Author Topic: MAX-S O S 35 - Info needed (Read 4210 times)

Paul Taylor · « **on:** July 22, 2009, 12:38:32 PM »

I am the proud new owner of a used Max-S OS 35. I would like to replace the screws in it, but I am getting some conflicting information. The guy that I got the engine from had the screws in a bag and mark them as 2.6 MM.
Someone posted to my ad, that the screws were M3 x .6 x 10 MM.

B4 I go and place an order I want to be 99.9% sure I am getting the correct ones.

Come some one help me out please?

Head screws and back plate screw size for MAX-S OS 35?

Steve Holt · « **Reply #1 on:** July 22, 2009, 03:26:44 PM »

Paul,
Those screws are really odd size and very difficult to find. There was someone on one of the forums selling stainless steel screws that fit but my old brain can't remember who just now. One other interesting fact about the screws is that they are not Phillips head. Although they look alike, the slots are actually JIS (Japanese Industrial Standard?) so you will need a special screwdriver to remove them. Some hobby shops carry sets of JIS screwdrivers and they work great on these screws. They also work on Phillips, so that is what I carry in my toolbox. Enjoy your Max, they are great stunt engines for smaller airplanes.
Steve

Rob Killick · « **Reply #2 on:** July 22, 2009, 03:53:21 PM »

Hi Paul ,

I see a lot of these types of "what kind of screws are these?" posted on this site ...

The best thing to do is purchase a standard/metric screw pitch gauge and a set of vernier calipers (digital read out) that is capable of converting from standard to metric and vice verse .
Always good to have the proper tools (saves lots of stripped threads) .

All the best ,

Rob Killick

Dick Byron · « **Reply #3 on:** July 22, 2009, 06:13:30 PM »

I have sets available $5.00 includes postage. Stainless steel allen head.

DICK BYRON
3325 GALAWAY BAY DR.
GRAND PRAIRIE, TX 75052

I am leaving for the Nats on Monday the 27th.

Bill Heher · « **Reply #4 on:** July 22, 2009, 06:47:31 PM »

Dick- would these also be the same size needed for Max-H .40 and the .35-.40 FP series??

Garf · « **Reply #5 on:** July 22, 2009, 07:01:46 PM »

Quote from: rootbeard on July 22, 2009, 12:38:32 PM

I am the proud new owner of a used Max-S OS 35.

If you want a killer setup and have a few expendable bucks, get a replacement P&C assy from Brian Gardner (Bristunt). Not cheap, but it is ABC and comes with a new wrist pin and con rod. Same as most ABC setups, it only takes a few runs to be able to fly it, but takes a lot of airtime to be fully broken in.

Paul Taylor · « **Reply #6 on:** July 22, 2009, 07:24:19 PM »

Quote from: Dick Byron on July 22, 2009, 06:13:30 PM

I have sets available $5.00 includes postage. Stainless steel allen head.

Dick,
Sent you a PM.

Steve Helmick · « **Reply #7 on:** July 22, 2009, 09:25:44 PM »

Quote from: Bill Heher on July 22, 2009, 06:47:31 PM

Dick- would these also be the same size needed for Max-H .40 and the .35-.40 FP series??

I believe Dick's cres socket head machine screws would fit the H.40, but they definitely are wrong for the .35/.40FP's.

The 5-40 is the standard replacement screw size for early ST and OS engines like the G.21 .29 > .46, ST .51 > .60, and OS .35S. I personally fitted one of PTG's OS .35S engines for 5-40's. It works very nicely. 35 years in trade and counting...tick...tick...tick.

Steve

Paul Taylor · « **Reply #8 on:** July 23, 2009, 07:08:10 AM »

Quote from: Steve Helmick on July 22, 2009, 09:25:44 PM

I believe Dick's cres socket head machine screws would fit the H.40, but they definitely are wrong for the .35/.40FP's.

I am so confused..

