Picco's.

David

computermonkey

My Feedback: (90)

Moki?

computermonkey

My Feedback: (90)

I just check some measurements. Looks like the Moki is a little smaller engine.

doxilia

My Feedback: (3)

SV,

I took the liberty of borrowing some nice pictures from Mike's Crusader build on another classic forum showing the BHE (Bridi Hobby Enterprises) mount. Below are some pictures showing the symmetric bolt pattern of the mount which allows you to drill the FW for a side mounted engine and then rotate the mount 90 degrees clockwise to position the engine with the cylinder in a vertical position. This is helpful during a build as it permits the use of the mounted engine while framing up the fuse without the cylinder head interfering with the right fuse side. The sides are framed up with the formers and having the engine in place then allows a nose ring balsa backer as well as the nose ring (1/16" ply typical) to be glued in place so that the nose ring to spinner gap is as desired (1/16" spacing also typical). The photos depict the engine mount in position for the side mounted engine and then shows the mount rotated and bolted in place without any misfit or offset of the bolt pattern. In short, the symmetric "square" bolt pattern is very useful but proper placement of the bolts is required as otherwise one ends up placing a motor mount bolt in a location which becomes inaccessible once the engine is bolted down on to the mount. Commercial mounts take this into account and I have not come across instances where one is "stuck" being unable to remove the bolts from a mount because the engine interferes. This is true for Dave Brown, BHE, and as far as I can tell, now also OS aluminum mounts which incidentially are also square and symmetic about the bolt pattern. The BHE has the advantage of also being symmetric in the "peripheral casting" of the mount while the OS is slightly different in shape in the vertical direction as it is in the horizontal. Not a major issue but one has to be careful as it could potentially give rise to issues with fuel tube and pushrod routing.

I also took some pictures of the versatile OS 905 mount (see next post) showing a NR Speed/13 bolted in place using a single bolt per side showing the matching holes in the adjacent bolt placement. The beam width of the mount is 44 mm which allows a 43 mm case width engine such as the S13 to just "drop in" on the beams and also allows a 43.5 or 44 mm wide engine (rare) to be accommodated provided the bolt spacing on the lug is 25 mm. Although the YS is only 40 mm wide, the wider mounting lugs and 52 mm across lug bolt spacing makes for a drop fit mount as well IF the mount was drilled and tapped for 20 mm bolt spacing.

Using this mount, I measured the FW (back of the mount) to thrust washer distance of the S13 to be 113 mm. For what it's worth, a useful measure if one is for example locating a FW in a set of CAD drawings. Last but not least, is a snap I took of the dimensional drawing that accompanied my YS 60FR engine showing the narrow 40 mm case width and the 20 mm lug bolt spacing.

My suggestion would be to basically machine an aluminum mount very similar to the OS 905 and/or the BHE mount making sure it is light (the rear of the OS mount is recessed removing 80% of the aluminum from half the thickness of the radial structure) yet structurally sound. Note the radial structure to beam gussets on the top and the sloping thickness of the beams as they approach the radial structure. The mount additionally has two perfectly flat polished surfaces upon which the engine lugs rest. The rear of the mount is also bored out in a circular fashion to allow fuel tubing to pass for instances where one wants to use a backplate pumped engine (e.g., OS SF-P, RF-P) or simply wants to pass the fuel lines across the FW though a hole as shown in Mike's Crusader FW setup.

Once the basic design of the mount is done, the only variation on the mount would essentially be side or rear exhaust. The latter would require a slight modification to the top center of the radial structure allowing a header to be passed. If one is going to be machining the mounts, this "allowance" might as well be designed in so that if one is going to use the mount for a RE engine, then the "gap" is already in place so one doesn't have to grind away aluminum. Other than this, the only other variable would be engine mount bolt spacing (20 or 25 mm) and fore-aft location on the mount. I think that with 4 different bolt location alternatives, we'd probably cover the gamut of engine possibilities placing the thrust washer (TW) for any given engine at the identical location in terms of FW to TW distance. If one wants to provide for the vintage "long" engines such as OPS/Picco, then these would set the maximum length required for the distance as these are the longest engines in the classic business. All other shorter engines would simply by mounted further forward on the beams (or partially further forward) locating the TW at the same spot - either through direct bolt down location or a combination of this and FW spacers. I think the trick would be to "meter" and tabulate the engine length differences so that the various combinations of engines and mount would result in standard "offsets" (if required) between FW and TW position so that any additional spacing needed can easily be accomplished (and perhaps offered with the mounts) by plywood FW/mount spacers.

