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What is an "Interference" engine?


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11 replies to this topic

#1 ajosefick

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Posted 16 February 2005 - 08:39 AM

What is the definition of an Interference type engine? What is it's advantage supposed to be?

Thanks,
A.J.

#2 Dazed Dreamer

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Posted 16 February 2005 - 08:45 AM

dont quote me on this and please correct me right away If I am wrong but I believe an "interference" engine will seize and lock if the timing belt breaks as apposed to a "non-intereference" which wont, other than that I dont know

#3 Smpol19

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Posted 16 February 2005 - 08:53 AM

in an interference the valves are positioned so if they are all the way down and the piston is all the way up they will colide. So if the timing belt breaks the valves and the pistons hit each other...its bad....The advantages? i'm not really sure i suppose the engine can be smaller, or maybe a longer stroke but someone else may be able to go more indepth there....

#4 Subarunation 713

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Posted 16 February 2005 - 09:12 AM

What is the definition of an Interference type engine? What is it's advantage supposed to be?

Thanks,
A.J.

The advantages; Intake and exhaust valve timing durations are longer and the lift is also increased. This allows more "fresh air/fuel" in and more exhaust out per cycle. The disadvantage is the piston and valve can "Kiss" if the timing belt breaks. The good thing, with normal maintenance and following manufacturer recommendations for changing the timing belt very few belts just break. If they do, it is very rare. Usually it is because the engine gets over revved, oil leaks from the cam seals on the belt, seized water pump or a bad idler pulley. If you have an interference engine change the timing belt when you should and you will be fine.
Greg

#5 slo5oh

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Posted 17 February 2005 - 06:57 PM

What is the definition of an Interference type engine? What is it's advantage supposed to be?

Thanks,
A.J.


as stated "interference" means that your valves and your pistons will hit eachother if your crank is not in time with with your cam(s).
the advantages?
#1 is compression. This is how much the air/fuel mixture is "compressed" (i.e. 9:1, 10:1, 14:1 etc.), more compession = more power. The less room between the head and the engine block (or pison more specifically) at Top Dead Center (TDC) the better off you are, and the more compression you have. Now we get into the complicated part. An engine will have a better burn on the air/fuel mix when both the head and the piston have a dish cut into them. This allows for a pocket or ball area in the center of everything for the explosion. This unfortunatly usually makes compression under 9:1. Therefore most engines use a flat top style pison (lowers cost also) and run them up almost flat to the head. Without the engine maker cutting a groove or "relief" for the valve there is no way that valve can be open with pison at TDC. I don't know of any modern engines that are not "interference" style. If you have a playstation watch the begining of Gran Turismo 3, it shows a cut away view of an engine running with the valves and pisons moving. Modern day engines are a work of science. So much time and money goes into design that it amazes me. I learned much about engines when I was sold the wrong cam for a 5.0 mustang. There's all sorts of fun terms like dwell, quench, valve float, duration, duration at 50 (actually written .050), lift, lobe center... i know there's more...

#6 Tom Dunn

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Posted 17 February 2005 - 10:08 PM

Am I correct in assuming that the 2.2 is this type of engine?

#7 All_talk

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Posted 17 February 2005 - 10:23 PM

I believe the general rule for Subie engines is single cam = non-interferenace, twin cam = interference.

BTW, there is also valve to valve interference.

Gary

#8 The Dude

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Posted 18 February 2005 - 08:08 AM

I believe the general rule for Subie engines is single cam = non-interferenace, twin cam = interference.

BTW, there is also valve to valve interference.

Gary


Actually, the general rule is all Subaru engines, including the 2.2, starting from 1997 and on, are interference engines. If you doubt this, look it up.

One other advantage of a interference engine is thermal efficiency. In general, the smaller the combustion area, the more heat is retained in the expanding gas column, and more power for the engine.

HOWEVER,
In real life the microscopic power increase of the interference engine can not even be felt by the driver. Car manufacturers are in a horsepower war. Every manufacturer tries to make their cars more attractive by wringing every last possible watt out of their engine.
It's not worth it. You are risking a $3,000-$4,000 engine repair for just a couple of extra horsepower from an interferential engine. It's like playing Russian roulette all by yourself. I'ts just stupid.

#9 Tom Dunn

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Posted 18 February 2005 - 08:27 AM

So, how would I determine if the 2.2 in my 91 Legacy is, or is, not an interference engine? I sweat a broken timing belt not simply because it will strand me, but because of the possibility of engine damage. Am I worring about damage for nothing? Being stranded I could deal with, damage to the motor is another matter.....

#10 The Dude

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Posted 18 February 2005 - 09:02 AM

So, how would I determine if the 2.2 in my 91 Legacy is, or is, not an interference engine? I sweat a broken timing belt not simply because it will strand me, but because of the possibility of engine damage. Am I worring about damage for nothing? Being stranded I could deal with, damage to the motor is another matter.....


Pre 1997 2.2 engines are NON-interference. Go to the head of the class.

#11 Tom Dunn

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Posted 18 February 2005 - 10:47 AM

I downloaded the Gates Timing Belt Replacement Guide. I don't think they've got it quite right. Supposedly, interference type motors are designated with a * in the guide. They don't show ANY of the Subie motors listed as being interference types. The years covered vary with the engine type.

http://www.gates.com...location_id=540

#12 Tom Dunn

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Posted 18 February 2005 - 05:42 PM

Because the guide did not go back to 1991, I sent an email to Gate inquiring about the proper belt and also asked about the motor. They were very quick to reply, which is both nice, and unusual!

The email I got, just FYI:

Thank you for contacting Gates for information on your 1991 Legacy
with the 2.2L engine.
The timing belt you need is a T172. We also have a timing component
kit available for this application which will include the belt/tensioner
and idlers and instructions. The kit, TCK172, does NOT include the hyd
cam that is used in this vehicle. The engine is NOT an interference type
engine.




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