lopflyers

My Feedback: (12)

J aja, I tried that idle bar glow pug in my Saito at no avail, get the onboard ignitor

BillS

I would consider removing the engine from the airplane and see if it can be made to run properly on the bench. Often when it is easy to get to everything the problem is easier to solve.

Did you read the cam timing instructions in the OS 91 Surpass manual?

Bill

jaka

Hi!
Are you sure the cam is set right!
Here is how it should be set. Dot on cam straight down when cam is pushed as far in as possible and ...T-markt on drive washer il-line with mold mark on crank case.

SJN

Hello Jaka.

I believe you are wrong.
Thet would also screw up the valve overlap period.

jaka

Hi!
I'm sure! Been around this hobby /sport for 38 years! That's the correct cam setting for all OS engines (four stroke engines ).


Why can't I send pictures???

SJN

Well, its never to late to learn Jaka

this is directly off of OS`s site:
http://www.osengines.com/faq/product-faq.html

How do I set the timing on my OS single cylinder engine?

We recommend you send your engine in for service rather than attempting to set the timing yourself.

However, if you're REALLY comfortable working on engines, these steps will allow you to set the timing. If you are unsure how to complete any one of these steps, we caution you against disassembling your engine and recommend instead that you send it to our warranty and service center for non-warranty repair.

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!
This should get your engine running well, if the timing was off. If it is still running poorly, be sure to send it in for service to avoid accidentally doing more damage.

MrShoes

My Feedback: (15)

Clarence Lee says the idle is the first thing to go when an engine is worn. There was a description exactly like yours in an old engine clinic and he said it was a worn piston ring. Good top end, midrange and below not good, bad idle.

SJN

Since this is an old engie, it is very likely that the ring is also worn. Ill try get a new one, and report back.
The liner seems to be in great condition.

jaka

Hi!
Well what OS says is really the same as I say, the difference is that what I told you was the recomendation from OS way back in the eighties. Just check a new OS fourstroke and you will see that we are both right.
I think my recommendation (and what OS told before ) is more easy understand and accomplish. If you doubt me, just check any new out of the box OS four-stroke from the eighties and till now.

SJN

Maybe on the old engines, but this one is not timed like that.
None of my current engines are timed like that.

These are a few in my collection which are not mounted on aircraft yet.

jaka

Hi!
All OS four-stokes are timed like I have said, and ASP, SC and Y&S too!

SJN

How can you say that, when the dot is pointing streight down at TDC is the same as the dot in line with the lifters/pushrods at TDC is the same ?

That makes no sense ?

SJN

I also have an YS 120 engine, and it is timed with the dot straight down, unlike the OS and ASP engines.


YS engine instructions:
CAM GEAR TIMING
If for some reason you have to disassemble your engine, please follow
these important steps on reassembling the cam gear.
1. Remove the carburetor and backplate assembly. Notice the
impression mark or dot opposite the rod journal on the crankshaft. This
mark is to point straight down or lined up with the outer case seam line at
the bottom.
2. Reinstall the cam with the dot facing you and is pointing slightly to the
left. This will allow the cam to turn to the right when properly installed.
The dot should be pointing starting up when cam is fully installed.
Reinstall cam cover and timing is now set.

SJN

picture example:

its not a great pictures, as the dot on the YS shoud ofcouse be shown in the 6 o-clock position, and not at the 5:30 position of the OS dot on the cam.

jaka

Hi!
Here is some pictures of the cam timing on a Nib OS FS .91 Surpass. At this point the piston is at its highest point and the cam dot mark is straight down and T-mark on drive washer is inline with mold mark on crankcase.
Same as on my OS FS.26 Surpass engines (have two), and on my OS FS 1.20 and on my old but Nib OS FS .40.

If you set the cam dot upwards as OS describe and at the same time set the T-mark against the mold mark on the crank case, the piston is at at its lowest point. This will of course be right too as the cam turns one turn when the crank turns two.
But... the problem with setting the dot mark this way is that you can not see the dot on the cam because of the cam lobe shadowing it.
Much easier the old OS way as I have described above.

SJN

hehe, you are one tough cookie

show me the valve overlap at TDC.
That will show exactly if it is off or not

jaka

Hi!
Don't know! What I have told you and showed pictures of is the timing of all OS fourstrokes! If you don't belive me...have a look at a Nib engine and see for yourself.

BillS

You should have had time to set the timing like the manual states and like you think it should be. Assuming you did not mess up and bend a valve you know the answer by now.

Bill

paulmedford

what was the final out cme of this engine? Was it the worn ring?

SJN

I scrapped the engine...used some parts for another os 91 I had, and used the carb on my ASP 400........so no cunclusion...sorry :-)

paulmedford

thanks for the reply. I sorted my engine out yesterday, turned out to be the fuel i was using, I used fresh fuel, and i retuned the engine and all is well so far. its in a p47 warbird.