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Hunting tooth Q for Will!

Posted: December 28th, 2013, 4:11 pm
by Guy Croft
Hi Will

sorry to bother you during the festive season but if you can possibly spare the time can you please tell me if I am OK with any available belts in the 99-105 tooth range (3/4 wide, trapezoidal 3/8 pitch) with the following:

crank 22 teeth - alternator 18 teeth - and waterpump 30 teeth (same pulley setup as we proved out thanks to you on Nix's Lada TC)

I have 105g belts but they are a bit long and I know 99 is aval but in between no idea. With 99g the belt may hit the tensioner nut and low pressure switch..

it is for Paul Eustace 2 liter 187bhp TC for his Stratos replica as shown on FB and below,

no worries if you are otherwise engaged but it would give me so much more confidence if you did it, anything I can offer in return just ask...

thanks tons,


Re: Hunting tooth Q for Will!

Posted: December 28th, 2013, 6:17 pm
by Will01
Hi Guy
I am hoping i can be of some service. I can't do any more advanced checks as i don't have my notes with me. But the info below should be sufficient.

First things first a hunting tooth in a synchronous belt is a good thing as it helps prevent localised damage caused by repetitive loading on one point of the belt. We therefore design in a hunting tooth to allow a different part of the belt to take the load on every rotation or load situation.

There are two ways of calculating hunting tooth on a synchronous belt drive.
One way which is most often used for industrial type drives involves dividing the Number of teeth in the belt by the number of teeth in the pulleys on the drive. If the answer is either a whole number or is a quarter/half or three quarters e.g. 14, 14.25, 14.5, 14.75 then there may well repetitive damage caused in particular areas on the belt. I tend to go a few points either side of these numbers as a type of safetyy factor unless i have used proper simulation program to confirm. Sorry i have no access to this outside of work.

The other way which is calculated for Automotive type drives is to take the number of teeth in a belt and multiply by the number of cylinders (as the firing cycle causes this type of repetitive damage) and then divide by the number of teeth in the pulleys on the drive.

Personally the type of drives I get involved with are on Automive engines, so i actually use both of them.
Please see attached a quick spreadsheet to show which belts i would not recommend (highlighted red).

On this type of drive i would not be concerned about if the waterpump pulley is divisble as above. From my quick checks i would recommend 101 (preferred choice until more advanced checks can be put in place), 102 or 104 tooth belt. The 99 tooth belt would be the worse of repetitive damage so is highly not recommended. If these were not available 105 could be used as a back up. As you have already mentioned if it is too long you may find other problems with tensioning, if the belt dynamic tension drops too low it can cause low tension degradation.

I hope this helps Guy. When i return to the office i can have a better look into this for you. I would then be able to look into available tooling and belt availability. Using the software it would also give me a better idea of all the belts you could use and would confirm or not if any other belts would be suitable between 99+103 teeth.

Re: Hunting tooth Q for Will!

Posted: December 28th, 2013, 6:20 pm
by Will01
excel attached just in case

Re: Hunting tooth Q for Will!

Posted: December 28th, 2013, 10:05 pm
by Guy Croft
Thank you so very much Will.

If you are able to perform full validation that would be marvellous.

In the meantime I think I have enough thanks to you for hot test.

Avoid 99g. Understood.


Thanks Will and Gates Power Transmissions. Pricless friends.

Re: Hunting tooth Q for Will!

Posted: January 1st, 2014, 1:02 pm
by Guy Croft
Thanks Tom for engaging with Will over this and thanks for updating Will,