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Old August 16th, 2011, 12:16 PM   #1
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Default Interference vs. Non-Interference Engines

My girlfriend drives a 2001 Chrysler Sebring with a 2.4 DOHC.

The other night the timing belt failed. I took it to a repair shop yesterday morning to get fixed. The mechanic told me the engine was an interference engine. He did a compression test and said 2 cylinders had no compression. He said he would pull the head and send it to the machine shop to get fixed.

I didn't think anything of it until I had a conversation with my dad this morning and he told me that this particular engine isn't an interference engine. I looked it up online here Gates . The Gates website confirms what he told me. I guess the question is, could there have been contact in the combustion chamber if it isn't an interference engine? I have never used this mechanic before and am just wondering if he is trying to sneak some extra work out of me. Any input? Thanks in advance.
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Old August 16th, 2011, 12:38 PM   #2
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It is a non-interference motor, unlike the 2.0 DOHC.
However, depending on cam position as the belt broke, the split second the first cam stops and the second cam stops rotating, its possible for valves to make contact with each other.

From what I've heard at least.
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Old August 16th, 2011, 12:44 PM   #3
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Yes, there can physically be interference in a non-interference engine if something were to break, piston to valve-clearance wasn't proper when an engine was built (usually high performance motors), it ingests something, etc. Usually it related to piston to valve clearance when the belt goes, and it looks like the sohc motor is the one he has yours confused with.

Did he fix the timing belt before doing the compression test? I'm no certified mechanic, but if the timing belt breaks, the cam will hold certain lifters open and certain ones closed, and with open valves, no compression will be achieved. I don't know that engine, and wonder if it's possible valves (intake and exhaust) will hit each other if the cams get out of sync, possibly bending a valve which would prevent sealing/compression, are there two separate timing belts (i don't know), and when he reinstalled the belt(s) to do the test if it was properly indexed before he ran the compression test, etc.

Call him out on the dual cam motor not being an interference engine. walk up the food chain. Ask another shop for an opinion or talk to a rebuilder who knows that engine.

Good luck and let us know what you find out.
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Old August 16th, 2011, 01:16 PM   #4
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Quote:
Originally Posted by Klumpper View Post

Did he fix the timing belt before doing the compression test? I'm no certified mechanic, but if the timing belt breaks, the cam will hold certain lifters open and certain ones closed, and with open valves, no compression will be achieved.
This!

Did he do a compression test after installing a new belt?
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Old August 16th, 2011, 02:17 PM   #5
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Quote:
Originally Posted by Paul04TJ View Post
It is a non-interference motor, unlike the 2.0 DOHC.
However, depending on cam position as the belt broke, the split second the first cam stops and the second cam stops rotating, its possible for valves to make contact with each other.

From what I've heard at least.
That makes sense. I didn't even think of that.

Quote:
Originally Posted by Klumpper View Post
Did he fix the timing belt before doing the compression test?

Call him out on the dual cam motor not being an interference engine. walk up the food chain. Ask another shop for an opinion or talk to a rebuilder who knows that engine.

Good luck and let us know what you find out.
He claimed he fixed it to run the compression test.

I talked to him and brought up the fact that it isn't an interference engine, and he became a little pissy with me. I tried to let him know that I was just curious about what I have found out, because I didn't want to piss him off yet. But, it would have been a little comforting to hear from him about the possibility of valve to valve contact (a bit of knowledge on his part, I guess).

I told him that when they pull the head and send it to the machine shop for inspection I would like to talk to them about it, for my own peace of mind. I am second guessing him, but for the $1500 quote he gave me, I feel like I deserve that.

Thanks for the responses, and I will let you know how it turns out.
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Old August 16th, 2011, 03:14 PM   #6
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yes its considered a non-interference engine. im not sure why though.

i have had several of those here that broke belts and bam the piston kisses the valves everytime.

as mentioned above you need to put a new belt on it to check for compression though.
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Old August 16th, 2011, 03:35 PM   #7
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You could loosen the cams, relieving tension on the valves allowing them to seat and inject regulated air into the cyl to see if a vavle is bent without installing a belt.
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Old August 16th, 2011, 04:17 PM   #8
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I have had those here with bent valves after a belt failure.
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Old August 19th, 2011, 04:22 PM   #9
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If a timing device breaks, just about every standard 2-3-4 valve configuration engine will have piston to valve interference. As it is, the piston chases the exhaust valve(s) closed and the intake valve(s) chase the piston as it drops on the intake stroke.
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Old August 23rd, 2011, 08:29 PM   #10
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I have seen several of those break without any other issues. The engines are considered non-interference,but the intake and exhaust valves could contact each other. So the guy put the belt on and then checked compression? Did you ok the belt to be put on?
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Old August 24th, 2011, 08:35 PM   #11
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Ill bet he didnt pull the valve cover, pull the caps, deal with the followers and all the good stuff that comes with simply unbolting the cams to do a compression check. THe common procedure would be to put a belt on then do a compression check, it would have taken less time anyway. THere is a 50 50 chance you dinged the piston but i would want to see how he did the compression check before i paid a grand to do a cylinder head. If he gets pissy, pull the car out of his shop and take it somewhere else. I wouldnt hesitate to do that in a minute. More than likely you only need a belt and tensioner and all that stuff. Good luck.
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Old August 24th, 2011, 08:52 PM   #12
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Lost the timing belt on my Toyota 5S-FE 2.2 liter which is non-interference, replaced the belt and idler pulley and off we went. Its been almost another 100k since it happened and no issues, bout time for a new belt again.

I would bring it somewhere else for sure, seems like a shady place. As mentioned before it would be impossible to perform an accurate compression test without replacing the belt or releasing the pressure the cam has on the valves. Without the belt in the system, the valves that were open when the belt snapped are still open since the cams haven't been moved. Chances are you will get a bill for a Head R&R and timing belt replacement, but the shop will only perform the timing belt service.

If you do end up having them (or anyone) perform the work, try to stop in or request to see the damage to the head after it is removed. Also, be sure to inspect your car after they show you the head to verify it was in fact removed from your engine and not just something they had laying around. It sounds paranoid I know, but I have seen and heard of many instances where people get taken to the cleaners but repair shops. You can't be too careful, and there are laws to protect you as well, but watching out for yourself to avoid getting scammed is the best way to prevent this.
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Old August 24th, 2011, 09:03 PM   #13
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why not just pull the valve cover? If you have bent valves he should be able to show you where you have clearance with the cams. You don't even need a engine builder to check it out.
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Old August 29th, 2011, 07:18 PM   #14
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So we got the car back the other day. Everything is in working order again. While he had the head off earlier in the week, before it went to the machine shop, he showed me the damaged valves and where the valve made contact with the piston. So, all in all, it turned out pretty good (considering). He was honest and straight forward with us. Kept in contact to let us know the status and actually came in $500 under his estimate.
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Old September 1st, 2011, 03:12 PM   #15
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