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Sachs dolmar

Old 02-22-2017, 10:05 AM
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yoavik
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Default Sachs dolmar

hey guys
i was trying to find some info about my "sachs dolmar", found two posts about the engine, but still couldnt figur out if it is the 4.2, 3.8, ( 70 cc, less or more) what's the HP on that engine, recomended prop, and thrust.
this engine was working on my 1/3 scale BLERIOT XI, with a 24X12 zinger (i think it should work with a22 prop) it fly's realy scale like, but with full throttle all the way, and without a drop of additional power!
the resson that i need all the teck details, is cause i'm planning on building a belt reduction sistem for it, so it could take a 32 inch prop, and take my 22 KG beast.. better!
thank you for your help!






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Last edited by yoavik; 02-22-2017 at 01:09 PM.
Old 02-22-2017, 01:05 PM
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CK1
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It looks very muchs like a 4.2 but numbers will tell the truth . Look at the base of the cylinder and give us the letters / numbers you see .
Example :49ZN .
If it is a 4.2 its a great engine , turns a 24x10 biela 2 blade prop around 6800 or more rpm . I would suggest looking into an elect ignition for it . You will get easier starts and a little more power , and it will shed some weight .

Last edited by CK1; 02-22-2017 at 01:09 PM.
Old 02-22-2017, 01:44 PM
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yoavik
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thanks alot CK1
at the base of the cylinder there is what seem to be "49ZN4 W2 MAHLE"
so, acording to your Knowledge, it is the 4.2!
what's the conversion to CC? is it a 70cc engine?
and what about the H.P ?
(it actualy starts very easy with the "spring start", one of the best engines i have got!)

Last edited by yoavik; 02-22-2017 at 02:15 PM.
Old 02-22-2017, 03:37 PM
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It is definitely a 4.2 49ZN indicate 49mm bore . As far as horse power I'm not sure and it's not really an accurate indication with regard to how we use the engines anyway . Prop it for the best performance with regard to your model . Ww1 and ww2 biplanes usually like larger diameter and lower pitch props . The 24 x12 that you have been using is too much prop for that engine / plane combo. A 24 x8 or 24x10 , or 26x 6 would be a better prop unless you go with a reduction drive.
Old 02-22-2017, 07:29 PM
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The orange case is usually magnesium and they were generally stronger, lighter, and better than the machined aluminum cases many manufactureres were building. It also should have the original saw crankshaft which is a plus! If it runs good and you and can flip it fast enough to get it to start dont mess with it! You wont get any more power out of it with electronic ignition. The zinger isnt the best prop, i cant remember what mine turned.. the 3.2 liked to rev a bit more i bet it would like a 26x6.. especially on that draggy bleriot.
Old 02-22-2017, 10:36 PM
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yoavik
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Originally Posted by CK1 View Post
It is definitely a 4.2 49ZN indicate 49mm bore . As far as horse power I'm not sure and it's not really an accurate indication with regard to how we use the engines anyway . Prop it for the best performance with regard to your model . Ww1 and ww2 biplanes usually like larger diameter and lower pitch props . The 24 x12 that you have been using is too much prop for that engine / plane combo. A 24 x8 or 24x10 , or 26x 6 would be a better prop unless you go with a reduction drive.
thanks man, i wanna go for the bigest prop (32-36), so i will need reduction!
Old 02-22-2017, 10:42 PM
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yoavik
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Originally Posted by 2walla View Post
The orange case is usually magnesium and they were generally stronger, lighter, and better than the machined aluminum cases many manufactureres were building. It also should have the original saw crankshaft which is a plus! If it runs good and you and can flip it fast enough to get it to start dont mess with it! You wont get any more power out of it with electronic ignition. The zinger isnt the best prop, i cant remember what mine turned.. the 3.2 liked to rev a bit more i bet it would like a 26x6.. especially on that draggy bleriot.
thanks, great info!
and as i said, i dont need an electronic ignition,
just looking for the full teck details in order to design my reduction system.
Old 02-23-2017, 11:06 AM
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still need to know whats the CC of the engine (i have been told its a 70 cc, can someone confirm?)
and horse power?
those two things are needed for the design of the reduction drive for it.
Old 02-23-2017, 11:14 AM
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68cc
Old 02-23-2017, 12:35 PM
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Originally Posted by w8ye View Post
68cc
thanks!!
do you own a similar engine?, or is that the conversion of 4.2?
Old 02-23-2017, 01:13 PM
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I have the chainsaw it was derived from
Old 02-23-2017, 01:16 PM
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Dolmar 120si super 4.2 ci , 68 cc , 4.9 hp
Old 02-23-2017, 02:16 PM
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Originally Posted by w8ye View Post
I have the chainsaw it was derived from
W8, I have never had my hands on one of those saws. How does it's power and overall performance compare to a more modern saw of similar size ... such as a Stihl or Husqvarna? Just curious. Vibration levels any different?
Old 02-23-2017, 03:05 PM
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I have several Husqvarna 372's and they carry a little more rpm in the cut. 70.5 cc. A comparable Stihl would be the 044/MS440 series

But the 120Si/6800i(H) while slightly heavier than a 372/044 are very nice productivity saws. They run a 20-24" bar. They were a logger's favorite for many years.

