disadvantage of non interference engine

RobAMerc

hi,

Just wondering if anyone knows why all manufacturers don't use non interference design for their engines.

I could be cynical and say because it gives mechanics something to do and makes the manufacturers a few bob.

I am more inclined to think interference engines :

a) Allow a better shape to the combustion chamber that proves much more efficient ?
b) Allow higher compression ratio or something ?

Any boardsies up on this at all ?

ta, Rob

Anan1

RobAMerc wrote: »

I am more inclined to think interference engines :

a) Allow a better shape to the combustion chamber that proves much more efficient ?
b) Allow higher compression ratio or something ?

That'd be my assumption too.

peasant

To be perfectly honest, I for one don't even know how a non-interference engine is supposed to work. I mean, the valves have to enter the top of the cylinder at some stage, don't they?

Anan1

peasant wrote: »

To be perfectly honest, I for one don't even know how a non-interference engine is supposed to work. I mean, the valves have to enter the top of the cylinder at some stage, don't they?

I think the idea is that the valves, even when fully open, don't come down far enough to meet the piston even at the top of its travel.

peasant

Anan1 wrote: »

I think the idea is that the valves, even when fully open, don't come down far enough to meet the piston even at the top of its travel.

...which in turn would probably neccesitate a shape of combustion chamber that is not thermodynamically ideal ....

robtri

Anan1 wrote: »

I think the idea is that the valves, even when fully open, don't come down far enough to meet the piston even at the top of its travel.

thats my understanding of it as well...

Anan1

peasant wrote: »

...which in turn would probably neccesitate a shape of combustion chamber that is not thermodynamically ideal ....

I'd imagine so. I'd have thought low-compression engines would therefore be more likely to be non-interference?

nmacc

The old Renault 12 engine was non-interference. If the cam chain wore or snapped, you'd get a failure to start and maybe a backfire or blowback through the carb. Replace the chain and re-time; no harm done!

galwaytt

peasant wrote: »

...which in turn would probably neccesitate a shape of combustion chamber that is not thermodynamically ideal ....

...tut, tut...Mazda MX-5 engine is non interference and runs quite well thank you !!..mine will bounce off the rev limiter all day without a care in the world.

RobAMerc

can I at least assume there is no such thing as a non interference diesel ?

Anan1

RobAMerc wrote: »

can I at least assume there is no such thing as a non interference diesel ?

While googling this (it seems you're right), I found a novel way of replacing a TB without having to reset the timing: I dont know if its the same on a supra because I have not had a close inspection but there is a really easy way to change your timing belt without the need for re-timing.

All you do is remove all the plugs and cam cover, get a sharp stanley knife and push it into the belt in the middle, NOT acrossways, along its length, then either turn the engine over by hand on the crank pulley bolt (best to get a mate to do this) or if you have a steady hand, crank the engine in short bursts (mate here would be useful)
Until you have cut the belt completely into two seperate "belts" that are still on the pulleys, pull the front half off, and put the new belt on, cut off the other half and push the new belt all the way on, job done! It definately works cos i've done it on several cars, and it saves a shedload of time and hassle.

What do you think?

galwaytt

....oh, I'm sure you can !!

At 22:1 CR, you can kiss non-interference goodbye !!

...unless it's a Detroit 2-stroke diesel.......which only has ex valves........would that make it a 'half-interference' or 'hit & miss' engine' ?? !!

And, of course, there's sleeve-valve engines........

galwaytt

Anan1 wrote: »

While googling this (it seems you're right), I found a novel way of replacing a TB without having to reset the timing: I dont know if its the same on a supra because I have not had a close inspection but there is a really easy way to change your timing belt without the need for re-timing.

All you do is remove all the plugs and cam cover, get a sharp stanley knife and push it into the belt in the middle, NOT acrossways, along its length, then either turn the engine over by hand on the crank pulley bolt (best to get a mate to do this) or if you have a steady hand, crank the engine in short bursts (mate here would be useful)
Until you have cut the belt completely into two seperate "belts" that are still on the pulleys, pull the front half off, and put the new belt on, cut off the other half and push the new belt all the way on, job done! It definately works cos i've done it on several cars, and it saves a shedload of time and hassle.

What do you think?

Holy Schweppes !! :eek: :eek:

david

Anan1 wrote: »

While googling this (it seems you're right), I found a novel way of replacing a TB without having to reset the timing: I dont know if its the same on a supra because I have not had a close inspection but there is a really easy way to change your timing belt without the need for re-timing.

