Help! First breakdown in 15 years

[Laird Scooby]

How different is the head? SOmething in the back of my mind says it will fit with the right gasket set but wait until someone else confirms that.

[chris s]

Hello Laird Scooby,

I'll try to get some photos of the two heads tomorrow. I should've taken a photo of the original one before buying another, but you live and learn don't you?

Cheers,
Chris

[Stephen Edwin]

Chris. Thanks for the update. I would take both heads to a motor engineering workshop and ask for advice.





But instead I'm going out to view some Rembrandt. Lucky me.

Good luck.

.

[Bugjam1999]

You could put the valves from the ‘new’ head into the ‘old’ one, but I expect you’ll be able to pick up another new head complete for low enough money that it won’t be worth the effort...

Of course if the ‘old’ head doesn’t have any other damage, just the valves...

Cheers

[Laird Scooby]

Originally Posted by Bugjam1999

Of course if the ‘old’ head doesn’t have any other damage, just the valves...

Cheers

.....then he'd still need to lap the valves in to the head and also check/adjust the clearance on each.

Correct me if i'm wrong, but doesn't the red block use shim adjustment for the valves?

[Clifford Pope]

Originally Posted by Laird Scooby

The cam shaft WILL stop as there is nothing to drive it if the timing belt breaks.

It will stop, but not instantaneously (remember Newton's Laws of motion? )

The momentum of the spinning shaft will keep it turning until the effort of compressing the valve springs or hitting some of the valves overcomes it.
It would depend on the speed of rotation at the moment the belt broke. Belts normally break at low speed, because the belt is then stressed more by the slow hammering of the cam lobes. At high speed the varying stress happens so quickly it evens out, so a fast spinning shaft takes less power to turn than a slow one.

Obviously in practice any damage is largely a matter of chance. I've read of engines completely trashed through a breaking belt, but also of miraculous escapes where even an interference engine has escaped all damage just through the lucky position of the cam shaft.

[Laird Scooby]

Originally Posted by Clifford Pope

It will stop, but not instantaneously (remember Newton's Laws of motion? )

The momentum of the spinning shaft will keep it turning until the effort of compressing the valve springs or hitting some of the valves overcomes it.
It would depend on the speed of rotation at the moment the belt broke. Belts normally break at low speed, because the belt is then stressed more by the slow hammering of the cam lobes. At high speed the varying stress happens so quickly it evens out, so a fast spinning shaft takes less power to turn than a slow one.

Obviously in practice any damage is largely a matter of chance. I've read of engines completely trashed through a breaking belt, but also of miraculous escapes where even an interference engine has escaped all damage just through the lucky position of the cam shaft.

Don't underestimate the power of valve springs to stop a camshaft turning! Remember they are designed to return the valves to the close position at high speed! Therefore Newtons Laws of Motion do come into play but the opposite way to how you're suggesting!

The main reason belts break at low speed is because of having to overcome the inertia of changing speed from zero (it it's during starting) to idling or from idling to 1500-2000rpm to pull away.
It can also happen at the end of a long, fast run where the change from being on throttle to being off throttle causes many dynamic changes within the engine.

[Bugjam1999]

Originally Posted by Laird Scooby

.....then he'd still need to lap the valves in to the head and also check/adjust the clearance on each.

Correct me if i'm wrong, but doesn't the red block use shim adjustment for the valves?

Hence me saying it might not be worth the effort.

Yes it does use shims.

Cheers

[mrredwards]

Hi Had my 240 for sometime so over the years i have repaired and replaced many parts.About 10 years ago i had a head gasket go ,I had the head skimmed put it back together it started and run but unfortunately i did not torque the crank bolt sufficient and it jumped a tooth.Luckily and i dont know why no damage to the valves just re timed it and it was fine..Strange?? When the cambelt went it destroyed all the valve,Regards Ron.

[Laird Scooby]

Originally Posted by mrredwards

Hi Had my 240 for sometime so over the years i have repaired and replaced many parts.About 10 years ago i had a head gasket go ,I had the head skimmed put it back together it started and run but unfortunately i did not torque the crank bolt sufficient and it jumped a tooth.Luckily and i dont know why no damage to the valves just re timed it and it was fine..Strange?? When the cambelt went it destroyed all the valve,Regards Ron.

I've known some engines to be 2-3 teeth out and will still run without valve damage, they just don't run very well!

You obviously had a guardian angel-mechanic looking after you that day though!