V-Belt

KeelsonGraham · July 12, 2022, 02:59:22 PM

Apologies, I'm posting a lot of questions at the moment and imposing on your good will.

By way of context, I've just done a 1100 mile trip to Spain and back across Biscay. In all that time at sea it wasn't navigation, weather or sailing that worried me - it was system health. This prompted by autopilot failure, a v-belt which was rapidly converting itself to dust and vibration from the engine/transmission! So, since getting back I'm firmly focussed on technical stuff!

So, to my next question. I'm trying to replace the v-belt with a new one which nominally has exactly the same (99cm) external circumference. The old (knackered) belt slips off easily. The new one I haven't yet got it on because it would require very considerable force with a lever or two to get it over the rim of the sheeve.

So, my first question is whether this is normal, or should a new belt just slip on relatively easily?

Second question, on measuring the old belt it appears to have an outside circumference of 101cm. This is way longer than the 99cm nominal specification of the belt. Do belts really stretch this much?

KWKloeber · July 12, 2022, 03:29:47 PM

I'd say 1mm is likely but 2mm might be possible but it all depends on many factors - how she was installed, tightened, treated, and the mfgr and type of belt.

Are you fully relaxing the alternator mount?
Get a Dayco "Top Cog" belt, it's the best belt you can run on our engines so it doent convert to dust.

Ron Hill · July 12, 2022, 03:41:54 PM

Keeelson : NO! that is NOT normal!! First there should be NO vibration from the engine or transmission that causes the belt to get chewed up if the alternator is solidly attached to the engine!!! The belt size depends on which alternator (& pully) that you have??? Not to sure of the correct size for the OEM alternator (M35B engine)??

On the M35B engine there are two bolt/nuts that can be loosened up to allow the alternator to swing so you can easily slip ON a new belt. You have to be careful with tightening the upper & lower bolts that goes thru the "ears" of the bracket that is attached to the engine!! Those "ears" on the bracket are made of an aluminum alloy alloy and if there is ANY slack space between those ears you can easily break them off when tightening - so be careful!! Just make sure that the belt has the ribs on the top (for cooling)

You should be able to push on the alternator to tighten it when the new belt is in place. (Don't believe that a belt tightener will fit/work) You need to make sure that the belt/pullies are aligned (Look down from the top. I use a straight edge rule to go from the bottom (drive pully) to the alternator pully. The bottom pully is the one to be the standard so you move the alternator/pully to match!! Good Luck

A few thoughts

waughoo · July 12, 2022, 07:31:49 PM

I had a pretty chunky alternator in the past and to replace my belt, I would have to loosen the alternator all the way and then remove the water pump pulley. Reinstall was the reverse of removal. My new set up is a bit skinnier so removal of the water pump pulley is not necessary.

KWKloeber · July 12, 2022, 10:57:50 PM

Put your known good belt against a Dayco 15385 Top Cog and see how this matches up:

Out. Circumference: 39.07 in / 99.24 cm
Effective Length: 38.5 in / 97.79 cm
Top Width: .44 in / 1.12 cm
Angle: 36

Your 35B and Ron's XPB would take the same size, given if both have the OEM alt and pulleys.

Ron Hill · July 13, 2022, 03:29:26 PM

Keelson : Once again - WITCH alternator do your Have??? Is it the OEM or a hi - outpt replacement???

A thought

KeelsonGraham · July 14, 2022, 08:49:24 AM

Quote from: Ron Hill on July 13, 2022, 03:29:26 PM
Keelson : Once again - WITCH alternator do your Have??? Is it the OEM or a hi - outpt replacement???

A thought

It's a higher output one (70 amps) than the original. The PO installed it, along with the presumably different V-belt used to drive it. I've no idea what make or model of alternator it is. But I do know that his arrangements worked fine for 16 years.

But, this isn't relevant to the issue I have, because I bought a new belt with the same specification as the PO's one. However, it's a Continental rather than a Dayco. I've given up trying to figure out why the old belt is so much longer than it's specified length.

Instead, I've now ordered the exact same Dayco one to see if this fits properly. I'm definitely not going to use brute force to prise on the Continental one!

Ron Hill · July 14, 2022, 01:43:59 PM

Keelson : What I did when I changed engines, but wanted to reinstall my Balmar hi- output was to get 3 belts of the approx. size and tried them out. However, it sounds like you might be in a place where that option is not practical.

Belts don't really stretch per-say, but as they wear they will seat further down in the "V" of the pully giving the impression that they have stretched. You might try to order a slightly longer Continental?
Sorry, can't give you a solid answer because you'll just have to try belts until you get one to fit that pully of your hi- output Alternator!!

Like I mentioned, be sure to check your alignment from the front as well as the top!! Good Luck

A few thoughts