32 replies to this topic

[HarrysMini]

Just a general question really, I've done a bit of searching but can't find anything.

 

I am thinking of doing a belt conversion and was wondering if it snapped would the valves hit the pistons? Of course, I would never let it get to the point of it snapping being questionable, but it would be quite useful to know.

 

Anyone know?

[carbon]

Yes, for most A-series engines the valves can hit the pistons.

 

As always there may be the odd exception, where the valve lift is very low and the combustion chamber deep enough to contain the full valve lift.

[albo]

mmm the trouble is there is no warnings of a belt snapping,and yes serious damage can be caused head/valves push rods ect damage to pistons and rods, yes there is a recomended belt time change,as far as i know its regular,at least a chain lets you know when it needs a service by its rattle,and rearly snaps,  

[monkey]

I appreciate that chain drive almost totally eliminates the worry of breakage and therefore engine damage, however most (if not all?) modern cars use a belt which if correctly maintained, very rarely snap?

[HarrysMini]

Well the engine I would be using it on has an MG Metro cam and an MG Metro head. 

 

I wouldn't let the belt get old enough to worry about it snapping, it would be replaced at, if not before, the recommended intervals. 

[HarrysMini]

I appreciate that chain drive almost totally eliminates the worry of breakage and therefore engine damage, however most (if not all?) modern cars use a belt which if correctly maintained, very rarely snap?

Exactly. Belt drive provides many more advantages too.

[The Matt]

IF correctly maintained is the key thing!

The belts are only going to snap if not properly fitted or serviced.

[Stiggytoo]

Some modern car manufacturers are moving back to timing chains.

[sonikk4]

Some manufacturers are extending there cam belt change to..........................................120,000 miles!!!!!!!!    

 

On my CC its now 4 years or 80,000 miles.

[Carlos W]

Some modern car manufacturers are moving back to timing chains.

 

But Mazda have had loads of trouble with chain stretch

[albo]

Some manufacturers are extending there cam belt change to..........................................120,000 miles!!!!!!!!    

 

On my CC its now 4 years or 80,000 miles.

yes on better modern engines, the mini cam drive is very similar in size to my old quancast lawn mower,as soon as the grass got over grown the belt was under stress it would snap time after time, that little mower would of been a good un if it was chain drivven,

[gazza82]

It's often the mechanical parts on a timing belt wbere the failures occur. Tensioners, idler whhels, even the water pump. Sometimes well inside service intervals too.

Edited by gazza82, 29 June 2014 - 10:00 PM.

[Cooperman]

BMW & Mercedes now use chain drive again and others are going back to it.

I think that with a standard cam the valves won't hit the pistons (nor is block pocketing necessary when putting a 940 head onto a 998 with a standard depth head & a standard cam).

If the depth from head deck level to valve face level is more than the valve lift, there is no risk. As with most engineering things, it just needs accurate measurement, which many on here always seem reluctant to do.

[albo]

I appreciate that chain drive almost totally eliminates the worry of breakage and therefore engine damage, however most (if not all?) modern cars use a belt which if correctly maintained, very rarely snap?

just to add yea they may rearly snap but are more often prone to losing teeth,hence timeing jump / engine damage, 

[albo]

BMW & Mercedes now use chain drive again and others are going back to it.

I think that with a standard cam the valves won't hit the pistons (nor is block pocketing necessary when putting a 940 head onto a 998 with a standard depth head & a standard cam).

If the depth from head deck level to valve face level is more than the valve lift, there is no risk. As with most engineering things, it just needs accurate measurement, which many on here always seem reluctant to do.

which many on here always seem reluctant to do?  well you clearly haven`t done this yourself as you wouldn`t be stateing  I THINK