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FREEDGUY 
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 Topic: Valve Clearance ??
Posted: 11 Jul 2020 at 6:51pm |
I have a close friend that bought an Audi 4 cylinder engine car(I don't know the year) that broke it's timing chain and incurred MAJOR valve train damage  . He insinuated that in the "old days", there was such a thing as "high interference/low interference" heads??? He just can not understand why an engineer would design an engine with NO room for a "chain" malfunction 
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Alberta Phil
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Posted: 11 Jul 2020 at 8:14pm |
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Quite a common thing with today's engines. Many have the cam or cams driven by a timing belt which is supposed to be replaced at a certain mileage. Failure to do so will sometimes result in a broken belt and if it's an "interference" type engine, much damage can result!! I don't get that type of "engineering " either.
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PaulB
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Posted: 12 Jul 2020 at 7:29am |
[QUOTE=FREEDGUY]
I have a close friend that bought an Audi 4 cylinder engine car(I don't know the year) that broke it's timing chain and incurred MAJOR valve train damage . He insinuated that in the "old days", there was such a thing as "high interference/low interference" heads??? He just can not understand why an engineer would design an engine with NO room for a "chain" malfunction [/QUOTE It's known as "Planned Obsolescence" Engineers plan for things to break to boost sales of new vehicles and repair parts and to justify their existence designing the wheel over and over again. Luckily The engineers at Allis Chalmers were not of that mindset, however Henry Ford has been quoted that everything should not last any longer than the warranty. When everyone was making Jeeps for WWII he wanted ever single part that left any of his factories to have the "FORD" logo imprinted onto them so he could not be charged for replacing something that some other place made. |
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DrAllis
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Posted: 12 Jul 2020 at 7:53am |
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Not any different than some older technology V-8's that have a timing chain and fiber camshaft gear wearing out. I have seen bent valves from that happening.
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plummerscarin
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Posted: 12 Jul 2020 at 3:01pm |
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Luckily The engineers at Allis Chalmers were not of that mindset
I discovered the hard that at least the 170 is an interference engine.
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DMiller
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Posted: 12 Jul 2020 at 3:21pm |
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Only engines that were truly Non Interference and Not designed for that reason, flatheads. Any diesel engine breaks a cam drive or a valve hangs in a guide looking at severe damage.
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FREEDGUY
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Posted: 12 Jul 2020 at 4:48pm |
My friend did say that "only" the exhaust valves got bent (8), but he replaced ALL 16. Why would only the exhaust valves get damaged  ??
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DMiller
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Posted: 12 Jul 2020 at 5:15pm |
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Engines tend to be on Down stroke for Intake, Up stroke for exhaust, belt breaks, gear fails and most times the intakes are already closed/closing. Not much momentum on a cam to keep it rotating.
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FREEDGUY
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Posted: 12 Jul 2020 at 5:41pm |
Thanks DMiller 
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jaybmiller
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Posted: 12 Jul 2020 at 5:49pm |
Why do 'engineers' design stuff like interfernece engines ??
Because they get paid to AND THEY don't ever have to work on them ( or PAY to have them fixed) !! We could (should ?) have a forum devoted to 'engineered booboos', 'cept it'd take up ALL the space on Darrin's harddrive !!
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FREEDGUY
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Posted: 12 Jul 2020 at 6:03pm |
 jaybmiller wrote:
Why do 'engineers' design stuff like interfernece engines ??
Because they get paid to AND THEY don't ever have to work on them ( or PAY to have them fixed) !! We could (should ?) have a forum devoted to 'engineered booboos', 'cept it'd take up ALL the space on Darrin's harddrive !!
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LeonR2013
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Posted: 12 Jul 2020 at 8:25pm |
Dave you're right about messing things up when you break a valve. Broke one on a 855 Cummins. Got the head, turbo, two inj. one piston and liner. Made a terrible racket. Leon
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Tbone95
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Posted: 13 Jul 2020 at 7:24am |
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Hmmm.....I'm no engine guru. But aren't there some very sound thermodynamic reasons for the "interference" design? Such as, to get the air/fuel charge at the correct compression, if there were more room at the top, there would have to be more air/fuel there to be at the same pressure. Then some things like air/fuel mixing efficiency in a larger volume. Seems a lot of interweaved little issues there.
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FREEDGUY
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Posted: 13 Jul 2020 at 6:15pm |
Tbone95 wrote:
Hmmm.....I'm no engine guru. But aren't there some very sound thermodynamic reasons for the "interference" design? Such as, to get the air/fuel charge at the correct compression, if there were more room at the top, there would have to be more air/fuel there to be at the same pressure. Then some things like air/fuel mixing efficiency in a larger volume. Seems a lot of interweaved little issues there. |
I was afraid that the "efficiency" (exhaust/pollution) might be a factor . This guy is used to big block truck/racing engines that could survive "minimal" $$$ damage when/if a timing chain/belt broke . Seriously, 4 valves/cylinder ?? This particular Audi does have 1 turbo though,maybe that's the need for that many valves ??
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LouSWPA
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Posted: 13 Jul 2020 at 6:26pm |
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ya beat me to it TBone, many, many times in my life I have said not nice things about the engineer who did this or that, but the reality is his job is not an easy job! There are a multitude of variables with just about any engineering task, cost, performance, appearance, longevity, size, weight, available materials, and, of course, marketing's wishes, to name a few. Yes, that engine could have been designed so that should the timing belt fail there would be no damage, but, at what cost somewhere else? performance? weight? complexity? initial production cost?
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steve(ill)
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Posted: 13 Jul 2020 at 10:04pm |
Yea, i have a 125 cubic inch Allis motor that weights about 300 pounds and puts out 20 HP..... using that same spec, you could build a 400 cubic inch truck engine with NO interference fit that put out a GOOD 75 HP !!!
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Tbone95
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Posted: 14 Jul 2020 at 8:13am |
FREEDGUY wrote:
Tbone95 wrote:
Hmmm.....I'm no engine guru. But aren't there some very sound thermodynamic reasons for the "interference" design? Such as, to get the air/fuel charge at the correct compression, if there were more room at the top, there would have to be more air/fuel there to be at the same pressure. Then some things like air/fuel mixing efficiency in a larger volume. Seems a lot of interweaved little issues there. |
I was afraid that the "efficiency" (exhaust/pollution) might be a factor . This guy is used to big block truck/racing engines that could survive "minimal" $$$ damage when/if a timing chain/belt broke . Seriously, 4 valves/cylinder ?? This particular Audi does have 1 turbo though,maybe that's the need for that many valves ?? |
More valves = more/easier breathing = more performance and efficiency. And yes, more "small" valves are better than just "bigger" ones.
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FREEDGUY
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Posted: 14 Jul 2020 at 7:09pm |
Thanks Tbone . I happen to run an '05 5.4 Ford F250, can I assume that the "TRITON" refers to multiple valves/cylinder? I bought it used and knew nothing(at THAT time) about that engine but have been learning more about it .
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DMiller
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Posted: 14 Jul 2020 at 7:16pm |
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Cams are problematic, cylinder heads on the earlier 5.4s were a disaster where plugs seized hard in the head threads, required special tooling to retrieve and ended with a Plug change to another type. Do NOT ignore engine odd noises that start out minor then grow as the timing chain tensioners were also a issue. Pre 2004 were only 2 Valve, after 04 three valve, Triton has nothing to do with that configuration, Just a Name.
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