Low compression - Yamaha ATV Forum
 
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post #1 of 8 Old 02-07-2019, 01:10 PM Thread Starter
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Does anyone know of ways to fix low compression without a engine rebuild? I'm getting zero compression and just looking at an alternate solutions instead of a rebuild. I have a 2002 Raptor 660.

2008 Yamaha Raptor 350

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post #2 of 8 Old 02-08-2019, 09:38 AM
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if you truly have zero and there was not some big event it is likely a stuck, broken, bent or out of adjustment valve. check you valve adjustment first. if it has been sitting a while you could have a valve that is stuck, sometimes a soak with marvel mystery oil will help. check that and we can move on from there
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post #3 of 8 Old 02-09-2019, 08:58 PM Thread Starter
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The valves are still set correctly. I was thinking about using the mystery oil also, but the mechanic at the local shop said I should just do a top and bottom end rebuild. Then I'll have a new engine basically. He said it would cost about $1,500. I'm thinking it has to be another way. Do I just put the mystery oil directly in the top end, oil pan, or oil filter? I've never used this product but heard of it and sea foam working in older cars.

2008 Yamaha Raptor 350
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post #4 of 8 Old 02-10-2019, 11:22 AM
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if your valves are in spec it is not a stuck valve, you would not be able to get them adjusted and the mystery oil wont help. sea foam is an awesome product but it wont do anything for you either. you are going to have to take it apart and see whats wrong. 1500 bucks for a rebuild is a pretty good deal but it is tough to spend 1500 bucks on a 1900 dollar bike. i just rebuilt a yfz and had 1100 in parts. at this point you have 2 options sell the bike cheap with a bad motor and move on or decide you love the bike and spend the money to make it new again. you might get inside and find it only needs a top end and that is cheaper. if you take it apart yourself be very diligent about storing and labeling all the parts i use cheap totes to keep it all together. if you have all the parts organized and labeled it will make it easier to sell or put back together. if you do the rebuild budget a couple hundred bucks to fix stuff you find during the project
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post #5 of 8 Old 02-10-2019, 11:25 AM
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oh yea if you still want to do the mystery oil. pull the plug and put 2 table spoons down the hole. turn it over slowly 3 times and let it set overnight. the next day leave the plug out, put an old rag over the hole and hit the starter button. that will blow any oil that is left in the cylinder out and then do another comp test
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post #6 of 8 Old 02-10-2019, 04:20 PM Thread Starter
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Ok, I'll give it a try. Thanks.

2008 Yamaha Raptor 350
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post #7 of 8 Old 02-12-2019, 08:10 PM
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If you have zero compression, and your timing chain is good, your valves are seated and not bent then you might as well rebuild it because that shit is toast.
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post #8 of 8 Old 02-13-2019, 02:13 PM Thread Starter
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I believe so too. But I'm going to try Mystery Oil, new spark plug and re-test the compression this weekend. If that all fails, I'll just have it rebuilt.

2008 Yamaha Raptor 350
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