OS FS cam questions
 

I have a few OS FS engines, 20, 26, 40 and 61. I sometimes take these apart for cleaning, but am afraid to mess with the cam since I am not sure how to realign it with the crank to keep cam timing correct. :confused: Are there alignment marks or another method of doing this? The cams are often the grungiest part in these engines. Thanks! :spinnyeye

FR

OS FS cam questions
 

This is described in the O.S. Max FAQ's. It applied to all single-cylinder O.S. Max 4-stroke engines:

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

OS FS cam questions
 

Go for it. The trick is to get the pushrods/guides aligned to the head. Just study it a bit before you rip it apart.

ZB

OS FS cam questions
 

Thank you Bax and ZB. I have spent much time on that OS sight but never looked at FAQ's. I'll give it a go.


FS

OS FS cam questions
 

It's strange. I can't get to the above mentioned sight at OS through their FAQ's pages. Only through this link.

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

At the bottom it has a link backwards to FAQ's, but from FAQ's you can't go forwards to this link.

FR

OS FS cam questions
 

Hi!
All OS FS engines use the same cam-setting procedure.
Turn the engine over so that the drive washer aligns with the small mark on the housing (the mark is located just behind the drive washer on on top of the housing that cointains the front ball bearing). Now the piston is at top dead center.
Open the cam-housing !
The cam has a punch mark on the side on one of the gear-tooth, this marked tooth should point straight down and align with one of the female teeth on the spiral gear crankshaft......that's it!


Regards!
Jan K
Sweden

OS FS cam questions
 

If you make the mark straight down on the cam, you will be one tooth advanced. Here is a quote from the above link that BAX, who is the warrantee manager for OS in the U.S., posted on here....

"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. "

The mark has to be either opposite or aligned with the pushrods and cam followers.

The best way is to remove the rocker arm assembly and raise the cam followers up out of the way. Then align the dot exactly where the cam follower would be. The gears are helical and the cam will twist a little going in. But when it's properly aligned, the mark will be right where the cam follower would be when the cam is seated.

One other problem of putting the mark opposite the cam follower is that you cannot be certain that you are exactly opposite the cam follower.

The cam moves at half the speed of the crankshaft therefore, the timing mark could be set either aligned with the cam followers or opposite them and the engine would still be in time.

There is a OS Four Stroke book written by some guy from England and printed by RCM and sold by others as well. This book describes setting the timing as Jaka (apologies) has said but it doesn't work very well on the front cam engines unless you are very lucky.

The clearance is .002" to .004" on the rocker arms for you guys in the U.S.

For the rear cam engines, there is a slightly different sequence that I could throw on here if anyone needs it?

Enjoy,

Jim

OS FS cam questions
 

Hi!
Doing it my way ( and the OS way) has always worked for me...
One has to be cautious though when pushing in the cam so that one gets the cam dot (mark) right...Yes I know that the helical gears twist the cam a little. One has to take that into ac**** when mounting the cam.
Regards!
Jan K

OS FS cam questions
 

Lines up with the push rods. Voice of experience! Learned the hard way! MAX H.

OS FS cam questions
 

My worthless piece of *#!t engine is now purring nicely.:confused:
I had a near new looking OS FS-26 which I had picked up at a club swap meet. I tried and tried but I could not get it to rev past half throttle without dying. I tried different props, different fuel, and much time monkeying with the carb. I was thinking that it may have never been broken-in or broken-in improperly. Finally pulled off the cam cover and it was hard to tell but it looked like it could have been off a tooth. Pulled the head, etc. moved the cam one tooth, put it together and it fired immediately and was running like a champ. I can't imagine why someone would have fiddled with the cam on such a new engine, or if it had come from the factory that way and the previous owner gave up on it.:spinnyeye