Drive belt tensioner

[compig]

Not in my case either.  The only answer is more tension and increased wrap angle on the flywheel (which is accomplished by minimizing the engine-to-generator spacing).  The number of belts doesn't affect the belt slip issue.  More belts will improve belt life, but that's not been an issue as far as I know.

Don't agree. More belts = more contact area = more friction = more grip. If slippage occurs with a belt theoretically capable of transmitting the torque then something else is wrong , like the groove isn't the correct size for the belt due to a possible machining error.

[Jim Mc]

...more contact area = more friction...

That's the part I don't agree with.  As I understand belt friction, it depends on the force (belt tension in this case), wrap angle (also known as 'arc of contact')  and coefficient of friction.  Contact area does not have much to do with it...

Here's an article supporting my position:

http://www.epi-eng.com/mechanical_engineering_basics/belt_drive_properties.htm


BTW, the slip issue in my case occurs on the flywheel, and there is no groove in it, nor is it painted.  Like Jens, I have a pretty big alternator (12.5 kVA, 1200 rpm) with a lot of rotating mass...

[MacGyver]

That's the part I don't agree with.  As I understand belt friction, it depends on the force (belt tension in this case), wrap angle (also known as 'arc of contact')  and coefficient of friction.  Contact area does not have much to do with it...

But wrap angle (arc of contact) is related to contact area.
More wrap = more contact area.
So it seems that contact area is a factor...  ?

[Jim Mc]

I look at it this way:  For a given wrap angle, a 1 inch wide belt is no better than a 1/2 inch wide belt, even though the 1 inch belt has twice the contact area.

And conversely, a 1/2 inch belt with twice the wrap angle as a 1 inch belt will work better, even though the two systems have the same contact area.

[mobile_bob]

a simple test for the unbelievers in the group

take a clean piece of round stock and put in in a vice, stickin up or out don't matter

wrap your belt around it and hold both ends of the belt, pull back some tension and then try to seesaw it back and forth
get a feel for how much pull you have to put on it to start to bind up.

now turn the belt over on its back and repeat

no contest is there?

as an interesting addition to your library, go to your local bearing house, and ask for an old Browning catalog
they will usually give you last years book, which is about an inch and a half thick

in the catalog you will find sections on all types of drives and the engineering steps to take to build up a drive
with all manner of prime movers,, includeing single cylinder diesels!!

use their formula and do the math and you wont have any chirping at all

other manufactures have similar formula, folks like goodyear, martin, dodge etc
but the browning catalog is just easier to use and better explanations in my opinion
easier to follow anyway.

bob g

[SteveU.]

Old Man are you out there listening?

Some very excellant points have been made by all.
To me a relative newbie, but haveing done a ton or achive researching here on this topic it SEEMS that BOTH double vee belts with grooved flywheels and gen head pulleys AND 6-8 groove Poly belts with flat flywheels and properly machined gen head pulleys are working fine for everyone wiih 6/1 3kw units.
So you'all wonder, "Whats all the rucas about?"

It also SEEMS that those with 20/2 12kw or larger set ups are having problems ireguardless of how rigid the mounting. I think Jens pretty accuratly analized and listed the major reasons.

Then there is the rest of us in between these extremes like my 12/1 (still without an AC head) wondering like the OldMan which style of drive system to go with.

So: use Poly/Serp belt with a flat flywheel being driven on the underside on a surface as Mobil Bob says rightly was never designed to be a driven surface. Could coat the flywheel surface as jtodd has with tacky plastic or use a double belt on one of TroyE.'s Double Width pulleys. They both claim no problems.
I personally have no confidence a tensioner will hold up long term to the abuse.

Or: use a triple B,C series vee belts. Works fine on my 20hp sawmill. But my sawmill doesn't have the severe 60 degree acceleration event every 720 that my Listeroid has. And again without a properly grooved flywheel I'd be drivng on the bottom side of the belts never designed to be a driven surface.
Anybody have a 23.6" Heavy Vee Grooved flywheel they want to sell? Yeah. I thought not.

I do like MBs idea of running double Poly/Serp belts turned over.
How to keep them on? Flanges? I've seen low hp barrel shaped driven pulleys in indusrial flat belt applications but again only on smooth power transfers.

Anyone want to trade two 6/1s for a 12/1?

So you see 6/1 3kw guys it isn't easy being BIG.

SyeveU.

[Tom]

Jens,

I've been thinking about your chirp and how there is also not enough load for your setup and I have a suggestion. Retard the timing a bit. From what I've heard (and I sure someone will chime in if this is wrong) it will smooth out the firing pulses and reduce carboning issues. Best of all, it won't cost anything to try.

[compig]

Not in my case either.  The only answer is more tension and increased wrap angle on the flywheel (which is accomplished by minimizing the engine-to-generator spacing).  The number of belts doesn't affect the belt slip issue.  More belts will improve belt life, but that's not been an issue as far as I know.

