poly-v belt tension

[justsomeguy]

Is anyone using an automotive style belt tensioner to keep the slack up on the generator drive?  It seems like an auto matic tensioner would keep tension constant on the "return path" to the flywheel as the belt stretches (under more or less load) and contracts, and as temperature increases/decreases and the belt ages.  Mounting would be somehwhat more simple too, as the generator head would not be required to slide.

[t19]

I had wondered about that as well, seems a simple solution

[Listeroidsusa]

Have you ever tried to stretch one of the kevlar serpentine belts? Even a razor knife has trouble cutting one. I put a 1/2 threaded adjusting rod with the bases I build to adjust the slack on my generator. It has never been touched since installation and the generator has 135 hours on it now. It just hasn't stretched a bit on my installation and it is pulling my entire machine shop's 3 phase load, lathe, bridgeport, cutoff saw, ect. (GM-90 6/1)

Mike

[SHIPCHIEF]

Yes.
I use an 8 rib serp belt. I got a 102 inch belt, and it slaps around until it comes off a couple of ribs, then rides the higher edge of the driven pulley.
I was thinking of using a self tensioning idler pulley, or using a 12v alternator with a tension spring?
Anyway, the generator will be mounted closer to the engine, either by using a shorter belt, or a tension system.
The problem is efficiency. Any parasitic load should be avoided. We use thermosyphon cooling to avoid waterpump loads, and keep the oil level lower than the connecting rod cap (but high enough for the dipper). A tension pulley has some drag. How much? Less than an alternator (which has a fan).
Also I will reduce the .062" cranksaft end float, to the .005 recomended. That should help keep the belt on too.
Ideal solution is no idler like Mike's. If the belt works without adjusting between oil changes / maintenance shutdowns, then it's probably good enough?

[hotater]

I'm still using the first six rib belt I bought 3700 hours ago and it's a cheap NAPA generic!  I tightened until all the slap was gone and never had it jump track or fail.  The serp belt is THE way to drive loads off the flywheels.

Multi-V pulley grooves are surprisingly hard to cut on a lathe.  There's a LOT of tool contact in deep Vees just as there is a lot of belt contact. It makes them hard to machine.

[solarguy]

I also run a six rib AC Delco serp belt.  Casting and machining the custom pulley was fun/challenging.  It took a couple tries to get a nice blank cast.  Once dialed in, I've only had to adjust the tension once in 1,500 hours of operation.  The lister is fixed/bolted to the frame, the gen head slides on a captive sled that rides on the I-beams of the gen frame.  I bought a spare but suspect it will die of dry rot before I ever wear the first one out.  I sort of prefer not have an idler/tensioner.  One less thing to fail.

Finest regards,

troy

[Tom]

Hey ShipChief,

Is it possible that your mounting frame has too much flex and that is why the belt won't stay tight? Also is the axis of the crankshaft parallel to the generator shaft? I'm having good luck with a generic 93" 6 rib napa belt.

[SHIPCHIEF]

Troy;
I had .063" crankshaft end clearance, so the belt tried to follow the crank as it battered back and forth. Also I think the mount holes in the frame had the engine setting a little crooked. I don't think the heavy wall I beam and Square tube frame is too flexible, it's pretty massive. The sub frame is too flimsy, and I've got more steel to truss it up. All in all, I plan to work on each aspect you mentioned, aslo a shorter belt with the gen head closer to the engine, I have a 102" 8 rib belt.
Scott E

[solarguy]

Good luck Scott/Shipchief,

Sounds like you have an excellent plan of attack.


But I think it was TOM who made the helpful suggestions, and not I.  Don't want to pinch credit that's not mine.

Finest regards,

troy

[SHIPCHIEF]

OH! Thanks TOM
Scott E