does any one know if the valves would bounce if the cam belt snaped ?????????

 

I have never seen this one covered - well done on picking up a new subject.

I have no idea mind you - sorry - but would love to know.

As it hasnt been mentioned as far as i am aware I can assume that there is not a major problem with scoobie cambelts going???

Pete

 

a cowboy type geezer has told me that my valves are all bent out of shaape ..he has not done any work on it ..but he recons that this is the case ...
a mate of mine has told me that the scoobie valves physicaly can not touch the pistons if this is true i would be happier ...does any one have a clue ???????

 

I would say, yes, it is an interference engine.

A certain STi had a cam belt failure at about 7k rpm and the engine is a right mess. Valves deffo. scrap, amongst other parts.

Cheers

Ian

 

One of my mates is a scooby mechanic and has told me that the valves cannot hit the pistons if the cam belt breaks .

 

Hi I changed a belt recently and checked to see if they do hit,and the answer is they do on both the inlets and exhausts (this was on a my98)

Something to bear in mind is that because there are 4 cams each cam is only opening/closing valves for half of each revolution.This means that if the belt was to break completly then the cams would,more than likely, come to rest with the valves shut.Its still possible for the valves to hit but I would think you would be unlucky if they did.

However if the belt just lost some of its teeth then some of the valves would stay open and the results would not be pretty

Andy

 

Andy,

Then work out what your chances are at 5, 6, or 7000rpm !!!!!!!.

Mark.

 

Slight change of subject but just purchased a belt to change mine and have been assured that it is a genuine belt.
Anyone know if 'Gates' is the genuine item for a WRX ?

 

I worked with a guy whos belt went on a 97 UK Turbo, no damage. I'd think about a second opinion just in case. If you don't then you'll always wonder and think you got ripped off.

Cammy

 

Find out. Either take the head off and have a look or put a new cam belt on and turn it over and see what it does.

 

I had the RAC out to my early WRX a while back and the Impreza Turbo shows as being 'non interference' on their technical database, which means the valves shouldn't hit anything in the event of a cam belt snapping.

 

[This message has been edited by Shaun (edited 30 January 2001).]

 

It depends on the MY/type of the Subie...

Does the belt say Subaru on it ? If not, its not a genuine subaru belt.

But later cars are interfence...dependant on valve train design

J.

 

So basically no-one really knows

Some say its an interference engine others not ....... I must say that I have not heard of a Scoobie engine being wrecked because of a cam belt break.

Come on all you tuning boys - you MUST know the answer to this one????

Pete

 

I dont know - all these people adding thousands of pounds of goodies to their babies and they dont know if the pistons hit the valves if the Cam-belt snaps???

Come on chaps - anyone with any knowledge of the boxer engine as fitted to scoobies?????

Pete

 

This may be a load of bollcoks but I was told that if you put impreza's on a trailer and leave them in gear to assist in keeping it stationary on the trailer bed, the cam belts can jump! Like i say this may be rubbish but worth asking about or at least keeping in mind.

 

I've had a cambelt failure on my car. General concensus from the people who i know and trust is that the engine is an interference design and that I will have bent a valve or two. As yet, we don't know what's been damaged, but there is a fair bit of inertia in the system when it lets go at just under 7000 rpm (over 110 revolutions per second! ).


IWatkins,

I'd be interested to hear more about this certain STI with the engine "in a right mess"... It would be useful to know what damage that car suffered so I have a better idea of what to expect when I get around to actually opening mine up and seeing the damage... cheers mate.

Moray

 

Moray,

You have mail.

Cheers

Ian

 

pslewis..

People do know.... and try and answer your questions (as well as they have been asked).. but if you dont bother reading the replies, then so be it.

J.

 

thanks for all the help guys.. but alass we put a new belt on today and turned it over only to here a loud rattling.... so i will have to open her up on the weekend .. i will post my findings on sunday ....

 

FireCox - it was a simple question - requires a simple answer - simple (or is that too complicated for you??)

I see your answer was - it depends on what MY or if its a UK spec or if the sun is shining or if the wind is coming from the west or east or what valve train I have fitted or whether - so thanks I DID read it!! thanks but it was about as much use as a chocolate frying pan!!

You DONT even know what your occupation is for gods sake!

Pete

[This message has been edited by pslewis (edited 31 January 2001).]

 

pslewis

I have posted above that if you remove the belt and turn one of the cams so that the valves it controls are full open, then turn the crank by hand the pistons do hit the valves.This is on a my98. So a UK my98 IS an interferance engine.

Wether or not you suffer damage as a result depends on how it failed so its not possible to give a simple 'yes' or 'no' answer.There is a load of waffle below explaining why this is if you can be bothered to read it

As soon as you remove the belt from a Scooby engine the cams spin around so that ALL the valves are shut.This is because there are only a few cam lobes on each camshaft.
On an engine with only 1 or 2 canshafts there are lobes all the way around it,so when it stops turning 1 or more valves will stay open.
The only time any valves would stay open on a Scooby is if the cam happened to come to rest with the valve full open.The chance of this has to be very small.

What this means is that if your belt was to break near to tick-over you would probably have no damage.If it broke at 6000 revs the inertia in the cams which are spinning at 50 revs per second(half crank speed)means there is a good chance of damage.

Also if the belt did not break but lost some teeth then you would definitly have some damage

Hope this helps

Andy

PS to the people who have had them let go when did it happen ? was it at high revs or near to tick-over?I have fixed a few cars that have had a belt go and most were at tick-over while sitting at trafficlights etc weird

 

Mine went at just under 7000rpm at 0.5bar of boost. I'm not yet sure if it's the belt or the tensioner that failed, but the same results would transpire. Incidently, I declutched in less than half a second from the failure but this won't have helped as the inertia is so high at 7k. Data logs are interesting... car fine, car fine, car fine, no sync, no anything...

 

Thank you Andy - very consise

I have had 4 cam belts go in the past and they all went at very low RPM - just as I was accelerating (not hard!) these were on the 2litre Ford Pinto engine and it does no damage - so it was just a case of new belt - sorted!!

Can I assume by this thread then that some Scooby engines are interference and some not??

Anyone know what a MY00 is??

Pete

 

The original question about bounce has not been addressed - Bounce is when the valves snap closed and come off the seats again, as the springs are not capable of keeping them shut at high revs. It wont happen in these engines as 1) the rev limiter is there to stpop the engine revving to a speed that would allow bounce to occur, and 2)the springs are within the limits of the RPM. In old british motorbike engines and ford/triumph engines of the 60s and 70s, you could rev them till the valves bounced, and at the same time the pushrods and rockers would be flexing horribly. Modern design has really done well to minimise valve bounce which can only really be stopped by desmodronic engine design where valve closure is a positive action, not a passive one.
On the basis of no knowledge at all, I would be gobsmacked if the subaru engines did not overlap. That suggests there is so much room in the combustion chamber that a quick power gain would be had by high lift cams. Even volvo 240 engines overlap, and they were pretty low tuned things!!

 

LEWEGIE,

GATES make alot of belts for alot of manufacturers, all the manufacturers do is stick their own stamp on it and double the price.

If you don't have SUBARU on your belt it would still be the same belt, but not bought from a dealer.

Scott