Valve Guide Replacement

Hey guys, recently i've lost a lot of compression on my bike and it's getting really hard to start using the decompression lever. I Can't find that sweet spot anymore :thumbsup: at all. I've checked the valve clearances and they're in spec as well as the decompression mechanism, which is fine. My riding buddy reckons that I probably have a leaky valve guide somewhere and an email from Rick Sieman confirmed this. So onto my question, How hard is it to replace the guides? A quick look in the manual and it seems like it is above my mechanical skill so i'll probably take it into the shop. How much is involved? Can I replace the leaking one only or do I have to replace all 5, is it possable to repair them? Do I need new valves to wear into the new guides or what? As you can see I have alot of questions so all information about this is appreciated.

The yamaha valve guides are iron and pardon the pun, wear like iron.

I have done quite a few yamaha heads and the guides are always good.

I would disassemble and inspect before trying determine the causes of said lack of compression.

a worn guide won't cause a loss of compression, well not directly anyway. It will cause the valve to float from side to side, which could wear the seat unevenly. Either way, do a leakdown test before you even remove the cam cover.

Bad valve guide seals will NOT cause a lack of compression. The valve guides are up in the valve ports, whne the valves are closed there is no way for air to get from the cylinder around the valve guides. My best advice is to get a leak down tester. Connect it and turn on the air. If your compression is bad then it will be leaking air through some part of the motor. Either around the intake/exhaust valves, around the piston or through the head gasget. With the air on, listen to the different parts of the motor. Put your ear to the airbox, ear to the exhaust, etc... and whever the air is coming out, that will tell you where your leaking.

Thanks for clearing that up guys, now I just gotta go find a leak down tester....

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