AD-10 1956 Johnson 7.5 Parts

[Bullie]

I picked up a 1956 Johnson 7.5 yesterday. Unfortunately, it has about 20lbs of compression. I am not having any luck finding a parts list for this motor. I am going to try a new head gasket and an impeller at minimum. I am sure that I am overlooking an obvious source but my searches haven't come up with anything.

 

[HighTrim]

PM me with your email address.

 

[HighTrim]

Is it a known good gauge?

If so pull the head, inspect the gasket and head. Check the bore. You can pull exhaust cover and see if rings still have bounce to them.

At least they are even. Hopefully tear in the head gasket between cylinders.

 

[Bullie]

deleted

 

[Bullie]

Is it a known good gauge?

If so pull the head, inspect the gasket and head. Check the bore. You can pull exhaust cover and see if rings still have bounce to them.

At least they are even. Hopefully tear in the head gasket between cylinders.

I tested my gauge on my 1951 7.5 and its reading 90+ pounds so I don't think its the gauge. I pulled the head and couldn't find any obvious issues with the gasket. The cylinders look really good. No scratches at all. Smooth all around. No carbon buildup in the head or on the pistons. Looks really good. I went back out and checked the spark with my tester. It will spark a little grounding the plugs to the block but will not jump an open gap of even 1/16 on my tester. I pulled the cover on the flywheel and it still has the original coils. Cracked up pretty bad. So, I need a head gasket, impeller, and coils. Condensers you think?

I did scrape a little white crud from around the cylinders. I assume that is salt. Not much of it and I didn't see any blockages.

 

[HighTrim]

I would not spend any money on it until you determine the cause of low compression. Could be worn cylinders, stuck rings, worn rings, warped head, etc...

Try dressing the head on a piece of emory on something perfectly flat, like plate glass, or machined edge. Do figure 8s with the head, it is likely low between the cylinders. Keep going until the sanding is uniform.

 

[Bullie]

I pulled the exhaust cover and the rings aren't stuck. No scoring, that I could see, on the pistons. It looked really good. I have a head gasket on the way and will clean the head up well like suggested. Hoping I get lucky and its the gasket.