Interference or non-interference engine?? - Subaru Forester Owners Forum
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post #1 of 10 (permalink) Old 04-28-2007, 01:44 AM Thread Starter
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Interference or non-interference engine??

Can anyone help me confirm this? I have a 2001 Forester L. (Answer Below)

Also, at what mileage was your FS timing belt replaced? (Answer Below)

Interference or non-interference engine: If the timing belts breaks, the pistons and valves will collide, they will hit each other and basically ruin the engine. The 2.2L engine is a non-interference engine, all 2.5L engine are interference.

Reference - http://www.cars101.com/subaru_terms.html


>> Could someone describe some symptoms of driving an eninge (or running it idle) with a bent valve or a damaged piston?

Last edited by rayalan; 04-28-2007 at 08:20 AM. Reason: Original questions were answered; Posting related question
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post #2 of 10 (permalink) Old 04-28-2007, 04:58 AM
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ALL 2.5L Subaru engines ARE interference engines according to Subaru.com. Your 2001 Forester has an interference engine.

" I can't" never accomplished anything.
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post #3 of 10 (permalink) Old 04-28-2007, 05:23 AM
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105K for your Forester.

Also referring to the quote in your post, since 1997 ALL USDM Subaru engines are interference. That includes the 1997 and newer 2.2L. That year the pistons and heads were redesigned ( which included 'solid' lifters ). They were also redesigned in 1999 again for the 2.2L. ( in 1999 they used the 2.5L SOHC head )

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post #4 of 10 (permalink) Old 05-04-2007, 07:44 PM
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Yes, the 2.5L's are all interference valves to pistons. The dohc's can also be interference intake to exhaust valves in addition to pistons to valves. Symptoms of a bent/knicked valve could include loss of power and poor fuel economy. To check for this, among other engine issues, you would do a compression and/or cylinder leak down test.
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post #5 of 10 (permalink) Old 05-05-2007, 01:49 PM Thread Starter
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Talking FYI: Compression Test Result

Compression test was conducted in a beginner auto mechanic class. Mileage of the 2001 SF-L was 121585, and result of each cylinder was listed below:

#1 - 170 lbs
#2 - 170
#3 - 180
#4 - 170

Please free feel to comment or to compare with your test!!
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post #6 of 10 (permalink) Old 05-05-2007, 02:20 PM
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>> Could someone describe some symptoms of driving an eninge (or running it idle) with a bent valve or a damaged piston?
The effect of a broken timing belt (caused by a seized waterpump) on my old Neon was instant death. And I missed the office Christmas party. But I got to buy my Forester ahead of schedule!

2003 XS Premium MT >200k miles! ● 2005 Impreza 2.5 RS MT ● Robin-Subaru Powered Generator
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post #7 of 10 (permalink) Old 05-05-2007, 02:45 PM
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Those are excellent compression test results. Was that dry or with a little oil shot into the cylinders?

I don't know for sure, but I think another symptom of bent intake valve could be backfiring.
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A single bent valve makes that cylinder useless. There will be no compression. A worn or leaky valve seat gives you lower compression ratios, as well as worn rings or damaged cylinder walls.

On the Subaru interference engines I have seen with a broken belt ( 1 was DOHC 2.5L, 2 were SOHC 2.5L ),
The DOHC had 11 bent valves and 3 damaged pistons.
One SOHC 2.5L had good compression so we replaced the belt. The owner sold that car 2 years later and it was still running fine.
The other SOHC 2.5L had 1 pummeled piston and all the valves in that cylinder were damaged. In fact we had to replace that head.

So a broken belt can have different results, but the message is, DAMAGE CAN HAPPEN. If it doesn't, consider yourself one of the Lucky ones.

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post #9 of 10 (permalink) Old 05-06-2007, 12:26 AM Thread Starter
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Talking Compression Test

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Originally Posted by porcupine73 View Post
Those are excellent compression test results. Was that dry or with a little oil shot into the cylinders?

I don't know for sure, but I think another symptom of bent intake valve could be backfiring.
Re: I believe it was dry test because all I did for each cylinder was to plug in the gauge and crank the engine for five times. What kind of oil would you add, and which test would give me a more accurate result?
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post #10 of 10 (permalink) Old 05-06-2007, 03:59 AM
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If those are dry results that's great. If you get less than ideal compression on a cylinder sometimes people will put a shot of engine oil in there. If the compression then improves, it's probably the piston rings leaking.
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