Perhaps this all sounds complicated but I think it is doable and I'm surprised on some way that engine mount manufacturers haven't undertaken this study thoroughly to make the process as transparent as possible to the hobbyist. Imagine if we always knew that the space required to mount a 60 size classic engine would be 115 mm as an example. For the ARF world that would be revolutionary and for those designing say classics (eh, hem, yours truly...), I would know that the distance needed between FW and nose ring would always be 115 mm regardless of what engine (or engines!) the builder/flyer intended to use. Now that would be shweet!

'twas a little long winded...

David

doxilia

My Feedback: (3)

To avoid confusion, I added the OS 905 mount and NR Speed/13 engine pictures in a separate post here. Note the 44 mm spacing between beams. Limes are very useful when it comes to supporting engine mounts!

The last picture shows the dimensional drawing of the YS 60FR which I understand represents all 60 size classic pattern YS engines - YS FR & R Classic short strokes and R & AR long strokes.

David

doxilia

My Feedback: (3)

CM,

I unfortunately don't have a Moki so please do post dimensions if you don't mind. I plan to augment Dominik's Excel sheet with various dimensions of the engines I have (a few too many...) and those that I don't through help with data provided by others.

How is it smaller? Width, length, inter-lug bolt spacing (< 52 mm?), lug bolt spacing (< 20 mm?)? According to Dominik's spread sheet, the Moki 61 LS is somewhat "non compliant" in that it uses a 28 mm lug bolt spacing and a 51 mm inter-lug spacing. His chart also mentions the Rossi's use 52.5 mm inter-lug spacing instead of 52 mm. I will check whether that 0.5 mm is material or whether they are in fact a drop in bolt in on the OS 905 mount. Every other engine except for the Moki and Rossi on his list uses 52 mm on the inter-lug.

Any and all dimensions you can provide will be useful.

David

computermonkey

My Feedback: (90)

Hi David, I'll get you some measurements.

doxilia

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I seem to be on a posting spree on this thread so thanks for posting this info Will. According to Matt, these IM plates don't quite "match up" between OS and YS options. It would be simple enough to make a set oneself as you suggest and account for any offset required between the two engines. I haven't checked the OS/YS offset issue yet but as soon as I can dig out a VF and an RF I will. I wonder if the offset is the same as it is between the YS and the NR - 1 mm.

It seems that those mounts are still available now from Ohio Superstar who bought the distribution rights of the DB product line (except Vortech spinners I understand). They are available here (see picture attached):

http://www.ohio-superstar.com/dave-b...4-cycle-mounts

While I have not seen or bought a Jett mount yet, so far I am very pleased and impressed with the quality of the OS aluminum mounts. Perhaps not so much with the price ($32 at Tower for a 905 60 size mount) but I suspect that Dub's mounts are similar in both cost and quality.

The question raised in this thread is whether a good machinist might be willing and able to produce a good quality aluminum mount that is "flexible" both in terms of exhaust direction as well as lug bolt spacing. I would be happy to spend $20-25 on an equivalent quality mount which was "smartly engineered" and wasn't brand specific as the OS and Jett mounts generally are (even though one can bolt in any other 25 mm engine on to an OS for example). An issue discovered with the OS for example, is the need to grind away the top of the mount to accommodate RE headers. This should be "engineered in" IMO. The mount shown here takes care of these sorts of issues but if one wanted a hard mount a single piece symmetric mount seems to make more sense and may be more economical on cowl space.

David

computermonkey

My Feedback: (90)

speed-panzer in post 7 is right on with the measurements for the Moki M12 LS.
For the M8 M measurement is the same as the Moki M12 at 56mm, E is 49.2mm and F is 22.8mm.

doxilia

My Feedback: (3)

CM,

thanks for the dimensions. Are these .49 (M8) and .73 (M12) cu in engines, respectively?

David

computermonkey

My Feedback: (90)

Moki M8 and M12 are both .61 engines. M8 is the short stroke and the M12 is the long stroke.

speed-panzer

My Feedback: (1)

BTW, the Moki is by far the most lightweight engine at just 500g. You can see this quite well from its outer appearance, it looks considerably more "petite" or grazile as compared to a massive Rossi.

If you like to take advantage of this excel spreadsheet, let me know, I can pm it to anybody interested.
I would be glad if you guys add more data from other engines to get a real broad overview.

