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TOPIC: Tower compression

Tower compression 8 months 4 days ago #131836

  • hodgify
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I have a 90 hp tower with 90 psi across all six cylinders , is that good or is it time to rering ?

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Tower compression 8 months 4 days ago #131840

even an older I6 should have 120lbs. time to check it out.

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Tower compression 8 months 4 days ago #131848

  • Dr.Go!
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If memory serves, last fall my 1965 100hp i6 had consistent compression of 125-126. Can you find a manual on line with specs for your 90? I don't know other motors like your year/model.

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Tower compression 8 months 3 days ago #131856

Yep as stated above. Time to look it over. Or double check that your gauge is reading right. 110 would be about minimum for me before I tore it down to see what is going on. My gauge shows 135psi on a fresh rebuild typically on a low dome motor. High dome pistons push 150 psi. If you post a picture once torn down I can tell you which pistons you have in it. Some 90's still came with high dome pistons.

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Tower compression 8 months 3 days ago #131860

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Thanks for the info , I do have hi dome pistons , guess I have another winter project.

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Tower compression 8 months 3 days ago #131865

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Very uncommon to see all cylinders wear to an even, low value. More likely that your gauge is inaccurate.

Have you run this motor, if so how does it perform? A powerhead with truly low compression would be extremely difficult to start and have poor performance. It wouldn't idle well in the water and likely stall in gear.

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Tower compression 7 months 3 weeks ago #132013

Agree with Ed on this one. Get another gauge and test again, or better still, do a leakdown test.

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Tower compression 7 months 3 weeks ago #132030

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Using a second new compression tester saved me from jumping to conclusion and avoided a possible deeper look... and that old junk tester did not even give me cosistant lower readings. New one was consistent and in the higher good range. The first reading made me think a few cylinders were way worse than others and all were initially lower than desired. Great advice here by others. I am NOT an expert in any way.

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Tower compression 7 months 3 weeks ago #132033

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Have not had a lot of time to look deeper, but considering my gauge came from harbour freight I will get a better gauge and double check be for I tear it apart. Did seem funny that all six cylinders were exactly 90 psi.

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