Yammie

[adzzy]

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

[Guest Aussie007]

did u remove all spark plugs while doing the compression test it should be reading around 115psi

[adzzy]

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

[pelican]

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

[IWANNABROCK]

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.

[a boat]

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.