G-2 compression

[slim67]

Does anyone know what is a good compression reading is for the 285cc in an '86 G-2? Couldnt find anything in the Yamaha section.

[TheNewGuy]

I don't know for sure but Dave will. Come on Dave!!

[slim67]

Originally Posted by TheNewGuy

I don't know for sure but Dave will. Come on Dave!!

You were the one (New) guy I was hoping would know. No big deal though. I got 30 pounds and did it 3 times and kept coming up with that number.

[TheNewGuy]

I can tell you 30 is not good. That's way too low.

[smallblock450sl]

I find a G2 engine ,at "wide open throttle" (remember...if one of the 2 accelerator cables are bad...you can't get "WOT") and a good battery (to turn the engine over fast enough) you sould have a reading of 165 to 175 lbs compression. At 30 lbs I would almost expect a push rod off one of the rocker arms. (valve adjustment should be 4 thousanths , both intake and exhaust, when the engine is "cold") The old mechanic"s test (no affence to old mechanic"s) is add alittle oil to the cylinder after the first test...if compression increases...bad rings. Be carefull about grounding the spark plug when compression testing...If the spark should "jump/miss"...you could damage the ignitor box that controls the spark. Hope this helps alittle. Let us know what you find...it may help the next guy. Later Dave

[Project G2]

Small Block

Can you go into a little more detail on valve adjustment. What position? Where do you measure the clearance?

Thanks

[slim67]

Thanks for the info Dave. I know about the oil test but didnt bother because I felt 30 lbs was too low for any engine. Coincendentally the exhaust pushrod was bent and about an inch of it I had to fish out. I replaced the pushrod, cleaned carb out in my parts washer and have good spark. I turned it over and nothing. Thats when I did a compression test and got those numbers.Ive got other projects around the house so it may have to wait for a couple weeks. Dont want to get the wife mad. Thanks again guys.

[cgtech]

It is not unheard of in my experience to see a old yamaha that consumes oil, while having fine compression / power. The oil control rings get gummed up. You can try "yamaha ring-free" treatment, but, it usually only lessens the smoke once it is at the point you are at. I use the treatment every few oil changes to try and prevent this condition on mine. A few years back, i was given a G2 that smoked like a chimney, i ran the treatment on it, it helped some. That cart still runs just fine today, and still uses oil to this day.