I’m slowly beginning some viability testing on an inexpensive, plain bearing industrial engine, for use as a ‘direct drive’ replacement/upgrade for the venerable Rotax 277.
Direct drive testing for three reasons. One is expense. Two is weight. Three is the limitations of a plain bearing engine. A 5/8” wide micro-groove belt can transmit 4 times the power this engine can put out. However, for it to transmit that much power without slippage (and rapid destruction), I am told that belt tension would have to be so high, that you would not be able to turn the crank in the plain bearings. So, in order for a ‘simple’ multi-groove belt to work, you need a very wide belt. This necessitates wide, heavy pulleys. So, I’m try to see what can be done with a direct drive configuration.
I will add photos and progress here as time permits.
I started by building 3 dynamometer test clubs. I wanted to be able to get a performance baseline of the stock engine first before making any modifications or alterations.
I know many have done loads of work using redrives, and I have purchased a belt drive unit with five different ratios for testing various configurations on different powerplants (from Ace Redrives). However, in this thread, I’m only going to discuss the direct drive configuration. Prop affixed directly to the pto shaft of the engine. It is a 1” diameter shaft, and since I am not an engineer, I will simply hope it does not depart the testing area with one of my hand crafted clubs during these tests. This is highly unlikely.
I manufactured the prop hub from 6160 aluminum. The method of attachment is the same as one would attach a sprocket or pulley to a shaft with a pair of split, tapered conical bushings. One of which was purchased at the local hardware store for sixteen dollars. The other was made on the lathe from a discarded, broken pulley. I statically balanced the clubs, and tested their moment of inertia. I spun one up on my dynamic balance rig, and it ran up so smoothly, I decided to use them as they were. After all, they are very light, as they are made frame the finest, bargain-bin white pine, boomerang shaped, 3/4” construction grade lumber at Home Depot.
The initial tests proved somewhat interesting. Either Harbor Freight is quite close on their horsepower claims, or my dyno clubs are not working as advertised.
The engine was run 3 times up to temperature with a cool-down to ambient temperature in between each run.
All cooling shrouds removed. Charge coils removed from behind flywheel. Governor removed. Low oil sensor removed. Complete exhaust system removed (approximately 14” of 1.25” tubing used for an exhaust pipe for each cylinder). Fresh 10-40 oil added. Stock ignition timing, stock carburetor. The engine weighed 76 pounds as tested. The stock flywheel (installed) weighs 16.71 pounds. This item will be replaced by a home-made flex-plate, that will allow for electric start and a charging system.
Baseline test results:
816 mm club. Turned 2,640 rpm at wide open throttle. 19.19 hp
757 mm club. Turned 3,120 rpm at wide open throttle. 21.80 hp
702 mm club. Turned 3,660 rpm at wide open throttle. 24.17 hp
Conclusion. For the baseline I could not be happier. The readings correspond with what I was lead to believe about the stock engine. It has a very nice flat hp curve at the speeds it will be used. The 24 hp is quite believable as I had removed the restrictive exhaust system and entire Intake silencer with filter element. Those deletions were believably responsible for the slightly higher than advertised power output.
More here later as I modify for more power at this same peak rpm. I want to see what power we can get at stock rpm, with the stock cam and rods, keeping the direct drive configuration.
Direct drive testing for three reasons. One is expense. Two is weight. Three is the limitations of a plain bearing engine. A 5/8” wide micro-groove belt can transmit 4 times the power this engine can put out. However, for it to transmit that much power without slippage (and rapid destruction), I am told that belt tension would have to be so high, that you would not be able to turn the crank in the plain bearings. So, in order for a ‘simple’ multi-groove belt to work, you need a very wide belt. This necessitates wide, heavy pulleys. So, I’m try to see what can be done with a direct drive configuration.
I will add photos and progress here as time permits.
I started by building 3 dynamometer test clubs. I wanted to be able to get a performance baseline of the stock engine first before making any modifications or alterations.
I know many have done loads of work using redrives, and I have purchased a belt drive unit with five different ratios for testing various configurations on different powerplants (from Ace Redrives). However, in this thread, I’m only going to discuss the direct drive configuration. Prop affixed directly to the pto shaft of the engine. It is a 1” diameter shaft, and since I am not an engineer, I will simply hope it does not depart the testing area with one of my hand crafted clubs during these tests. This is highly unlikely.
I manufactured the prop hub from 6160 aluminum. The method of attachment is the same as one would attach a sprocket or pulley to a shaft with a pair of split, tapered conical bushings. One of which was purchased at the local hardware store for sixteen dollars. The other was made on the lathe from a discarded, broken pulley. I statically balanced the clubs, and tested their moment of inertia. I spun one up on my dynamic balance rig, and it ran up so smoothly, I decided to use them as they were. After all, they are very light, as they are made frame the finest, bargain-bin white pine, boomerang shaped, 3/4” construction grade lumber at Home Depot.
The initial tests proved somewhat interesting. Either Harbor Freight is quite close on their horsepower claims, or my dyno clubs are not working as advertised.
The engine was run 3 times up to temperature with a cool-down to ambient temperature in between each run.
All cooling shrouds removed. Charge coils removed from behind flywheel. Governor removed. Low oil sensor removed. Complete exhaust system removed (approximately 14” of 1.25” tubing used for an exhaust pipe for each cylinder). Fresh 10-40 oil added. Stock ignition timing, stock carburetor. The engine weighed 76 pounds as tested. The stock flywheel (installed) weighs 16.71 pounds. This item will be replaced by a home-made flex-plate, that will allow for electric start and a charging system.
Baseline test results:
816 mm club. Turned 2,640 rpm at wide open throttle. 19.19 hp
757 mm club. Turned 3,120 rpm at wide open throttle. 21.80 hp
702 mm club. Turned 3,660 rpm at wide open throttle. 24.17 hp
Conclusion. For the baseline I could not be happier. The readings correspond with what I was lead to believe about the stock engine. It has a very nice flat hp curve at the speeds it will be used. The 24 hp is quite believable as I had removed the restrictive exhaust system and entire Intake silencer with filter element. Those deletions were believably responsible for the slightly higher than advertised power output.
More here later as I modify for more power at this same peak rpm. I want to see what power we can get at stock rpm, with the stock cam and rods, keeping the direct drive configuration.
