Timing belt tensioner failed, 8 bent valves
07-07-2006, 12:48 PM
#16
Race Car
You can easily make 9.5 to 1 compression without interference design. As mentioned, some people modified the STOCK pistons to be non interference with NO problems. Porsche designed some stupid $hit and this is a prime example. Timing belts are not the problem but chains in Chevys last well over 100k (they stretch but don't break unless you do a 200k mile change or something really stupid). As mentioned, there are plenty of cars with chains and aluminum engines (bmw 318i e36 body style all have them and you never hear problems). A chain driven non interference design would be the best combination for reliability. I have seen many e32 735i with over 300k miles on the original timing chain running great so if all the chain has to drive is a 4 cylinder 8 valve engine, I would imagine it would last just as long if not more.
Try to find engine harmonic problems in a bmw or bent valves.
Try to find engine harmonic problems in a bmw or bent valves.
07-07-2006, 04:30 PM
#18
Race Car
Who do you know with that problem and what is the source of your information? Are you refering to the cast iron block of the 2.5L 6 cyl or the 1.8 alum engine I was refering to?
07-07-2006, 05:02 PM
#19
Addict
Rennlist Member
Rennlist Member
Originally Posted by testarossa_td
Early 928 where non-interference....and some on this board are making their 44/51's non.
Originally Posted by Legoland951
...
As mentioned, some people modified the STOCK pistons to be non interference with NO problems.
...
As mentioned, some people modified the STOCK pistons to be non interference with NO problems.
...
Sorry, just don't like to be “anonymized”.
Laust
07-07-2006, 06:24 PM
#20
Instructor
Join Date: Sep 2005
Location: Dacula, GA
Posts: 157
Likes: 0
Received 0 Likes
on
0 Posts
Perhaps it has something to do with compactness. A chain would have to be encased within the block and head as part of the crankcase so that it runs in oil. Then you also have the issue of turning the balance shafts as well. They would have had to make the front of the car longer.
07-07-2006, 07:05 PM
#21
Race Car
The space in front of the 944 engine taken by the timing belt and balance shaft belts out to the front cover takes much more space than a chevy DOUBLE chain assembly. Then you won't have the leaky cam seal, o-ring, balance shaft seals as they will all be internal. There is a definite reason why the e36 generation BMW engines require less maintenance when they went to the chain 2.5L blocks as opposed to their belt driven e30 engines where the head has a tendency to self destruct due to BELT failure and their INTERFERENCE design.
Just imagine how much cheaper ownership of a 944 be without having to replace bent valves (basically completely head job), timing belts, and all kinds of front seals for pretty much the life of your car.
Just imagine how much cheaper ownership of a 944 be without having to replace bent valves (basically completely head job), timing belts, and all kinds of front seals for pretty much the life of your car.
07-07-2006, 07:06 PM
#22
Racer
Join Date: Jun 2005
Location: Greensboro, NC
Posts: 367
Likes: 0
Received 0 Likes
on
0 Posts
I'm pretty sure they could have found an extra half an inch in the engine bay to make room for a chain as opposed to a belt.
I wonder if it has something to do with how long and complex the routing of the belt is in an OHV engine. In most chain driven engines the cam is in the block and runs directly off the crank making for a pretty short and directly routed chain. Perhaps there's too much mass in a large complex chain, or perhaps it just won't funtion reliably in a complex system???
I wonder if it has something to do with how long and complex the routing of the belt is in an OHV engine. In most chain driven engines the cam is in the block and runs directly off the crank making for a pretty short and directly routed chain. Perhaps there's too much mass in a large complex chain, or perhaps it just won't funtion reliably in a complex system???
07-07-2006, 08:02 PM
#23
Addict
Rennlist Member
Rennlist Member
If someone has too much time on their hand, then it could be interesting to see the ratio of new cars with chain vs. belt driven cams as a function of time. I believe that the belt was the “next best thing” in the early 80’s and advertised as “silent belts” until data began trickling in on their real life reliability.
Belts actually can be very reliable. I once deliberately pushed the first belt change to 130k miles in a Toyota MR2 and it appeared to have another 30k miles in it.
On the other end of the scale Lamborghini designed the first V8 Urraco P250 with belts, but got “cold feet” and changed it to chain drive for the later P300, Silhouette and Jalpa.
Laust
Belts actually can be very reliable. I once deliberately pushed the first belt change to 130k miles in a Toyota MR2 and it appeared to have another 30k miles in it.
On the other end of the scale Lamborghini designed the first V8 Urraco P250 with belts, but got “cold feet” and changed it to chain drive for the later P300, Silhouette and Jalpa.
Laust
07-07-2006, 09:32 PM
#24
Three Wheelin'
I think the important thing is that with both the chain or the belt, if you maintain them properly, they are a non issue, except for freak events like this CCCP's tensioner stud breaking off of the block. This is the first failure I have heard of that was not due to neglect or some owner thinking they were capable of doing the belt job themselves when they probably did not have the ability.
07-07-2006, 10:19 PM
#25
Rennlist Member
Speaking of which, I should PROBABLY check my tension before autox sunday.. bleh. I just find it annoying with all new rollers, new waterpump, etc and perfect tension set by hand then checked and verified with p9201 , some roller(s)? are still whining. i ignore it as my car has always whined with either engine, but oh well. Having a spare head sitting in the shop causes me to almost be over-calm about the timing belt disaster possibility...
