Saito 120S Help Needed
08-13-2004, 10:02 PM
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Saito 120S Help Needed
I had my engine stop in flight shortly after take-off (at ~2/3 throttle). The plane didn't make it under/over some power lines and fell ~20 feet to the ground breaking the cowl, spinner and motor mount (remarkably the plane had little other damage). After removing the engine, I found it would not turn over. I checked the top end (ok) and then removed the rear cover. I found the engine would turn over fine and had good compression with the cover removed.
I tried re-seating the crankshaft by tapping with a wood block and mallet, but the crankshaft is hitting the backplate preventing rotation. What am I missing? I believe that the crankshaft problem was caused by the ground contact and that the deadstick was likely losing exhaust pressure. Thanks in advance.
Bill
I tried re-seating the crankshaft by tapping with a wood block and mallet, but the crankshaft is hitting the backplate preventing rotation. What am I missing? I believe that the crankshaft problem was caused by the ground contact and that the deadstick was likely losing exhaust pressure. Thanks in advance.
Bill
08-14-2004, 04:49 AM
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RE: Saito 120S Help Needed
Bill:
Sounds like you have moved the prop drive washer forward on the crank. Was the prop hub crushed? Or were the prop nuts loose?
There is a hard step in the crankcase to keep the front bearing forward, and thus the crank is kept from moving to the rear, You may also have moved the crank in the rear bearing, but it should be a free fit there and be able to slide forward again, unless the rear bearing is displaced.
Using a felt marker or similar, mark the back side of the rod for an assembly reference. Then pull the four screws holding the cylinder to the crankcase, with the rear cover off you can disconnect the con rod without pulling the piston from the cylinder, lift the cylinder from the case with the piston still inside. Don't take it out until you have to service the valves or replace the ring.
Now look between the crank and the front bearing. If you see a gap the crank has moved in the bearing. If no gap the bearing has moved back with the crank, and this is why you can't get it to move forward. While you're here, mount the case in a firm holder and spin the crank - you may have bent it. If the crank is bent, stop, bag all the parts and send them to me. I'll give you $50 for the complete engine with the damage. If not bent pull the prop drive, the cam housing, push the crank out, and look at the front face of the front bearing. If it's pushed down inside, the face lower than the metal of the case surrounding it, you've damaged the case. Bag and $50 time again. If the bearing is flush, put the case with bearings in the oven set at 275F. This wont hurt the bearings. After it has cooked for a while, grab the case with an oven mitt, and being careful not to burn yourself, push the crank firmly into the case through the bearings. After it cools, with the crank still in place, put the rear cover back on. You should now have clearance. Provided the crank turns smoothly, you've fixed the problem. If you feel any roughness you've brinnelled the bearings, you'll need to replace them.
If ok, clean all the parts, reassemble the engine, put it back in your repaired airplane and avoid power lines in the future. Haw.
If at any point you decide you're in over your head you can bag the parts and send them to me, I'll inspect and report. If you have me put it together the only charge I make is parts and postage on a Saito, no labor charge. Or I'll send you $50, whichever you might prefer.
Bill.
Sounds like you have moved the prop drive washer forward on the crank. Was the prop hub crushed? Or were the prop nuts loose?
There is a hard step in the crankcase to keep the front bearing forward, and thus the crank is kept from moving to the rear, You may also have moved the crank in the rear bearing, but it should be a free fit there and be able to slide forward again, unless the rear bearing is displaced.
Using a felt marker or similar, mark the back side of the rod for an assembly reference. Then pull the four screws holding the cylinder to the crankcase, with the rear cover off you can disconnect the con rod without pulling the piston from the cylinder, lift the cylinder from the case with the piston still inside. Don't take it out until you have to service the valves or replace the ring.
Now look between the crank and the front bearing. If you see a gap the crank has moved in the bearing. If no gap the bearing has moved back with the crank, and this is why you can't get it to move forward. While you're here, mount the case in a firm holder and spin the crank - you may have bent it. If the crank is bent, stop, bag all the parts and send them to me. I'll give you $50 for the complete engine with the damage. If not bent pull the prop drive, the cam housing, push the crank out, and look at the front face of the front bearing. If it's pushed down inside, the face lower than the metal of the case surrounding it, you've damaged the case. Bag and $50 time again. If the bearing is flush, put the case with bearings in the oven set at 275F. This wont hurt the bearings. After it has cooked for a while, grab the case with an oven mitt, and being careful not to burn yourself, push the crank firmly into the case through the bearings. After it cools, with the crank still in place, put the rear cover back on. You should now have clearance. Provided the crank turns smoothly, you've fixed the problem. If you feel any roughness you've brinnelled the bearings, you'll need to replace them.
If ok, clean all the parts, reassemble the engine, put it back in your repaired airplane and avoid power lines in the future. Haw.
If at any point you decide you're in over your head you can bag the parts and send them to me, I'll inspect and report. If you have me put it together the only charge I make is parts and postage on a Saito, no labor charge. Or I'll send you $50, whichever you might prefer.
Bill.
