Acceptable compression range

[Randy White, Sr]

What’s considered an acceptable compression PSI  for an Evinrude 7518?  (1955 7.5 hp)  TIA

[Buccaneer]

It will probably run with 60 psi but may not idle well.
70 psi would be nice, and 80 psi great.

Prepare to be boarded!

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Randy White, Sr

[Don]

Don’t get too worried about low compression readings, especially if the readings are the same on both cylinders.  Many compression gages are very inaccurate when used on engines with small combustion chambers like this one, especially when the gage has a long hose on it.  Readings may come up a bit once the engine has run also.

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Randy White, Sr

[JACQUES]

any specific problem with the 7.5hp …or are you just starting a refurb or conversion

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Randy White, Sr

[Randy White, Sr]

Thanks. Mine is showing 75 psi in both cylinders.
Just starting a refurb on this Evinrude 7518 that younger son grabbed at an estate sale. No known history.  Appears very clean, with no rust or corrosion visible, so guessing it was mainly used in freshwater. .  Found 4 Ohio registration stickers ion inside of engine cover, dated late 60’s to early 70’s.

[JACQUES]

Randy   if you don’t have it yet  dowbload yourself a copy of  the Johnson service manual…..   the  Evinrude 7.5   is just a cousin

https://www.socalaomci.com/library/johnson_service_manual_10th_edition.pdf

print locally  or store on your pc .. 450 pages +    has all you need

Joining AOMCI has priviledges 🙂

[Don]

Randy White, Sr wrote:

Thanks. Mine is showing 75 psi in both cylinders.
Just starting a refurb on this Evinrude 7518 that younger son grabbed at an estate sale. No known history.  Appears very clean, with no rust or corrosion visible, so guessing it was mainly used in freshwater. .  Found 4 Ohio registration stickers ion inside of engine cover, dated late 60’s to early 70’s.

75PSI compression on both cylinders is just fine…

[seakaye12]

The location of the Schraeder valve affects readings on small volume engines.

 

[outbdnut2]

If you don’t have it running yet, get it running and check compression again – it often comes up on old motors after running them a bit.
Dave

[Author]

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