Suprash Posted April 14, 2012 Share Posted April 14, 2012 So a NA block is a non interface engine and a TT is an interface setup meaning if a cam belts snaps on a NA block pistons dont hit valves. But if you had a NA block and NA head with TT pistons, would that still be a non interface setup or would that now make it an interface setup meaning if your cam belt snapped would the pistons foul the valves ? Quote Link to comment Share on other sites More sharing options...
stevie_b Posted April 14, 2012 Share Posted April 14, 2012 I thought both the NA and TT engines were non-interference, but that's only forum-lore (mainly opinions and unsubstatiated posts) that I've picked up on here. Quote Link to comment Share on other sites More sharing options...
Suprash Posted April 14, 2012 Author Share Posted April 14, 2012 I thought both the NA and TT engines were non-interference, but that's only forum-lore (mainly opinions and unsubstatiated posts) that I've picked up on here. Interesting I have always read on here that the NA was non interface and TT wasnt, will await other responses to see Quote Link to comment Share on other sites More sharing options...
V8KILR Posted April 14, 2012 Share Posted April 14, 2012 So a NA block is a non interface engine and a TT is an interface setup meaning if a cam belts snaps on a NA block pistons dont hit valves. But if you had a NA block and NA head with TT pistons, would that still be a non interface setup or would that now make it an interface setup meaning if your cam belt snapped would the pistons foul the valves ? Both the NA and TT engines are non-interference engines. Its only when you put in cams with over ~9.5mm lift, that you turn the engine into an interference engine. Quote Link to comment Share on other sites More sharing options...
Abz Posted April 14, 2012 Share Posted April 14, 2012 I thought both the NA and TT engines were non-interference, but that's only forum-lore (mainly opinions and unsubstatiated posts) that I've picked up on here. Just like Steve I'd picked this up on the forum & to my understand they both ate non-interference. Quote Link to comment Share on other sites More sharing options...
Nic Posted April 14, 2012 Share Posted April 14, 2012 Yes both are non-interference. Quote Link to comment Share on other sites More sharing options...
Suprash Posted April 14, 2012 Author Share Posted April 14, 2012 Excellent, so if my cam belt was to snap, shit wouldnt destroy itself ? Weighing up the risk factor of running a cam belt with a small hole in it for Round 1 as I dont think Im going to have time to replace it before..... Quote Link to comment Share on other sites More sharing options...
Swampy442 Posted April 14, 2012 Share Posted April 14, 2012 No it would be fine. Quote Link to comment Share on other sites More sharing options...
garethr Posted April 14, 2012 Share Posted April 14, 2012 Not true for VVTi engines though, IIRC. Quote Link to comment Share on other sites More sharing options...
Suprash Posted April 14, 2012 Author Share Posted April 14, 2012 Ah, maybe thats where I got the interferance and non interferance thing mixed up, it may be non VVT-i engines that arent and VVT-i's that are, thanks all Quote Link to comment Share on other sites More sharing options...
D8MOA Posted April 14, 2012 Share Posted April 14, 2012 Not true for VVTi engines though, IIRC. this is true Quote Link to comment Share on other sites More sharing options...
j_jza80 Posted April 14, 2012 Share Posted April 14, 2012 Still best to get your belt changed according to the service schedule Quote Link to comment Share on other sites More sharing options...
chrispot Posted April 15, 2012 Share Posted April 15, 2012 this is true do VVTI's have more valve lift than non vvti engines, if not then they would be ok if the belt broke? Quote Link to comment Share on other sites More sharing options...
V8KILR Posted April 15, 2012 Share Posted April 15, 2012 do VVTI's have more valve lift than non vvti engines, if not then they would be ok if the belt broke? If the VVTI is an interference engine, then it will be because the valves are opening much sooner and will be nothing to do with the lift. Quote Link to comment Share on other sites More sharing options...
Suprash Posted April 15, 2012 Author Share Posted April 15, 2012 It will be becuase of the changed opening and closing times of the valves which will be changed by the VVT-i, not the amount of valve lift Quote Link to comment Share on other sites More sharing options...
chrispot Posted April 15, 2012 Share Posted April 15, 2012 If the VVTI is an interference engine, then it will be because the valves are opening much sooner and will be nothing to do with the lift. an interference engine has got nothing to do with the timing of the valves, vvti or not its the valve lift which can cause the valve to hit the piston. the timing of the valves is lost once the belt breaks. Quote Link to comment Share on other sites More sharing options...
