quick question on pulley belts

[dart451]

Putting a new engine on a mixer...gonna have to shorten the belts slightly to make it fit in housing. Presently have two 4L350 belts on double pulleys...do I go 1" shorter or 1/2" shorter belt? The engine pulley and the mixer pulley are approx. 3" apart with the existing belt so I do not need too much to clear. I forget how much actual space you lose with 1" smaller belt. Does 1" mean 2" difference and 1/2" mean 1" shorter distance or am I out of the ballpark here?

[KE4AVB]

I think it is the other way around. I believe 1" shorter belt would move the pulleys closer together by a 1/2". This does depends the size of the pulley in relation to each other too as belt angle affects the amount of movement.

[dart451]

Ok, thanks KE4AVB...you're probably right!

[38racing]

http://www.calculatoredge.com/mech/vbelt%20length.htm

[madmantrapper]

http://www.calculatoredge.com/mech/vbelt%20length.htm

Very handy to know. I had a slide chart many years ago for this.

[KE4AVB]

Just remember to use the pulley[s] effective diameter[s]. By this I mean if you have a dual belt size pulley[s] the smaller of the two belts will ride at a smaller effective diameter (ride deeper in the pulley v groove). I have been upgrading a few MTD rider decks the last few years with "B" belt instead of "A" belts which require longer v-belts because of the effective diameters. It takes a while to get to size conversion right due the 3 and 4 V pulleys involved in deck drive system. Plus MTD haven't always used the same spindle pulley diameter over the years.

On the 2005 42" G decks this requires a v-belt that is nearly 1-1/2" longer normally when going to the "B" v-belt. Now if the v-belt is borderline tight it will throw the v-belt as it does on my mower if I engage the deck when lowered on initial use but I must have this belt due the cutting conditions mower operates in. Not many of us or users needs to cut 1-1/2 foot tall grass on regular basis but I do several times due to having 6 acres to cut and need my cuttings into my shop operations hours due rainy conditions. It also why the mower has a 21 hp engine instead of the smaller 16.5 hp it came with from the factory.

Something else to think about on older mowers is pulley wear which why you need a shorter belt at times. But many times the pulleys are so worn that you need to replace them instead of changing belt sizes.

[Walt 2002]

I have calculated them but any more I take an old belt, cut it and route it the way it goes then measure that belt.

Walt Conner