Kevlar Timing Belt - Worth it?
11-02-2010, 11:50 PM
#199
Rennlist Member
Thread Starter
Join Date: Sep 2008
Location: Northern NJ
Posts: 779
Likes: 0
Received 0 Likes
on
0 Posts
11-03-2010, 02:29 AM
#201
Three Wheelin'
Congrats Travis! Since the technical debate here seems to be over (for good reason) I'm wondering why the word "tool" became an insult. I know it's been that way for many years. Anyone know the history? Tools are awesome- they allow is to build and fix things and separate us from less intelligent species. They also fit in our hands, as do our very personal "tools" that are used for things like making babies. Oh wait- I just figured it out.. never mind 
11-03-2010, 08:23 AM
#202
Addict
Rennlist Member
Rennlist Small
Business Sponsor
Rennlist Member
Rennlist Small
Business Sponsor
Now Travis gets to change more than just belts…..and more often than 30K miles!
Congrats, start training the new pit crew!
Congrats, start training the new pit crew!
11-03-2010, 11:13 AM
#203
Site Sponsor
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Join Date: Aug 2002
Location: A great big building in the woods, FL.
Posts: 6,527
Likes: 0
Received 3 Likes
on
2 Posts
Now I have to go finish turning that parts closet into a nursery. You guys better watch out or you might get a dirty diaper as packing with your order.
11-03-2010, 11:45 PM
#204
This is what these belts are made of... check out the article. Im convinced this is the belt for us. Now, if we could only get the balance shaft belts and rollers and waterpump to be as durable as the timing belt 
http://www.azom.com/details.asp?ArticleID=537
http://www.azom.com/details.asp?ArticleID=537
11-04-2010, 04:08 PM
#205
Rennlist Member
can we have a group buy now
so travis can pay for all those diapers now HAHA!
Mike
so travis can pay for all those diapers now HAHA!
Mike
01-06-2011, 01:08 PM
#207
Advanced
Join Date: Dec 2008
Posts: 68
Likes: 0
Received 0 Likes
on
0 Posts
What is the reason for setting the correct belt tension? Would I be correct in thinking that the belt tension is specced such that the belt is at a point where it isn't going to significantly increase in length due to additional tension. Surely the stretch of a belt due to tension decreases exponentially up to the point that the belt snaps. So what you want to do is spec a tension that will give the belt sufficient overhead such that it does not come clost to snapping under expected operating conditions but also minimises the stretch of the belt to maintain timing to as accurate a level as possible.
Additional belt tension would come from heating of the engine and resultant expansion of the distances between the rollers and from the increased force required to spin the cam and pulleys at high rpm.
As well as having an effect on the length of a belt due to stretching the belt tension will also extert a force on the rollers such as crank and cam. This will increase with belt tension and will increase frictional losses about the rollers. This effect should be minimised as it is purely negative.
With a very inflexible belt like the kevlar one my thoughts would be that you could reduce the belt tension minimising the forces applied to the rotating components without increasing the length of the belt from additional tensioning forces.
Additional belt tension would come from heating of the engine and resultant expansion of the distances between the rollers and from the increased force required to spin the cam and pulleys at high rpm.
As well as having an effect on the length of a belt due to stretching the belt tension will also extert a force on the rollers such as crank and cam. This will increase with belt tension and will increase frictional losses about the rollers. This effect should be minimised as it is purely negative.
With a very inflexible belt like the kevlar one my thoughts would be that you could reduce the belt tension minimising the forces applied to the rotating components without increasing the length of the belt from additional tensioning forces.
01-06-2011, 03:58 PM
#209
Addict
Rennlist Member
Rennlist Member
Because these are "interference" engines, having a belt come loose, or snap, can have catastrophic consequences. It makes sense to attempt to get the tension as close as possible to somewhere "in the middle setting" since engine heating, etc. could change the dyamics. Will it change enough with the stiffer and harder belt composition to be a concern? Dunno. I'm hesitant to experiment with loosening the tension and taking that risk...or having the stiffer belt be too tight and cause premature roller bearing or water pump failures...or premature cam gear teeth wear. Porsche just raised the price on their 928 cam gears to more than triple of last year's price. I suspect the 944 and 968 guys can expect to see these kinds of price increases too.
Perhaps the difference in actual use is inconsequencial? Or maybe not? On the 928, belt tension has to be more critical than on the shorter (and MUCH BETTER DESIGNED) 968 belt system.
Maybe we won't really know the answer until enough of them are in use and 40,000 or so miles of experience shows no issues? Or users start noticing problems. It's something worth watching. The 944 guys seem to use their cars the most/hardest so I thought they might notice something first.
I'm debating whether I want to take the chance or not. I like the belt concept and I bought one so I'm leaning towards using it. I just wish I knew how to tension it for optimum performance and minimal risk.
H2
Perhaps the difference in actual use is inconsequencial? Or maybe not? On the 928, belt tension has to be more critical than on the shorter (and MUCH BETTER DESIGNED) 968 belt system.
Maybe we won't really know the answer until enough of them are in use and 40,000 or so miles of experience shows no issues? Or users start noticing problems. It's something worth watching. The 944 guys seem to use their cars the most/hardest so I thought they might notice something first.
I'm debating whether I want to take the chance or not. I like the belt concept and I bought one so I'm leaning towards using it. I just wish I knew how to tension it for optimum performance and minimal risk.
H2
