Piston rings replacement project on my 4.5 HP

[merc20076]

Have a tired Evinrude 4.5HP, compression is between 60-70 PSI on both cylinders and it burns way to much gas. It smokes and over smells and it is not fun at all while fishing. I cleaned the carb, did a decarb job, replace spark plugs and not much changed for compression so I am pretty sure that the problem is the pistons rings.

I know that it's a big job but I think I would be able to do it myself, I am not bad in mechanics. Do I need expensive special tools for the job.

I've checked on Crowley Marine and most of the parts are still available. I wonder if I should get just the rings set?



http://www.crowleymarine.com/johnson-evinrude/parts/7310.cfm

if I get the job done properly, I'll give the motor a good paint job with new decals, it will be a nice restoration job. The lower unit is in very good condition.

 

[wilde1j]

Re: Piston rings replacement project on my 4.5 HP

I don't think compression is much over what you got on most pull start motors. Sounds like it's running too rich from your description, especially the smell and gas use. Rings won't fix that.

I would try decarbing:
http://forums.iboats.com/showthread.php?p=2648076#post2648076

 

[robert graham]

Re: Piston rings replacement project on my 4.5 HP

Could be the rings are stuck in their grooves with carbon. My 3HP Tanaka does that and I just slip the cylinder off(air cooled)and carefully unstick the rings, spray off with carb cleaner until rings are nice and free, put it back together. Of course yours is water cooled and it'll be a lot more of a job. Could you try the straight 100% synthetic outboard oil(less smoke) and lighten up a bit on the ratio?, then run a few tanks of gas with a "deposit removal" dosage of Ringfree to loosen the rings(if they're in fact stuck) It's going to be quite a job to replace your rings and you'll need to break the glaze on your cylinder walls so the new rings will seat properly. Good Luck!

 

[BigB9000]

Re: Piston rings replacement project on my 4.5 HP

Would the cylinders have to be bored? or just a simple ring replacement & hone?

 

[merc20076]

Re: Piston rings replacement project on my 4.5 HP

-Engine starts well when cold but after 5-10 minutes I shut it down, when I wan't to restart it, it's hard, very often I got to pull the choke again. And even, sometimes, it takes 4-5 pulls to get it back on.

-Somekind of a dark-brown/ black oil leaks from exhaust when not it use, it makes a real mess on my garage floor.

-I did a decarb job, cleaned the carb, it did helped a bit but still very low compression and same problems. Called a Evinrude dealer and said it's very low, should get at least 100 PSI. Up t'ill last year, I had a Mercury 20HP pull start and had 125 PSI.

Looks like I will buy a brand new 2.5 HP or another used outboard if it's a risky job to do...

 

[Chinewalker]

Re: Piston rings replacement project on my 4.5 HP

100 psi out of a little 4.5 is asking a lot. 70 psi is about average for those little guys - maybe on the low side, but it should be fine. Your issue sounds more like a carb issue - float level set per spec? Carb settings correct? The leaking you're seeing sounds like unburned fuel - pointing to running rich. A little is normal, but a lot is a sign that something is amiss.

 

[merc20076]

Re: Piston rings replacement project on my 4.5 HP

Could it be just a new carburator kit needed? It runs very good the first 10-15 minutes and then it starts smelling and smoke more. Used it again tonight. When cold, it starts on the 2nd or 3rd crank pull.

 

[BigB9000]

Re: Piston rings replacement project on my 4.5 HP

i have 5- 6hp outboards

all put out between 65-75 psi

I have a very low hour 1973 4hp. Mint condition. puts out 73ish psi.

I have a 1982 4hp, many hours, putting out 100psi

I think in the 80's the compression #'s went up.