The 120 and 6800 only difference is the brake mechanism. They have the same piston/cylinder. The 6000i/6800i superseded the 116Si/120Si in 1997 and was itself superseded by the Dolmar 6400/7300/7900 along about 2003.
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Last edited by w8ye; 02-23-2017 at 03:21 PM.
Old 02-23-2017, 03:20 PM
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Originally Posted by w8ye View Post
I have the chainsaw it was derived from
great thanks!
Old 02-23-2017, 03:23 PM
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Originally Posted by CK1 View Post
Dolmar 120si super 4.2 ci , 68 cc , 4.9 hp
thanks alot!!
Old 03-17-2020, 02:13 PM
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Hey guys I have the orange Sach-Dolmar 4.2....NEW never run...and I need to have a prop extension made (can't find one anywhere...I need about 1.5 in so when I put it in my Ziroli Skyraider I will have room for the dummy radial.
1) How the heck do you get the current prop hub and flywheel off
2) Any suggestions as to how to get/make an extension??
Thanks,
Lee
Old 03-18-2020, 06:27 AM
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Those engines are great but since they fell out of favor to the likes of lighter engine not many people produce those hubs for them anymore . You may have a few options though ,you could take it to a machine shop and they could make you one . I would try the local community college machine shop , check with the instructor and see if they could do it . You could try to find Ralph Cunningham (rcignitions ) I believe he visits the other rc sites (FG , rcgroups) . Truturn may make you one . Shindin machine is another possibility. Keep an eye on the market place , you may find a complete engine for less than the cost of a hub . Oh by the way I forgot to mention the prop hub usually is the extension . They were made in different lengths at one time , you just picked the length you needed when ordering . I have seen a few different methods to mounting the hub /extension but it probably is just threaded onto the crankshaft ( right hand threads ) ,it replace the nut that retained the flywheel .

Last edited by CK1; 03-18-2020 at 06:39 AM. Reason: Added content
Old 03-18-2020, 06:56 AM
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CK1. Thanks for the help here...OK, so to remove it I go couterclockwise to remove it? I tried pretty hard to get it loose that way.
Counterclockwise to remove? Maybe I have to heat it?? I think I can get a longer one made somewhere locally and thanks for all the great suggestions on that...
I'll let you know how I get on with it...
Lee

Last edited by rclbsimmo; 03-18-2020 at 07:02 AM.
Old 03-18-2020, 08:10 AM
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Those 4.2's like to turn between 6500 to 7000. Find a prop that will turn that rpm on the ground even if it has to be something like a 26x4. The secret is to prop the motor to turn in it's power band. The prop you are using is probably a 1000 or more rpm down. Those orange case engines are the best, I had one powering a Don Smith F6F Hellcat at 34 lbs and it flew the h out of it. They have fallen out of favor because they are not sexy enough looking anymore. They still will be running long after any of the newer motors have bit the dust. Most guys don't know how to properly prop a piston ported motor and don't let them rev up enough. I have never had any trouble hand starting the magneto version of the motor so you don't need to convert to electronic ignition unless you want too. Your engine is basically the same as a Brison, FPE, Fox and several other motors the same displacement. All used a Sachs Dolmar cylinder and piston, connecting rod and crank with custom machined cases. All are very good motors.
Larry
Old 03-18-2020, 11:10 AM
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While the Fox, Brison and FPE engines use the Sachs cylinders and pistons, these three engines use their own cantilever crankshaft and aluminum rod. They still run very well but they are not quite as smooth as engines that use the dual counterweight stock crank. The Taurus engines used the whole rotating assembly from a Sachs engine in a custom machined crankcase. In my opinion, the Taurus engines were one of, if not the best Sachs conversion around. I still regularly fly a Taurus 3.2 and have always loved that engine. I have (3) Brison 2.4 and a FPE 4.2. All Sachs based and very good engines. Yes, they all have to be propped for a bit higher RPM than similar reed valve engines. Modern props raise their performance levels from what we expected some years back when props like Zingers were popular.
Old 03-18-2020, 11:29 AM
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Its going in a Ziroli Skyraider, probably about 34 lbs. The bugaboo right now is I need a new longer prop hub so I can use a dummy radial.
Going to try to remove the old hub today, so I can see if someone can make a longer one.
I got it from B&B (Dick Bennet ) a long time ago for this airplane....just now getting it going.
I tried getting the hub off, no luck, so I will use some heat today, maybe they used red locktitie??
Thanks,
Lee
Old 03-18-2020, 11:50 AM
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Originally Posted by rclbsimmo View Post
Its going in a Ziroli Skyraider, probably about 34 lbs. The bugaboo right now is I need a new longer prop hub so I can use a dummy radial.
Going to try to remove the old hub today, so I can see if someone can make a longer one.
I got it from B&B (Dick Bennet ) a long time ago for this airplane....just now getting it going.
I tried getting the hub off, no luck, so I will use some heat today, maybe they used red locktitie??
Thanks,
Lee
I worked on one B&B Sachs 4.2 some years and if I remember correctly the hub just screwed off in the normal direction. I remember that hub because it only had a few threads of engagement and I questioned its safety.
Old 03-18-2020, 12:03 PM
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Ah, OK thanks...I'l give it another go...
Old 03-18-2020, 12:05 PM
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Lee , I would apply some heat to the hub it's either corroded to the crank or it has loctite on it . In either case the heat should help.

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