Timing belts.

[daytona365]

With all the fretting over timing belt changes, why don't more manufacturers build 'non interference' engines ? Mazda for one do, and still get respectable power from their engines ?

[shake n bake]

It's a huge turnover loss to run a chain driven engine, think of all those belt changes and rebuilds when they go pop.

[daytona365]

That's what I thought.

[crossy67]

shake n bake said:

It's a huge turnover loss to run a chain driven engine, think of all those belt changes and rebuilds when they go pop.

Non interference doesn't mean chain. It means the pistons don't hit valves when the timing gear fails.

[kiethton]

Why would it be in a manufacturers interests to do that?

Broken belt = new car sold as they'll clear the warranty period by some margin and likely be uneconomic to repair

A belt change, given likely age and mileage would more often than not be done by an indi and may not even use OE parts so the manufacturer wouldn't benefit, a belt change would also make long lease costs more, dissuading high mile lease co.'s, therefore making their cars more expensive to lease and therefore less desirable.

They would be shooting themselves in the foot on two levels so not worth it...

[SuperPav]

Whether an engine is interference or not is defined purely by the combustion chamber and requirements for valves/piston to be sized adequately. Nothing to do with how the cams are driven.

Most engines tend to be interference because when you need the compression that petrol (NA) and turbo diesels run, you're not left with much volume for all your many valves, once you consider the most efficient combustion chamber shape.


Belts are cheaper for the manufacturer. Potentially also more efficient/quieter, but this isn't always the case.


Revenue stream for the manufacturer from timing belts approaches zero. 90% of a cambelt change is labour, of which the manufacturer sees nil as it goes straight to the dealer. The actual cost of a belt with tensioner is negligible.