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Author Topic:   1985 70hp johnson compression

billmontauk posted 03-23-2004 08:18 AM ET (US)
I just had my engine tested and the compression was 80to 85 in all three cylinders. My question is is it worth it to have the engine worked on, or should I run it the way it is and hope to get another year or so out of it, will I suffer greatly on performance. I value this forums input.
Thanks Bill
JBCornwell posted 03-23-2004 10:58 AM ET (US)
Hi, Bill.
You probably have a healthy engine.
Absolute compression measurements vary greatly from one technique, guage, etc, to another.
In a compression test, it is the relative readings that matter most. The relative range on your engine, 80 to 85psi is very good, less than 10%.
Though some would consider readings below 90psi a trouble sign, that would only be valid with a screw-in calibrated guage, engine warmed, fully charged battery, throttles wide open and at least 5 revs per measurement.
It would also make a difference if the wrench doing the testing has a tuition payment due at his daughter's boarding school. (Joke, guys, just a joke.)
Red sky at night. . .
JB
billmontauk posted 03-23-2004 08:15 PM ET (US)

JB Thanks for your advice I was really worried that I was going to have to re-power, I just purchased boat currituck 1975 converted into center console with 1985 70 hp johnson in November. Did sea trial back then but no real engine inspection. If I was to re-power what is the best setup for this hull..
JBCornwell posted 03-23-2004 10:24 PM ET (US)
Ahoy, Bill.
For repowering any 16/17 Boston Whaler I am sold on the Suzuki/Johnson DF70 EFI 4 stroke.
It is quite a bit heavier than the Johnny 70 you have, but is very strong for a 70.
I have a 2001 Suzuki DF70 on my 1980 Montauk and am very happy with it.
Red sky at night. . .
JB
Bigshot posted 03-24-2004 01:44 PM ET (US)
Make sure carbs are clean and run it.....when/if she blws, drop a Johnson/Suzuki 70 4 stroke on her....I did.

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Author	Topic: 1985 70hp johnson compression
billmontauk	posted 03-23-2004 08:18 AM ET (US) I just had my engine tested and the compression was 80to 85 in all three cylinders. My question is is it worth it to have the engine worked on, or should I run it the way it is and hope to get another year or so out of it, will I suffer greatly on performance. I value this forums input. Thanks Bill
JBCornwell	posted 03-23-2004 10:58 AM ET (US) Hi, Bill. You probably have a healthy engine. Absolute compression measurements vary greatly from one technique, guage, etc, to another. In a compression test, it is the relative readings that matter most. The relative range on your engine, 80 to 85psi is very good, less than 10%. Though some would consider readings below 90psi a trouble sign, that would only be valid with a screw-in calibrated guage, engine warmed, fully charged battery, throttles wide open and at least 5 revs per measurement. It would also make a difference if the wrench doing the testing has a tuition payment due at his daughter's boarding school. (Joke, guys, just a joke.) Red sky at night. . . JB
billmontauk	posted 03-23-2004 08:15 PM ET (US) JB Thanks for your advice I was really worried that I was going to have to re-power, I just purchased boat currituck 1975 converted into center console with 1985 70 hp johnson in November. Did sea trial back then but no real engine inspection. If I was to re-power what is the best setup for this hull..
JBCornwell	posted 03-23-2004 10:24 PM ET (US) Ahoy, Bill. For repowering any 16/17 Boston Whaler I am sold on the Suzuki/Johnson DF70 EFI 4 stroke. It is quite a bit heavier than the Johnny 70 you have, but is very strong for a 70. I have a 2001 Suzuki DF70 on my 1980 Montauk and am very happy with it. Red sky at night. . . JB
Bigshot	posted 03-24-2004 01:44 PM ET (US) Make sure carbs are clean and run it.....when/if she blws, drop a Johnson/Suzuki 70 4 stroke on her....I did.