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Discussion Starter #1
Hey everyone! I bought a compression tester today and checked my 87 trx 350. It is 158 pounds. Manual says from 172-206 is spec. I just did a valve adjustment so I'm pretty sure that's not the cause. Think I need new valves? Seats? Both!!?? Do you think i can ride it for the summer and save it for winter project? I mean it's not THAT low! It starts great,runs almost perfectly and has plenty of power for a 350. I do ride a lot though. I juse didn't know if there was a magic number you shouldn't let it get below. Thanks a lot guys. Any info much appreciated!!
 

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The magic numbers are advised in the service manual, 172 being the lowest. It's best to play it safe and get the job done now if you do lots of miles, you could end up with a complete top end disaster otherwise.
Edit: Low compression would usually suggest you need a piston/ring replacement. You can inspect the valves whilst doing this.
 

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Discussion Starter #3
Thanks for your reply. I meant that I am sure that the culprit isn't the valves being out of adjustment because I just adjusted them. So you think new rings would fix it? Because I need to remove the rocker arm cover and apply new yamabond(or hondabond) anyhow and while I've got it that far apart... I might as well just order new rings and install new ones.
 

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What else do you know about that motor? Does it burn any oil? Any noises coming from the motor? Have you checked the timing chain slack to see how much it has worn? Were the valves way off when you adjusted them? Did you hold the throttle wide open while cranking during the compression test?

Before you take it apart check the timing chain wear so you'll know whether you will need to address that while its apart or not.

You said you got a new compression tester... have you verified that it is accurate? Test another known motor before trusting it... most of them are china made nowadays, regardless of the brand name.

Have fun with it,

Edit:
Don't buy any parts until you have the big picture... If you buy rings thinking you're gonna get lucky, universe will beat you over the head with them and show you a worn out cylinder, or one that is already bored out to the next oversize. Put eyeballs on everything before you buy anything.
 

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IF you have a half decent compression tester, and you are not in spec... rings are the issue, not the valves.

Just my 2 cents...
 
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Discussion Starter #6
I did hold the throttle wide open when testing. I hadn't thought of it not being acurate! It burns no oil! Absolutely none. Weeps a little from the rocker arm cover. I just adjusted the valves again and 1intake was too tight and the other too loose, and the same with the exhaust valves. I was a little nervous the first time and wasn't thorough enough. Tonight it took me forever but I know they're perfect. The first time I adjusted them 1 intake and both exhaust valves were .004 instead of .003. It has the "Honda tick" and really no noises that make me think something is amiss. I've been meaning to check the cam chain and I read retro's post on how to do it on another thread. I'm going to do that tomorrow evening as well as recheck my compression now that the valves are spot on. I appreciate the advice regarding buying what I think I'll need BEFORE looking to see. I'll hold off, that is if I even need to worry about it. Thanks again for taking the time to help me with advice. I really want to do this stuff right. I'll post again tomorrow with what I find out with the new compresion test and the cam chain.
 

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It doesn't sound too bad... thats encouraging! I would not trust a compression tester until there are a few tests done on known good motors though.... I've seen so much junk over the years... even expensive brands that were useless right out of the package. I know its a chore, but if you can test a few other cylinders with it before relying on it to test your 350, do that. A topend rebuild would not be a wasted expense on your motor, but if its fine right now your money could be put to work elsewhere refreshing bearings and seals on the chassis, relubing etc.

Incidentally, after you perform the initial compression test at starter cranking speed, pull the spark plug out (reattach the spark plug to the plug wire and ground the plug while cranking the motor -- else ignition coil may unload internally shorting the coil out) and perform a "wet" compression test on it. You do so by pouring motor oil into the cylinder through the spark plug hole, then while the spark plug is still out crank the motor over for a few seconds to distribute the fresh oil around the cylinder/combustion chamber and to expel any excess oil. Then recheck the compression as you did initially. Write each result down for comparison and to gain clues where pressure is leaking... valves or piston rings etc. Its almost as useful as a leakdown test... its just a poor mans method... :)
 

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Discussion Starter #8
Hey guys. I went for a long ride today and had a blast! I just made a new thread accidently, I should've just posted it here. I messed up while checking the cam chain tension. I won't bother to go into detail here because I just explained it all in the other post. Hope to hear from you guys over there. Thanks again!
 
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