All you do is remove all the plugs and cam cover, get a sharp stanley knife and push it into the belt in the middle, NOT acrossways, along its length, then either turn the engine over by hand on the crank pulley bolt (best to get a mate to do this) or if you have a steady hand, crank the engine in short bursts (mate here would be useful)
Until you have cut the belt completely into two seperate "belts" that are still on the pulleys, pull the front half off, and put the new belt on, cut off the other half and push the new belt all the way on, job done! It definately works cos i've done it on several cars, and it saves a shedload of time and hassle.

What do you think?

Someone give this man cake :pac:

RobAMerc

Anan1 wrote: »

then either turn the engine over by hand on the crank pulley bolt (best to get a mate to do this) or if you have a steady hand, crank the engine in short bursts (mate here would be useful)

Too chicken to turn it over using the starter motor ?

Rovi

Anan1 wrote: »

While googling this (it seems you're right), I found a novel way of replacing a TB without having to reset the timing: I dont know if its the same on a supra because I have not had a close inspection but there is a really easy way to change your timing belt without the need for re-timing.

All you do is remove all the plugs and cam cover, get a sharp stanley knife and push it into the belt in the middle, NOT acrossways, along its length, then either turn the engine over by hand on the crank pulley bolt (best to get a mate to do this) or if you have a steady hand, crank the engine in short bursts (mate here would be useful)
Until you have cut the belt completely into two seperate "belts" that are still on the pulleys, pull the front half off, and put the new belt on, cut off the other half and push the new belt all the way on, job done! It definately works cos i've done it on several cars, and it saves a shedload of time and hassle.

What do you think?

Holy carp, that sounds like the coolest tip evah! :eek:

This will most certainly be looked at the next time I have the front off an engine.


As david suggested, tuck in:

peasant

what about the tensioner / water pump if necessary?

Anan1

peasant wrote: »

what about the tensioner / water pump if necessary?

Don't be a spoilsport.;)

Rovi

peasant wrote: »

what about the tensioner / water pump if necessary?

Yeah, that's a good point actually.

<rescinds cake>

ART6

RobAMerc wrote: »

hi,

Just wondering if anyone knows why all manufacturers don't use non interference design for their engines.

I could be cynical and say because it gives mechanics something to do and makes the manufacturers a few bob.

I am more inclined to think interference engines :

a) Allow a better shape to the combustion chamber that proves much more efficient ?
b) Allow higher compression ratio or something ?

Any boardsies up on this at all ?

ta, Rob

Ford CVH (Compound Valve Hemisphere) engine. The valves enter into hemispheres in the piston and so can never touch it. For that reason if a timing belt breaks it does no damage to the engine at all. I replaced the belts in two Sierras after they had broken and the engines were unharmed. Best design when belts rather than chains are used in my opinion.

bushy...

Rovi wrote: »

Yeah, that's a good point actually.

<rescinds cake>

Should still work if the pump , easier if the cam wheels are spoked.
Pass a cable tie through between two spokes of each wheel and around the belt .The idea is to hold it tight against the wheel to stop it jumping teeth. At the crank use something to keep it against the wheel.

Other useful one , for valve seals : lift the cams , followers/buckets ,spark plugs . Block anywhere the collets could fall down.
Put first cylinder at BDC , feed climbing rope in plug/injector hole. ( tie a knot in rope so if its a short piece so it doesnt fall in) .
Gently bring piston up the bore so it+rope touch the head/valves.

Make a tool to compress the valve springs , change the seals on that cylinder and move onto the next.

Zube

ART6 wrote: »

Ford CVH (Compound Valve Hemisphere) engine

Not a great ad for non-interference engines, as it was nicknamed the Ford NVH.

galwaytt

bushy... wrote: »

Should still work if the pump , easier if the cam wheels are spoked.
Pass a cable tie through between two spokes of each wheel and around the belt .The idea is to hold it tight against the wheel to stop it jumping teeth. At the crank use something to keep it against the wheel.

Other useful one , for valve seals : lift the cams , followers/buckets ,spark plugs . Block anywhere the collets could fall down.
Put first cylinder at BDC , feed climbing rope in plug/injector hole. ( tie a knot in rope so if its a short piece so it doesnt fall in) .
Gently bring piston up the bore so it+rope touch the head/valves.

Make a tool to compress the valve springs , change the seals on that cylinder and move onto the next.

hmmm....there's a kit for that, somewhere, iirc. It uses an adaptor in the plug hole, and compressed air to keep the valve home...