Compression

[James McClymont]

Is 50 psi to low? For 1930 2.75 hp 2 cylinder thx

[Tubs]

Even with the prop out of the water, pulling it over with a rope, I’d be surprised if you could get it started with the compression that low.   The rings could be stuck in the pistons. 

A "Boathouse Repair" is one that done without having tools or the skills to do it properly.

[PM T2]

You would normally want to see at least 60 lbs in each cylinder. My experience has been that at between 50 and 60 they’ll still run but may be hard to start the closer you get to 50 or less. Have you had the powerhead disassembled to check for stuck rings as Tubs mentioned?

Best,
PM T2

He's livin' in his own private Idaho..... I hope to go out quietly in my sleep, like my grand-dad did..... and not screaming, like the passengers in his car...

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James McClymont

[Sam M.]

I’ve run a 5hp single cylinder 4-stroke engine that was in the low 60s for psi if I remember correctly (though the compression tester I used seemed worn – it had a bent needle).  That engine ran wonderfully and was a first pull engine once primed, so I think 50 psi is enough to run.

Some people have found a little lubricant in the cylinder will increase the reading, if you haven’t tried that yet.

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James McClymont

[crosbyman]

check for sparks and clean the carb…  you can always try some lubricant in the cyl to soak the rings a few days  then try it…

if it runs.. go fishing  my 9622a  9.5 runs fine   with 60-65 psi

if your meter has a long  hose it may distort the psi reading on a small cyl. .. try a short hosed meter to see if psi’s go up a bit

 

Joining AOMCI has priviledges 🙂

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James McClymont

[fleetwin]

Please remember that compression gages are notoriously inaccurate on little engines with small combustion chambers, especially if the gages have long hoses and valves…

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seakaye12, James McClymont

[seakaye12]

Great point Fleetwin.

There are compression testers with the schrader valve at the spark plug end of the hose.  Those are said to be designed with very small displacement engines in mind….to minimize the error induced by long hose models with the valve at the gauge.

 

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Sam M.

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