Bill Heher · « **Reply #9 on:** July 23, 2009, 07:32:34 AM »

Paul - what may have you confused is the different models of O.S. Max .35s ( and .40s). Early ones with the muffler attached by a strap around the case and OS MAX-S or MAX-H ( in the .40) were traditional iron / steel piston / liner types, . The old Max-H .40 also has a ball bearing supported crankshaft.

The newer ones are the FP series and have muffler attached with screws through ears on each side of the exhaust port into the muffler. The box for thr C/L version of the FP series still says O.S. Max on it, and the instructions call them FP .35-S and FP .40-S. The .20 made famous as the Brett Buck Tune Up for Flite Streak ARFs ( and .25) is the same series. These are ABC or ABN ( Aluminum piston in a Brass/chrome or brass/nickel plated liner), and bushings in the case to support the crankshaft. These were the basic OS engine series of sport engines before the LA series was introduced.

I was asking Dick if the same screws were used in both the newer FP series and the Older Max-H and Max-S ones.

john e. holliday · « **Reply #10 on:** July 23, 2009, 07:33:36 AM »

As has been stated many times on engine questions about machine screws. If in doubt take the engine to your local Ace Harware and go to the metric section. That is where I get all my metric socket head screws and also for the American made engines. DOC Holliday

Ward Van Duzer · « **Reply #11 on:** July 23, 2009, 08:51:04 AM »

Some time ago I was wrapped up in OS .35 s's and someone sent me a bunch of socket heads for these. These may be the ones discussed above. They are marked "M3 X 0.6 Socket heads. 12 mm (length) for heads. Cut shorter for OS .35 Crankcase."

That's my input. It may be correct. It may not.

Proceed with caution.

BTW, Randy Smith and Big Art are/were pretty much the experts on these.

Ward-O

RandySmith · « **Reply #12 on:** July 23, 2009, 11:31:58 AM »

Hi Paul

The Stock ,and correct size screws for the OLD style OS MAX 30 and 35S are M3-.60 x 10 , they use JIS heads..these mic at .1140

Many people use a 4-40 x 1\2 for the replacements..these mic at .1110, these go into the case pretty easy, and I have many engines that have had the 4-40 in them for years.

some people use a M3-.50 x 10 ..these mic at .1115, these will work but will bend the threads inside the case slightly, they have much more drag on them going in than say the 4-40s

DO NOT use a 5-40 they are much larger, .1200 ,and they are much harder to thread into a stock case that has not had the threads altered, the 5-40 maybe an option if you need to retap the case for a slightly larger diameter bolt

The 5-40 screws were perfect fits for the Older Super Tigre G-21 35 , 40 and 46

The Newer OS FP 35 and 40 uses a M3-.05, which is differant than the ones for the old 35S. I use M3 x.5 x 12mm for the ones I setup, these also fit the OS FSR and newer Thunder Tiger,
They also fit the OS VF 40 46 heads, the front housing bolts are 3.5mm though
M3-.50 also fits many Magnum motors, and Most all of the OS FSR clones such as the Royal and many others.

Randy

Dick Byron · « **Reply #13 on:** July 23, 2009, 11:34:59 AM »

The sets I sell are 8mm and 10mm in length. I have sold 200 sets in the last 4 years and use them in all my OS 35S engines.

Kim Mortimore · « **Reply #14 on:** July 23, 2009, 12:39:09 PM »

Another factor with the MAX-S OS 35 is that the con rod is made of unbushed soft aluminum and the crankpin hole will wear from round to egg-shaped in a relatively short time (ask me how I know), resulting in loss of power.

If you plan to fly this engine a lot, be prepared either to replace the con rod once a year of so, or get a higher-quality replacement. Engine rework guys used Super Tiger rods back in the day. Maybe Randy or Dick or someone else has better rods available.

It's a good engine, which ruled stunt for a time between the dynasties of the Fox .35 and ST .46 (just ask the Adamisin clan!) I had one fly a Humongous very nicely, and that's a whole lotta plane for a .35.

Kim Mortimore
Santa Clara, CA

Alan Hahn · « **Reply #15 on:** July 23, 2009, 01:44:26 PM »

Of course there is nothing wrong with the original screws--as long as they are not already buggered up and you have the correct screwdriver.

