cutarug

I have a 1.20 Magnum and after dismantling for recondition can't find any timing marks or info on the cam timing.
Does any one have any info on how to set up the cam timing.

w8ye

My Feedback: (16)

The Magnum manual says one was and ASP another

I get more power timing them like this with the piston at top dead center

wcmorrison

My Feedback: (2)

Right on!

Chip

gkamysz

My Feedback: (19)

It seems to vary. I assembled a Magunum 91 as shown above and it was wrong. The mark needed to be inline with the casting boss below the camshaft bore.

w8ye

My Feedback: (16)

I've had 7 Magnum four strokes. My last one was a ASP 120. I never had reason to set or check the timing on any of them.

The ASP 120 was a 15 X 6 engine. It ran nice, good idle and did very well with a 15 X 6 but just didn't sound good with a 15 X 8. I bought it new from Just Engines in 2003 but have never flown it. My Saito 125 and FG-20 engines had much more power. But it was a big old slug whale compared with all my Saito 125's

About a month ago, I saw it in the drawer and was feeling of the compression and bearings etc. While watching TV and by blowing through the muffler with the carburetor open, I observed the valve overlap interval and it's relationship to TDC. To my surprise, the over lap interval was complete some 15 degrees before TDC. This was very odd because most four strokes, the valve overlap interval crosses over TDC but typically the center of the interval is some 5 degrees before top dead center. So I pulled the cam box cover and looked at the timing. It was straight up and down at 6:00. So I retarded the cam one tooth which made the timing mark in line with the pushrods when the crank was at top dead center. Now I checked the valve overlap interval and it overlapped TDC but was perfectly centered about 5 degrees before TDC.

I ran the engine with a APC 15 X 8 and 10% Wildcat Premium fuel 1100' 68 F. It made the APC 15 X 8 prop tips sing even better than a Saito 125.

So this engine is staying like shown in the picture in my previous post above.

gkamysz

My Feedback: (19)

Yes, but it varies by model. As the thread title is not specific to the model readers might like to know that not every Magnum, ASP, or SC four stroke is timed the same way. Obviously the manufacturer can't even keep it straight by the engine you received. As noted, set the timing so the valve overlap is centered over TDC.

http://www.justengines.unseen.org/ac...s_-_RCM_E.html

w8ye

My Feedback: (16)

This ASP 120 is the only Magnum/ASP I currently have at this time though I owned many others previously


In a review of the ASP FS91 the author had this to say about timing. . . . . .

"Easy to time, this is the first job on re-assembly, with the big end at top dead centre , the dot aligns with the pushrods. It just takes a little tooing and frowing and a slight rotation of either the crankshaft or the cam to get the correct alignment."

http://www.justengines.unseen.org/ac...FS__Ring_.html


Yet in the magnum manual, used to say straight up and down for the cam timing but any more there is no mention of cam timing in any of the on line manuals

To move the cam by 1 tooth the change is significant

asmund

W8YE has nailed it allright.
I own/have owned the .30 fs, .61fs, .91fs and the 180 fs and all have been timed in line with the pushrods and all my engines produce top notch power for their size.

DarZeelon

If one is in doubt, regarding what the 'dimple' on the cam-gear should line up with; engine theory should be utilized...

Bringing the piston up to TDC is virtually a no-brainer...

What happens when the piston passes TDC?
Two events occur alternatively; the first being the change from the compression phase to the power-stroke; and the second being the change from the exhaust phase to the intake-phase.

The first even is characterized by both valves being closed, so both cam-lobes are situated, so the base-circle faces the cam-follower/lifter.
The event take a rather long time - both valves are closed for more than half the rotation of the camshaft - a pretty long duration.

The second event is characterized by valve-overlap; i.e. both valves are somewhat open. This event is of a much shorter duration.
With the camshaft out of the engine, it can be scrutinized.
So the 'handler' can easily learn how to determine where the 'other' lobe's peak (the one obscured by the cam-gear) is pointed, from just looking at the visible lobe's peak.

Once the camshaft is installed, so the valves are around the middle of the overlap period, the handler can peak what the 'dimple' on the cam-gear points to, so he can have a reference for the next time the engine must be reassembled.


Also, installing a camshaft one-tooth-off is, I believe, too wide not to notice; with just 26 teeth on the cam gear...

gkamysz

My Feedback: (19)

I guess my experience didn't happen. That's OK the engine runs fine anyway.

w8ye

My Feedback: (16)

Even though I had my experience with my own ASP 120's factory position, discovered more or less by accident, and given the discrepancy of the true position (or positions) something is going on with the Magnum ASP engines timing positions. There may very well be different settings?

I never had reason to suspect them before. I had both Magnum and a ASP FS61's and they ran identical. I had a FS65 and it turned a ASP 13 X 6 over 10,000 rpm. FS91's with little difference from my OS 91 Surpass I. I never had reason to bother with the timing before. I never had any problems with bearings or any reason to have the cam out. I traded all these engines to the same guy and he still uses them and never had a reason to take the cam out.

