Like with any poly "V" belt system, the reduction belt on the Black Devil engine will have to be kept tensioned from time to time, especially in the first hours of usage.
During the first hours of operation the belt will stretch and if not re-tensioned it will start to slip.
Belt slippage will cause difficult starts, belt wear and even belt failure.
To keep the belt tensioned, please, follow the instructions below:
1) Remove the propeller
Now, you can see all the parts we will be talking about:
2) Loosen or better, completely remove the back bolt that holds the big pulley tight to the reduction plate
3) Completely remove the side bolt in the reduction plate
4) Insert a flat screwdriver in the reduction plate slot and slightly tap on it with a small hammer. Using a wrench that is inserted on the eccentric shaft, turn the shaft in the direction
needed to move it AWAY from the small pulley.
Note: Sometimes it is enough to insert the wrench on the eccentric shaft which can be turned without inserting a flat screw driver into the reduction plate slot.
However, it is better to completely remove the belt and inspect the grooves of the pulleys.
If the belt was loose for too long, you will notice black cake accumulated in the grooves.
Now it is time to clean it.
If left in place, the black deposits will wear the new or existing belt regardless if it is tensioned correctly!
In order to remove the belt, turn the eccentric shaft in such a way that the big pulley will get as close to the small pulley as possible.
In this position, the belt can be removed with no effort whatsoever.
Once the belt removed, inspect the grooves of both pulleys (big and small)
If there are any black deposits in the grooves remove them as instructed below.
Starting fluid works great on big deposits. Carburetor cleaner or gasoline (with NO oil in it) also work well.
Please, soak the deposits for a while and then, get to the next step described below.
Next, using a copper wire brush, remove the deposits and use more solvent if needed.
The grooves need to be absolutely clean.
Next, we check the belt grooves. A belt with any cracks or missing grooves qualify for replacement.
After the above operations, we can proceed to install the belt.
Insert the big pulley in place (if it was removed) and turning the eccentric shaft make sure the big pulley is in its lowest position ( it is as close to the small pulley as possible)
Doing this, will allow us to have plenty of slack to install the belt.
5) Use medium Locktite compound on the back bolt and slightly tighten it to pull the eccentric shaft close to the reduction plate.
Also, now it is time to check the pulleys for alignment.
For more info, please read the article on The Inventions Page about it.
For your convenience, here is the direct link: Reduction Pulley Alignment
If the pulleys are aligned we can go to the next step as described below:
6) Insert the side bolt into the reduction plate after using some medium Locktite compound on the first 4-5 threads closer to the bolt head that will go into the left part of the reduction plate (looking from behind the engine)
There is NO need to apply Locktite on all the threads. This may cause difficulties when removing the bolt next time.
7) After reaching the correct tension on the belt, hold the shaft in place with the wrench, tighten the back bolt completely and torque the side bolt as well.
There have been many speculations as how tight the belt should be.
Based on an idea that I received from Wayne Mitchler, I experimented with the tension and at the end of this material, you will see the correct tension that I found. The belt involved is an OPTIBELT.
To check or establish the belt tension I use a simple torque wrench.
Insert the wrench on the center nut of the small pulley and holding the propeller with your hand, turn the torque wrench to the RIGHT.
If the belt slips at 1,8 meter kilogram, the tension is correct. At least this is what I found to work well and in the same time, there is not excessive stress on the bearings of the big pulley.
Note: on the electric started models, the belt tension is NOT as critical as on the hand started ones.
The reason is:
- the Black Devil needs only 50-55 RPM to generate a decent spark; when using the pull start, the pilots reach these RPMs; there is NO way that using the pull start, the acceleration is smooth; any jerks will cause a loose belt to slip
-the more the belt slips, the more it wears out and will slip in the same or close position
-when the engine fires, in a fraction of a second, the RPM will go up from 55 to 2,200.
This acceleration puts a tremendous stress on the belt and if it is loose, this is another
time when it really wears out.
On the electric started models, the electric starter turns the engine at a constant of 250-300 RPM or even more on the models with a decompressor.
Obviously, when the engine fires, the stress is much less because it will accelerate only from 300 RPM or more to 2,200 RPM.
This is why the belt tension is so important on the hand start models.
Note: a new belt will stretch and it will have to be retightened a few times, according to the Black Devil manual. All POLY "V" reduction belts will stretch on any other engine (Solo, Simonini, Zenoah etc.)
Now let us return to the subject: checking the belt tension.
Again, this will be done with a torque wrench inserted on the central nut of the small pulley.
Again, once we immobilize the propeller, we turn the wrench to the RIGHT.
In the picture below, the horizontally placed wrench will have to be turned downwards.
In the picture blow, we show the scale of this very simple and cheap torque wrench which should be in the toolbox of any paramotor user, regardless of brand.
The Black Devil manual contains all the torques on the main bolts and nuts and this simple and inexpensive wrench, available at auto part stores, will allow us to check the torque on the cylinder head nuts, small reduction pulley nut (if removed) magnetic wheel nut and many others.
The wrench has a meter kilogram and a foot pounds scale for easy cross reference.
After establishing the correct tension, I strongly suggest that we mark the bolts for easy preflight reference.
I also suggest that all bolts and nuts on the engine and frame be marked with paint. This will let us know in time if something is going loose and will prevent a lot of problems in flight.