Dominik

doxilia

My Feedback: (3)

Dominik,

PM sent.

David

SuperViking

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Yes I am familiar with Bridi mounts, my mind went blank with BHE. I still am waiting hopefully for a progress report from the machine shop who seems pretty busy at the moment. I will post an update as soon as he contacts me. It might take a little while considering the shop has real work to complete.

doxilia

My Feedback: (3)

These were/are my favorite FRP mounts from back in the day - very sensible. Maybe though, they are not as well suited for a machined aluminum mount as the OS 905 is. I would be inclined to using the latter mount as a "mold" or template for the "pre-tapped" machined ones.

What!? Machining classic pattern engine mounts IS real work! Anything else is of little interest...

I look forward to seeing what he comes up with.

David

lfinney

My Feedback: (44)

just want to add two bits of info, one is that the Jett 60 thru 90 size engines have the same mounting hole dimensions as rossi and OS, second you can find the jtec/tatone mounts on fleabay as well that are predrilled and tapped for the OS 61 engines. I am using one on a tiger 60 right now and I swap out the Rossi and Novarossi and Jett engines as needed to break them in. I dont think the mount will need ny clearance work for a rear exhaust engine.

Huang

My Feedback: (27)

SuperViking - I'm keen on ordering a set of the aluminum mount as well if this comes through.

David - I thought the Ohio/Dave Brown soft mount was predrilled for the YS 4-strokes. I've not taken the YS 4-bangers out to compare mounting tabs with the 2C yet but I vaguely recall they are different.

One other mount that I was looking at is the Gator mount that Central Hobbies carries. I've not used this before but I'm sure some of you have since I remember they were pretty popular during the long stroke - early 4C era.

The good thing I can see about this mount for our rear exhaust 2C application is that: (1) the mount width is adjustable, (2) You drill/tap to suite the engine holes and firewall/spinner length, so it'll fit all engines, (3) there's no cross members to get in the way of the header, (4) the rails looks to be sturdy aluminum, (5) dampers to take out vibrations, (6) slightly cheaper than other soft mounts

Not sure of their vibration damping qualities or if they will be too soft for the YS-61R classic. Any experience or thoughts? Should I go with this or the adjustable Hyde mount with the cheap looking GP adjustable nylon rails? Not sure if the header will clear though. Photos of both below.

8178

My Feedback: (17)

I used this soft mount in my Tiporare and it works very well http://www.sullivanproducts.com/MotorMountsContent.htm

flywilly

My Feedback: (121)

Huang,
here's my 2 cents:
The Dave Brown rail mounts are predrilled for the YS 91-115 which also fits all OS .61 2-strokes, but you can buy the rails undrilled/tapped (I've used them for Webras). It is a nice mount especially when a hardwood beam is already present like the MK kits. You can use the 'T' beams, but I think there are better alternatives.
The Dave Brown sport-tab mount works very well as does the sport-beam mount.
The Gator mount is well made, but better suited for 2-stroke engines as the vibration damping is relatively minimal. It was designed with for 120 and larger engines so the beams are a bit longer than needed for a 60.
Sullivan still makes a backplate mount very similar to the Dave Brown sport-tab mount except it uses a one piece aluminum backplate instead of four separate 'tabs'. I have used these mounts since they were first introduced in the late '80s as well as the sport beam mount. Easy to install, durable, good vibration damping for 60s and easy to swap different engines.
Budd Engineering makes a clone of the Hyde mount which also works very well. It uses a removable aluminum plate to mount the engine which can be purchase separately for easy engine swapping. It has excellent vibration damping and they are on sale (and have been for at least 6 months) as the demand (in the pattern world) for glow soft mounts has dropped significantly. They can be used without a nose ring with a two stroke 60, though one is recommended.
Lastly, the Hyde mount. There are several variations of this mount, but for use with a 2-stroke 60 the mount shown above is more than adequate. It does not need a nose ring, provides excellent vibration damping and is amazingly durable. Merle Hyde claims 3,000 or more flights and after extensive testing, I believe him. The Hyde mount for the YS 91-115 fits the OS .61 perfectly (I am using one in a Desire with a Hanno Special). The Hyde mount is also the priciest, but well worth the investment if you plan on flying the airplane more than 500 flights.
My current 'fleet' utilizes 2 Hyde mounts (Desire-Hanno Special 123 flights; Extra 260 OS 1.20AX 46 flights), 2 Sullivan backplate mounts (Flash-Hanno Special with 866 flights; a slightly reduced Tyhoon 900 -Hanno Special 12 flights), MK beam mount (Topstar-OS 140 854 flights)
Sullivan used to make a relatively primitive 'soft' mount which was a recessed, rubber rectangle which fit over the engine lugs and was bolted/screwed to a beam mount with an aluminum cage retainer. Not very much vibration damping, but really easy to swap engines.
I hope this helps.
-Will

