# Subaru Outback Intermittent Knocking **URL:** \ **Category:** General Discussion\ **Created:** [December 15, 2014, 8:51pm UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382 "2014-12-15T20:51:41Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![sammerz](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@sammerz](https://community.cartalk.com/u/sammerz)\ **Post date:** [December 15, 2014, 8:51pm UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/1 "2014-12-15T20:51:41Z")
The car in question is a 1998 Subaru Legacy Outback. Just had the heads resurfaced and new gaskets, and timing belt. Runs great. Acceleration is good, stays cool. However, it has developed an intermittent knock/tapping. it sounds like its coming from the top end of motor. I added Marvel Mystery and the noise left for about a week but came back. Is this the beginning of the end? Or could it be a small problem involving the lifters/followers/valves? I’m prepared for the brutal truth! Thanks! ---
**Author:** ![insightful](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/insightful/32/2732_2.png) [@insightful](https://community.cartalk.com/u/insightful)\ **Post date:** [December 15, 2014, 11:15pm UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/2 "2014-12-15T23:15:19Z")
When is it most likely to tap? Right after start-up? After it warms up? At idle? At tip-in (just opening throttle)? When accelerating? Coasting?.. ---
**Author:** ![sammerz](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@sammerz](https://community.cartalk.com/u/sammerz)\ **Post date:** [December 16, 2014, 12:16am UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/3 "2014-12-16T00:16:59Z")
Definitely after it warm ups…then at idle and acceleration(me working the throttle body). don’t notice it when on the highway or even driving in light traffic. Thanks for response! ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [December 16, 2014, 12:29am UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/4 "2014-12-16T00:29:20Z")
Have you tried a higher octane gasoline? Milling the head can increase the compression to a point where preignition introduces itself. That can take the form of pinging and/or knocking. Take some compression readings and post them here. ---
**Author:** ![sammerz](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@sammerz](https://community.cartalk.com/u/sammerz)\ **Post date:** [December 16, 2014, 1:06am UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/5 "2014-12-16T01:06:50Z")
Thanks so much!! will do! ---
**Author:** ![Barkydog](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/barkydog/32/2470_2.png) [@Barkydog](https://community.cartalk.com/u/Barkydog)\ **Post date:** [December 16, 2014, 4:38am UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/6 "2014-12-16T04:38:29Z")
Double check the timing and try the next best gas, low to mid or mid to premium. What conditions can you replicate the knocking, going uphill etc.? ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [December 16, 2014, 6:30am UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/7 "2014-12-16T06:30:19Z")
If there’s a way to retard the ignition timing a tad, might be worth an experiment. And it might pay off to have a shop inspect that the valve clearance is within spec and if hydraulic lifters, that they are working properly. ---
**Author:** ![insightful](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/insightful/32/2732_2.png) [@insightful](https://community.cartalk.com/u/insightful)\ **Post date:** [December 16, 2014, 7:37am UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/8 "2014-12-16T07:37:22Z")
A small exhaust manifold gasket leak can make a ticking noise. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [December 16, 2014, 9:24am UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/9 "2014-12-16T09:24:50Z")
Good point @insightful … OP could use a piece of garden hose as a stethoscope to see if the sound was coming from the exhaust manifold area. ---
**Author:** ![sammerz](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@sammerz](https://community.cartalk.com/u/sammerz)\ **Post date:** [December 16, 2014, 11:17am UTC](https://community.cartalk.com/t/subaru-outback-intermittent-knocking/88382/10 "2014-12-16T11:17:50Z")
Man! Preciate you guys. I feel like a patient getting great advice from a panel of doctors. Exhaust manifold gasket? never thought of that. I am definitely curious about the valve clearance and lifters working properly…and the timing…which was messed with as a new timing belt was put on??? I am taking all of these ideas to my mechanic and have him consider all. Thanks so much fellas.I will keep you posted!