Nissan 2.5 HP Compression Question

[111torrance111]

I have a 2.5 HP Nissan that only has 20Lbs of compression, I'm use to larger motors that typically have from 75to 175 Lbs. of compression.

Model: NS2.5A 314-1 Serial # 83460

Is this normal for small motors, I haven't started it yet, just checking things out first.

This motor also has an internal gas tank that sits on top of the engine with a small leak, what product is best to patch plastic fuel tanks?

Jerry

 

[robert graham]

Re: Nissan 2.5 HP Compression Question

20 lbs. sounds pretty low but maybe a valve is stuck a bit or out of adjustment....best to run the motor some and check compression again...there is no patch/repair for plastic fuel tanks...I've heard of folks trying to melt/weld a plastic tank but not sure of success?....good luck!

 

[pvanv]

Re: Nissan 2.5 HP Compression Question

That unit is ancient and obsolete, but many parts are available. It's valued on small sail boats and dinghies for the light weight. There aren't any valves to stick. 20 pounds is very low. Standard compression for the 2.5/3.5 is about 78 pounds when fully warm at WOT. You will not get a good reading cold, but I would still expect more than 20 PSI. They will run with low compression, but will make a lot less power. Still, it may run OK.

The A models had the water pump impeller on the prop shaft, and no provision for neutral gear -- they start in gear. Forget fixing the tank. Verify whether there is a crack. More common is a bad fuel ****.

If you do need fuel system parts, here are what we use most often on that model, available from any dealer, including several forum members (even me):
309700202M FUEL CAP 2.5/3.5 $12.92
309700103M FUEL TANK-INTEGRAL 2.5/3.5 $40.25
309700110M FUEL **** $18.24

 

[111torrance111]

Re: Nissan 2.5 HP Compression Question

Thanks pvanv,

I'll run the motor with an external tank and recheck the compression after she's warm, if it comes up then I'll be looking to purchase the new fuel tank/cockpit valve.

Thanks for the advice.

Jerry

 

[111torrance111]

Re: Nissan 2.5 HP Compression Question

When I first started working on this motor it was stuck, had to lube the cylinder & use a wrench on the flywheel nut to loosen it. Got it started and seems to run ok, the next day it seems stuck again, had to loosen with a wrench then the pull rope would work again.

Any thoughts on why it would keep freezing up? I assume the 2 stroke oil (50/1) should be enough lubricate.

Jerry

 

[pvanv]

Re: Nissan 2.5 HP Compression Question

After storage, or for new break-in, we double the oil. You may have a bit of rust or scuffing, which may or may not clean up after running an hour or 2.

 

[TOHATSU GURU]

Re: Nissan 2.5 HP Compression Question

It will be hard to run that engine from an external fuel tank as it does not have a fuel pump.