philfun

My Feedback: (58)

Hello,
How to position the cam shaft when reassembling the engine ?

Thanks

asmund

http://www.rcuniverse.com/forum/m_92..._1/key_/tm.htm

Picture in post nr2 says it all, piston at top or bottom dead center

jaka

Hi!
Or more easÃ*ly done...
Cam mark straight down...and at thesame time T-mark on drive washer in line with mold mark on engine housing.

Campgems

You can not rely on the mark on the drive hub, if there is one, unless it is a keyed hub. A lot of them are held with a tapered collet and there is no hard timing.


Just Top dead center. 1/2 revolution of thecrank is only 1/4 revolution of the cam. All timing is at Top dead center. With the crank at TDC, the dot can be either up or down along the push rod line as shown in the photo.


Don

w8ye

My Feedback: (16)

This statement that the cam timing mark goes straight up and down when the crankshaft is at top dead center is not correct!

The timing mark is to be positioned in line with the cam followers.

The proof is in observance of the intake/exhaust cam overlap interval and the fact that it must be positioned about top dead center on the non combustion stroke. If the cam mark is positioned straight up and down, the overlap interval is complete before top dead center and you loose breathing efficiency

jaka

Hi!
All OS four strokes that I have seen have drive washers that are keyed to the crankshaft!
Ofcourse it's correct!
Just check every OS four stroke made!!! Open the cam housing and have a look!

w8ye

My Feedback: (16)

I have six OS four strokes and have had many others and they were all timed with the cam mark in line with the cam followers.

You are the one that inspired me to look at all of them.

Some ASP/Magnum type four strokes do not have a keyed prop drive hub. The last one I had was the ASP 120FS and it was keyed.

w8ye

My Feedback: (16)

The Magnum 30RFS does not have a Woodruff key in the prop drive hub but instead is indexed with a flat spot on the crankshaft and a corresponding shape in the prop drive hub that will only let it fit in one position. It is not fixed by a tapered collet like the 80/91 RFS are.

The Magnum 52/61 have a Woodruff key locating system for the prop drive hub.

asmund

Oooops, yes you are absolutely correct[sm=red_smile.gif] the dot can be either at top or botton, but the piston must be at top dead center. This is how I have timed my ASP .30 fs, two .61 fs, the .91 fs and also the mighty 180 fs. They come this way from the factory too

philfun

My Feedback: (58)

Thanks all,
Ball bearings replaced,cleaning inside out, set up the dot in line with the puhsrods ,piston at TDC.
Work great horizontal and vertical ,easy start,higher RPM,no fuel spitting from
the carb, good response from the needle valves.So far so good.
I noticed a leak between the carb and head due to the third screw on the carb(misalignement)
Screw replaced with a M2.6 DIA .
No more issues.
Thanks

blw

My Feedback: (3)

Glad to hear that you did it the right way and it runs like it's supposed to.