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HTD pulleys vs trapezoid pulleys


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If you do keep your trapezoidal pullies, remember there's a stronger blue belt option, the Gates T104RB

The Jensen Healey engine had a fixed tensioner and suffered the issue with the start on very cold mornings causing belt to jump teeth. So they very quickly designed the spring tensioner and added belt

My 82 Turbo engine, now rebuilt with HTD setup and fixed tensioner.  Other photo shows drilling jig for tensioner mounting hole.  

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Anyone know if the HTD pulleys and associated belt can be used with the semi-/automatic tensioner?

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I very much doubt there'd be any issue in running the HTD's with the semi-auto rig. AFAIK, one distinct advantage in the newer cog profile is in greater certainty of meshing, as compared to the original Gilmer type.

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12 hours ago, Fridge said:

Anyone know if the HTD pulleys and associated belt can be used with the semi-/automatic tensioner?

I am thinking about converting the auto tensioner into a manual one to avoid drilling so with a bit of luck I can let the engine in the car. 

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6 hours ago, lotus-62 said:

I am thinking about converting the auto tensioner into a manual one to avoid drilling so with a bit of luck I can let the engine in the car. 

Hi, I've been thinking about such a mod..Some sort of threaded rod passing through the adjuster. How were you planning to do it?

On 25/02/2021 at 08:17, Escape said:

I think most (if not all) engines now use an automatic tensioner. But that could be for ease of fitting more than reliability.

Interestingly, I've replaced the timing belt on a Land Rover earlier this week and found the keyway in the drivepulley to be about twice as wide as the key itself. This is intentional, to allow some freedom on kickback and avoid shock loads or slack on the belt. I know Gates has developped pulleys with varying diameter (only very slightly) to further smoothen the load on the belt.

Filip

 

19 hours ago, RichardJGC said:

My 82 Turbo engine, now rebuilt with HTD setup and fixed tensioner. 
Other photo shows drilling jig for tensioner mounting hole.

 

14ACC55E-BF29-4620-8DE5-7EC43E6F2723.jpeg

372BD0B9-82E3-4599-B40E-AF99486A7875.jpeg

Excellent and thankyou 

 Lovely looking engine !

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2 hours ago, PrecisionMike said:
2 hours ago, PrecisionMike said:

Hi, I've been thinking about such a mod..Some sort of threaded rod passing through the adjuster. How were you planning to do it?

same way, replacing the spring with a solid something but will have a better look when I take it of, maybe a one piece with tread 

 

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On 28/02/2021 at 19:00, 910Esprit said:

Why not just replace the internal springs with a distance piece?

I have been considering this too but feel some small range of spring compliance would be beneficial in coping with thermal expansion and contraction.  I will give the matter further thought and post my solution when ready.

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Consideration of harmonics compounding components flexing may be in order. Would the risk of jumped teeth be reduced with use of the fixed tensioner, that having precluded opportunity for crank flex permitting the belt to elude the auto-adjust process at certain RPM? As I see it the fundamental theory of a synchronous ( i.e.toothed ) belt system amounts to a low inertia geartrain, thereby eliminating one potential contributor to disharmony between the synchronised components. Pretty deep water for my level of education, I'll admit. 

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Both methods work. The original design, for Jensen, suffered from cold-start issues, this was investigated and fixed.

Then later on, Lotus moved to the HTD belt and lower-cost fixed tensioner which also works.

I dont think there is a need to over-think this or swap between one and the other.

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1 hour ago, Andyww said:

I dont think there is a need to over-think this or swap between one and the other.

Think that's absolutely true and there are no issues with with a well maintened 'legacy' trapeziodal belt system.   But you should remember to treat the tensioner assembly itself as a service item when you do the belt.

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2 hours ago, Andyww said:

I dont think there is a need to over-think this or swap between one and the other.

the trapezoidal tooth shape results in high stress concentrations at the belt-pulley interface, which can lead to high wear rates when the transmitted torque or speed is high.  (inlet cam pully due to the very short contact area between the belt and pulley)

the curvilinear (HTD) tooth profile was developed to alleviate the stress concentrations found in trapezoidal profiles and improve on torque and speed capabilities.   (the tradeoff, however, is that curvilinear designs have higher backlash than trapezoidal profiles) 

 

a quick google search found me the above information, sounds good to me. 

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