idler woes

[jens]

removed

[ronmar]

Well I see some potential for engine movement in your frame.  With the ends of those box tubes that the engine block is mounted to not being capped, they are probably twisting/flexing with the torque pulses. What is their wall thickness? Engine mount flex could be causing tension and alignment changes

What size/material is the boom that supports your idler pully made out of?  IF it is too light weight, it too could be flexing/twisting as the belt comes under tension with each torque pulse.  Most serpentine belt pullies I have seen are spring loaded(wifes mitsu is manually adjusted) and those are on engines with a much smoother power delivery.  Large torque/stretch pulses to deal with on this type setup.  You might try adding some kind of compressible buffer pad/spring between the top of the jack and the bottom of the idler boom.  This would allow a little movement of the boom before the stresses become great enough to bend/twist it unpredictably.  The required tension is also going to vary slightly as things change sizes with belt/pully temp changes, so again I think spring tensioner is the way to go here. 

Ron 

[gpkull]

sweet set up it looks like a 16 or above . these are good at 1000 and can maintain pretty close to with a little tlc. the problem will be gov control when you try to maintain 500 or so.the tuned springs and weights for a g will respond differently at 1/2 . when i had my 24/2 bolted to a frame similar it tryed to catch the street sweeper. i had 4 1300lbs casters bolted to the frame and the riod destroyed them. i did shake the mole from the yard. i used 2x4 x1/4 rec tubing as the price was right. i ended up bolting to a slab i poured i think it was 33 80lbs quick creet. before i shook the driveway now i shake the dishes in the cabinet next door. have isolation under way but do want to balance in the future

[mike90045]

Does your ribbed serpentine belt run on a flat engine flywheel ?
 In my truck, all pulleys are grooved to not crush the belt ribs.

[clytle374]

I have a dual speed setup also.  I went with 2 belt and 2 idlers, the second one is 3.75" out on a 5/8-11 bolt.  I used spacers to help add strength.
I have noticed that the the belt tracks the worst under no load at low engine RPM.  I believe that is because the flywheel effect of the gen head is over running the engine on compression, making the tensioner side of the belt the tight drive side.  Amplified at low speed when the engine/head energy ratio favors the gen head.
I don't seem to have a problem, but have given this much thought since the weaker(further out) is the high speed pulley and it runs better.   
This is the idler I'm using, might add guides and convex diameter to your idler?
http://www1.mscdirect.com/CGI/NNSRIT?PMAKA=35428481
Looks to be a real nice setup.  Let us know how it works out.
 

[hotater]

Jens--

Time will tell if the frame is heavy enough....I'd sink it half depth in concrete if it were mine.  

The idler is arranged so any tension on the belt is transferred 'linerally' to the idler instead of 'trailing'. This tends to bounce and set up harmonics that might throw the belt off.

You'll probably be VERY surprised how much tension it takes to settle the belt down, but I'd hinge the idler from the generator side to correct the lack of 'trail' in the wheel first.

I've found the belt that has more than a quarter inch 'flop' under load is too loose.  There is NO need for grooves on four feet of contact around the flywheel.  The ribs don't flatten and it works worderful.

[hotater]

Jens---

It's the difference like pushing a broom stick along the sidewalk or trailing it behind you.   If pushing it, any forces pushes lenghth-ways down the shaft and you feel it...it's very rough.  If the broomstick is trailing behind, it 'rolls' over the bumps with no stress on your hand.   Same with the idler wheel.

[clytle374]

According to the broom analogy it looks to be trailing, unless the idler is on the tension side.

[hotater]

Right you are...it is trailing.  The belt on the 'wrong' side fooled me.  (I don't want to be cranking and dodging the belt at the same time.)

From my limited experience with serp belts, I'd say it needs more tension to run right.

BTW-- You can run serp belts on 'flat' pulleys, too.  They have a little crown on them and will self-center. 

[Eco Diesel]

Hi Jens!
 I like your existing swing arm style idler design. Maybe it could be beefed up if made from 2 pieces of 1 1/4" x 1/2" bar stock and the same material used for cross bracing (could be bolted together if the cross braces were keyed into the side arms or welded to eliminate flex) This could be hinged at the frame by using a heavy (but accuratly reamed) hinge base and pin. Then a threaded adjustment ( using 5/8 thread all) could be used like a turn buckle incorporating a rotating wrist pin that has been drilled and threaded installed mid point or slightly higher on the swing arm (This wrist pin would rotate to prevent binding the thread as the swing arm rises or lowers) and  two base shoes be mounted to accept the stationary end of the threaded shaft (which you machine to fit nicely into the ball nose drilled shoe (When I say shoe I mean like the thing a pole vauter sticks his pole into)(And No I am not talking Dirty!) could be drilled using a 3/8" or 1/2" ball nose cutter. A jam nut could then lock the adjustment. I used a similar setup for quick adjustment or removal of my water pump drive belts and it has worked great. You might be able to see a glimps of this adjuster on one of the pictures on my website. The idler could also be initialy made to have straight raised sides to help with visualizing the alignment durring mock up/instalation. The other suggestion I would offer is that the belt be placed opposite the starting side for safety reasons. I think you'll feel safer for having swapped the belt to the other side. By the way, nice job on your 2 speed pulley!

Troy

[BruceM]

Nice work, Jens.  Lovely piece of design and I'm glad you posted about it so I could learn from it.

The flat flywheel provides zero belt centering force, and thus the positioning on the idler is very important. I think some fine tuning adjustments for the idler shaft tilt might be very helpful.  Sort of like the adjustment provided on belt sanders- you just adjust to get the belt to track right.

Best Wishes,
Bruce M
Meto 6/1
Snowflake, AZ

[oliver90owner]

I think Hotator is closest to the solution. 

All, or nearly all, belt pulleys on tractors are domed slightly, or in some cases, quite a lot. 

Years ago, there was a lot of belt work with tractors and farmers had few problems with alignment.  Flat belts often had a huge amount of sag but still stayed on at about 2600 feet per minute - a bit slower than the belt run here. 

Some pulleys were machined with sides, to control flat belt tracking, only on the smaller of the pair. 

This installation might even be better tensioning from the inside the belt as long as it is near the engine, as the contact area would not be particularly compromised by pulling the belt outwards.  The idler could then be grooved and track with the belt.

Regards, RAB

[clytle374]

BTW-- You can run serp belts on 'flat' pulleys, too.  They have a little crown on them and will self-center. 

Crown, thats the word i was looking for when I said convex.

[hotater]

Jens---

Maybe you see some of the forces that prompted some of us to question the mounting frame.   

Welding caps on all the box tube will go a long ways to stiffen them, but for the BEST solution weld round pipe between them as bracing.

[clytle374]

Not mention the obvious, but how close are your flywheel and pulley to being parallel?