I do feel that the Valve overlap interval should be about both sides of TDC center though. This is easy to determine even with the engine on the plane by determining TDC on the compression stroke and then looking for the the position of the valve overlap interval by blowing through the exhaust with the carb open. This should be found by turning the propeller 360 degrees from the TDC found during the compression stroke.

Carpilot

I just went through my old Magnum .52 four stroke (a few years old) I think it is a little bit different than the newer ones. my friend has a Magnum .52 that is only a couple months old and it is a little different.

Mine is basically a copy of an O.S engine, it times just like one too. at TDC the timing mark on the cam gear is straight down at 6 O'clock.

at any rate for $150 I'm very pleased with the engine overall, mine is going to need some new poke sticks pretty soon though. not sure why I'm getting the wear but I guess I won't worry about it until I have no more adjustment.

w8ye

My Feedback: (16)

OS engines do not time the cam at 6:00 and neither do Magnums

The mark is aligned with the lifters

Carpilot

Well ok but I have a magnum 52 four stroke (Magnum #XLFS52AR) that DOES time at 6 O'clock and an OS 1.20 Spurpass 1 pumped that DOES time at 6 O'clock.


And an O.S 91 Surpass II that times with the mark pointed towards the lifters.... again it seems to me the difference is the age of the engines. my O.S. 91 is only a couple years old while my O.S. 1.20 is many years old, it's the old pumped version with the crank driven gear pump.

w8ye

My Feedback: (16)

<u>This is the proof</u>

The valve overlap interval must rest on both side of TDC. With the timing mark at 6:00 the overlap interval is almost complete by TDC

The engine will start and tune very well with the cam advanced one tooth (6:00)

But doesn't develope its full power potential

You can confirm your valve overlap position without removing the engine from the plane or taking any part of the engine off. Just read previous posts to determine your current cam timing position

DarZeelon

Quote:

ORIGINAL: w8ye

OS engines do not time the cam at 06:00 and neither do Magnums.

The mark is aligned with the lifters.


[img][/img]

I beg to differ slightly, Jim!


The camshaft rotates at half the crankshaft's speed; completing 180°, for every complete turn (360°) of the crankshaft.

The camshaft position shown in the photo is about '11:30'. But this position is exactly the same as it it were 180° from there; i.e. at '05:30'.


If one assembles the camshaft, as the photo shows; and then proceeds to rotate the crankshaft exactly one turn, that 'dimple' would appear exactly at '05:30'...
...Which is also in line with the lifter bores, by the way, but on their far side.


You are right that '05:30' is not exactly '06:00', though...

w8ye

My Feedback: (16)

The mark is down on the compresion stroke and up on the overlap stroke

It doesn't matter which way you set it as long as it is inline with the lifters at top dead center.

It is more accurate to set it at the top where you can be assured it is in alignment with the lifters

Carpilot

Well I tried it on my Magnum 52 and at top TDC (on the compression stroke)the timing mark will not quite line up directly with the lifters, I go 1 tooth each way and tried it but it still won't line up with the center of the lifter. I tried it anyway and it ran but with no power. so i put it back to where it was with the timing mark at 6 O'clock at TDC.


I also noticed while typing here that the cam gear in my Magnum .52 is marked differently than the picture shows, when I time my engine correctly the timing mark is pointing exactly at 6 O'clock but the visible cam lobe is pointing the same direction as the picture shows. same situation in my O.S. 1.20

It's just a difference in the way the gears are marked.

asmund

It is very strange that the .52 is timed at 6 o`clock, because my .61 is timed in line with the push rods like all my other ASP/Magnums. 180 fs, .91 fs, .61 fs, .30 fs. I even timed my YS 110 like this and I guess it must be right since it runs great.

jeffof1975

I just purchased a .52 4-stroke and out of just plain adventure. I removed cam cover and found tdc on the crank. I found that the cam is one tooth advanced from center of the lifter. I seen in earlier posts that due to the overlap in the cam, it should be a notch fast. Give me a degree wheel and some cam specs. and I will be much more to the good. Now that would be totally un-realistic. Whats totally the truth, I have yet to find any set up info from the mfg. I new to this forum thing myself and any reply or info is +.. Oh should of listed magnum xl 52 rfs.</p>

w8ye

My Feedback: (16)

They will run either way

In line with the lifter
or
Straight up and down

They have more top end power and rpm with the cam aligned with the lifters

They idle slower with the timing advanced one tooth (cam mark straight up and down)

Brian1987

Does anyone know how to time a MAGNUM .91 4-sroke engine/motor?

w8ye

My Feedback: (16)

jaka

Hi!
This is the oldest timing recommendations from OS.

Look in all your OS four strokes and you'll see that the below pictures are correct

w8ye

My Feedback: (16)

This is simply not correct. If you set your cam timing at 6:00 or 12:00 , the engine will idle well but will be sick on the top end. You will have to use one size smaller prop and everyone else's engine will be out performing yours.