Huang

My Feedback: (27)

Thanks Will, very helpful and thorough. Looks like you've used every one of the soft mounts made and have had extensive usage on some. It looks like we have more options than I thought! Some thoughts:

- I'm surprised the Sullivan back mount worked so well after 800+ flights because it mounts using the smaller crankcase backplate screws on the engine. The limitation seems to be that the distance from the firewall is dependent on the length of the engine or you will have to shim the mount at the firewall.

- The Dave Brown rail mounts with rail only look like a slightly modified copy of the MKs. The Sport Tab mount seem similar to the Sullivan back mount. The Sport Beam mount looks like an easy solution and actually looks to be the cheapest/easiest of all options.

- I've not heard of Budd engineering - cool find. It indeed looks like a Hyde mount with swappable engine plate, but the plate itself looked a little bit wimpy. Not sure if this is stronger or the adjustable nylon mount on the Hyde.

- I've used Hyde mounts in the past and believe they are superior, but never the adjustable Hyde mounts. The other question is whether a FIRE engine header will clear the Hyde. Anyone?

My current application is the Zigsaw Atlanta '86 version with firewall (no wood rails) for a YS 61 classic. So the limitations are firewall mounted, and the rear exhaust header needs to clear the mount. I'd like a solid enough (soft) mount that dampen enough vibration, while not shake all over the place. Otherwise, I'll hard mount with an aluminum mount.

Matt

flywilly

My Feedback: (121)

Hey Matt,
I have the Hyde mount pictured, a YS classic and an Aurora header which I believe is very close to the Atlanta header. I don't have an Atlanta. If you would just send me the Atlanta, I can check the fit of the mount, engine, header and, oh, possibly the flight characteristics... .
Seriously, what are the dimensions of the firewall? The sport beam will definitely work and I'm pretty sure the Hyde mount will as well. I will look at the Hyde mount, YS classic later today and report back.
-Will

doxilia

My Feedback: (3)

Matt, Will,

great info! I just picked up some Korean made glass (FRP) mounts which have an interesting lightened truss like design. They are two part mounts so RE headers are not an issue. They are quite versatile in terms of fore aft engine position as they have "slotted" holes so locating the engine for the spinner distance is a simple matter of tightening the bolts in the correct position. Once mounted for a 52 mm bolt width, most all 60 size engines would fit so it would be easy to swap at will. The disadvantage if say is that they may result in some power loss compared to a hard aluminum mount. I'll post some pictures later.

Matt, the OS 4 banger 90's have the same mount dimensions as the 2c OS 60's. But you are probably right about the YS 2c and 4c. The latter might also be 25/52 mm spacing.

David

Huang

My Feedback: (27)

Thanks Will! I just checked my Aurora header vs the Atlanta, basically the same. Would be great if you could check whether that clears the Hyde. I am a bit weary of the nylon rails though, as I've used GP adjustables in the past on ARFs and it was definitely flexy.

David, It seems most of the mounts are pre-drilled for the OS. My MK Aurora & Arrow both came with OS RFs installed and I wanted to swap for the YS. Similar to the OP I came to find out they are not interchangeable and the 5mm difference between them makes it a bit if a headache to remount. The split Korean mount with the slotted holes is a good solution between brands. Which reminds me, Hangar 9 makes an aluminum version of that exact mount for their 60/90 Warbirds. I've swapped from the OS Surpass to the YS-110 without any mods. That might work well for our application too.

flywilly

My Feedback: (121)

Hey Matt,
Plenty of clearance between the header and the mount. The Hyde mount is 2 13/16" in diameter. At maximum width of the adjustable mount, the YS engine lugs are still slightly too wide and spring the mounting arms apart. This is because the diagonal support bracing interferes with the lugs and should be ground flush with the top of the mounting arms as far back as necessary.
I will try to post some photos tomorrow.
-Will

Huang

My Feedback: (27)

That's great to know, thanks Will!
I'm assuming you have the .40-.80 one (30mm-44mm crankcase width) not the .90-1.15 one (34mm-46mm crankcase width)?