Don't agree. More belts = more contact area = more friction = more grip. If slippage occurs with a belt theoretically capable of transmitting the torque then something else is wrong , like the groove isn't the correct size for the belt due to a possible machining error.

Yeah, the part that is wrong is the fact that the flywheel isn't grooved .....

Jens

Ah , that I didn't know.  Dare I suggest having the flywheel grooved ?

[SteveU.]

Hey. Lets stop beating up on Jens. I'm the one who asked him to comment on his tensioner experiments. He answered. Kudos.
 Lets beat on SteveU. for a while.
I am going to be trying flat belting two Poly/Serps on the flat backsides FIRST after I finally get an AC head and get the mounting sorted out. I already own the pulley: came with the engine Free.
The Indians and their international market Must be using flat belts.
How are they keeping them from walking off??

SteveU.

[diesel guy]

Tom is correct about the timing, being retarded a bit would help reduce the sharpness of the power stroke and increase engine life. My 14/1 has a big bore and long stroke and it’s a single. My belt don’t chirp and I have a 128 lbs. flywheel mass on my generator. My timing is set at 16 degrees BTDC.

But mine is direct injected and on an indirect injected engine, maybe 18 degrees BTDC, instead of 20 degrees BTDC. I also have 23.5 inch diameter heavy flywheels. I think as we went over this in the past, more flywheel mass and larger diameter flywheels are best. This would absorb the power pulses and totally eliminate the belt chirp.

The belt chirp is not because there is not enough traction between the flywheel and the belt, or there is a heavy mass on the generator head. It is the lack of stored kinetic energy potential (too small diameter and too little mass) in the flywheel system per given instantaneous torque output, that is the route of the problem. The heavier and larger diameter (with increased surface area) flywheels the better.

The Start - O - Matics flywheels were correct for generator use and  anything less has short comings. See how long it takes for this engine to build up stored potential at start up and then release the stored potential when shut down stop. Massive stored kinetic potential.

http://www.youtube.com/watch?v=wBhjwEBBuo4

These belts don’t slip and it has a heavy mass on the generator head because of the V belt, but also the flywheels are heavy and large diameter and the engine’s instantaneous torque output can not accelerate the flywheels fast enough to cause a slip. This is just my option, for what it‘s worth.

Diesel Guy


 

[Tom]

Jens,

I've been thinking about your chirp and how there is also not enough load for your setup and I have a suggestion. Retard the timing a bit. From what I've heard (and I sure someone will chime in if this is wrong) it will smooth out the firing pulses and reduce carboning issues. Best of all, it won't cost anything to try.

Can you quantify 'a bit' ? I did actually fiddle with that at one point although I have no clue any more what the timing was set to (I should really write this kind of stuff down).

Jens

If it were me I'd go in increments of 2 deg retarded until the chirp stops. Unless someone with some real world experience wants to chime in.

[Wizard]

Snip

The Start - O - Matics flywheels were correct for generator use and  anything less has short comings. See how long it takes for this engine to build up stored potential at start up and then release the stored potential when shut down stop. Massive stored kinetic potential.

http://www.youtube.com/watch?v=wBhjwEBBuo4

Diesel Guy

Finally I can see the vibration more clearly.  I can see the shimmy (shaking) from the inertia of piston going up and down and bit of "wham" every other crank rotation (ingition).

What lister needs is counter balance shafts to counter the piston inertia and part of the con-rod (going up and down) and better balancing of crank and big end of con rod.

Cheers, Wizard

[Jim Mc]

From the pic, it doesn't appear to be spring-loaded.  That being the case, it serves two purposes, I suppose:  It allows you to tighten the belt without needing to slide the generator, and it increases the wrap angle.  Wrap angle is very important.  Increasing  it a little can allow a lot more torque before slipping.  I forget the details, but it's not a linear relationship.

I hope he used good bearings in it.  Looks to me like it'll be spinning at 7000+ rpms.  IOW,  a larger diameter idler pulley might be worth a thought...

[SteveU.]

And I, an American have purchased engine parts for Troy E. and other Americans complete engines. He will work with you. I highly recommend him. He has the double wide gen head pulleys. He  can still offer CROME cylinder sleeves for Lister/iods.
And now I see he is a much better welder than me too!

SteveU.

[Old Man]

Thank all of you guys for all the good posts on my question.

 The reason I wrote the post question, I owned and ran Deutz air cooled gensets for 30 years at a summer resort. The 3L and 4L-912's and Bf-513 all used spring loaded V-belt tensioners on their axel fan drives and I never had any trouble with them. I would think a strong well built on that wouldn't twist and tweek under load would give a nice wrap on the generator pulley and take up the surge when the engine fires and stop the chirp if it is coming from the generator pulley and not the flywheel.
Thanks again,
old man