Egbert McGillicutty

I took an old OS engine I had laying around for about 18 years, and put it in my old avistar to see if it still had any life to it. After a while I got it started and flew it for a day, but it started sounding very rough and gravely. I took it apart and found the rear bearing wore through the part of the bearing (?) that actually contacts the crank. I removed the front and rear bearings, ordered some new ones, but froze in terror as I realized I have no idea how to set the timing when I put it back together. It is a OS FS 40 surpass, so if anyone knows how to set the timing, I would like to hear from them!

Thanks in advance

JimTrainor

Here:

http://www.osengines.com/faq/product-faq.html#q15

Motorboy

Here are the picture how to set timing the camshaft in engine.

Jens Eirik

Egbert McGillicutty

Thanks Jens and Jim, thats what I needed! Someone in California has a question, and within hours it is answered by folks in Canada and Norway,..too cool!!!

Thanks Again!!!!

Bax

My Feedback: (11)

Sorry, but the above picture has a bit of an error. The dot on the side of the cam gear should line up with the center of the cam follower and pushrod. It will be canted aft, and not at 90-degrees to the axis of the crankshaft. The red line in the picture is turned too far forward. If you email us, we can send you a diagram of the proper orientation of the cam gear when the piston is at top dead center.

jaka

Hello!
Are you shure of this Bax??! All OS fourstrokes I have owned have had the cam timed the way Jens picture shows ...with the punch mark straight down ...I just had a look inside an OS FS-40 (new in box, never run ) that I bought in the beginning of the eighties and this engine had the cam mark the way Jens picture shows...and so does my two OS-FS .26 engines.....!
Regards!
Jan K
Sweden

Sport Flyer

My Feedback: (10)

I have a confession to make. I took an old OS40 Surpass apart for a rebuild without noticing anything regarding the timing. There was quite a bit of rust in the engine and I didn't notice any timing marks so when I reassembled it I set the timinging by sight - engine should draw in as the piston goes down, exhaust as the piston comes up. That was over a decade ago and that engine (which wouldn't run for its previous owner) has performed flawlessly ever since!

(Sport Flyer pats self on back again)

johncdh

I just went thru this on a new Magnum 61RFS (an OS clone), I could get no better than 8700 RPM on a 12-6 prop and the engine didn't pull worth a darn. After much reading and research I came across a couple posts talking about the cam timing, I pulled my cam cover and found the timing mark at 90 degrees to the crank. After moving it one tooth to the "5:30" position (in line with the push rods) I was able to get over 10K rpm on the same prop before a couple clicks rich. This was a brand new engine so I feel very lucky to have found the problem. It will run at 90 degrees to the crank but it will run badly.

Motorboy

Bax, it is right Jaka said about timing the camshaft gear in OS engines. I has both Magnum, SC and OS and all these engines i have has same method to locate timing mark as picture shows.

When the camshaft are placed as picture shows, then turn crankshaft 360, see after these valves are changing, it shall be correct.

If you set as you wrote it will not give enough power and make risk to knock these valves agains piston.

Jens Eirik

johncdh

Bax is correct.

This is a direct quote from the OS web sight.


The proper way to set the timing in all O.S. single-cylinder engines with the front camshaft is:

1. Rotate engine so that the piston is at Top Dead Center.
2. Locate the timing mark on the side of the cam gear.
3. Insert the cam gear so that the timing mark is in a direct line with the center of the cam followers and the centerline of the pushrods. It is NOT at a 90 degree angle to the crankshaft. The angle will be slightly back.
4. Replace the cam cover and you're ready to go!

w8ye

My Feedback: (16)

I have five of the OS Surpass engines and they are all timed as BAX says.

The Y-S, Magnum, ASP, & SC four strokes are also timed as BAX says for the OS engines.

It is best to push the exhaust cam follower up out of the way and put the mark in line with the bottom of the cam follower. It is more accurate that way.

Enjoy,

Jim

Bax

My Feedback: (11)

Just to remind those who may not be familiar with me, I have been the head of O.S. Max service in North America ever since the distribution of O.S. engines was taken over by Great Planes Model Distributors in the early 1980's. I have been personally involved with thousands of O.S. Max engines over the past two decades.

Hobbsy

My Feedback: (102)

If you will note, the red line is not lined up with the timing mark because the engine is tilted back, the red line needs to be parallel with the centerline of the cam follower.

Pepe J

My Feedback: (2)

Jen's photo shows the correct timing, but a poor example of the reference (red) line. If one expands the photo, you will note that the line is not in center with the cam center or on the timing mark which is at the "root" of the tooth.

Hold the straight edge of a piece of paper to your screen. Line up the cam timing mark and run the edge through the cam center and it will be very close to being parallel with the push rods. Because the timing mark is on the tooth center, you have to compensate for the helix angle and the centers of the of the gear teeth. If you offset the paper (straight edge) slightly to the left on the cam timing mark, this will put the straight edge parallel with the push rods.

