teamcrossworks

I'm finally about to purchase and change my timing belt (about time).

Is it worth it to go Kevlar?

Understanding the 30,000 or 3 year rule (I don't even come close to the mileage) is a good practice, would the Kevlar belt extend the guidelines of this "golden rule" to maybe 30,000 miles or 5 years?

Mark944na86

It's quite possible a kevlar belt will actually require you to change your rollers and waterpump *more often* than a standard belt.

Why? The kevlar belts will stretch less as the engine warms up and expands, putting more tension on the rollers and waterpump, shortening their lives.

The stock belts have been well-researched, and their operating limits are well understood. Stick with a stock belt, and the recommended maintenance regime, and you will be set-up as well as you can be.

Tellingly, the purveyors of the kevlar belts are careful never to make any direct claims about longer maintenance intervals by using these belts. Really, they are an (expensive) gimmick best, and possibly counterproductive at worst. Put the $$$ you'll save by sticking with the stock belts towards more regular maintenance if you are particularly prone "belt paranoia". BTW, the vast majority of "belt failures" aren't really down to the belt itself failing, but rather a moving part (waterpump, rollers) seizing or otherwise failing from a lack of proper maintenance (which includes checking the belt tension is correct). Put your efforts and $$$ into keeping these items in top condition, change the belt at the specified interval, and you will be in good shape.

Black51

To answer your question with a question, did Porsche find it worth it to go kelvar?

There's a saying that goes: "don't fix it if it ain't broke". Well, at least that goes along with changing to kevlar after 24+ years.

blade7

Last time I checked there wasn't a Kevlar balancer belt so you will have to change that at the regular intervals.

CurtP

Rennbay sells the Gates kevlar belt. I have one, love it. I will buy another one next time around too. I'm less worried about longevity than I am sheared teeth which seems to happen way too often with standard belts.

Mark944na86

Teeth shear off when a roller or waterpump seizes and stops turning. A kevlar belt won't help one bit when that happens.

CurtP

It happens even without water pumps and rollers failing. Why wouldn't I use newer technology on something like this? If it affords me an extra margin of safety preventing the valves from kissing the pistons, StrekStrekStrekStrek yeah I'm going to use it.

When my #4 cylinder cracked and hydrolocked, my kevlar belt didn't shear and trash my freshly rebuilt head. I was able to reuse the head on my new engine. Do I know for certain that a standard belt would have failed? No, but I'm sure glad I didn't have a standard belt on it to find out.

I, for one, am very thankful that Travis is having these belts made for us. I've seen countless threads where guys are whining about the belt change interval and wanting something better. Now that something better is out there, I see posts crying that the old tech belts are better or they cost too much. If I hear word that these belts are going to be discontinued, I'll buy as many as I can so I don't have to go back to the old belts.

Mark944na86

The recommended belt change interval is exactly the same for the kevlar belt as the stock belt. I wonder why that is?

As I explain above, I'd recommend changing even more frequently because of the potential extra stress on the roller and wp once the engine is up to temp and the belt is fully tensioned.

It's good the belt makes you feel more secure (in the end, that's really what you are paying for), but there is perception, and there is reality.

Fishey

Hold on, your making completely bogus claims here #1.

First, the factory belt has to be installed on the upper part of the tension range because of known stretch (added stress on your bearings and waterpump). This is a known fact because it will strech over time and that is why it has a inspection interval after a few thousand miles of use to check to make sure its still within factory spec but if its not it gets tensioned into spec. Regardless after that time the belt doesn't have any real aditional stretch.

Second, After said stretch is out your saying it will stretch under heat cycles of the engine? Ugh, sure buddie it just stretches and goes back to original as the engine cools down. (lol) No, simply put it does not have any stretching left to do untill the end of its life so it acts no different then the kevlar belt under use.

Third, Remember that original higher tension we had to put on the O.E. belts? Well not needed as much with kevlar because it doesn't stretch nearly as much in its orginal few thousand miles. As such you can put less pre-tension on it and save the stress on your waterpump and bearings. (100% opposite what you just said)

Also, your basing your claim that because the replacement interval isn't higher its not more durable?

I don't think that Rennbay has got the time or resources to do extensive testing on the Kevlar belts to test durabilty. Also, with the size of the market gates isn't going to do any testing for durability of the belts for service interval on our application. As such Rennbay isn't going to make any claims that it cannot prove in the court of law. So in the end of the day you have to look at what Gates says about there belts in general.

Gates Racing Performance Timing Belts are 300% stronger than stock belts and deliver up to three times the heat resistance (from catalog)

Sounds alot better to me when it comes to what we know since I am sure gates has done testing on there belt compound. As such I would figure service length is going to be longer in the real world even if no one can say it..

Mark944na86

I think you misunderstand the basic point I'm making. Why do we have a timing belt, and not a chain? Because the belt needs to be able to stretch as the engine heats, and contract as the engine cools.

The standard belt tension measurement for a new belt is for a cold engine. If you put two different belts with different elasticity on a cold engine with the same initial tension, they will have different tensions when the engine is hot. The stiffer belt will be at higher tension.

The kevlar belt is *supposed* to be stiffer... it's the main selling point. The only way to know for sure what the difference in tension when the engine is hot over a stock belt is to measure it, and if someone wants to do the experiment, that would be useful data to post here.

But until someone actually does the experiment, just to be on the safe side, I would assume the kevlar belt is running at a higher tension on a hot engine compared to stock, even if they are at the same tension on a cold engine, and plan my maintenance schedule accordingly.

If the tension is not significantly higher, then the kevlar belt is simply a waste of money, rather than a waste of money *and* something that is going to put more wear and tear on your rollers and waterpump. LOL.

Baptizo

I was over at Rennbay and found the kevlar belt - I'm glad someone brought it up for discussion.

At this point it's purely subjective about the durability of the kevlar over the original design but if they're used by a racing team, I'm inclined to give one a try when it's time for a new one.

teamcrossworks

I appreciate everyone's input though I have to say I'm still on the fence...

CurtP

Valve train harmonics for one. Cost for another. How many OHV engines used chains when these cars were built? What did they do about expansion?

Feels like I'm on a kiddie board

hot-J

I run a gates kevlar on my 951 and cosworth kevlar on each of the high hp subarus in the family. I chose cosworth for the subarus because I believe they know what they are doing. The gates belt is avalable for the subarus too. Interesting side note..... I run gates kevlar PS and alt belts on the subarus too.

Baptizo

Mitsubishi used a timing chain on their venerable 2.6L used in the Starion/Conquest twins.