Steve Helmick · « **Reply #16 on:** July 23, 2009, 07:50:58 PM »

Quote from: Steve Helmick on July 22, 2009, 09:25:44 PM

I believe Dick's cres socket head machine screws would fit the H.40, but they definitely are wrong for the .35/.40FP's.

The 5-40 is the standard replacement screw size for early ST and OS engines like the G.21 .29 > .46, ST .51 > .60, and OS .35S. I personally fitted one of PTG's OS .35S engines for 5-40's. It works very nicely. 35 years in trade and counting...tick...tick...tick. Steve

The .35/.40FP and .40/.46LA use 3mm x .5mm x 12mm screws in the heads, and 8mm long in the backplate.

Near as I have been able to determine, the "standards" changed on the metric screws, for 3mm, from .6mm pitch to .5mm pitch. That's the peak to peak dimension on a metric thread...one thread, vs. how many per inch. This is just nuts and bolts; it's not rocket science. They didn't ask me, or tell me when they did it, but it's just different now. The 5-40 is a good solution. If you just oil the screw up good (old thick STP!), you can screw it right in, they say. The screw, that is, no tapping. I couldn't quite bring myself to doing that. I got a 5-40 tap and ran it into PTG's crankcase, and that was traumatic enough for me. Howzat working, Phil?

If anybody has one of these that's broken/worn beyond repair, I'd like one to try various repair methods on.

Steve

Dallas Hanna · « **Reply #17 on:** July 23, 2009, 11:52:43 PM »

Quote from: Steve Helmick on July 23, 2009, 07:50:58 PM

The .35/.40FP and .40/.46LA use 3mm x .5mm x 12mm screws in the heads, and 8mm long in the backplate.

Near as I have been able to determine, the "standards" changed on the metric screws, for 3mm, from .6mm pitch to .5mm pitch. That's the peak to peak dimension on a metric thread...one thread, vs. how many per inch. This is just nuts and bolts; it's not rocket science. They didn't ask me, or tell me when they did it, but it's just different now. The 5-40 is a good solution. If you just oil the screw up good (old thick STP!), you can screw it right in, they say. The screw, that is, no tapping. I couldn't quite bring myself to doing that. I got a 5-40 tap and ran it into PTG's crankcase, and that was traumatic enough for me. Howzat working, Phil?

If anybody has one of these that's broken/worn beyond repair, I'd like one to try various repair methods on. Steve

To add to Steve's input on the "old and new" metric system threads, the Japs and early European engine makers used the old System Internationale (SI) screw thread system. The thread in question, the M3 in the SI system used the 0.6mm pitch. The later ISO system changed to the M3 x 0.5. There are others in the system which are only 0.1mm difference in pitch, one being the thread used on the Enya 09 crank which is M5 x 0.9 whereas the ISO is M5 x 0.8.

Randy S... I'm a bit confused and can't follow the sizes you posted above eg. M3-.50 x 10 ..these mic at 1.115 Can you clear this up for us.

HH

RandySmith · « **Reply #18 on:** July 24, 2009, 10:37:57 AM »

Dallas the mic measurements are in inches

Dallas Hanna · « **Reply #19 on:** July 24, 2009, 05:10:10 PM »

Quote from: RandySmith on July 24, 2009, 10:37:57 AM

Dallas the mic measurements are in inches

Thought so Randy but did you mean 0.115 rather than 1.115 and 0.140 rather than the 1.140.

Some of the metric sizes do look strange but those European fellows sure did screw up the metric system in those early days just the same as we all did with the imperial system! We were changed back in the 70s to metric but most of us "oldies" in the trade still talk the imperial system quite well. I still prefer the Unified system, especially in the under 1/4" sizes.

HH

RandySmith · « **Reply #20 on:** July 24, 2009, 07:52:44 PM »

Quote from: Dallas Hanna on July 24, 2009, 05:10:10 PM

Thought so Randy but did you mean 0.115 rather than 1.115 and 0.140 rather than the 1.140.

