Another timing belt question

[Pete Boole]

In people's experience, once the timing belt tension is set how many miles does it stay within spec?

Thanks

Pete

[Hawaiis0]

I'm looking to replace mine next month. Been on for 5 years and 15,000 miles. Still good.

It's the worn pulley that's scaring me

[AndyC]

In people's experience, once the timing belt tension is set how many miles does it stay within spec?

Thanks

Pete

The belt will loose tension after only a little use, but that's still within spec, as the original figures (90-95 etc) are for a new belt, and shouldn't be applied to a belt that's been used.

[Pete Boole]

Thanks guys! The reason I'm asking is because my belt tensioner is eventually going to be half hidden behind the blower drive pulley. The only way to re-adjust the tension once it's all installed will be to remove the accessory drive belt, blower belt and crankshaft pulley, but if I only need to do this for a belt change every few thousand miles it won't be an issue.

Pete

[Hawaiis0]

Switch to auto adjustment

[AndyC]

The semi-auto adjusters are known for the piston sticking, so they're not great.

[Pete Boole]

Defo staying with a "manual" adjuster. Will also be using a further two on the serpentine belts for the blower and the a/c compressor/water pump/alternator.

Pete

[Jason.goad]

Glad you're going down the blower route Pete. With your engineering excellence, it's going to be a sight to behold. Don't think you'll have a problem with the belt tension, but you could always fit a couple of snubbers like the ones used on the semi automatic tensioner. They would stop the belt jumping if tension is lost.

[Pete Boole]

Thanks Jason . I'm hoping the snubber won't be needed, but good idea! I'm going to Helicoil the hole that the adjuster stud fits into as I'll be using a cap head bolt instead and counter-boring the adjuster to give me more clearance. Haven't made much progress recently on this

Pete

[Esprit2]

The black belt tension evolved through the years, and finally settled on 95 Burroughs. Consider 90 as a minimum due to belt stretch over time, and time to re-tension the belt. Don't let the tenson go below 90.

If you tension a new black belt to 95, "initial stretch" will cause the tension to drop off. Check the new belt's tension every 500 miles, and retension as necessary. Continue the 500 mile check until the tension stabilizes... usually by 1000-1500 miles.

To avoid the necessity to re-tension a new belt, set the initial tension a little too tight. Over the years, I observed that a new belt would loose 3-5 lbs due to initial stretch, so I set the initial tension high by that amount. Still check the new belt every 500 miles, but it's unlikely that it will ever drop to or below 95.

For both Trapezoidal and HTD black belts, I use:
97-100 Burroughs for a new belt to allow for initial stretch
95 Burroughs to re-tension a used, worn-in belt.
90 Burroughs as a minimum... don't let the tension go below 90.

The Gates Racing Blue belts are thicker, and the Burroughs gauge is thickness sensitive. So a numerically lower tension is required for the blue/ HNBR rubber belts.

For both Trapezoidal and HTD Blue belts, I use:
82-85 Burroughs for both new and used Blue belts.

After installing a new blue belt, check the tension frequently at first as with the black belts. But the blue belts are so stable that, 'IF' they were properly tensioned when installed, it's very unlikely that you will ever have to retension them again... either initially, or long term. But 'checking' is easy, continue to do it on schedule.

The Blue HNBR rubber, trapezoidal tooth belt was initially made by Gates Racing, which is Gates' specialty products division. The part number is Gates T104RB. However, it now appears that the HNBR trapezoidal belt is also being produced by Gates Rubber. The part number is the same, T104RB, but it's black. The 'blue' is a Gates Racing trademark, and isn't used by Gates Rubber. Whether blue or black, T104RB is the same, excellent, HNBR belt.

Regards,
Tim Engel

[Pete Boole]

Thanks very much for your detailed reply Tim. I recently bought a Burroughs gauge from a fellow forum member so setting it up should be straight forward. Over-tightening slightly at the beginning sounds like a good plan.

Pete

[Johnwindwood]

I'm looking to replace mine next month. Been on for 5 years and 15,000 miles. Still good.

It's the worn pulley that's scaring me

Tut tut. Belt change is 2 years........

[TrevorK]

I watched the Harry's Garage episode on his Testarossa the other day. He said that it's recommended to change its belts every so many miles or every 2 years but most owners, because of the low miles they do, change them every 3 or 4 years which I though was interesting.

[Hawaiis0]

I watched the Harry's Garage episode on his Testarossa the other day. He said that it's recommended to change its belts every so many miles or every 2 years but most owners, because of the low miles they do, change them every 3 or 4 years which I though was interesting.

I feel that is sound advice. The 2 year rule was based (I feel) on old technology. Modern materials makes belts today far superior.

I have just changed my belt after 5 years in situ. And I do above average miles for an excel owner.

Most will scoff at my insanity but the old belt was like new still

[Pete Boole]

Our old Audi had a belt replacement interval of 50k miles!

Pete