force 120 crankshaft

[jones7403]

I just picked up my 92 bayliner with the force 120 from a local mechanic who is supposed to be "the best around". I took the boat to him to fix a high speed miss. When I arrived at his house his first question was has the boat ever ran. I told him yes and reminded him about telling me how he had ran the boat 2 days prior. He proceeded to tell me that the boat now would not even start. I was pretty mad so I just took it home. The first thing I did once at home was remove the flywheel and checked the key. Low and behold the key had sheared. After removing all the pieces I noticed that the keyway in the crankshaft was wallered out to the point that a new key would no longer locate the flywheel as it should. Has anyone else had this problem? Would you try welding the key way and reworking it with a die grinder? My dad and I both have a combined total of 60 years of machinists/ tool maker work. I just don't know what the tolerance is on the location of the key way. I really don't want to purchase a new/ used crank.

 

[Frank Acampora]

Well, if you are that experienced and that good and precise a welder, it can be repaired. HOWEVER Keyway (for a modified woodruff key) location is critical as it locates the flywheel magnets for the timing ring. If you are off by a couple of degrees, the error can be corrected by timing the engine but anything too much and you will pass the point where timing can compensate.--unless you make a new timing link with left and right hand threads. But now you are getting into uncharted territory.

Remember: the flywheel has marks for TDC and a pointer on the block. if you move the key, you will need to re-mark either the block pointer or the flywheel

You need to be careful about the taper because it is a locking taper and before torqueing the flywheel nut to 95 foot pounds you need a MINIMUM of 85 to 90 per cent mating.

 

[pnwboat]

I've welded up a wallowed out key way on a couple of Force 4 cylinder crankshafts. Followed up with a die grinder and a file. Worked good enough to hold up for 6 or 7 years so far. Make sure the TDC mark on the flywheel lines up with the pointer when the number one cylinder piston is actual at Top Dead Center.

 

[jones7403]

Thanks for the quick response! I got it fixed today and boat idles like it did before taking it to the local mechanic. Now my next question is what could be causing the high speed miss? I know very little about boat motors but am willing to tackle it myself. Any help as to where to start?

 

[pnwboat]

First you need to determine if it's a fuel problem, ignition problem or something else. First thing that I do when I get a used motor is to check compression, replace the fuel pump diaphragm and water pump impeller. They are relatively inexpensive and not hard to replace, however, if any of those items are bad, it can be a show stopper. Might want to try that for starters. It might be helpful if you can post a video of the motor while it's running at WOT.

Here is a video of a Force out board at WOT with what initially appears to be a miss. It's actually the forward clutch dogs in the gear case slipping then engaging. You can see the motor actually jerk when the clutch dogs catch.

https://www.youtube.com/watch?v=AxxBl-8bykI