To check that the timing is correct, place the straight edge on the center of a tooth, (both sides of the timed tooth) run it through the cam center and take note were it lines up with the push rods.

Happy fly'n...

Motorboy

What other mean about red line are wrong at photo, i has not drawned red line at photo. Found in other webside about how to repair 4 stroke engine and want to show where the dot are placed...

Today i has tried to set camshaft with dot in line with lifter, let us say dot clock 11 agains lifter. Then i turned the crankshaft carefully, discovered there was wrong timing,there was not "overlap" at right place when piston was at top dead centre. It was to late in all inlet and exhaust timing[X(]. There are risk if it is little spacing between valves and piston.

Tried again with dot at clock 6 and piston at top deadcentre, there was correct overlap when piston was at top. Overlap can all engine owner or car mechanic see when turn crankshaft (piston at top) a bit in both ways and see valves/valverocker moving in same time.

All was clearly, the dot can set clock 6 (both valves closet) or 12 (valves at "overlap period", also both valves are open in same time, "changing" with other word, see at picture with red line) and piston positioned at top.

It is whole i know because i am car mechanic and has knowledge about valvetiming[8D]... has not coal to criticize other peoples about this[]... better to be at sure place.

Jens Eirik

aggie84

Hey guys, thanks a lot for all the posts on this thread. I have an OS 91 and a week ago my flying mentor commented that the engine sounded a little rough. I'm fairly new to the hobby and this was my first 4 stroke so I really hadn't noticed. On inspection he also said that the bearings felt real dry and suggested (strongly) that I replace them before putting my plane at any more risk. When I was taking the engine apart my camshaft fell out before I could see how it was aligned. Boy, was this thread ever a big help! Got it back together Saturday and absolutely could not believe my ears. The engine is screaming. (BTW, I went ahead and changed out gaskets and, of course, set valves while I was in there.)

Two things were noticable immediately:
1. Much, much cooler running temperature. Before changing my bearings my prop nut had actually caused some melting on my spinner insert 30 minutes after a flight, now I can hold my fingers on the head 10 minutes after a 30 minute run.
2. More throttle range. Previously I only had throttle control for the first 70% of my throttle movement. After that, any change in RPM was very small, now I have it for the full range. I guess the bearings were heating up and causing some siezing to take place on the crankshaft and robbing my RPMs.

Saturday, during a breakin run I hit 9200+ RPM with a Graupner 3-blade 12" prop with the engine running rich enough to show lots of smoke out of the exhaust. Man, I'm pumped.

Anyway, thanks for the help, I'd have been lost otherwise

Aggie

w8ye

My Feedback: (16)

These four strokes must be made different in Norway? Mine run correctly when set as Bax says.

Enjoy,

Jim

Motorboy

No, same engine as you has....

Allways check overlap are correct with piston at top dead center to be sure camshaft are at right place...

Jens Eirik

w8ye

My Feedback: (16)

Bax, Hobbsy, Pepe J, John CDH, and I can clearly see in your picture, that you supplied us early on in this thread, that your timing is set exactly as we and the OS site said and it is not at a 90 degree angle or straight up and down as you say. You set your engines and we'll set ours.


Enjoy,

Jim

jaka

Hi!
AAAAH...The fact is that we all set them the same.......Bax and jens are both correct!
If you take a new..never run... OS engine and watch the cam with its dot mark inside the cam-housing...you will notice that the crank could rock slightly and still the T-mark on the drive washer will be aligned against the line mark on the engine housing......but the dot mark on the cam will move just a little.

Jens say (and I say )"set the dot mark straight down when the T-mark is in line with the line on the engine housing".

Bax say: "Set the dot mark on the cam pointing down...so that it is parallel to the valve lifters when the T-mark is in line with the line on the engine housing"

These recommendations are saying exactly same thing .......check it out yourself in practice and you will see that there is no difference!!!

Regards!
Jan Karlsson
Sweden

Motorboy

Do not forget the gear ratio are 1:2, then dot will be up or down.

Jens Eirik

JrBluz2

Jen,
I work on real airplanes for a living. I am really surprised that you can get a problem across to person the way you write. I am lost reading your articles. I understand what I believe you mean.

w8ye

My Feedback: (16)

The correct way to set the valve timing on the OS and Magnum four strokes.
The mark can be up or down as long as it is in line with the cam followers. The Mark is not 90 degrees to the crankshaft

barry wetherell

Ok, guys, why is it, when all timing marks are correct, the the engine has more compression turning backwards, than in the correct direction??? (l/h looking from the front)

jaka

Hi!
The picture you show is not the way OS first told how to set the timing on their fours strokes.
The manual I got in my FS .40 told of pointing the dot on the camshaft straight down at the same time the T-mark on the drive washer was in line with the line on the cylindr housing! That was the official OS recommendation in the late seventies/ early eighties!