Stretched timing chain - why?

[technics1974]

I've read in a few places that accelerating from low engine speeds causes the timing chain to stretch / belt to snap.

Why is this? I understand the engine works harder to pull the car forward but how, specifically, does that affect the timing chain / belt?

BTW, I don't labour my engines. I prefer to drop down a cog than hear my engine struggle.

[scaryoldcortina]

I don't think it does. I can't see why the output load on the crank would affect the cam.

I think mainly, snapped/stretched timing chain or belt is down to poor maintainance - infrequent oil changes damaging the cam bearings and increasing drag to the point where the weakest link gives out first.

[technics1974]

Apr 18, 2012 11:24:39 GMT scaryoldcortina said:

I don't think it does. I can't see why the output load on the crank would affect the cam.

That's exactly what I think, but I've heard and read to the contrary!

[optima21]

isn't there high loading on the cam and valve gear at low engine revs? and why they recommend running cams in for a period of time at speeds about 2500 rpm etc?

[ChasR]

I thought also that cambelts were stressed more when idling. Oddly enough, most of the snapped cambelts I have seen have snapped at low engine revolutions.

[scruff]

At idle the engine is accelerating/decelerating rapidly as the engine revs hunt, might only be tiny but the belt tension is changing all the time. Also oil pressur eis low at idle which won't help.

When revving the load ont he belt is much more stable, higher, but stable and oil pressure is up too.

[Deleted]

yer most belts snap at low rev's because there isn't enough rotating inertia so the belt take's more kick back loads and its the low speed variable load that snaps the belt, especialy when you let out the clutch.

[djefk]

Wow - Never even thought about that!