Logo
FULL SITE MENU

Will new rings fix this low-compression 6hp?

S

SteveInMN

New member
I have a 1976 6hp Johnson. Compression in both cylinders is 50 psi.

Oddly, the motor runs well (pushes a 14 foot alu hull ~15 mph) and idles well. It does take quite a few pulls to start, 5 - 10. Warm restarts are pretty easy.

I am pretty confident the gauge is accurate - I cross checked it with a bike pump equipped with a tire gauge -- 50 equalled 50.

Soaked a couple days with Marvel -- no change.

Replaced head gasket - no change.

Cylinder walls look fine. Too smooth, but no evidence of damage.

So, next steps as far as I know:

Ignore the readings, accept the balky starting and run it.
OR
Replace the rings and lightly hone cylinders.
OR
Bore engine for OS pistons.

3 is pretty unlikely due to cost.

Are new rings often a good solution here? Or is that pointless? Is there some cause of compression this low I am overlooking?
 
OR

Sell it and buy a better motor.

Would you rather spend more time fixing outboards or more time on the water ?
 
Acknowledged as a missed option. Although I do enjoy a good repair project.
Frankly, this 1976 thing does most all I expect/need - other than start crisply. It does start reliably, it just takes a few more pulls.
 
Last edited:
Wow----Never thought that aftermarket would supply those.----Picked up 3 of these 6 HP motors the other day.----A good magneto will jump a 1/4" gap all day long.----Using the plugs on the block is a test.----But not a very good test.-----This magneto was first built in 1950 and installed on ~~ a million motors from 1.5 HP to 40 HP
 
Last edited:
Hard to believe it has low compression if it is pushing a 14' boat at 15 mph or idling for that matter. What is your starting procedure?
 
flyingscott said:
Hard to believe it has low compression if it is pushing a 14' boat at 15 mph or idling for that matter. What is your starting procedure?
Click to expand...

Squeeze the bulb.
Engage choke.
Turn the throttle as high as it will go w/o interlocking.
Pull till I get a sign of life.
Disengage choke.
Pull till it starts.

I agree, it does better than one would expect. It was pushing me and the wife (300#s combined) @ 10 - 11 mph tonight, and started 2nd pull (!!!). The 15 mph is with me alone (170#s)
I suppose it's 'possible' the gauge I used to verify the compression tester gauge was also bad - but it is a bike tire gauge on a decent pump, they are usually pretty accurate out of necessity.
 
Last edited:
What happens if you leave the choke on until it actually starts? I usually leave the choke on until the motor is physically running. Once it's running I will push the choke off when it starts to bog.
 
flyingscott said:
What happens if you leave the choke on until it actually starts? I usually leave the choke on until the motor is physically running. Once it's running I will push the choke off when it starts to bog.
Click to expand...

I don't know, but I can try. Most days I worry more about flooding than additional pulls.

Getting back to the core question, I do wonder if simply changing rings might lift the current indicated 50psi to something respectable (80-ish plus)? If anyone could contribute their experience that would be super,
 
Being a project-addict myself (I would rather repair a motor than go fishing, for instance) I can tell that curiosity is going to kill you...change the rings and report back. Now I really want to know if it will make a difference!
 
It probably does not need a rebore (you said the walls are smooth). Rings probably are carbon-stuck. Remove the exhaust cover and poke at the rings to confirm.
 
Just did compression checks on 3 of these 6 HP motors the other day.-----2 were stuck from sitting.----Got them turning and compression was from 70 to 80 PSI.----Taking all 3 apart for inspection.
 
Just sold a 1975 6 and it had 75 to 80 psi. I sell 'em for $550 to $750, with a real gas hose and steel tank. These are perhaps the best all around fishing motor ever made. I'll take every one that I can get....that includes the old 5 1/2's too. They are brilliantly engineered, lightweight, dependable, quiet, economical, and timeless. Why go fishing, when you can get somebody else on the water with no worries? Just sold this one to an 84 year old vet, who fishes L. Superior with his wife. They need something reliable, not a computer with a tiller handle. He got fed up waiting for his 4 stroke in the shop 'cause they "can't find parts". Ha!....Okaaaay!
 

Attachments

  • IMG_20220728_180840354_HDR_compress15.jpg
    IMG_20220728_180840354_HDR_compress15.jpg
    500.8 KB · Views: 7
Last edited:
Oh, here is what you get for that money.
I give a one year warranty. If you can't trust your own work, than WHO can you trust? (Besides your 2nd wife.)
IMG_20220727_192304168~2_compress32.jpg
 
Back
Top