adzzy Posted December 8, 2008 Share Posted December 8, 2008 (edited) Hi all I just did a compression test on a motor i am thinking of buying and it read 100 psi in all cylinder is this low? Its a 1987 70 hp yammie looks to be in excellent condition and does not miss a beat Cheers Adzzy Edited December 8, 2008 by adzzy Link to comment Share on other sites More sharing options...
Guest Aussie007 Posted December 8, 2008 Share Posted December 8, 2008 did u remove all spark plugs while doing the compression test it should be reading around 115psi Link to comment Share on other sites More sharing options...
adzzy Posted December 8, 2008 Author Share Posted December 8, 2008 did u remove all spark plugs while doing the compression test it should be reading around 115psi Hey gazza yah buddy had all the spark plugs out and tested it hot and cold with a new big battery and the tester is also new the push in type Adzzy Link to comment Share on other sites More sharing options...
pelican Posted December 8, 2008 Share Posted December 8, 2008 (edited) Check your guage as many read low or high al the time and were never calibrated correctly. Have you got access to another tester or can you test a motor that has a known compression from a recent test with a reliable tester? Edited December 8, 2008 by pelican Link to comment Share on other sites More sharing options...
IWANNABROCK Posted December 8, 2008 Share Posted December 8, 2008 Hey gazza yah buddy had all the spark plugs out and tested it hot and cold with a new big battery and the tester is also new the push in type Adzzy Did you also try a wet test? a couple of drop's of oil in the cylinder's to seal the bore's up. the push in tester's are normally a bit tricky as they can leak,try to get one that screw's into the sparkplug hole's,much more accurate. Link to comment Share on other sites More sharing options...
a boat Posted December 8, 2008 Share Posted December 8, 2008 Hi, a screw in comression tester is what we use here and as stated a little oil in the bores can sometime increase compression and if so the rings maybe stuck. 100PSI can be OK as long as they are all even. Considering its age and if I was going to buy it I would want to remove the cycliner head B4 purchase and confirm the condition of the bores and more importantly for a Yamaha the state of corrosion in the water passages. If OK, buy it and fit new internal anodes and new head gaskets. these two things are preventative maintance anyway and should eb done about every 10 years. Cheers, Huey. Link to comment Share on other sites More sharing options...
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