What should 1987 stock OMC 15A compression be..?

[25xs]

Looking at a stock 1987 Johnson 15A for friend and wondering if 75psi to 80psi is way too low compression..?

[61-W]

Everyone's gauges read a little different, but most of the time my fresh rebuilt engines are between 125-128 psi on my gauge.

Jeff Scheffler

[Rex Hall]

Looking at a stock 1987 Johnson 15A for friend and wondering if 75psi to 80psi is way too low compression..?

Any thing less than 100 psi is not good.

[ZUL8TR]

Yes it is low. Squirt some outboard oil in each cylinder, pull it over to distribute oil open carb butterfly and retest compression. If it goes up a lot rings stuck or rings and cylinders worn a lot. Using same gage you will at least have relative results. If CD ignition ground plugs while testing.

[25xs]

Thanks guys... I'll get my own compression readings to verity my friend's compression readings. Also need to replace charge coil (open circuit = infinite resistance on ohms test and zero peak voltage reading while cranking). New coil has been ordered.

[25xs]

Thanks again guys... I'm reporting back as I said I would do last week. With my own (well used) compression gauge, the engine came in at 124psi and 125psi. The charge coil was shorted out and replaced with a new one. Still no spark and after replacing CD powerpak with a brand new aftermarket unit it still had no spark. After a couple hours with a meter diagnosing the entire ignition system, I pulled a powerpak off my 1988 40hp engine and it fired right up! Will NEVER buy aftermarket ignition parts but it's what was handed to me. Cost me 1/2 day of head scratching, but got this Johnson 15A engine running and will be helping rig it for a 10yr old new driver to run the Top-O-Michigan race this summer.

One dead OEM charge coil, one dead OEM PowerPak, one D.O.A. aftermarket PowerPak... One well used 40hp Powerpak and engine up and running.

All is well.

[ricochet112]

Depends on the brand of aftermarket. The only quality aftermarket is CDI, Rapair. Any other brand I wouldn't trust.

I will never install an OEM Mercury stator on any job I do, only CDI...

Are you using just a VOA to test or with a DVA? Testing only Ohms is a noninclusive test.

[mercguy]

CDI aint great either!! Id take a factory Merc stator any day over CDI! Ive had 3 POS CDI omc powerpacks fail in 2yrs...

[25xs]

For what it's worth... CDI Electronics (used to be CDI/Rapair) is now the OEM for most older Mercury and OMC ignition components now. Have ordered them from OMC System Match and they come is a CDI box with OMC sticker covering the label and a CDI instruction sheet. I've always received great quality and even greater phone support from their Tech Services staff as well.

RIchochet: It was a "Titan Marine" aftermarket box with absolutely no markings on the 2-cyl Powerpak at all... Really cheesy looking (and was D.O.A. to boot!). I replaced it with a factory 1988 Powerpak off my 1988 Johnson 40hp engine, dirt, grease and all, and the Johnson 15A runs fine now.

Edit: Also, I do have a DVA adapter on my Fluke meter...