Some of the metric sizes do look strange but those European fellows sure did screw up the metric system in those early days just the same as we all did with the imperial system! We were changed back in the 70s to metric but most of us "oldies" in the trade still talk the imperial system quite well. I still prefer the Unified system, especially in the under 1/4" sizes.

HH

Hi Dallas yes I was in a hurry and put the decimal in the wrong place, I fixed it, the screws are all a bit above a tenth of an inch not just over 1 inch..my bad

regards
Randy

Steve Holt · « **Reply #21 on:** July 25, 2009, 10:46:08 AM »

Quote from: Kim Mortimore on July 23, 2009, 12:39:09 PM

Another factor with the MAX-S OS 35 is that the con rod is made of unbushed soft aluminum and the crankpin hole will wear from round to egg-shaped in a relatively short time (ask me how I know), resulting in loss of power.

If you plan to fly this engine a lot, be prepared either to replace the con rod once a year of so, or get a higher-quality replacement. Engine rework guys used Super Tiger rods back in the day. Maybe Randy or Dick or someone else has better rods available.

Kim Mortimore
Santa Clara, CA

Kim,
If you use all castor or mostly castor fuel with at least 25% oil, the rods last pretty well. I use 25% castor and 3% synthetic just like on my Foxes.

Leonard Neumann had a batch of rods made up out of harder aluminum. He might still have some. They are drop-in replacements for the originals.
Steve

RandySmith · « **Reply #22 on:** July 25, 2009, 02:36:54 PM »

""If you plan to fly this engine a lot, be prepared either to replace the con rod once a year of so, or get a higher-quality replacement. Engine rework guys used Super Tiger rods back in the day. Maybe Randy or Dick or someone else has better rods available. ""

The super Tiger 35 rod was used by many people, you needed to machine the inside bottom end of the rod to .250 inch, to fit the OS crank and many of the rods also had to be machined to a smaller diameter on the outside of the bottom end , I also made many of these, plus some from scratch and vented (drill oiling holes) in the top and bottom of the stock rod. RPM also made many rods for me for the OS 35S.
So the rod was a big problem with the 35S but the piston was also a big problem, the skirt is so thin the wrist pin hole wore very fast, when that happened the piston could rock back n forth and would go downhill fast, this would also cause the top of the rod to wear into a big oval.
The other big problem was the wrist pin, the metal pads they put into the ends would and did in most everyone I looked at that had a lot of time on it, wear grooves and deep scratches in the side of the sleeve, I have ones with plastic pads that don't scar the sleeve sides in stock, along with lots of other parts for the 30 and 35 S...P/S sets are pretty much gone though

Randy

So if you have any old 29 or 35 ST rods you can make them work

Dave Adamisin · « **Reply #23 on:** July 25, 2009, 06:09:45 PM »

Hi Paul. Alternatively to the rod surgery the Max requires three teflon pads (the wrist pin and one in the crankpin) and a ST needle valve in a .277 - .283 venturi. The crankpin pad is the hardest to do part but no problem if you have/have access to a lathe. The crank pin pad replaces the hard steel thrust washer behind the prop driver. You make it about .250" in dia with a pin that slips into the hole in the crank pin. The thickness needs to be adjusted to allow for .010 - .020 end play in the crank with the backplate tightened down. Do it before you assemble the rest of the engine and it's easy. The pad face should be convex to encourage a point contact with the backplate. Tightening down the end play is what saves the rod big end. The stock washer lets it travel too far back and forth which is what wears the big end, the top end of the rod and stresses the pin bosses. Also on the big end of the rod use a needle file to lightly (~.010 deep) file a set of grooves (4 total) across the front of the rod thrust face at about 1:30, 4:30, 7:30, and 10:30. Don't try to run it like a modern abc in a wet two it won't last long. See piston pin boss pound out.. A clean four on what ever you like to run for fuel and it should last long enough to get boring...

Author Topic: MAX-S O S 35 - Info needed (Read 4210 times)

Alan Hahn

Dave Adamisin