Suprash Posted April 15, 2012 Author Share Posted April 15, 2012 an interference engine has got nothing to do with the timing of the valves, vvti or not its the valve lift which can cause the valve to hit the piston. the timing of the valves is lost once the belt breaks. The timing of the valve is lost once the belt snaps which is why an interferance engine will have problems if that does happen. Looking at it from your point of view, if it was valve lift that causes the issue, then say for arguments sake your engine hass high valve lift, once the belt snaps the timing is still lost resulting in bent valves, but it wasnt the high lift that caused it, it was the timing of the valves or shall we say lack of due to the belt snap. If you have a non-interferance engine, maybe due to the fact that the valve lift is a lot shorter, then the snapping belt would have no effect as it doesnt matter what postions the valves are in the piston will never meet it. Now I think I've just proved both answers are correct, no ? lol...... Quote Link to comment Share on other sites More sharing options...
stevie_b Posted April 15, 2012 Share Posted April 15, 2012 I'm no expert but I think chrispot's correct. AFAIK the definition of a non-interference engine is one where the path of the pistons never crosses over the path of the valves, no matter where in their respective cycles they are. Interference engines rely on the relative timing of the pistons and valves to keep them from smashing into each other. As you know, it's the timing belt that maintains the relative timing of them. Quote Link to comment Share on other sites More sharing options...
Graham S Posted April 15, 2012 Share Posted April 15, 2012 Wow, You lot are rather confusing! Now..... trying to put it in its easiest terms, a NON interference engine can have the pistons at any position in the cycle and have a complete turn of the camshafts and will not come into contact with the piston crowns. An INTERFERENCE engine, should it come out of correct timing (belt slip, snap, whatever!), WILL cause the valves to come into contact with the pistons or the pistons to come into contact with the valves, whatever way you want to look at it. Non interference engines become interference when the camshafts are changed with higher lift cams, I think the reasoning is in the title there and doesn't need explaining? Quote Link to comment Share on other sites More sharing options...
Suprash Posted April 15, 2012 Author Share Posted April 15, 2012 Wow, You lot are rather confusing! Now..... trying to put it in its easiest terms, a NON interference engine can have the pistons at any position in the cycle and have a complete turn of the camshafts and will not come into contact with the piston crowns. An INTERFERENCE engine, should it come out of correct timing (belt slip, snap, whatever!), WILL cause the valves to come into contact with the pistons or the pistons to come into contact with the valves, whatever way you want to look at it. Non interference engines become interference when the camshafts are changed with higher lift cams, I think the reasoning is in the title there and doesn't need explaining? What are you even doing here Thanks though I was confusing myself in the end lol.... Quote Link to comment Share on other sites More sharing options...
chrispot Posted April 16, 2012 Share Posted April 16, 2012 ]It will be becuase of the changed opening and closing times of the valves which will be changed by the VVT-[/u]i' date=' not the amount of valve lift [/quote'] in your statment you infer that the vvti is a inteferance engine because of the changing valve timing given that the non vvti engine is a non interferance engine and the vvti has the same valve lift, it makes no difference with the opening and closing times of the valves. the valves will not touch the pistons what ever the timing Quote Link to comment Share on other sites More sharing options...
Guest Budz86 Posted April 16, 2012 Share Posted April 16, 2012 I was under the impression an engine would be classed as non interference if at the highest point in the pistons cycle ie; top dead centre it wouldn't touch the valves, so even if the cam belt snapped and the valve was left open (so stick out of the head into the combustion chamber) the piston wouldn't reach high enough to cause damage to the valve. By increasing the travel of the piston is the only way you would cause damage to the valve. Just got me thinking though, if say the inlet valve is open, and the piston completes the combustion part of the cycle, how do the exhaust gases exit the chamber if the cam belt is snapped (meaning the exhaust valve won't open)? Also, what would be the effect if the gases could not exit? Quote Link to comment Share on other sites More sharing options...
pedrosixfour Posted April 16, 2012 Share Posted April 16, 2012 I know it's not strictly MKIV tech but could anyone say with any degree of certainty whether a 1JZ-GTE, non VVT-i, stock cammed engine is a non-interference lump? Quote Link to comment Share on other sites More sharing options...
D8MOA Posted April 16, 2012 Share Posted April 16, 2012 it may also be that the vvti has bigger intake valves? all i no is a tech i worked with done a camebelt and tensioner on one...while putting the tensioner on let the washer on the back fall off.. started the car which caused the belt to slip and bent ALL the intake valves Quote Link to comment Share on other sites More sharing options...
Guest Budz86 Posted April 16, 2012 Share Posted April 16, 2012 it may also be that the vvti has bigger intake valves? all i no is a tech i worked with done a camebelt and tensioner on one...while putting the tensioner on let the washer on the back fall off.. started the car which caused the belt to slip and bent ALL the intake valves Ouch! Still, it's the sort of mistake that only happens once! Quote Link to comment Share on other sites More sharing options...
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