120 hp force problems

[usmc_hemb]

i just recently had my 1994 120 hp force bored 0.20 over. i also just rebuilt it from scratch. the problem im having is the engine wont crank a full rotation when fully hooked up. it will complete full rotations when the spark plugs are removed. im seeking any advice.

 

[Frank Acampora]

Re: 120 hp force problems

Sometimes on a rebuild, especially if you used a lot of assembly oil, the cranking compression is much higer than normal. Try removing the sparkplugs and squirt into each cylinder a good shot of fuel pre-mix. Then crank the engine. This should help wash out the excess oil while still having enough oil to lubricate.

Replace the plugs and try to start it. Hopefully it will crank faster. First try without choking since the engine may be flooded.

As usual, do not forget to double check all connections to ensure adequate power to the starter motor.

 

[usmc_hemb]

Re: 120 hp force problems

I tried doing what you said and spray some premix into the cylinders and checked all the connections and tried it and it did the same thing. I even hook the power directly to the starter to see if it was the connection and it did the same thing. Is there any possible way that the starter is just not putting out enough power to get a rebuilt powerhead to crank properly?

 

[Frank Acampora]

Re: 120 hp force problems

Certainly! Brushes on the starter may be worn or the commutator may be dirty, not allowing the starter to develop its full power.

However, I still think that if the starter was adequate before you rebuilt the engine, it should be adequate now. Remember that the rings are not seated and may be tight, plus there is more oil than usual in the seals and rod bearings. All this adds up to more power needed to turn over the engine. If your starter was marginal to begin, it may still be adequate to turn over a broken-in engine, but not a new one.

I suspect that if you can get the engine to start and run it for a half hour or so, the problem will go away.

You can try cranking with the plugs loose in their holes. If the engine starts, no damage will be done except to blow some oil out them. Hopefully, you will have them in 4 or so turns so they do not blow out of the head if the engine does start. Run it for a minute or so then try again with the plugs hand tight. If she now starts, torque them down.

You do know that with that engine, it is possible to rope start it with the ignition switch on. And, If you have a friend to help, while he turns the key to start and choke, if you pull the rope, you may be able to start the thing. This is not exactly the safest thing to do, so use utmost care. Be certain the helper is far enough away so that he does not get whipped by the rope as it comes off the flywheel and you must be careful of the unguarded flywheel as well as making sure you can quickly let go of the rope if it hangs up on the flywheel. A wood handle on the rope and leather work gloves are a must.