What is the problem with designing non-interference engines? Does it take too much space / cost more to build?

I was thinking about the physics of suck, squeeze, bang, blow and in particular compression ratios.

What is the problem with designing non-interference engines?

No problem

Does it take too much space / cost more to build?

No. They are just not as powerful or economical. That's why they are favoured in countries where fuel is cheap.

<< breaking or skipping due to stretch and tensioner failure >>

How much of that is genuine stretch, and how much due to wear on the dozens of small spindles ?

Does it make a difference?

<< breaking or skipping due to stretch and tensioner failure >>

How much of that is genuine stretch, and how much due to wear on the dozens of small spindles ?

Does it make a difference?

Probably not, but it might be interesting to know.

NONE and ALL, respectively, near as dammit

It makes a difference because stretch, if it happened, would be the inevitable consequence of the mechanical tension load on the chain, and could only be ameliorated by structural change.

Wear can be ameliorated by better lubrication. which is generally good in cars.

Its lousy in bicycles and motorcycles, which run in a grit paste, unless the latter have an enclosed chain, which are sooo uncool because Rossi doesn't have one, so fitted yo very few contemporary offerings.

I learnt my lesson earlier in life. Around 25 years ago I bought a Toyota Corolla 1.3 from someone who promised me he changed the belt at the right schedule. I was younger and naive and took it on his word.

Six month later I was zooming down the M25 when the belt broke.

It was an interference engine and so it went to the scrap.

I'll be in a similar dilemma soon. My belt is due in 10,000 miles (about seven months). Don't think I've got the stomach to change it. It's a fiat with 180000 miles on the clock so worth scrap value only. Still on original clutch, turbo, exhaust etc. The suspension clonks, there is rust on the sill. Would have though they would've built in a bit if tolerance regarding interval hopefully. Will let you know in 10k!

I've known two friends who had snapped belts from overshooting the service interval, a Clio and a Rover, these were middle-aged cars at the time and in both cases the cars were scrapped as the cost of repair was too much. A ridiculous waste on what were otherwise good cars that would have gone on for many more miles just for the cost of a belt change at probably a few hundred in today's money.

I had a Rover with the 1.6 Honda engine, cambelt snapped but that was a non-interference engine so once recovered to my local indie only needed a new belt to be back to full health.

Is it not possible to make a cam belt that dosen't just go or at least give a warning.?

VW forums have lots of discussion about inconsistent belt changes. Crazily the recommended intervals vary significantly across markets for identical engines.

I think it is because some recommenders err on the cautious side and have a vested interest in the work involved. An expensive garage with a VW sign above the door and on the notepaper doesn't necessarily imbue either the proprietor or the employees with either the expertise or the authority of VW's Wolfsburg engineers.

It's basically all about the percentage risk of failure at a certain mileage. Even a 0.5% failure rate before, say, 100,000 miles would negate a reputation for reliability, especially in a mass produced engine powering hundreds of thousands of cars. Sadly, this means that if, say, 1% of probably unnecessary changes at a 'recommended' 50,000 miles are mucked up by careless mechanics, there will be more unhappy owners than if they had left well alone. Any bearing, whether wheel, water pump, or tension pulley, can unluckily fail at 40,000 miles or less when other identical bearings might last five times longer.

I believe mainland Europe is inspection at 160k kilometers.

Be interesting to know what they "inspect", since the usual story is you can't predict a belt failure from its appearance.

Could there be some (secret?) measurable parameters that predict remaining life, (seems unlikely) or are they actually inspecting anciliaries like belt tensioners and guides?

VW forums have lots of discussion about inconsistent belt changes. Crazily the recommended intervals vary significantly across markets for identical engines. Golf Mk7 UK is 5 years and 60k miles (from memory). I believe mainland Europe is inspection at 160k kilometers

When we bought the Leon 1.4 TSi on 2013 we also looked at the Golf 1.4 TSi. In the Golf printed brochure supplied by our local dealer it clearly stated that the Conti belt used was fitted for the life of the car. The Seat dealer insisted that the identical engine in the Leon required a belt change at 3 years or 30,000 miles at a cost of about £350.

The Leon was £5000 less than the Golf so the one extra £350 belt change during our expected 5 year ownership was a drop in the ocean so we bought the Leon but it still nagged me. So I e-mailed Seat Customer Services who replied that the belt in the 1.4 TSi required its condition checking at 60,000 miles and every 20,000 miles after that. But once the belt had done 120,000 miles or was 6 years old it required replacing.

That made me happy, no belt change required but I wonder if VW still have the "fitted for life" page in the manual.