Checking timing on a Saito 80
10-29-2010, 09:45 AM
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Checking timing on a Saito 80
I have just redone the bearings on my Saito 80 and rebuilt it. Timing marks were lined up as they should but hard to know if it moved a tooth when dropping down the housing.
Anyway I can check the timing by say which valve is open/closed in relation to crank pin position or any method to confirm the timing is correct before I try to start it up.
Anyway I can check the timing by say which valve is open/closed in relation to crank pin position or any method to confirm the timing is correct before I try to start it up.
10-29-2010, 10:20 AM
#2
RE: Checking timing on a Saito 80
You can pull the glow plug and valve covers. There is a spot at TDC where there is valve overlap. In other words both valves are slightly opened. So put a tooth pic or small wooden dowel in the glow plug hole and turn the engine till both valves are open. Your piston should be at TDC.
David
David
10-29-2010, 10:40 AM
#3
RE: Checking timing on a Saito 80
The exact center position of the valve overlap position where the rocker arm tops are parallel with each other is some 5 degrees before Top Dead Center.
However, the overlap event should cross over top dead center before completion.
I usually just find top dead center by feel and then open the carburetor and blow in the exhaust to find the limits of the cross over event. Half way in between the limits is the center where the rocker arm tops will be parallel with each other. This way, I do not have to take anything apart on the engine.
One tooth retarded and the center will be just past top dead center. This engine will have poor idle
One tooth advanced and the overlap event will be complete before top dead center. This engine will have poor top end power but a great idle.
However, the overlap event should cross over top dead center before completion.
I usually just find top dead center by feel and then open the carburetor and blow in the exhaust to find the limits of the cross over event. Half way in between the limits is the center where the rocker arm tops will be parallel with each other. This way, I do not have to take anything apart on the engine.
One tooth retarded and the center will be just past top dead center. This engine will have poor idle
One tooth advanced and the overlap event will be complete before top dead center. This engine will have poor top end power but a great idle.
10-30-2010, 01:34 PM
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RE: Checking timing on a Saito 80
fired it up and flew it today, seemed ok although the needle valve is much further out than it used to be.
Main reason for changing bearings was the engine seemed down on power dont know if that has changed so maybe problem is elsewhere.
Anyway after the third flight it stopped on approach and when I turned the prop it had very little compression, so it will have to come out again and investigate.
Main reason for changing bearings was the engine seemed down on power dont know if that has changed so maybe problem is elsewhere.
Anyway after the third flight it stopped on approach and when I turned the prop it had very little compression, so it will have to come out again and investigate.
10-30-2010, 02:58 PM
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RE: Checking timing on a Saito 80
The factory method of timing the engine, is to use a timing tool that inserts in the intake cam follower bore. There is a timing hole that lines up with the intake push rod at TDC.
Since most of us won't have that special tool, no problem. Before attempting to time engine, remove the intake cam follower before installing the cam gear housing. If you have the timing correct, you will be able to clearly see the timing hole in center of the cam follower bore when the crank is at TDC. If you're one tooth off either way, the timing hole will not be anywhere near the center of the cam follower bore. Takes all the fun and guesswork out of timing them
To get the cam follower out, you will probably have to remove the cam gear and push in out that way. Ii have tried, without success, to pull them out with a strong magnet , probably due to a slight mushrooming of the cam follower on the surface that rides the cam, just clean it up, before dropping it back in from the outside, after you're sure the timings correct.
I hope this is of some use. It has always worked well for me.
Pete
Since most of us won't have that special tool, no problem. Before attempting to time engine, remove the intake cam follower before installing the cam gear housing. If you have the timing correct, you will be able to clearly see the timing hole in center of the cam follower bore when the crank is at TDC. If you're one tooth off either way, the timing hole will not be anywhere near the center of the cam follower bore. Takes all the fun and guesswork out of timing them
To get the cam follower out, you will probably have to remove the cam gear and push in out that way. Ii have tried, without success, to pull them out with a strong magnet , probably due to a slight mushrooming of the cam follower on the surface that rides the cam, just clean it up, before dropping it back in from the outside, after you're sure the timings correct.
I hope this is of some use. It has always worked well for me.
Pete
