Non-interference (SWMBO?)

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Gareth Wales
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Non-interference (SWMBO?)

Post by Gareth Wales » Sat Apr 08, 2006 3:10 pm

Could someone kindly tell me what a non-interfence engine is. I understand that such an engine will survive a cam-belt breakage. Therefore, you won't find one on a BX??
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Post by Stewart (oily!) » Sat Apr 08, 2006 3:23 pm

Its an engine where the valves clear the pistons in the event of cambelt breakage, due to their inherent high compression few if any diesel engines are this way, in our beloved XUD motors the pistons hit the valves which in turn snap the camshaft and push the bearing caps upwards, snapping them and bending the studs, sometimes valve guides are destroyed too, the worst one I have repaired had six bent valves, the easiest none, just got a cam from the scrapyard with the cap and studs, built it up and away it went, mind you that one had the belt fall off at tickover.
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Post by Philip Chidlow » Sat Apr 08, 2006 3:26 pm

Do any BX engines have this characteristic? What about the petrol ones?
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Post by (CZ)enda » Sat Apr 08, 2006 3:31 pm

I know of only one cambelt-snappage-proof :) engine family: FIAT's FIRE (Fully Integrated Robotized Engine) engines.
These were first used on Uno/Panda from circa 1985-7, AFAIK there is 3rd line of them being produced now.

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Post by DavidRutherford » Sat Apr 08, 2006 5:46 pm

The Vauxhaul SOHC petrol engine from the 80's and early 90's is also a non-interference engine. I know this for sure as I had a belt snap on me at high engine speed, and it just cuts out.

Had an odd one recently... a Renault 1.9TD engine in a Volvo. Aux belt got wrapped up in the cambelt, and it jumped several teeth. Rather than mashing the valves etc. it sheared the keyway on the camshaft pulley, and no damage was done internally. New pulley, new belts and new tensioners and it was away again.... Blind luck?

Conversley, the TUD engine (1.4/1.5) in pug 106 and citroen AX/paxo is VERY seceptible to this. I was being distracted (IE, cocked up) while fitting a belt once, and got it wrong. Cranking the engine on the starter bent 2 valves, and shattered the bucket tappets. Arses!
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Post by Mr B » Sat Apr 08, 2006 8:44 pm

The old OHC Pinto engine in the Cortina wasn't a valve bender either, just re-time pop a belt on, away they went. Then again you had to either take the engine out or take the head off to change a camshaft :roll:
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Post by ernst stavro blofeld » Sat Apr 08, 2006 8:54 pm

DavidRutherford wrote:
Conversley, the TUD engine (1.4/1.5) in pug 106 and citroen AX/paxo is VERY seceptible to this. I was being distracted (IE, cocked up) while fitting a belt once, and got it wrong. Cranking the engine on the starter bent 2 valves, and shattered the bucket tappets. Arses!
Which is why the engine should always be turned through at least two full revolutions using a socket on the end of the crank and a chalkmark, before the key is reinserted.

And if it tightens up, you have the opportunity to find out why instead of wrecking an engine with preventative maintenance.

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Post by DavidRutherford » Sat Apr 08, 2006 9:20 pm

ernst stavro blofeld wrote:
DavidRutherford wrote:
Conversley, the TUD engine (1.4/1.5) in pug 106 and citroen AX/paxo is VERY seceptible to this. I was being distracted (IE, cocked up) while fitting a belt once, and got it wrong. Cranking the engine on the starter bent 2 valves, and shattered the bucket tappets. Arses!
Which is why the engine should always be turned through at least two full revolutions using a socket on the end of the crank and a chalkmark, before the key is reinserted.

And if it tightens up, you have the opportunity to find out why instead of wrecking an engine with preventative maintenance.
I know.

That had been done. The problem was that the TUD engine does not have the same sprung loaded tensioner that the XUD engine has, and the tensioner was tight enough to allow the engine to be rotated on a bar, but skipped a number of teeth when the starter was turned.
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Post by AlanS » Sun Apr 09, 2006 12:07 am

The 1.8 litre engine on the Mazda Traveller/Ford Spectron, both 8 seater people movers which had the same engine I understand as a 929(?) also had a non interference engine.
It was also such a low compression engine that it could run on 91 octane unleaded without any pings or strange noises. :roll: :roll:


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Post by cavmad » Sun Apr 09, 2006 11:27 am

I`m with David on that! I`d just bought (like that day) a Cav Mk2 1.8SRi off a mate from work and was pleased as punch with it. Newest car I`d ever owned. 21 miles later the cambelt snapped :cry:
Luckily not a single bit of damage. One new cam belt later and the engine`s perfect :lol:
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